Cell Tissue - Questions and Answers
1. What is the logical order in which the concepts of atoms, molecules, cells... up to biosphere are associated?
Atoms form molecules that form cells that form tissues that form organs that form systems. Systems, in their turn, constitute individuals that form populations that compound (biological) communities that form the biotic components of ecosystems. All ecosystems of earth form the biosphere.
2. From the zygote, pluricellular organisms are formed by serial mitosis. Would this formation be possible if each cell made by mitosis had an identical life in relation to its antecedent cells? How did evolution solve that problem?
The formation of complex and distinct pluricellular organisms would not be possible if mitosis in embryos produced only daughter cells with an identical life history as the mother cell, since there would not be differentiation and structural or functional specialization among cells.
Evolution solved the problem creating the cellular differentiation process by which, motivated by stimulus not yet well-known by science, different and specialized cell lineages gave birth to different tissues, organs and systems that, as a whole, form the pluricellular organisms.
Cellular differentiation probably is a very intricate process that activates and inactivates some genes within the cell in response to some stimulus.
3. What are the main types of animal tissue?
The main animal cell tissues are the epithelial tissue, the nervous tissue, the muscle tissue and the connective tissue.
Cell Tissue - Image Diversity: epithelial tissue nervous tissue muscle tissue connective tissue
4. What are epithelial tissues? What are their general function and how is that function associated to the features of the tissue?
Epithelial tissues, also called epithelia, are tissues specialized in the covering of external and internal surfaces of the body.
The general function of the epithelium is to provide protection and impermeability (or selective permeability) to the covered structure. This justifies the epithelium's typical features: the cellular juxtaposition forming layers of very proximate cells with diminished or none intercellular space between each two neighbor cells.
Cell Tissue - Image Diversity: epithelial cell
5. Of which cells is the nervous tissue constituted? How is the generic function of this tissue related to the characteristics of the main cell type that forms it?
The nervous tissue is formed of neurons and glial cells.
The function of the nervous tissue is to receive and to transmit neural impulses (reception and transmission of information). This function justifies the characteristic morphology of neurons, with membrane projections (dendrites) to get information and an elongated membrane projection (axon, or nerve fiber) to transmit information at distance. In their turn, the glial cells support the neurons and facilitate their work (sometimes acting as insulators).
Cell Tissue - Image Diversity: neuron glial cell
6. What are muscle tissues? How is the function of this tissue related to the typical characteristics of its cells?
Muscle tissues are tissues made of cells able to perform contractions and thus to generate movement.
The function of the muscle tissue is to pull bones (skeletal striated muscle), to contract and move viscera and vessels (smooth muscle) and to make the heart to beat (cardiac striated muscle). The muscle cells have internal structures called sarcomeres where there are myosin and actin molecules disposed to create contraction and distension (movement).
Cell Tissue - Image Diversity: muscle cell
7. What is the typical biological function of the connective tissues? How is this function associated to the main features of its cells?
The typical function of the connective tissues is to fill empty spaces among other body tissues.
This function is related to the great capability of the cells of the connective tissue to secrete substances that constitute extracellular material, like collagen and elastic fibers, creating a significant spacing between these cells.
(There are other important biological features of the connective tissues, such as substance transportation, defense of the organism, etc.)
8. Of which type of tissue are cartilages and bones made?
Bones and cartilages, tissues with great amount of intercellular material, are formed of connective tissue.
9. Are the cells of the connective tissue far or near to the others?
The relative great spacing between cells is a typical feature of the connective tissue. There are much intercellular material generally secreted by the tissue cells.
10. What are the general functions of the connective tissues?
The main functions of the connective tissues are: supporting and filling of spaces; cellular nutrition; energetic storage (fats); hematopoiesis (formation of blood, blood cells and blood components); immune defense (specialized cells).
11. What is connective tissue proper?
The name connective tissue proper is used to designate the connective tissue that fills interstitial spaces as opposed to the specialized connective tissues (blood, bones, cartilage, adipose tissue, etc.). The connective tissue proper secretes collagen, elastin and reticular fibers.
12. What are the main cells of the connective tissue proper? What is the name given to the intercellular material that surround these cells?
The main cells of the connective tissue proper are the fibroblasts, cells that secrete the intercellular material. These cells are the majority of cells of the tissue. Fibroblasts later are transformed into fibrocytes, mature cells with restricted secretory role.
The intercellular substance that fills the interstice is called interstitial matrix, or just matrix.
Cell Tissue - Image Diversity: fibroblast fibrocyte interstitial matrix
13. What are the three types of protein fibers of the connective tissue proper?
The matrix of the connective tissue proper is made of collagen fibers, elastic fibers and reticular fibers.
Cell Tissue - Image Diversity: collagen fibers elastic fibers reticular fibers
14. What is the function of the collagen fibers of the connective tissue?
There are different collagen types. The main function of these proteins is to keep the shape and the structural rigidity of the tissue. (Collagen is the most abundant protein of the human body.)
15. Of which substance do elastic fibers of the connective tissue are made? What are some functions of these fibers?
The elastic fibers are made of a protein called elastin.
Elastic fibers abound in artery walls, helping the maintenance of the arterial blood pressure in these vessels. They are also present in the lungs, providing them with elasticity (some respiratory diseases are caused by destruction of these fibers). In many other organs and tissues the elastic fibers are found in the interstitial matrix.
16. What are the reticular fibers of the connective tissue and where can they be found?
The reticular fibers are very delicate interstitial fibers made of a special type of collagen known as collagen type III. They can be found in many organs and tissues such as in lymphnodes, in the spleen, in the liver, in blood vessels and also covering muscle fibers.
17. What are diseases of the connective tissue? What are some of them?
Diseases of the connective tissue are hereditary or acquired diseases(many of autoimmune cause) characterized by deficiency in structure or function of components of the connective tissue, for example, deficiencies of collagen, elastin, etc. Some of such diseases are lupus, dermatomyositis, cheloid, scleroderma, mixed connective tissue disease, mucinosis and Marfan's syndrome.
Blood Questions Review
1. What are the main functions of the blood?
The blood is a means of substance transportation throughout the body. The blood distributes nutrients, oxygen, hormones, antibodies and cells specialized in defense to the tissues and collects residuals like nitrogen wastes and carbon dioxide from them.
2. What are the constituent elements of the blood?
The blood is made of a liquid and a cellular part. The fluid part is called plasma and in it there are several substances, like proteins, lipids, carbohydrates and mineral salts. The cellular constituents of the blood are also known as blood corpuscles and they comprise the erythrocytes (red blood cells), leukocytes and platelets.
Blood Questions - Image Diversity: red blood cells leukocytes platelets
3. What is hematopoiesis?
Hematopoiesis is the formation of blood cells and other constituent elements of the blood.
4. Where does hematopoiesis occur?
Hematopoiesis occurs in the bone marrow (mainly within flat bones), where erythrocytes, leukocytes and platelets are made, and in the lymphoid tissue, responsible for the maturation of leukocytes and found in the thymus, spleen and lymphnodes.
Blood Questions - Image Diversity: bone marrow
5. In which bones can bone marrow chiefly be found? Is the bone marrow made of osseous tissue?
Bone marrow can mainly be found in the internal cavities of flat bones, like the vertebrae, the ribs, the scapulae, the sternum and the hips.
The bone marrow is not made of osseous tissue, although it is a connective tissue as bone tissue is.
6. What are blood stem cells?
Stem cells are undifferentiated cells able to differentiate into other types of specialized cells.
The stem cells of the bone marrow originate the differentiated blood cells. According to stimulus from specific growth factors the stem cells are turned into red blood cells, leukocytes and megakaryocytes (cells that form platelets). Research shows that stem cells of the bone marrow can also differentiate into muscle, nervous and hepatic cells.
Blood Questions - Image Diversity: blood stem cell
7. What are the other names by which erythrocytes are known? What is the function of these cells?
Erythrocytes are also known as red blood cells (RBCs), or red corpuscles. Red blood cells are responsible for oxygen transport from the lungs to the tissues.
8. What is the name of the molecule that transports oxygen in red blood cells?
The respiratory pigment of the red blood cells is hemoglobin.
9. What is the molecular composition of hemoglobin? Does the functionality of hemoglobin as a protein depend upon its tertiary or upon its quaternary structure?
Hemoglobin is a molecule made of four polypeptide chains, each bound to a iron-containing molecular group called a heme group. So the molecule contains four polypeptide chains and four heme groups.
As a protein composed of association of polypeptide chains, the functionality of hemoglobin depends upon the integrity of its quaternary structure.
Blood Questions - Image Diversity: hemoglobin molecule
10. On average what is the life duration of the red blood cells? Where are they destroyed? What is the destination of the heme groups after the destruction of hemoglobin molecules?
On average red blood cells live around 120 days. The spleen is the main organ where old red blood cells are destroyed.
During the red blood cell destruction the heme groups turn into bilirubin and this substance is then captured by the liver and later excreted in the bowels as part of the bile.
11. What are the functions of the spleen? Why is a total splenectomy (surgical removal of the spleen) compatible with life?
The spleen has many functions: it participates in the destruction of old red blood cells; in it specialized leukocytes are matured; it helps the renewal of the hematopoietic tissue of the bone marrow when necessary; it can act as a spongelike organ to retain or liberate blood from or for the circulation.
Total splenectomy is not incompatible with life as none of the functions of the spleen are vital and at the same time exclusive of this organ.
12. What is anemia? What are the four main types of anemia?
Anemia is low concentration of hemoglobin in the blood.
The four main types of anemia are the nutrient-deficiency anemia, anemia caused by blood loss, hemolytic anemia and aplastic anemia.
Nutrient-deficiency anemia is caused by dietary deficiency of fundamental nutrients for the production or functioning of the red blood cells, like iron (iron deficiency anemia), vitamin B12 and folic acid.
Anemia caused by blood loss occurs in hemorrhagic conditions or in diseases like peptic ulcerations and hookworm disease.
Hemolytic anemia is caused by excessive destruction of red blood cells, for example, in diseases like malaria or in hypervolemic conditions (excessive water in blood that causes lysis of red blood cells).
Aplastic anemia occurs from deficiencies of the hematopoiesis and it happens when the bone marrow is injured by cancers from other tissues (metastasis), by autoimmune diseases and by intoxication from drugs (like sulfas and anticonvulsants) or by chemical substances (like benzene, insecticides, paints, herbicides and solvents in general). Some genetic diseases also affect thebone marrow causing aplastic anemia.
13. What is the difference between white and red blood cells? What are leukocytes?
Red blood cells are erythrocytes and white blood cells are the leukocytes.
Leukocytes are cells specialized in the defense of the body against strange agents and they are part of the immune system.
14. What are the types of leukocytes and how are they classified into granulocytes and agranulocytes?
The types of leukocytes are lymphocytes, monocytes, neutrophils, eosinophils and basophils. Granulocytes are those in whose cytoplasm there are granules (when viewed under electronic microscopy): neutrophils, eosinophils and basophils are granulocytes. Agranulocytes are the other leukocytes: lymphocytes and monocytes.
Blood Questions - Image Diversity: lymphocytes monocytes neutrophils eosinophils basophils
15. What is the generic function of leukocytes? What are leukocytosis and leukopenia?
The generic function of leukocytes is to participate in the defense of the body against strange agents that penetrate it or are made inside the body.
Leukocytosis and leukopenia are clinical conditions in which the count of leukocytes in a blood sample is abnormal. When the leukocyte count in a blood sample is above the normal level for the individualleukocytosis is defined. When the leukocyte count is lower than the expected normal level leukopenia is defined. The multiplication of these defense cells, leukocytosis , generally takes place when the body is suffering infections or in cancers of these cells. The lowering of these defense cells, orleukopenia, occurs when some diseases attack the cells, like in AIDS, or when immunosuppressor drugs are used.
In general the body creates leukocytosis as a defense reaction when it is facing infectious or pathogenic agents. The clinical condition of leukocytosis is thus a sign of infection. Leukopenia occurs when there is a deficiency in the production (for example, in bone marrow diseases) or excessive destruction of leukocytes (for example, in case of HIV infection).
16. What are the mechanisms of hemorrhage contention called?
The physiological mechanisms of hemorrhage contention (one of them is blood clotting) are generically named hemostasis, or hemostatic processes.
17. How are platelets formed? What is the function of platelets? What consequences does the clinical condition known as thrombocytopenia yield?
Platelets, also known as thrombocytes, are fragments of giant cells of the bone marrow called megakaryocytes. With their properties of aggregation and adhesiveness they play a direct role in blood clotting and they also liberate substances that activate other hemostatic processes.
Thrombocytopenia is a clinical condition in which the platelet count of the blood is lower than normal. In this situation the person becomes susceptible to hemorrhages.
18. How does the organism understand that a clotting process must begin?
When there is some tissue wound with injury of blood vessel the platelets and endothelial cells of the wall of the damaged vessel liberate substances (respectively platelet factors and tissue factors) that trigger the clotting process.
19. How can the blood coagulation (clotting) process be described?
Blood clotting encompasses a sequence of chemical reactions whose respective products are enzymes that catalyze the following reactions (that is why the clotting reactions are called cascade reactions). In the plasma thromboplastinogen transforms into thromboplastin, a reaction triggered by tissue and platelet factors liberated after injury of the blood vessel. Thromboplastin then catalyzes along with calcium ions the transformation of prothrombin into thrombin. Thrombin then catalyzes a reaction that produces fibrin from fibrinogen. Fibrin, as an insoluble substance, precipitates to form a network that traps red blood cells and platelets forming the blood clot and containing the hemorrhage.
Blood Questions - Image Diversity: clotting cascade
20. What are clotting factors?
Clotting factors are substances (enzymes, coenzymes, reagents) necessary for the clotting stages to happen. Besides those triggering factors and reagents already described (tissue and platelet factors, thromplastinogen, prothrombin, fibrinogen, calcium ions), other substances participate in the blood clotting process as clotting factors, like factor VIII, whose deficiency causes hemophilia A, or the factor IX, whose deficiency causes hemophilia B.
21. What is the organ where most of the clotting factors are produced? What is the role of vitamin K in the blood coagulation?
Most of the clotting factors are produced in the liver.
Vitamin K participates in the activation of several clotting factors and it is fundamental for the well-functioning of the blood coagulation.
22. What is factor VIII? What is the genetic disease in which this factor is absent?
Factor VIII has the function of activating factor X that in its turn is necessary for the transformation of prothrombin into thrombin in the clotting cascade. Hemophilia A is the X-linked genetic disease in which the individual does not produce factor VIII and so is more susceptible to severe hemorrhages.
23. How is hemophilia treated? Why is hemophilia rare in females?
Hemophilia is medically treated with administration of factor VIII, in case of hemophilia A, or of factor IX, in case of hemophilia B, by means of blood or fresh frozen plasma transfusions.
Hemophilia, A or B, is an X-linked recessive inheritance and for a girl to be hemophilic it is necessary for both of her X chromosomes to be affected while boys, that have only one X chromosome, are more easily affected. A girl with only one affected chromosome does not present the disease since the normal gene of the unaffected other X chromosome produces the clotting factor.
24. What is the epidemiological association between hemophilia and HIV infection?
Since hemophilic patients need frequent transfusions of clotting factors (VIII or IX) they are more susceptible to contamination by infectious agents present in the blood from which the transfused elements come. In the past the blood banks did not usually perform HIV detection tests and many hemophilic patients have become infected with the virus.
25. What are anticoagulants? What are the practical applications of anticoagulants, like heparin, in Medicine?
Anticoagulants are substances that block the clotting reactions and thus stop the coagulation process. Ordinarily there are anticoagulants circulating in the plasma since under normal conditions the blood must be kept fluid.
In Medicine anticoagulants like heparin are used in surgeries in which tissue injuries made by the surgical act could trigger undesirable systemic blood clotting. They are also used to avoid the formation of thrombus inside blood vessels of patients facing increased thrombotic risk.
26. What is dicoumarol? How does this substance act in the clotting process and what are some examples of its toxicity?
Dicoumarol is an anticoagulant drug. Due to its molecular structure dicoumarol competes with vitamin K for the binding to substrates blocking the formation of clotting factors and interrupting the making of prothrombin. Dicoumarol is found in some vegetables undergoing decomposition, and it can cause severe internal hemorrhages when those vegetables are accidentally ingested. Coumarinic anticoagulants cannot be administered during pregnancy since they pass the placental barrier and can cause fetal hemorrhages.
27. Streptokinase is a substance used in the treatment of acute myocardial infarction. How does this substance act?
Substances known as fibrinolytics, like streptokinase and urokinase, can destroy thrombi (clots formed inside blood vessels, capillaries or within the heart chambers) and are used in the treatment of obstructions of the coronary arteries or other blood vessels.
Streptokinase destroys the fibrin network and so it dissolves the thrombotic clot. Its name comes after the bacteria that produce it, the streptococci.
Learn the Concept of Homeostasis Here
1. What is metabolism?
Metabolism is the set of physical and chemical processes upon which the life of the cells of a living being depends.
2. What is the difference between anabolism and catabolism?
Metabolism comprises two opposing processes: anabolism and catabolism. Anabolism is a set of synthesis reactions that transform simpler compounds into organic molecules in general with energy spending. Catabolism is a set of reactions that break organic molecules into simpler and less complex substances in general with liberation of energy. The energy liberated in catabolism may be used in vital processes of the organism, including anabolism.
3. What is homeostasis? What are the sensors, controllers and effectors of homeostasis?
Homeostasis comprises the processes by which the organism maintains adequate intra and extracellular conditions to keep possible the normal reactions of the metabolism.
Homeostatic sensors are structures that detect information from the inner and outer environment of the body. These sensors may be nervous receptor cells, cytoplasmic or membrane proteins and other specialized molecules. Controllers are structures responsible for processing and interpreting information received from the sensors. Controllers in general are specialized regions of the central nervous system but on the molecular level there are also some of them, like DNA, a molecule that can get information from proteins to inhibit or stimulate the expression of some genes. Effectors are elements commanded by the controllers that have the function of bringing about actions that in fact regulate and maintain the equilibrium of the organism, like muscles, glands, cellular organelles, etc., and in the molecular level structures that participate in the genetic translation, the produced proteins, etc.
4. How do antagonistic mechanisms manage homeostatic regulation?
The homeostatic maintenance of the body mostly occurs by means of alternating antagonistic compensatory mechanisms. There are regulators that lower the pH and others that increase it, there are effectors whose function is to increase the body temperature and others that lower it, hormones exist that, e.g., reduce the level of glucose in the blood and others that increase the glycemic level. The use of antagonistic mechanisms is a strategy found by evolution to solve the problem of the maintenance of the body equilibrium.
5. What is an example of negative feeback of the homeostatic regulation?
Negative feedback happens when the response to a given action generates an effect that inhibits that action. For example, when the carbon dioxide concentration in blood is high the pulmonary respiration is stimulated for the CO2 excess to be expelled through expiration. Hyperventilation, however, lowers the carbon dioxide concentration in blood too much generating anegative feedback that commands the reduction of the respiratory frequency.
Negative feedback is the main mechanism of homeostasis and it occurs in a variety of processes, such as in blood pressure control, glycemic control, muscle contraction, etc.
6. What is an example of positive feedback of the homeostatic regulation?
In positive feedback the effect caused by an action stimulates the action even more. This is a rarer mechanism of the homeostatic regulation.
An example of positive feedback is the blood clotting process in which each chemical reaction produces enzymes that catalyze the following reaction until the formation of fibrin. Therefore the products of the antecedent chemical reactions are consumed and the equilibrium of each reaction is dislocated towards the production of more enzymes (apositive feedback).
Nutrition Vitamins
1. What is a nutrient?
A nutrient is every substance used in the metabolism and which is acquired from the diet. For example, vitamins and essential amino acids are nutrients.
2. What is the difference between macro and micronutrients?
The classification criterion of nutrients into macro and micronutrients has no relation to the size of the molecule. Macronutrients are those needed in great amount, for example, proteins and carbohydrates. Micronutrients are those needed in small quantities, likevitamins.
3. According to their functions how can nutrients be classified?
One possible and utile functional classification for nutrients is the one that separates them into energetic, structural and regulatory.
Energetic nutrients are those used as energy source for the metabolism; mainly they are the carbohydrates (but fats and proteins can also be converted into acetyl-CoA and “cycle” the Krebs cycle). Structuralnutrients are those used in the support and structure of cells and tissues; they are the amino acids that form structural proteins, like collagen, the membrane proteins, the cytoskeleton proteins, the contractile proteins of the muscle tissue, etc. Regulatorynutrients are those that constitute enzymes and coenzymes of the homeostasis, metabolites of the osmotic and electrolytic equilibrium of cells and hormones; some amino acids,vitamins and mineral salts are part of this group.
4. What are vitamins? What are the main vitamins needed by humans?
Most vitamins are coenzymes (fundamental substances for the enzyme functioning) that are not produced by the organism and must be obtained from the diet.
The main vitamins needed by humans are vitamins A, C, D, E, K, the vitamins of the B complex (including folic acid), biotin and pantothenic acid.
5. What is the difference between water-soluble and fat-soluble vitamins? Why can fat-soluble vitamins cause harm when ingested in excess?
Water-soluble vitamins are those soluble in water. Fat-soluble vitamins are those soluble in oil (lipids, fat). Vitamin C and the vitamins of the B complex are examples of water-soluble vitamins. Vitamins A, D, E and K are examples of fat-soluble vitamins.
Fat-soluble vitamins, since they are not soluble in water, cannot easily be excreted by the body. So they tend to accumulate in tissues with toxic effect when they are ingested in amounts over what is necessary.
6. What are the main harms caused by vitamin A deficiency? How does this vitamin act in the physiology of vision?
Deficiency of vitamin A (retinol) may cause night blindness, corneal dryness (xerophthalmia) and predisposition to skin injuries.
In the physiology of vision, vitamin A participates in the formation of rhodopsin, a pigment responsible for the visual perception in less illuminated places.
Nutrition Vitamins - Image Diversity: vitamin A deficiency
7. What is folic acid? Why is the anemia caused by deficiency of folic acid known as megaloblastic anemia?
The folic acid (when ionized it is called folate) is a coenzyme that participates in the synthesis and duplication of DNA and for this reason it is fundamental for cell division. If there are not enough folic acid in cells with great turnover, like red blood cells, they have their production reduced.
In folic acid deficiency precursor cells (reticulocytes) that would originate erythrocytes (red blood cells) begin cell division but the process is very slow while the cytoplasm growth is normal. So the cells became abnormally large, a typical feature of this kind of anemia calledmegaloblastic anemia.
Megaloblastic anemia can be caused also by vitamin B12 (cyanocobalamin) deficiency since this vitamin is important for cell division too. Both types of anemia are nutrient deficiency anemias.
Nutrition Vitamins - Image Diversity: megaloblastic red blood cell
8. What are the vitamins which make up the B complex? Which problems does the lack of these vitamins cause?
Vitamins of the B complex are: thiamin, or vitamin B1; riboflavin, or vitamin B2, and niacin (B3), essential for the constitution of the hydrogen acceptors FAD, NAD and NADP of the energetic metabolism; pyridoxine, or B6; and cyanocobalamin, or vitamin B12.
Deficiency of vitamin B1 causes beriberi, loss of appetite and fatigue. The lack of vitamin B2 causes mucosal injuries in the mouth, tongue and lips. Deficiency of niacin causes nervousness, digestive disturbances, loss of energy and pellagra. Lack of vitamin B6 causes skin lesions, irritation and convulsions. Vitamin B12 acts together with folic acid and its deficiency causes cell division disruptions leading to pernicious anemia (a type of megaloblastic and nutrient deficiency anemia).
The absorption of vitamin B12 depends on another substance called the intrinsic factor secreted by the gastric mucosa.
Nutrition Vitamins - Image Diversity: pellagra
9. How does vitamin C act in the body? What is the harm caused by insufficiency of vitamin C? Why was this deficiency also known as “sailors' disease”?
Vitamin C, or ascorbic acid, participates in the metabolism of collagen and it is fundamental for the integrity of blood capillaries.
Scurvy is the disease caused by a lack of vitamin C. It is characterized by tissue lesions in the skin, lips, nose and joints. Scurvy, or scorbutus, was also known as sailors' disease because in maritime voyages of the past it was not common to get on board food that contained vitamin C, like citric fruits. So the sailors became ill with scurvy.
Nutrition Vitamins - Image Diversity: scurvy
10. Why isn't the cooking of vitamin C-containing foods appropriate for vitamin C supply?
To obtain vitamin C, for example, from an orange dessert, the vitamin-containing food cannot be submitted to high temperatures (cooking) since vitamin C is thermolabile, i.e., it is inactivated by heat.
11. What is the association between vitamin D and sunrays?
Vitamin D, or calciferol, is synthesized in the skin by the action of the ultraviolet range of sunrays upon precursor molecules. Later it is transformed into its active form in the liver and the kidneys.
Nutrition Vitamins - Image Diversity: vitamin D synthesis
12. What is the disease caused by vitamin D deficiency? Which tissue does it affect?
The lack of vitamin D causes the disease known as rickets (rachitis), characterized by decalcification of bones and bone deformities. Vitamin D is fundamental for absorption of calcium and thus it is related to the osseous tissue health.
Nutrition Vitamins - Image Diversity: rickets
13. What is the function of vitamin E? In which foods can it be found?
Vitamin E, or tocopherol, is a fat-soluble vitamin that participates as coenzyme in the respiratory chain, the final stage of the aerobic cellular respiration. Its deficiency may cause sterility, spontaneous abortions and muscle dystrophy.
Vitamin E is mainly found in corn oil and peanut oil, wheat germ, milk, eggs and leafy vegetables.
14. Why are some types of hemorrhagic diseases caused by genetic or acquired deficiency of the vitamin K metabolism?
Deficiency of vitamin K predisposes to hemorrhages since this vitamin is fundamental for the formation of prothrombin in the blood clotting process.
15. What are the functions of biotin and pantothenic acid for the body? How are these vitamins obtained?
Biotin (also know as vitamin B8) is a vitamin that acts in the metabolism of amino acids and other acids. Pantothenic acid (also known as vitamin B5) is important for the aerobic cellular respiration since it acts in the transport of acetyl and acyl radicals.
Biotin is made by bacteria that live in the human digestive tube (under interspecific harmonious ecological interaction) and this supply in general is enough for the body. Biotin and pantothenic acid are found in vegetables, cereals, eggs, fish, milk and lean meat.
16. What are the main mineral salts responsible for the cellular osmotic regulation?
The main ions that act in the regulation of the osmotic pressure in cells and tissues are the chlorine anion, the sodium cation and the potassium cation.
17. What are the main cellular functions of potassium?
Besides being important for the osmotic regulation and for the acid-base equilibrium (pH) potassium is fundamental for the excitatory mechanisms of nerves and in muscle contraction.
18. What are some examples of mineral salts from the diet that act as coenzymes?
Magnesium, zinc and copper are examples of biological coenzymes.
19. What is the disease caused by dietary iodine deficiency?
Iodine deficiency causes hypothyroidism, an abnormally lower production of thyroid hormones that need iodine to be synthesized.
Nutrition Vitamins - Image Diversity: thyroid goiter
20. What is the importance of iron in diet? What is the disease caused by iron deficiency?
Iron acts as a constituent of the hemoglobin molecule and of enzymes of the digestion and energetic metabolism. Dietary iron deficiency causes iron deficiency anemia, abnormal lowering of hemoglobin concentration in blood due to lack of iron. (In pregnancy there is a high consumption of iron by the fetus and this fact can lead to anemia.)
Digestive System - Questions and Answers
1. What is digestion?
Digestion is the breaking down of larger organic molecules obtained from the diet, e.g. carbohydrates, fats, proteins, into smaller ones, like glucose, fatty acids, glycerol and amino acids.
2. How different are intracellular and extracellular digestion? What is the evolutionary advantage of extracellular digestion?
Intracellular digestion is that in which the breaking down of macromolecules takes place within the cell. Extracellular digestion is that in which macromolecules are broken down in places outside the cell (in the extracellular space, in the surrounds, in the lumen of digestive tubes, etc.)
The advent of extracellular digestion in evolution allowed organisms to benefit from a greater variety of food. The breaking down of larger molecules into smaller ones outside the cell permitted the use of other foods than those that, due the size of their molecules, could not be interiorized by diffusion, phagocytosis or pinocytosis.
3. How is extracellular digestion related to cellular and tissue specialization?
A variety of specialized cells and tissues appeared with extracellular digestion to provide enzymes and special structures for the breaking down of dietary macromolecules.
This phenomenon allowed other cells to be liberated for other tasks and differentiations while benefiting from nutrients distributed through the circulation.
4. What is the difference between a complete digestive system and an incomplete digestive system? How are these types of digestive tubes associated or not to extracellular digestion?
Animals with an incomplete digestive system are those in which the digestive tube has only one opening (cnidarians, platyhelminthes). Animals with a complete digestive system are those in which the digestive tube has two openings, mouth and anus (all other animal phyla, with the exception of poriferans, that do not have any digestive tube).
In animals with incomplete digestive tubes the digestion is mixed, it begins in the extracellular space and finishes in the intracellular space. In animals with complete digestive systems extracellular digestion within thedigestive tube predominates.
5. What are some evolutionary advantages of animals with complete digestive tube?
The complete digestive tube allows animals to continuously feed themselves without waiting for residuals to be eliminated before beginning the digestion of new foods. In this way the absorption of larger amount of nutrients is possible and therefore bigger and more complex species can develop. Digestive tubes with two openings also make digestion more efficient since they provide different sites with different physical and chemical conditions (mouth, stomach, bowels) for the action of different complementary digestive enzymatic systems.
6. What is mechanical digestion? In molluscs, arthropods, earthworms, birds and vertebrates, in general, which organs respectively participate in this type of digestion?
Mechanical digestion is the fragmentation of food aided by specialized physical structures, such as teeth, previous to extracellullar digestion. The mechanical fragmentation of food helps digestive enzymatic reactions because it provides a larger total area for the contact between enzymes and their substrates.
In some molluscs, the mechanical fragmentation is done by the radula (a teeth-like structure). Some arthropods, like lobsters and dragonflies, have mouthparts that make mechanical digestion of food. In earthworms and birds, the mechanical digestion is made by an internal muscular organ. In mandibulate vertebrates there are mandibles and chewing muscles to triturate food previous to the chemical digestion.
7. Concerning extracellular digestion what is meant by chemical digestion?
Chemical digestion is the series of enzymatic reactions to break macromolecules into smaller ones.
8. Which type of chemical reaction is the breaking of macromolecules into smaller ones that occurs in digestion? What are the enzymes that participate in this process called?
The reactions of the extracellular digestion are hydrolysis reactions, i.e., breaking of molecules with the help of water. The enzymes that participate in digestion are hydrolytic enzymes.
9. Which organs of the body are part of the human digestive system?
The digestive system, also known as “systema digestorium”, or gastrointestinal system, is composed of the digestive tube organs plus the digestive adnexal glands. The digestive tube is composed of mouth, pharynx, esophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (caecum, colon, rectum) and anus.
Digestion System - Image Diversity: human digestive system
10. What are peristaltic movements? What is their role in human digestion?
Peristalsis is the process of synchronized contractions of the muscular wall of the digestive tube. Peristaltic movements may occur from the esophagus until and including the bowels.
The peristaltic movements are involuntary and they have the function of moving and mixing food along the digestive tube. Peristaltic movement deficiency, for example, in case of injuries of the innervation of the muscular wall of the digestive tube caused by Chagas’ disease, can lead to the interruption of the food traffic inside the bowels and to severe clinical consequences like megacolon (abnormal enlargement of the colon) and megaesophagus (enlargement of the esophagus).
Digestion System - Image Diversity: peristaltic movements
11. From the lumen to the external surface what are the tissues that form the digestive tube wall?
From the internal surface to the external surface, the digestive tube wall is made of mucosa (epithelial tissue responsible for the intestinal absorption), submucosa (connective tissue beneath the mucous membrane and where blood and lymphatic vessels and neural fibers are located), muscle layers (smooth muscle tissue, two layers, one interior circular and other exterior longitudinal, structures responsible for the peristaltic movement), serous membrane (associated epithelial and connective tissue forming the external surface of the organ). In the bowels the serous membrane prolongs to form the mesentery, a serosa that encloses blood vessels and supports the bowels within the abdominal cavity.
Digestion System - Image Diversity: histology of the digestive tube
12. What is the location of the salivary glands in humans?
There are 6 major salivary glands and they are located one in each parotid gland, two beneath the mandibles (submandibular) and two in the base of the tongue (sublingual). More than 700 other minor salivary glands exist dispersed on the lip mucosa, gingiva, palate and pharynx.
13. What is the approximate pH of the salivary secretion? Is it an acid or basic fluid? What are the main functions of saliva?
The saliva pH is approximately 6.8. It is thus a slightly acid pH.
Saliva lubricates the food bolus and initiates the enzymatic extracellular digestion of food. It also works as a buffer for the mouth pH and it has an important role of having IgA antibodies (also present in tears, colostrum, mother’s milk and in the mucosae of the intestine and airways) that protect the organism against pathogens.
14. What is the salivary digestive enzyme? Which type of food does it digest and into which smaller molecules does it transform the food?
The salivary hydrolase is known as salivary amylase, or ptyalin. Ptyalin digests carbohydrates breaking starch and glycogen, glucose polymers, into maltose (a glucose disaccharide) and dextrin.
15. Why doesn't the food enter the trachea instead of going to the esophagus?
When food is swallowed the swallow reflex is activated and the larynx elevates and closes to avoid portions of the food bolus entering the trachea causing aspiration of strange material to the bronchi.
Digestion System - Image Diversity: esophagus
16. Is the esophagus a muscular organ? Why even in a patient lying totally flat on a hospital bed can the swallowed food reach the stomach?
The esophagus is a predominantly muscular organ so the assertion is correct. The esophagus is a muscular tube formed in its superior third of striated muscle tissue, in its middle third of mixed muscle tissue (striated and smooth) and in its lower third of smooth muscle tissue. The peristalsis of the esophagus provides the movement of the food towards the stomach even without gravitational help.
17. What is the route of the ingested food from swallowing until the duodenum?
Until reaching the duodenum the food enters the mouth, passes the pharynx, goes down the esophagus and passes the stomach.
18. what is the valve that separates the stomach from the esophagus called? What is its function?
The valve that separates the stomach from the esophagus is the cardia. It has the function of preventing acid gastric content from entering back into the esophagus. Insufficiency of this valve causes gastroesophageal reflux, a disease in which patients complain of bloating and heartburn (retrosternal burning).
Digestion System - Image Diversity: stomach
19. What is the valve that separates the duodenum from the stomach called? What is its function?
The valve that separates the stomach from the duodenum is the pylorus. It has the function of keeping the food bolus within the gastric cavity for enough time to allow the gastric digestion to take place. It also has the function of preventing the intestinal content from going back into the stomach.
20. What is the pH inside the stomach? Why is there a need to keep that pH level? How is it maintained? Which are the cells that produce that pH?
The normal pH of the gastric juice is around 2. So it is an acid pH.
It is necessary for the gastric pH to be kept acid for the activation of pepsinogen (a proenzyme secreted by the gastric chief cells) into pepsin, the digestive enzyme that acts only under low pH. This pH level is attained by the secretion of hydrochloric acid (HCl) by the parietal cells.
Digestion System - Image Diversity: parietal cells
21. Besides being fundamental for the activation of the main gastric digestive enzyme how does HCl also directly participate in digestion?
With its corrosive effect, HCl also helps the rupture of the adhesion between food particles, facilitating the digestive process.
22. How is the gastric mucosa protected from the acid pH of the stomach?
The gastric epithelium is mucus secretory, i.e., it produces mucus. The mucus covers the stomach wall preventing corrosion by the gastric juice.
23. What is the digestive enzyme that acts within the stomach? Which type of food does it digest? What are the cells that produce that enzyme?
The digestive enzyme that acts in the stomach is pepsin. Pepsin has the function of breaking proteins into smaller peptides. The gastric cells that produce pepsinogen (the zymogen precursor of pepsin) are the chief cells.
Digestion System - Image Diversity: chief cells
24. What name does the food bolus that passes from the stomach to the duodenum get?
The partially digested and semifluid food bolus that leaves the stomach and enters the duodenum is called chyme.
25. Which are the three parts of the small intestine?
The small intestine is divided into three portions: duodenum, jejunum and ileum.
Digestion System - Image Diversity: small intestine
26. By generally dividing food into carbohydrates, fats and proteins and considering the digestive process until the pylorus (exit of stomach), which of these mentioned types of food have already undergone chemical digestion?
Until the exit of the stomach, carbohydrates, in the mouth, and proteins, in the stomach, have already undergone chemical breaking by digestive enzymes. Carbohydrates have suffered action of the salivary amylase (ptyalin) and proteins have suffered action of the enzyme pepsin of the gastric juice. Fats, until reaching the duodenum, do not undergo chemical digestion.
27. What is the substance produced in the liver that acts in the small intestine during digestion? How does that substance act in the digestive process?
Bile, an emulsifier liquid, is made by the liver and later stored within the gallbladder and released in the duodenum.
Bile is composed of bile salts, cholesterol and bile pigments. Bile salts are detergents, amphiphilic molecules, i.e., molecules with a polar water-soluble portion and a non-polar fat-soluble portion. This feature allows bile salts to enclose fats inside water-soluble micelles in a process called emulsification for them to be in contact with intestinal lipases, enzymes that break fats into simpler fatty acids and glycerol.
Digestion System - Image Diversity: gallbladder
28. What is the adnexal organ of the digestive system in which bile is stored? How does this organ react to the ingestion of fat rich food?
Bile is concentrated and stored in the gallbladder.
When fat rich foods are ingested the gallbladder contracts to release bile inside the duodenum. (This is the reason why patients with gallstones must not ingest fatty food, the reactive contraction of the gallbladder may move some of the stones to the point of blocking the duct that drains bile into the duodenum, causing pain and possible severe complications.)
29. What are the digestive functions of the liver?
Besides making bile for release in the duodenum, the liver has other digestive functions.
The venous network that absorbs nutrients from the guts, called mesenteric circulation, drains its blood content almost entirely to the hepatic portal vein. This vein irrigates the liver with absorbed material from the digestion. So the liver has the functions of storing, processing and inactivating nutrients.
Glucose is polymerized into glycogen in the liver; this organ also stores many vitamins and the iron absorbed in the intestine. Some important metabolic molecules, like albumin and clotting factors, are made in the liver from amino acids of the diet. In the liver ingested toxic substances, like alcohol and drugs, are inactivated too.
Digestion System - Image Diversity: liver
30. Besides the liver which is the other adnexal gland of the digestive system that releases substances in the duodenum participating in extracellular digestion?
The other adnexal gland of the digestive system is the pancreas. This organ makes digestive enzymes that digest proteins (proteases), lipids (lipases) and carbohydrates (pancreatic amylases). Other digestive enzymes, like gelatinase, elastase, carboxipeptidase, ribonuclease and deoxyribonuclease are also secreted by the pancreas.
Digestion System - Image Diversity: pancreas
31. How does the pancreatic juice participate in the digestion of proteins? What are the involved enzymes?
The pancreas secretes trypsinogen that, undergoing action of the enzyme enterokinase secreted by the duodenum, is transformed into trypsin. Trypsin in its turn catalyzes the activation of pancreatic chymotrypsinogen into chymotrypsin. Trypsin and chymotrypsin are proteases that break proteins into smaller peptides. The smaller peptides are then broken into amino acids by the enzyme carboxipeptidase (also secreted by the pancreas in a zymogen form and activated by trypsin) helped by the enzyme aminopeptidase made in the intestinal mucous membrane.
32. How does the pancreatic juice resume the digestion of carbohydrates? What is the involved enzyme?
Carbohydrate digestion begins with the action of the salivary amylase (ptyalin) in the mouth and it continues in the duodenum by the action of the pancreatic juice. This juice contains the enzyme pancreatic amylase, or amylopsin, that breaks starch (amylum) into maltose (a disaccharide made of two glucose molecules).
33. How does the pancreatic juice help the digestion of lipids? What is the involved enzyme?
The enzyme pancreatic lipase is present in the pancreatic juice. This enzyme breaks triacylglycerol (triglyceride) into fatty acids and glycerol.
34. Besides the pancreatic juice in the intestine there is the releasing of the enteric juice that contains digestive enzymes too. What are these enzymes and which type of molecule do each of these enzymes break?
The enteric juice is secreted by the small intestine mucosa. The enzymes of the enteric juice and their respective functions are described as follows:
Enterokinase: enzyme that activates trypsinogen into trypsin. Saccharase: enzyme that breaks sucrose (saccharose) into glucose and fructose. Maltase: enzyme that breaks maltose into two glucose molecules. Lactase: enzyme that breaks lactose into glucose and galactose. Peptidases: enzymes that break oligopeptides into amino acids. Nucleotidases: Enzymes that break nucleotides into its components (nitrogen-containing bases, phosphates and pentoses).
35. Coming from the acid pH of the stomach which pH level does the chyme find when it enters the duodenum? Why is it necessary to maintain that pH level in the small intestine? What are the organs responsible for that pH level and how is it kept?
Entering the duodenum the chyme meets the pancreatic juice under a pH of approximately 8.5. The neutralization of the chyme acidity is necessary to keep adequate pH level for the functioning of the digestive enzymes that act in the duodenum. Without the neutralization of the chyme acidity the mucous membrane of the intestine would be injured.
When stimulated by the chyme acidity the duodenum makes a hormone called secretin. Secretin stimulates the pancreas to release the pancreatic juice and also the gallbladder to expel bile in the duodenum. The pancreatic secretion, rich in bicarbonate ions, is released in the duodenum and neutralizes the chyme acidity; this acidity is also neutralized by the secretion of bile in the duodenal lumen.
36. What are the five human digestive secretions? Which of them is the only one that does not contain digestive enzymes?
The human digestive secretions are: saliva, gastric juice, bile, pancreatic juice and enteric juice. Among these secretions only the bile does not contain digestive enzymes.
37. Why do protease-supplying cells of the stomach and of the pancreas make only precursors of the active proteolytic enzymes?
The stomach and the pancreas make zymogens of the proteases pepsin, chymotrypsin and trypsin and these zymogens are released into the gastric or duodenal lumen for activation. This happens to prevent the digestion of these organs' (stomach and pancreas) own cells and tissues by the active form of the enzymes. So the production of zymogens is a protective strategy against the natural effects of the proteolytic enzymes.
38. After digestion the next step is absorption done by cells of the mucous membrane of the intestine. For this task a large absorption surface is an advantage. How is it possible in the small internal space of the body of a pluricellular organism to present a large intestinal surface?
Evolution tried to solve this problem in two ways. The simplest is the long and tubular shape of the bowels (approximately eight meters in extension), making possible that numerous small intestine loops fold closely. More efficient solutions are the intestinal villi and the microvilli of the mucosal membrane cells.
The intestinal wall is not smooth. The mucous membrane, together with its submucosa, projects inside the gut lumen like glove fingers forming invaginations and villi that multiply the available surface for absorption. In addition the epithelial cells that cover these villi have themselves numerous hairlike projections called microvilli on the external face (lumen face) of their plasma membrane. The absorptive area of the intestines is thus increased hundreds of times with these solutions.
In the jejunum and ileum there are folds that have the function of increasing the absorption surface too.
Digestion System - Image Diversity: intestinal villi microvilli
39. In which part of the digestive tube is water is chiefly absorbed? What about the mineral ions and vitamins?
Most part of water, vitamins and mineral ions are absorbed by the small intestine. The large intestine, however, is responsible for the reabsorption of nearly 10% of the ingested water, an important amount that gives consistency to feces (colon diseases can cause diarrhea).
Digestion System - Image Diversity: colon
40. From the intestinal lumen through to the tissues - what is the route of nutrients after digestion?
Monosaccharides, amino acids, mineral salts and water are absorbed by the intestinal epithelium and collected by capillary vessels of the intestinal villi. From the capillaries, nutrients go to the mesenteric circulation, a system of vessels that drains the intestinal loops. The blood of the mesenteric circulation is drained to the portal hepatic vein and some nutrients are processed by the liver. From the liver, nutrients are gathered by the hepatic veins that discharge its blood content into the inferior vena cava. Blood from the inferior vena cava then gains the right chambers of the heart and is pumped to the lungs for oxygenation. From the lungs the blood then returns to the heart where it is pumped to the tissues distributing nutrients and oxygen.
41. What is the special route that lipids follow during digestion? What are chylomicrons?
Triglycerides emulsified by the bile within micelles suffer the action of lipases that break them into fatty acids and glycerol. Fatty acids, glycerol and cholesterol are absorbed by the intestinal mucosa. In the interior of the mucosal cells fatty acids and glycerol form again triglycerides that together with cholesterol and phospholipids are packed in small vesicles covered by proteins and called chylomicrons. The chylomicrons are released in minuscule lymphatic vessels not in blood vessels and they gain the lymphatic circulation. So the lymphatic system plays an important role in the absorption of lipids.
The lymphatic circulation drains its content to the venous blood circulation. In that manner chylomicrons reach the liver where their lipid content is processed and released in the blood under the form of protein-containing complexes called lipoproteins, like HDL, VLDL and LDL.
Digestion System - Image Diversity: chylomicrons lymphatic circulation
42. What are the so-called “good” and “bad” cholesterol?
Lipoproteins are complexes made of lipids (triglycerides and cholesterol) and proteins. The lipoproteins present different densities according to the relationship between their protein and lipid quantities since lipids are less dense than proteins. Low-density lipoproteins (LDL) are those with a low protein/lipid relation; high-density lipoproteins (HDL) have a high protein/lipid relation; another group is the very low-density lipoproteins (VLDL) with very low protein/lipid relation.
LDL is known as “bad cholesterol” because it transports cholesterol from the liver to the tissues and so induces the formation of atheroma plaques inside blood vessels, a condition called atherosclerosis (do not confuse with arteriosclerosis) that can lead to severe circulatory obstructions like acute myocardial infarction, cerebrovascular accidents and thrombosis. HDL is known as “good cholesterol” since it transports cholesterol from the tissues to the liver (to be eliminated with the bile) and elevation of the HDL blood level reduces the risk of atherosclerosis. (VLDL transforms into LDL after losing triglycerides in the blood).
43. Why does the ingestion of vegetable fibers improve the bowel habit in people that suffer from hard stools?
Some types of plant fibers are not absorbed by the intestine but play an important role in the functioning of the organ. They retain water inside the bowels and thus contribute to the softening of the fecal bolus. A softer fecal bolus is easier to be eliminated during defecation. People that eat less dietary fiber may suffer from hard stools and constipation.
44. What are the main functions of the bacterial flora within the human gut?
Bacteria that live inside the gut have great importance in digestion. Some polysaccharides like cellulose, hemicellulose and pectin are not digested by the digestive enzymes secreted by the body, instead, they are broken by enzymes released by bacteria of the gastrointestinal tract. The intestinal bacterial flora also make vital substances for the functioning of the bowels facilitating or blocking the absorption of nutrients and stimulating or reducing peristalsis. Some gut bacteria are the main source of vitamin K for the body and so they are essential for the blood clotting process.
In the intestinal flora there are utile but also potentially harmful bacteria. It is estimated that more than 100 trillion bacteria live in a human gut. Some bacteria are useful too because they compete with other species preventing excessive proliferation of these bacteria.
45. The releasing of digestive secretions is controlled by hormones. What are the hormones that participate in this regulation?
The hormones that participate in the regulation of digestion are gastrin, secretin, cholecystokin and enterogastrone.
46. How is it produced and what is the function of gastrin in the digestive process?
The presence of food in the stomach stimulates the secretion of gastrin that in its turn triggers the releasing of the gastric juice.
47. Where is it produced and what is the function of secretin in the digestive process?
Secretin is made in the duodenum. The chyme acidity causes the duodenum to release this hormone that in its turn stimulates the secretion of the pancreatic juice.
48. How is it produced and what is the function of cholecystokin in the digestive process?
The fat level of the chyme detected in the duodenum stimulates the secretion of cholecystokin (CCK). CCK acts by stimulating the secretion of the pancreatic juice also, and the releasing of bile by the gallbladder.
49. Where is it produced and what is the function of enterogastrone in the digestive process?
When the chyme is too fatty there is a secretion of enterogastrone by the duodenum. This hormone reduces the peristalsis of the stomach thus slowing the entrance of food into the duodenum (as the digestion of fats takes more time).
50. What are the special structures of the avian digestive tube and their respective functions?
The digestive tube of birds has special structures, in this sequential order: the crop, the proventriculus and the gizzard.
The crop has the function of temporary storage of ingested food and it is a more dilated area of the avian esophagus. The proventriculus is the chemical stomach of the birds where food is mixed with digestive enzymes. The gizzard is a muscular pouch that serves as a mechanical stomach where the food is ground to increase the exposure area of the food particles for the digestive enzymes to act.
Digestion System - Image Diversity: avian digestive system
51. Compared to mammals do birds absorb more or less water in their digestive system? Why is this phenomenon an adaptation to flight?
Bird feces are more liquid than mammal feces, i.e., less water is absorbed in the avian digestive system. The more frequent elimination of feces in birds due to their less solid feces is an adaptation to flight since their body weight is kept lower.
52. What is meant by “mutualist exploration of cellulose digestion”, a phenomenon that occurs in some mammals and insects?
Herbivorous animals eat great amounts of cellulose, a substance not digested by their digestive enzymes. In these animals regions of the digestive tube are colonized by microorganisms that digest cellulose. This mutualist ecological interaction between animals and microorganisms occurs, e.g., in horses, cows, rabbits and in some insects such as termites.
53. Cows swallow their food once and then this food goes back to the mouth to be chewed again. How can this phenomenon be explained?
The food ingested by cows and other ruminant animals passes first within two compartments of the digestive tube called the rumen and the reticulum. Within them the food suffers the action of digestive enzymes released by microorganisms that live there in mutualist ecological interaction. In the reticulum the food is divided in some food bolus too. After passing the reticulum the food (cud) is regurgitated to the mouth to be again chewed and swallowed in a process called rumination. The digesting food then enters the omasum where it is mechanically mixed. After that the food goes to the abomasum, the organ where the chemical digestion takes place. After leaving the abomasum (the true stomach) the food bolus gains the intestine.
Digestion System - Image Diversity: ruminant digestive system
The Breathing Process - Questions and Answers
1. What is the difference between respiration meaning gas exchange and cellular respiration?
Respiration meaning gas exchange is the process in which an organism absorbs from the environment gases necessary for its cellular metabolism and expels gases that are products of this metabolism. Cellular respiration (aerobic or anaerobic) is the chemical reaction in which organic molecules are degraded to make ATP molecules, the main energy source for the metabolism.
Gas exchange is fundamental for cellular respiration since the supplying of some reagents (oxygen, in aerobic cellular respiration) and the expelling of some products (e.g., carbon dioxide) of this chemical reaction depends on gas exchange.
2. What is the chemical equation of the aerobic cellular respiration?
The chemical equation of the aerobic cellular respiration is the following:
C6H12O6 + 6 O2 + 36 ADP + 36 P --> 6 CO2 + 6 H2O + 36 ATP
3. Considering the chemical equation of the aerobic cellular respiration which molecules does the cell need and which molecules does it liberate in the process?
Considering the chemical equation of the aerobic cellular respiration it is observed that glucose and molecular oxygen are needed as reagents and carbon dioxide and water are released. The process also spends ADP and phosphate that turn into ATP.
4. What are the different types of gas exchange that occur in animals?
In beings from the kingdom Animalia the gas exchange may occur either by diffusion, tracheal respiration, cutaneous respiration, branchial respiration or pulmonary respiration.
5. Oxygen comes from the environment and carbon dioxide in the end returns to the environment. How do small animals solve the problem of taking away and bringing these molecules from/to their cells? Why isn't that solution possible for larger animals?
Small animals whose tissues make direct contact or are very close to the environment, like cnidarians and poriferans, make gas exchange by diffusion.
Larger animals with cells without direct contact with the environment or far from it need special gas transportation systems. In these animals the respiratory and the circulatory systems play this role.
Breathing Process Review - Image Diversity: respiratory system
6. Beings from four phyla of the animal kingdom “breath” (do gas exchange) by diffusion. Which are those phyla? How is this type of respiration associated to features present in those animals?
The phyla of the animal kingdom whose beings do gas exchange by diffusion are the poriferans, the cnidarians, the platyelminthes (flatworms) and the nematodes (roundworms). This type of respiration in these beings is possible because their tissues and cells are relatively close to the exterior.
7. Which animals make tracheal respiration? Is there a blood-like fluid that participates in this process?
Insects and arachnids are the arthropod animals that make tracheal respiration. In the body surface of these animals there are many orifices called spiracles that communicate with small tubules, the tracheae, through which air penetrates andcarbon dioxide is expelled. The tracheae ramify into tracheoles that reach all tissues of the animal.
In the circulatory system of insects the blood only transports nutrients; gases are independently transported by the tracheal system.
8. What is the difference between respiration by diffusion and cutaneous respiration? Does blood participate in cutaneous respiration?
Cutaneous respiration is not as simple as diffusion. In diffusion the gases diffuse directly between the external environment and the cells. In cutaneousrespiration molecular oxygen penetrates through the skin and it is collected by the blood circulation that then distributes the gas to the tissues.Carbon dioxide is also collected from the tissues by the blood and taken to the skin to be eliminated to the environment. So there is important participation of blood in cutaneous respiration.
Breathing Process Review - Image Diversity: cutaneous respiration
9. Which animals make cutaneous respiration?
Terrestrial annelids and adult amphibians make cutaneous respiration (in amphibians there is also pulmonary respiration).
The thin skin and the need for living in moist surrounds are typical features of these animals are.
10. What are branchiae? What are examples of animals that “breath” through branchiae?
Branchiae, also known as gills, are small portions of richly vascularized tissues internal or external to the body and in direct contact with the surrounding water. The gills are organs that makegas exchange in aquatic annelids, crustaceans, fishes and amphibian larvae (e.g., tadpoles).
Breathing Process Review - Image Diversity: gills
11. What is the difference between gills and lungs?
Gills and lungs are richly vascularized organs that serve for gas exchange between the environment and the circulatory system.
The lungs differentiate from gills in that they are saclike structures always internal to the organism and specialized in gas exchange in terrestrial environment. Branchiae, in their turn, are internal or external laminar structures in direct contact with water and specialized ingas exchange in aquatic environment.
Breathing Process Review - Image Diversity: lungs
12. Besides vertebrates two invertebrate phyla contain species that make pulmonary respiration. Which are these phyla?
Terrestrial molluscs and the arachnid arthropods are the invertebrates that present pulmonary-like respiration. Some terrestrial molluscs have a mantle cavity filled with air that makes contact with richly vascularized tissues that work as rudimentary lungs. Besides their trachealrespiration some arachnids have book lungs (thin folds resembling leaves of a book) that make gas exchange.
13. What are the three types of respiration in which the circulatory system transports gases?
The circulatory system has an important role in cutaneous respiration, branchial respiration and pulmonary respiration. The respiratory function of the blood is tailored for transportation of gases for exchange between tissues and respiratory surfaces in contact with the exterior (skin, gills, lungs).
14. What are respiratory pigments? What are some respiratory pigments and in which animal groups can each of them be found?
Respiratory pigments are molecules present in the blood that bind to oxygen transporting it to the tissues.
In vertebrates the respiratory pigment is hemoglobin, reddish due to the iron of its composition. In crustacean and arachnid arthropods and in some molluscs the respiratory pigment is hemocyanin, blue due to the copper of its composition. Annelids have hemoglobin, hemerythrin and chlorocruorin as respiratory pigments.
Breathing Process Review - Image Diversity: respiratory pigments
15. What are the organs that form the human respiratory system?
The organs that are part of the human respiratory system can be divided into three groups: lungs, airway and respiratory muscles.
The lungs are the right and the left lungs made of alveoli where gas exchange (entrance of oxygen and exit of carbon dioxide) takes place; the lungs are covered by the pleura (a serous membrane). The airway comprehends the nose, the pharynx, the larynx (including the vocal cords), the trachea, the bronchi and the bronchioles. The muscles upon which the breathing process depends are mainly the diaphragm and the intercostal muscles (muscles between the ribs).
Breathing Process Review - Image Diversity: airway
16. What is the anatomical reason for the left bronchus to be more elevated than the right bronchus? Why in most cases of aspiration of foreign material by children is the object found in the right bronchus?
The left bronchus is more elevated than the right bronchus because of the position of the heart in the left side of the chest, anterior and inferior to the left bronchus.
Accidentally aspired objects are frequently found in the right bronchus because the inferior angle between the trachea and this bronchus is lower than the inferior angle between the trachea and the left bronchus since the left bronchus is more horizontalized. Therefore aspired objects tend to fall in the right side (bronchus) and not in the left.
17. How does the body defend itself from microorganisms and other harmful substances that enter the airway during the breathing process?
The epithelium of the airway is a ciliated epithelium and has mucus-secreting specialized cells. The secreted mucus covers the internal wall of the airway retaining organisms and foreign particles that then are swept by the cilia of the epithelium.
In the mucous ciliated epithelium of the airway there is also intense activity of the immune system with antibodies and leukocytes inactivating and destroying foreign agents.
Other defense mechanisms of the airway are the sneeze and the cough. They help the elimination of solid and semifluid particles like pathologic residuals (sputum) and accidentally aspired objects.
Breathing Process Review - Image Diversity: airway epithelium
18. Which are the respiratory muscles in mammals?
In mammals the muscles that participate in the breathing process are the diaphragm and the intercostal muscles. In respiratory insufficiency other muscles can help the respiration, the muscles of the shoulders, neck, thorax and abdomen.
Breathing Process Review - Image Diversity: respiratory muscles
19. How are inhalation and expiration carried out?
The diaphragm (exclusive of mammals) and the intercostal muscles can contract or relax varying the volume of the thorax (the compartment where the lungs are located). The changing of the thorax volume forces inhalation or expiration.
When the thorax volume is increased an internal pressure lower than the atmospheric pressure (external) is created and gases naturally enter the lungs. When the thorax volume is lowered the internal pressure rises above the external pressure and the air is expelled from the lungs.
20. What is the difference between arterial and venous blood?
Arterial blood is the oxygen-rich and carbon dioxide-poor blood that irrigates the tissues. Venous blood is the oxygen-poor and carbon dioxide-rich blood collected from the tissues.
21. What is hematosis? In humans where does hematosis occur?
Hematosis is the oxygenation of the blood. Venous blood (oxygen-poor) after hematosis is transformed into arterial blood (oxygen-rich).
In humans hematosis takes place in the lungs.
22. What are the blood vessels that carry venous blood to the heart? What is the blood vessel that collects arterial blood from the heart?
The blood vessels that debouch in the heart carrying venous blood are the inferior and the superior vena cava. The blood vessel that carries arterial blood from the heart is the aorta.
Breathing Process Review - Image Diversity: vena cava aorta
23. What is the gas exchange unit of the mammalian lungs?
The gas exchange units of the mammalian lungs are the alveoli.
Breathing Process Review - Image Diversity: alveoli
24. What is the physical process through which gas exchange is accomplished in the pulmonary alveoli?
The gas exchange (entry of oxygen and exit of carbon dioxide) in the pulmonary alveoli occurs by simple diffusion in favor of the partial pressure gradient.
When the oxygen partial pressure in the inhaled air is higher than the oxygen partial pressure of the capillaries of the alveoli the air diffuses to the circulatory system. If the oxygen partial pressure in the air is lower (a rare situation since the blood that reaches the alveoli is venous blood) the oxygen exits the circulatory system. The same is true for carbon dioxide.
25. What is the structure of the central nervous system that regulates pulmonary respiration?
The pulmonary respiration is controlled by the neural respiratory center located within the medulla (the lower part of the brain continuous to the spinal cord).
Breathing Process Review - Image Diversity: medulla respiratory center
26. What is the chemical equation of the formation of bicarbonate from carbon dioxide and water? What is the enzyme that catalyzes this reaction?
The chemical equation of the chemical equilibrium of the formation of bicarbonate having as reagents carbon dioxide and water is as follows:
CO2 + H20 --> H2CO3 --> H+ + HCO3-
The reaction is catalyzed by the enzyme carbonic anhydrase present in red blood cells.
27. What are the consequences of shifting the chemical equilibrium of the formation of bicarbonate from carbon dioxide and water towards the increase of product (bicarbonate) formation?
The increase in product formation in the chemical equilibrium of the formation of bicarbonate from carbon dioxide and water heightens the concentration of hydrogen ions and thus lowers the pH of the solution.
28. What are the consequences of shifting the chemical equilibrium of the formation of bicarbonate from carbon dioxide and water towards the consumption of products of the reverse reaction?
The shifting of the chemical equilibrium of the formation of bicarbonate from carbon dioxide and water into the reverse reaction (production of water and carbon dioxide) means spending of hydrogen ions and thus it increases the solution pH.
29. How does the pulmonary ventilation affect the carbon dioxide concentration in blood? What happens to the carbon dioxide concentration and to the blood pH when the respiratory frequency is either lowered or increased?
The pulmonary ventilation frequency (number of inhalations per time unit) rises or lowers the carbon dioxide concentration in blood. If it is intense the gas is more eliminated to the exterior and if it is reduced the gas is retained inside the organism.
Applying the principles of chemical equilibriums to the formation of bicarbonate from carbon dioxide and water one gets the following: if the carbon dioxide concentration is increased the equilibrium shifts towards the formation of bicarbonate and liberation of hydrogen ions and the pH of the solution is lowered; if the carbon dioxide concentration is lowered the equilibrium shifts reversely towards the formation of water and carbon dioxide and also of more hydrogen ions spending and the pH of the solution is raised.
30. What are acidosis and alkalosis?
Acidosis is the condition in which the blood pH is abnormally low. Alkalosis is the condition in which the blood pH is abnormally high. Normal pH levels for the human blood are between 7.35 and 7.45 - slightly alkaline.
31. How does the breathing process correct acidosis?
If the body experiences acidosis the respiratory center located in the medulla gets the information and induces the increase of the respiratory frequency. The increment of the respiratory frequency makes the body eliminate more carbon dioxide and to shift the equilibrium of the formation of bicarbonate towards the spending of more hydrogen ions and thus the blood pH raises.
32. How does the breathing process correct alkalosis?
If the body undergoes alkalosis the respiratory center located in the medulla gets the information and induces the lowering of the respiratory frequency. The reduction of the respiratory frequency makes the body retain more carbon dioxide and to shift the equilibrium of the formation of bicarbonate towards the production of more hydrogen ions and thus the blood pH lowers.
33. What is the difference between respiratory acidosis and metabolic acidosis and what is the difference between respiratory alkalosis and metabolic alkalosis?
Respiratory acidosis is that in which the blood pH is low due to increased retention of carbon dioxide caused by the lowering of the respiratory frequency or by pulmonary diseases that impair the gas exchange. So the cause of the respiratory acidosis is the pulmonary respiration. Metabolic acidosis is that in which the blood pH is low not due to the pulmonary retention of carbon dioxide but due to metabolic disturbances. Some metabolic disturbances result in liberation in the blood of nonvolatile acids that release hydrogen ions lowering the blood pH (e.g., diabetic ketoacidosis).
Respiratory alkalosis is that in which the pH is high due to increased expelling of carbon dioxide caused by elevated respiratory frequency. Metabolic alkalosis is the alkalosis caused by metabolic disturbances that increase the concentration of bases (alkalis) in the blood.
34. Where are the chemoreceptors that detect the acidity of the blood and trigger the respiratory compensation located?
The chemoreceptors that participate in the ventilation control are structures that collect information about the acidity and alkalinity of the blood. The information is then transmitted by nervous fibers to the respiratory center located within the medulla. The center then commands the respiratory muscles to compensate the abnormal pH.
There are central and peripheral chemoreceptors. Peripheral chemoreceptors of pH, carbon dioxide partial pressure and oxygen partial pressure are located in the walls of the aorta and of the carotid arteries. Central chemoreceptors that get pH information are located within the medulla in the respiratory center. (The pulmonary ventilation is also controlled by receptors that receive pH information from the cerebrospinal fluid.)
The Circulatory System
1. What is circulation?
Circulation is the movement of substances like nutrients and gases within blood vessels and cavities throughout the organism.
2. Do all animals have a circulatory system?
Not all animals have a circulatory system.
Poriferans, cnidarians, platyhelminthes and nematodes (in these there are the pseudocoelom fluid but no vessels) are avascular animals. Echinoderms do not have true circulatory systems either.
3. What is the alternative means for transport of substances in animals without a circulatory system? Why is blood important for larger animals?
In animals that do not present the circulatory system the transport of substances occurs by cell to cell diffusion.
The blood is a fundamental means of substance transport for larger animals since in these animals there are tissues distant from each other and from the environment thus making diffusion impossible.
4. What are the two types of circulatory systems?
The circulatory systems can be classified into open circulatory system and closed circulatory system.
5. What is an open circulatory system?
Open circulatory system is the one in which blood does not circulate only inside blood vessels but it also falls in cavities that irrigate tissues. In the open circulatory system the blood pressure is low and generally the blood (called hemolymph) has low cellularity.
Arthropods, molluscs (the cephalopods are exception) and protochordates have open circulatory system.
The Circulatory System - Image Diversity: open circulatory system
6. What is a closed circulatory system?
A closed circulatory system is one in which blood circulates only inside blood vessels. For this reason the blood pressure is higher in animals with closed circulatory system. The cellularity of the blood is also higher with many specific blood cells.
The closed circulatory system is a feature of annelids, cephalopod molluscs and vertebrates.
The Circulatory System - Image Diversity: closed circulatory system
7. What are the advantages of the closed circulatory system over the open circulatory system?
The closed circulatory system is more efficient. Since blood circulates only inside blood vessels it can do it with more pressure reaching farther distances between the organs where hematosis happens and the peripheral tissues. In addition the circulatory speed also heightens making possible more oxygen supply to great consuming tissues, like the muscle tissues that then can perform faster movements. Animals withan open circulatory system (with the exception of insects that do gas exchange independently from the circulation) are generally slower and have a low metabolic rate.
8. What is the difference between octopuses and mussels regarding their circulatory systems? How does that difference influence the mobility of these animals?
Cephalopod molluscs, like octopuses and squids, have a closed circulatory system with blood pumped under pressure flowing within vessels. Bivalve molluscs, like mussels and oysters, have an open circulatory system (also known as lacunar circulatory system) where blood flows under low pressure since it falls in cavities of the body and does not only circulate within blood vessels. Molluscs with closed circulatory systems are larger, agile and can actively move; molluscs with open circulatory systems are smaller, slow and some are practically sessile.
9. Why, even thoough they have an open circulatory system, can flying insects like flies beat their wings with great speed?
In insects the circulatory system is open but this system does not participate in the gas exchange process and in oxygen supply to the tissues. Gases go in and out through the independent tracheal system that allows direct contact of cells with the ambient air. Therefore an insect can supply the great oxygen demand of its fast-beating wing muscles even having opencirculatory system.
10. What are the typical components of a closed circulatory system?
The typical components of the closed circulatory system are the blood vessels within which blood circulates (arteries, veins and capillaries), a pumping organ (heart) and the blood or bloodlike fluid.
The Circulatory System - Image Diversity: blood vessels
11. How does the heart impel the blood?
The heart is a muscular organ that contains chambers (right atrium and right ventricle and left atrium and right ventricle) through which blood passes. The blood enters the heart in the atria, goes to the ventricles and then leaves the organ.
The blood is pumped out of the heart by the contraction of the muscle fibers that form the ventricular walls. The contraction reduces the ventricle volume thus increasing the internal pressure and the blood then flows to the exit vessels (pulmonary artery for the right ventricle and aorta for the left ventricle). When ventricular muscle fibers distend the ventricles regain their original size and receive new blood flow coming from the atria.
The Circulatory System - Image Diversity: heart structure
12. What is the difference between systole and diastole
Systole and diastole are the two stages into which the cardiac cycle is divided. Systole is the stage when the contraction of ventricular muscle fibers occurs and the ventricles are emptied. Diastole is the stage of the cardiac cycle when the ventricular muscle fibers distend and the ventricles are filled with blood.
The Circulatory System - Image Diversity: cardiac cycle
13. What are arterial vessels, arteries and arterioles?
Arterial vessels are every blood vessel that carries blood from the heart to the tissues. Arteries and arterioles are arterial vessels. Arterioles are thin arteries that end in capillaries.
Not all arteries however contain arterial blood (highly oxygenated blood). The pulmonary artery and its ramifications, arteries that carry blood from the right heart ventricle to the lungs, contain venous blood.
The Circulatory System - Image Diversity: arteries arterioles
14. What are venous vessels, veins and venules?
Venous vessels are every blood vessel that carries blood from the tissues to the heart. Veins and venules are venous vessels. Venules are thin veins that are continuous to capillaries.
In general venous vessels carry venous blood. The pulmonary veins that carry blood from the lungs to the left atrium of the heart however contain arterial blood.
The Circulatory System - Image Diversity: veins venules
15. What are the capillaries of the vascular system?
Capillaries are small blood vessels that perform exchange of substances between the blood and the body tissues. Capillaries are neither arteries nor are they veins since they have distinct features. In capillaries the wall is made of a single layer of endothelial cells through whichsubstances are exchanged. These vessels receive blood from the arterioles and drain to the venules.
The Circulatory System - Image Diversity: blood capillaries
16. What is the part of the vascular system that performs exchange of gases and other substances with the tissues?
Only capillaries perform exchange of gases and other substances with the tissues.
17. Are the arteries or the veins constituted of more muscle tissue? How different are the walls of these two types of blood vessels?
The arterial system has thicker muscle walls since within arteries the blood circulates under higher pressure. The veins are more flaccid than arteries.
From the lumen to the external layer both types of vessels are made of endothelium, muscle tissue and connective tissue. In both the endothelium is a single layer of cells. In arteries the muscle tissue portion is thicker than in veins and in these vessels the external connective tissue is thicker than in arteries.
Arteries are the pulsating blood vessels. The arterial pulse can be felt in a medical examination, for example, by the palpation of the radial artery in the internal and lateral face of the wrist near the base of the thumb.
The Circulatory System - Image Diversity: artery histology vein histology
18. What are the valves of the venous system? What is their function?
The valves of the venous system are structures inside the veins that permit blood to flow only in the normal way (from the tissues to the heart) and forbid it to return in the reverse way in favor of gravity. The valves close when the pressure of the fluid column above (after, regarding normal flux) is higher than the fluid pressure before them. Valves are thus fundamental for the returning of blood to the heart.
The Circulatory System - Image Diversity: Venous valves
19. How do the muscles of the legs and of the feet contribute to the venous return?
The muscles of the legs, mainly the muscles of the calves, contract and compress the deep veins of the legs impelling the blood to the heart.
The plantar portion of the feet retains blood and when it is compressed against the ground it impels its blood volume and aids venous return.
20. What are varices? Why are they more common in the inferior limbs?
Varix means abnormal enlargement of veins. Varices occur when excessive pressure against the normal blood flux creates enlargement of the vein and thus insufficient functioning of its valves (venous insufficiency).
Varices are more common in the veins of the inferior limbs since the fluid column above these vessels is higher. This is the reason why people that spend much time standing (e.g., surgeons) are more susceptible to varices.
In general varices are not the apparent superficial veins that appear in the leg of varix patients. These apparent vessels are the consequences of internal varices (venous insufficiency) in the deep internal veins of the legs and they appear because the blood flux is diverted to superficial veins. (Popularly however apparent superficial veins are called varices.)
The Circulatory System - Image Diversity: varices
21. What is the lymphatic system?
The lymphatic system is a network of specialized valved vessels that drain interstitial fluid (lymph). The lymphatic system is also responsible for the transport of chylomicrons (vesicles that contain lipids) made after the absorption of fats by the intestinal epithelium.
In the way of the lymphatic vessels there are ganglial-like structures called lymph nodes that contain many cells of the immune system. These cells filter impurities and destroy microorganisms and cellular wastes. The lymphatic vessels drain to two major lymphatic vessels, the thoracic duct and the right lymphatic duct, that in their turns drain into tributary veins of the superior vena cava.
The Circulatory System - Image Diversity: lymphatic system
22. Why in inflammatory and infectious conditions may clinical signs related to the lymphatic system occur?
The lymph nodes, or lymph glands, have lymphoid tissue that produces lymphocytes (a type of leukocyte). In inflammatory and infectious conditions the enlargement of lymph nodes of the lymphatic circuits that drain the affected region due to the reactive proliferation of leukocytes is common. This enlargement is known as lymphadenomegaly and sometimes it is accompanied by pain. The search for enlarged or painful lymph nodes is part of the medical examination since these findings may suggest inflammation, infection or other diseases.
The Circulatory System - Image Diversity: lymphadenopathy
23. Which are the heart chambers respectively where the entrance and the exit of blood occur?
The heart chambers through which blood enters the heart are the atria. There are the right atrium and the left atrium.
The heart chambers through which the blood exits the heart are the ventricles. There are the right ventricle and the left ventricle.
The Circulatory System - Image Diversity: heart chambers
24. Concerning the thickness of their walls how different are the heart chambers?
The ventricle walls are thicker than the atrium walls since ventricles are structures responsible for the pumping of the blood to the lungs or tissues. The muscular work of the ventricles is harder and their muscle fibers develop more.
The left ventricle is more muscular than the right ventricle because pumping blood to the lungs (the right ventricle task) is easier (needs less pressure) than pumping blood to the other tissues of the body (the left ventricle task).
25. What is vena cava? Which type of blood circulates within the vena cava?
The vena cava are either of two large veins that debouch into the right atrium. The superior vena cava drains all blood that comes from the head, the superior limbs, the neck and the superior portion of the trunk. The inferior vena cava carries blood drained from the inferior portion of the trunk and the inferior limbs.
Venous blood circulates within the vena cava.
The Circulatory System - Image Diversity: vena cava
26. Which is the first (human) heart chamber into which blood enters? Where does the blood go after passing that chamber? What is the name of the valve that separates the compartments? Why is that valve necessary?
The venous blood that comes from the tissues arrives in the right atrium of the heart. From the right atrium the blood goes to the right ventricle. The valve that separates the right ventricle from the right atrium is the tricuspid valve (a valvular system made of three leaflets). The tricuspid valve is necessary to prevent returning of blood to the right atrium during systole (contraction of ventricles).
The Circulatory System - Image Diversity: heart circulation
27. What is the function of the right ventricle? To where does the right ventricle pump the venous blood?
The function of the right ventricle is to get venous blood from the right atrium and pump the blood to be oxygenated in the lungs.
The venous blood is carried from the right ventricle to the lungs by the pulmonary artery and their ramifications.
28. What is the valve that separates the right ventricle from the pulmonary artery? Why is that valve important?
The valve that separates the right ventricle and the base of the pulmonary artery is the pulmonary valve. The pulmonary valve is important to prevent blood from the pulmonary circulation to flow back to the heart during diastole.
The Circulatory System - Image Diversity: pulmonary valve pulmonary artery
29. Do the arteries that carry blood from the heart to the lungs contain arterial or venous blood? What happens to the blood when it passes through the lungs?
Arteries of the pulmonary circulation are arteries that carry venous blood and not arterial blood.
When the blood passes within the alveolar capillaries of the lungs hematosis (oxygenation) occurs and carbon dioxide is released to the exterior.
30. What and how many are the pulmonary veins?
The pulmonary veins are part of the pulmonary circulation. They are vessels that carry oxygen-rich (arterial) blood from the lungs to the heart. There are four pulmonary veins, two that drain blood from the right lung and other two that drain the left lung. The pulmonary veins debouch into the left atrium bringing arterial blood to the heart. Although they are veins they carry arterial blood and not venous blood.
The Circulatory System - Image Diversity: pulmonary veins
31. To which heart chamber does the blood go after leaving the left atrium? What is the valve that separates these compartments?
The arterial blood that has come from the lungs to the left atrium passes then to the left ventricle.
The valve between the left ventricle and the left atrium is the mitral valve, a bicuspid (two leaflets) valve. The mitral valve is important because it prevents the regurgitation of blood to the left atrium during systole (contraction of the ventricles).
The Circulatory System - Image Diversity: mitral valve
32. What is the function of the left ventricle? Where does the blood go after leaving the left ventricle?
The function of the left ventricle is to get blood from the left atrium and to pump the blood under high pressure to the systemic circulation. After leaving the left ventricle the blood enters the aorta, the largest artery of the body.
The Circulatory System - Image Diversity: aorta
33. What is the valve that separates the aorta from the heart? What is the importance of that valve?
The valve between the left ventricle and the aorta is the aortic valve. The aortic valve prevents the retrograde flux of blood to the left ventricle during diastole. Besides, as the aortic valve closes during diastole, part of the retrograde blood flux is impelled through the coronary ostia (openings), orifices located in the aorta wall just after the valvular insertion and contiguous to the coronary circulation responsible for the blood supply of the cardiac tissues.
The Circulatory System - Image Diversity: coronary ostia coronary circulation
34. Is the ventricle lumen larger during systole or during diastole?
Systole is the stage of the cardiac cycle on which the ventricles contract. So the lumen of these chambers is reduced and the pressure upon the blood within them is heightened.
During diastole the opposite occurs. The muscle fibers of the ventricles relax and the lumen of these chambers enlarges helping the entrance of blood.
35. What is the stage of the cardiac cycle during which the ventricles are filled?
The filling of the ventricles with blood occurs during diastole.
The Circulatory System - Image Diversity: cardiac cycle
36. Of which type of tissue is the heart made? How is this tissue oxygenated and nutrified?
The heart is made of striated cardiac muscle tissue. The heart muscle is called the myocardium and it is oxygenated and nutrified by the coronary arteries. The coronary arteries come from the base of the aorta and ramify around the heart penetrating the myocardium.
Diseases of the coronary arteries are severe conditions.
The Circulatory System - Image Diversity: myocardium
37. Which are the two main metabolic gases transported by the blood?
The main metabolic gases transported by the blood are molecular oxygen (O2) and carbon dioxide (CO2).
38. How do respiratory pigments act?
Respiratory pigments are oxygen-carrying molecules present in the blood. When the oxygen concentration is high, for example, in the pulmonary alveoli, the respiratory pigments bind to the gas. In conditions of low oxygen concentration, e.g., in tissues, the respiratory pigments release the molecule.
In the human blood the respiratory pigment is hemoglobin, present within the red blood cells.
39. How different are oxyhemoglobin and hemoglobin? Where is it expected to find a higher concentration of oxyhemoglobin, in peripheral tissues or in the lungs?
Oxygen-bound hemoglobin is called oxyhemoglobin. In the lungs the oxygen concentration is higher and so there is a higher oxyhemoglobin concentration. In the peripheral tissues the situation is the reverse, the concentration of oxygen is lower and there is more free hemoglobin.
The Circulatory System - Image Diversity: oxyhemoglobin
40. What is hemoglobin F? Why does the fetus need a different hemoglobin?
Hemoglobin F is the hemoglobin found in the mammalian fetus and hemoglobin A is the normal hemoglobin. Hemoglobin F has higher affinity for oxygen.
The fetus needs hemoglobin capable of extracting oxygen from the mother’s circulation. Therefore the fetus uses hemoglobin F since it has higher affinity for oxygen than the mother’s hemoglobin.
The Circulatory System - Image Diversity: hemoglobin F
41. In high altitudes is it necessary for the blood to have more or less hemoglobin?
In high altitudes the air is rarefied and oxygen concentration is lower than in low altitudes. In this situation the efficiency of the respiratory system must be greater and thus the organism synthesizes more hemoglobin (and more red blood cells) trying to get more oxygen. This phenomenon is known as compensatory hyperglobulinemia.
The compensatory hyperglobulinemia is the reason why athletes that will compete in high altitudes need to arrive in the place some days before the event so there is time for their body to make more red blood cells and they will be less affected by the effects of the low atmospheric oxygen concentration (fatigue, reduced muscular strength).
42. What is the substance that stimulates the production of red blood cells? Which is the organ that secretes it? Under what conditions does this secretion increase?
The substance that stimulates the production of red blood cells by the bone marrow is erythropoietin. Erythropoietin is a hormone secreted by the kidneys. Its secretion is increased when there is deficient tissue oxygenation (tissue hypoxia) caused either by reduced oxygen availability (as it occurs in high altitudes) or by internal diseases, as in pulmonary diseases.
43. Why is carbon monoxide toxic for humans?
Hemoglobin “likes” carbon monoxide (CO) much more than it likes oxygen. When there is carbon monoxide in the inhaled air it binds to hemoglobin forming carboxyhemoglobin by occupying the binding site where oxygen would bind. Due to the higher hemoglobin affinity for carbon monoxide thus (e.g., in intoxication from car exhausts) there is no oxygen transport and the individual undergoes hypoxia, loses conscience, inhales more carbon monoxide and may even die.
Intoxication by carbon monoxide is an important cause of death in fires and in closed garages.
44. What is the stage of cellular respiration during which carbon dioxide is liberated?
In aerobic cellular respiration the release of carbon dioxide happens in the transformation of pyruvic acid into acetyl-CoA (two molecules) and in the Krebs cycle (four molecules). For each glucose molecule, six carbon dioxide molecules are made.
45. How is carbon dioxide released by cellular respiration transported from the tissues to be eliminated through the lungs?
In vertebrates almost 70% of the carbon dioxide is transported by the blood in the form of bicarbonate, 25% bound to hemoglobin and 5% dissolved in the plasma.
46. What is the difference between double closed circulation and simple closed circulation?
Double closed circulation, or closed circulation, is that in which the blood circulates through two associated and parallel vascular systems: one that carries blood to and takes blood from the peripheral tissues (the systemic circulation) and the other that carries blood to and takes blood from the tissues that perform gas exchange with the environment, e.g, the lungs (pulmonary circulation). Double circulation occurs in amphibians, reptiles, birds and mammals.
Simple closed circulation, or simple circulation, is the one in which the tissues that perform gas exchange are associated in series with the systemic circulation, as in fishes.
47. How many chambers does the fish heart have?
The fish heart is a tube made of two consecutive chambers: one atrium and one ventricle.
48. Does the fish heart pump venous or arterial blood?
The venous blood coming from the tissues enters the atrium and passes to the ventricle that then pumps the blood towards the gills. After oxygenation in the gills the arterial blood goes to the tissues. So the fish heart pumps venous blood.
49. Why is the fish circulation classified as a simple and complete circulation?
Complete circulation is that in which there is no mixture of venous blood and arterial blood. Simple circulation is that in which the blood circulates only in one circuit (as opposed to the double circulation that have two circuits, the systemic circulation and the pulmonary circulation). In fishes the circulatory system is simple and complete.
50. How many heart chambers does the amphibian heart have?
The amphibian heart has three heart chambers: two atria and one ventricle.
51. Why can the amphibian circulation be classified as double and incomplete?
The amphibian circulation is double because it is composed of systemic and pulmonary circulations: respectively, heart-tissues-heart and heart-lungs-heart. Since amphibians have only one ventricle in the heart, venous blood taken from the tissues and arterial blood coming from the lungs are mixed in the ventricle that then pumps the mixture back to the systemic and to the pulmonary circulations. The amphibian circulation is classified as incomplete because venous and arterial blood mix in the circuit.
The blood oxygenation in amphibians occurs also in the systemic circulation since their skin is a gas exchange organ.
52. What is the difference between the amphibian heart and the reptile heart?
The reptiles have double and incomplete circulation too, three heart chambers (two atria and one ventricle). The reptile heart however presents the beginning of a ventricular septation that partially separates a right and left region of the chamber. With the partial ventricular septation the mixture of arterial with venous blood in the reptile heart is less than in amphibians.
53. How many chambers do the bird heart and the mammalian heart have? Concerning temperature maintenance what is the advantage of the double and complete circulation of these animals?
The bird and the mammalian hearts are divided into four chambers: right atrium, right ventricle, left atrium and left ventricle.
Birds and mammals are homeothermic, i.e., they control their body temperature. The four-chambered heart and the double circulation provide the supply of more oxygenated blood to the tissues making possible a higher metabolic rate (mainly cellular respiration rate). Part of the energy produced by the cellular respiration is used to maintain the body temperature.
54. Concerning the mixture of arterial with venous blood what is the difference between the human fetal circulation and the adult circulation?
In the human fetal circulation there are two communications between arterial and venous blood characterizing an incomplete circulation. One of them is the oval foramen, an opening between the right and the left atria of the fetal heart. The other is the arterial duct, a short vessel connecting the pulmonary artery to the aorta. These communications close a few days after birth and so they are not present in the adult heart.
55. How is heart contraction triggered?
Heart contraction is independent from neuronal stimulus (although it can be modulated by the autonomous nervous system). In the heart there are pacemaker cells that trigger by themselves the action potentials that begin the muscle contraction. These cells are concentrated at two special points of the heart: the sinoatrial node (SA node) located in the superior portion of the right atrium and the atrioventricular node (AV node) located near the interatrial septum.
The action potentials generated by depolarization of the SA node cells propagate cell to cell throughout the atria producing the atrial contraction. The atrial depolarization also propagates to the AV node that then transmits the electric impulse to the ventricles through specialized conduction bundles of the interventricular septum (the bundle of His) and then to the Purkinje fibers of the ventricle walls causing ventricular contraction. (The atrial contraction precedes the ventricular contraction for blood to fill the ventricles before the ventricular contraction.)
The repolarization of the SA node makes the atria relax and then the ventricles relax too.
The Circulatory System - Image Diversity: heart conduction
The Excretory System - Get the Knowledge
1. What is excretion?
Excretion in Physiology is the process of elimination of metabolic wastes and other toxic substances from the body.
2. What are nitrogen wastes?
Nitrogen wastes are residuals derived from the degradation of proteins. They are made from chemical transformation of the amine group of amino acid molecules.
3. What are the three main types of nitrogen wastes excreted by living beings?
The main nitrogen wastes excreted by living beings are ammonia, uric acid and urea. Living beings that secrete ammonia are known as ammoniotelic. Creatures that secrete uric acid are known as uricotelic. Organisms that secrete urea are called ureotelic.
The Excretory System - Image Diversity: ammonia molecule uric acid molecule urea molecule
4. Why are most ammoniotelic beings aquatic animals?
Aquatic animals, like crustaceans, bony fishes and amphibian larvae, generally are ammoniotelic since ammonia diffuses more easily through membranes and it is more water-soluble than the other nitrogen wastes. Ammonia is still the most energetically economical nitrogen waste to be synthesized.
5. Why after the passage of animals from the aquatic to the terrestrial habitat does the abandonment of the ammoniotelic excretion occur?
Ammonia is a highly toxic molecule if not diluted and quickly excreted out of the body. For this reason the ammoniotelic excretion was abandoned in terrestrial habitats because the availability of water for dilution is reduced in this medium and wastes cannot be excreted so promptly to the exterior.
6. Comparing toxicity and the need for dilution in water how different are the ureotelic and the uricotelic excretions? What are some examples of animals that present these respective types ofexcretion?
Urea is more water-soluble than uric acid (an almost insoluble substance). Urea is also more toxic. Both however are less toxic than ammonia.
Some invertebrates, chondrichthian fishes, adult amphibians and mammals are ureotelic. Reptiles, birds and most arthropods are uricotelic.
7. What is the nitrogen waste in amphibian larvae and in the adult animal?
Since amphibian larvae are aquatic they excrete ammonia. The terrestrial adult excretes urea.
8. Why is the uricotelic excretion essential for avian and reptile embryos?
In reptiles and birds the excretory system is uricotelic since uric acid is insoluble, less toxic and suitable to be stored within the eggs where their embryos develop.
9. How do embryos of placental mammals excrete nitrogen wastes?
Placental animals, including embryos, excrete urea. In the adult placental mammal urea is excreted through the urine. In embryos the molecule passes to the mother’s blood through the placenta and it is excreted in the mother’s urine.
10. What is the main nitrogen waste of humans?
Human beings excrete mainly urea eliminated with the urine.
11. How is urea formed in the human body?
Urea is a product of the degradation of amino acids. In the process amino acids lose their amine group which is then transformed into ammonia. In the liver ammonia reacts with carbon dioxide to form urea and water, a process called ureogenesis.
In the intermediary reactions of the ureogenesis a molecule of ornithine is consumed and another is produced. For this reason ureogenesis is also known as the ornithine cycle.
The Excretory System - Image Diversity: ureogenesis
12. Which are the organs of the excretory system?
The excretory system is formed of kidneys (two), ureters (two), bladder and urethra.
The Excretory System - Image Diversity: human excretory system
13. What are the vessels that carry blood to the kidneys? Is this blood arterial or venous?
The arterial vessels that carry blood to be filtrated by the kidneys are the renal arteries. The renal arteries are ramifications of the aorta and so the blood filtered by the kidneys is arterial (oxygen-rich) blood.
The Excretory System - Image Diversity: kidneys
14. Which are the vessels that drain filtered blood from the kidneys?
The venous vessels that collect the blood filtered by the kidneys are the renal veins. The renal veins carry the blood that has been reabsorbed in the nephron tubules.
15. What is the functional unity of the kidneys?
The functional (filtering) unity of the kidneys is the nephron. A nephron is made of afferent arteriole, efferent arteriole, glomerulus, Bowman's capsule, proximal tubule, loop of Henle, distal tubule and collecting duct.
In each kidney there are about one million nephrons.
The Excretory System - Image Diversity: nephron
16. What are the three main renal processes that combined produce urine?
Urine is made by the occurrence of three processes in the nephron: glomerular filtration, tubular resorption and tubular secretion.
In the nephron the blood carried by the afferent arteriole enters the glomerular capillary network where it is filtered. The filtration implies that part of the blood returns to the circulation through theefferent arteriole and the other part, known as the glomerular filtrate, enters the proximal tubule of the nephron. In the nephron tubules (also known as convoluted tubules) substances of the glomerular filtrate like water, ions and small organic molecules are resorbed by the cells of the tubule wall and gain again the circulation. These cells also secrete other substances inside the tubules. The urine is formed of not resorbed filtered substances and of secreted (by the tubules) substances. Urine is drained by the collecting ducts to the ureter of each kidney, then it enters the bladder and later it is discharged through the urethra.
The nephron tubules are surrounded by an extensive capillary network that collects resorbed substances and provides others to be secreted.
17. What is the main transformation presented by the glomerular filtrate in comparison to the blood?
Glomerular filtrate is the name given to the plasma after it has passed the glomerulus and entered the Bowman’s capsule. The glomerular filtrate has a different composition compared to urine since the fluid has not yet undergone tubular resorption and secretion.
The main difference between the blood and the glomerular filtrate is that in the latter the amount of proteins is at a minimum and there are no cells or blood platelets.
18. What is proteinuria? Why is proteinuria a sign of glomerular renal injury?
Proteinuria means losing of proteins through urine. Under normal conditions proteins are too big to be filtered by the glomerulus and they are practically absent in the urine (the few filtered proteins may also be resorbed in the nephron tubules). Proteinuria is an indication that a more than expected amount of proteins is passing the glomerulus suggesting glomerular disease, e.g., in diabetic nephropathy.
The glomerulus also blocks the passage of blood cells and platelets (hematuria is often a sign of urinary disease although less specific of kidneys since the blood may come from the lower parts of the excretory tract).
The Excretory System - Image Diversity: glomerulus
19. Where does most of the water resorbed after glomerular filtration go? What are the other substances resorbed by the nephron tubules?
Only 0.5 to 1% of the glomerular filtrate is eliminated as urine. The remaining volume, containing mainly metabolic ions, glucose, amino acids and water, is resorbed through the nephron tubules (by means of active or passive transport) and gains the blood circulation again.
The convolute tubules of the nephron are responsible for the resorption of substances.
The Excretory System - Image Diversity: nephron tubules
20. Why do cells of the nephron tubules present a great amount of mitochondria?
The cells of the tubule wall have high number of mitochondria because many substances are resorbed or secreted through them by means of active transport (a process that spends energy). Therefore many mitochondria are necessary for the energetic supply (ATP supply) of this type of transport.
21. What is tubular secretion? What are some examples of substances secreted through the renal tubules?
Tubular secretion is the passage of substances from the blood capillaries that surround the nephron tubules to the tubular lumen for these substances to be excreted with urine. Ammonia,uric acid , potassium, bicarbonate and hydrogen ions, metabolic acids and bases, various ingested drugs (medicines) and other substances are secreted by the nephron tubules.
22. In which nephron portion does the regulation of acidity and alkalinity of the plasma occur?
The regulation of the acid-basic equilibrium of the body is done by the kidneys and depends upon the tubular resorption and secretion.
23. How do kidneys participate in the regulation of the acid-basic equilibrium of the body? How are alkalosis and acidosis respectively corrected by the kidneys?
Kidneys can regulate the acidity or alkalinity of the plasma varying the excretion of hydrogen and bicarbonate ions.
In alkalosis (abnormally high level of the plasma pH) the kidneys excrete more bicarbonate and the equilibrium of formation of bicarbonate from water and carbon dioxide shifts towards formation of more hydrogen ions and bicarbonate and then the plasma pH is lowered. When the body undergoes acidosis (abnormal low level of the plasma pH) the kidneys excrete more hydrogen ions and retain more bicarbonate thus the equilibrium of formation of bicarbonate from water and carbon dioxide shifts towards more hydrogen consumption and the plasma pH is increased.
24. How do kidneys participate in the blood volume control? How is the blood volume of the body related to the arterial pressure?
The kidneys and the hormones that act upon them are the main physiological regulators of the total blood volume of the body. As more water is resorbed in the nephron tubules the more the blood volume increases; as more water is excreted in urine the more the blood volume lowers.
The blood volume in its turn has a direct relation to blood pressure. The blood pressure increases when the blood volume increases and it lowers when the blood volume lowers. That is the reason why one of the main groups of antihypertensive drugs is the diuretics. Doctors often prescribe diuretics for the hypertensive patients to excrete more water and thus lower their blood pressure.
25. Which are the three hormones that participate in the regulation of the renal function?
Antidiuretic hormone (or ADH, or vasopressin), aldosterone and atrial natriuretic factor (or ANF) are hormones that participate in the regulation of the excretory system.
26. What is the function of the antidiuretic hormone? Where is it made and which are the stimuli that increase or reduce its secretion?
The antidiuretic hormone is secreted by the hypophysis (also known as pituitary) and it acts in the nephron tubules increasing the resorption of water. When the body needs to retain water, for example, in cases of blood loss and abrupt blood pressure lowering or in cases of abnormally high blood osmolarity, there is stimulus for ADH secretion.
When the body has an excess of water, as in cases of excessive ingestion or in abnormally low blood osmolarity, the secretion of ADH is blocked and the diuresis increases. ADH is also known as vasopressin since it increases the blood volume and thus heightens the blood pressure.
27. Why does the ingestion of alcohol increase diuresis?
Alcohol inhibits the secretion of ADH (antidiuretic hormone) by the pituitary. That is why when it is drunk to excess the person urinates too much.
28. How does aldosterone act and where is it produced?
Aldosterone is a hormone that acts upon the nephron tubules stimulating the resorption of sodium. Therefore it contributes to the increase of the blood osmolarity and consequently to the increase of the blood pressure.
Aldosterone is made by the adrenals, glands located over the superior portion of the kidneys.
29. What is an evolutionary explanatory hypothesis for the secretion by the heart of a hormone that regulates the renal function? Which is that hormone?
The renal regulator hormone secreted by the heart is the atrial natriuretic factor (or ANF). The ANF increases the excretion of sodium in the nephron tubules causing less resorption of water, more urinary volume, and thus lowering the blood pressure. The atrial natriuretic factor is secreted when there is an increase of the length of the heart muscle fibers in response to high blood pressure. The ANF is a natural antihypertensive substance. Since the health of the heart depends largely upon the stability of the normal blood pressure the evolution should have preserved the atrial natriuretic factor to allow information from the heart to be an additional mechanism for the renal control of the blood pressure.
30. What is hemodialysis?
Hemodialysis is the artificial blood filtration made by specific machines in substitution of the kidneys. Hemodialysis may be necessary in patients suffering from diseases that cause renal failure, like diabetic renal complications, lupic renal complications and others. During hemodialysis the blood of the patient is deviated to the filtering machine and after the filtration it returns to the body.
Hemodialysis is generally done two, three or more times a week in a process that takes several hours. Sometimes kidney transplantation is an alternative to hemodialysis.
The Excretory System - Image Diversity: hemodialysis
ليست هناك تعليقات:
إرسال تعليق