pituitary hormones

pituitary hormones

pituitary hormones

The hypothalamus and pituitary form a functional unit concerned with the control of most of the endocrine system.
Secretion of the anterior pituitary hormones is controlled by the secretion of hypothalamic factors, which may be stimulatory or inhibitory to each specific hormone. The control is by feed back loops, which "turn - off " the trophic hormone when the level of the target hormone rises.

Anterior pituitary hormones:

 

- Basal plasma GH levels are of little value in diagnosis. Increases can be caused by stress or exercise and this forms the basis of the insulin-hypoglycemia stress response test.
- Hyperfunction of GH-secreting cells (adenomas of the anterior pituitary) leads to gigantism if the disorder occurs before closure of the epiphyses of long bones, and to acromegaly if it occurs after their closure. Diagnosis of these disorders is based on:
* High basal plasma (GH) levels
* Response to oral glucose tolerance test: normally, plasma (GH) falls to less than 2 mU/L at some time during the test. In patients with acromegaly and gigantism, plasma GH does not fall in response to the stimulus of hyperglycemia.
- Hypofunction of the anterior pituitary and short stature in children can be diagnosed by the insulin-hypoglycemia test (0.10 - 0.15 insulin unit /Kg). Normally, hypoglycemia causes a marked increase in plasma GH to more than 2O mU/L, but this does not occur in pituitary dysfunction. Care must be taken against the occurrence of dangerous hypoglycemia. Induction of hypoglycemia can be achieved by strenuous exercise.
Prolactin, FSH and LH:
Measurements are indicated in cases of amenorrhea, oligomenorrhea, subfertility and galactorrhea.

Posterior Pituitary Hormones

The posterior pituitary is an integral part of the neurohypophysis. It produces mainly two hormones, oxytocin and arginine vasopressin. (AVP) often called anti-diuretic hormone (ADH). This peptide is released in response to a rise in plasma osmolality, or to a fall in extracellular fluid (ECF) volume. It increases the permeability of the distal tubules and collecting ducts of the kidney to water.
- Over production of AVP may occur with head injury, cerebral tumor, and ectopic hormone secreting tumors, [inappropriate secretion of ADH (SIADH)].
- Deficiency of AVP gives rise to diabetes insipidus. It may be primary (idiopathic, familial) or secondary (pituitary disease or injury)