THE PITUITARY GLANDب�س�م� ا�ل�ل�ه� ا�ل�ر�ح�م�ن� ا�ل�ر�ح�ي�م

:THE PITUITARY GLANDIt consist of two portions the anterior or adenohypophysis and the posterior pituitary. Though very closely related anatomically they are embryo logically and functionally quite distinct. The anterior one comprises primarily glandular tissue while the posterior one is of neural origin; the pituitary gland is situated at the base of the brain in close relation to the hypothalamus which has an essential role in the regulation of pituitary function.

ANTERIOR PITUITARY HORMONES :*Secretes several hormones some of them are tropic, that is they stimulate the activity of several other endocrine glands.*the secretion of hormones by the anterior pituitary is controlled by hormones secreted by the hypothalamus which reach the pituitary through a system of portal blood vessels.* The secretion of hypothalamic hormones is influenced by higher centers in the brain and secretion of both is regulated by feed back from the hormones whose production they stimulate in target organs.

GROWTH HORMONE:.Is a191 A.A polypeptide hormone.*Essential for normal growth although in the main it acts indirectly by stimulating the liver to produce insulin-like growth factor-1 (IGF-1).This also known as somatomedine-C.*release of GH is controlled by hypothalamic hormone GHRH and somatostatin.* Somatomedin – C Exerts (-ve) feed back at the level of the pituitary it mediate the action of GHRH. And at the level of hypothalamus where it together with GH it self stimulates the release of somatostatin.

METABOLIC ACTION OF GROWTH HORMONE Increases lipolysis (hence ketogenic) .

Increases hepatic glucose production and decreases tissue glucose uptake (hence diabetogenic).

Increases protein synthesis (hence anabolic).

TABLE OF METABOLIC ACTION OF GROWTH HORMONE

*THE CONCENTRATION OF GH in the blood varies widely through the day and it may be undetectable (<1mU/L) with present assays for long periods.*physiological secretion occurs in sporadic bursts, lasting one to two hours mainly during sleep. *peak concentration may be as high as 40Mu/L.

*secretion can be stimulated by (stress, exercise, a fall in blood glucose concentration ,fasting and ingestion of certain amino acids.) THISSTIMULI CAN BE USED IN PROVOCATIVE TESTS FOR DIAGNOSING (GH DEFICIENCY IN CHILDREN.)*Secretion is inhibited by arise in blood glucose and this effect provides the rationale for the use of the oral glucose tolerance test in the diagnosis of excessive GH secretion.*EXCESSIVE SECRETION DUE TO APIYUIYARY TUMOUR CAUSES GIGANTISMIN CHILDREN AND ACROMEGALY IN ADULTS, DEFICIENCY CAUSES GROWTH RETARDATION IN CHILDREN AND CAN CAUSE FATIGUE AND LOSS OF MUSLE STRENGTH IN ADULT.

Prolactin:Is a 198 A.A polypeptide hormone its principal physiological action is to initiate and to sustain lactation.Its secretion is controlled by the hypothalamus through the release of dopamine, which inhibits the process.There is no known hypothalamic prolactin releasing hormone.

Although both TRH and VASOACTIVE INTESTINALPOLYPEPTIDE (VIP) stimulate prolactin secretion.ITis not thought that this is physiologically important.*the secretion of prolactin is pulsatile, increases during sleep and stress, and in women is dependet5 upon estrogen status ,making it difficult to define a precise upper limit for plasma prolactin concentration in normal men and women,(400mU/L)is often regulated as the upper reference value. There is no defined lowered reference value for plasma prolactin concentration.

Its secretion increases during pregnancy but concentrations fall to normal within approximately seven days after birth if a woman does not breast feed. With breast feeding, concentrations start to decline after about three months, even if breast feeding is continued beyond this time.Prolactin deficiency is uncommon but does occur, for example with pituitary infarction; its only manifestation is failure of lactation.

HYPERPROLACTINAEMIA:*It’s a common endocrine disorder.*it’s an important cause of infertility in both males and female, also in impotence in males and menstrual irregularity in females.*theseeffects are thought to be mediated through inhibition of the pulsatility of GnRH by prolactin.

CausesphysiologicalStress,sleep, pregnancy ,sucklingDrugsDopaminergic receptor blockers,e.g. phenothiazines, haloperidol, dopamine –depleting agentse.g.methyldopa, reserpine others e.g. estrogens,TRH.

Pituitary disorders Prolactin- secreting tumour (prolactinoma)Tumours blocking dopaminergic inhibition of prolactin secretion Pituitary stalk section and surgery

OthersHypothyroidismEctopic secretionChronic renal failure

Causes of it are sumariesed in this table:

The causes include various drugs which either block pituitary dopaminergic receptors or deplete the brain of dopamine, in addition to pituitary tumors and destructive pituitary lesions which interfere with the normal inhibition of prolactin secretion. Prolactinomas are usually small micro adenomas<10mm diameter) but larger tumours (macro adenoma) do occur which erode the pituitary fossa and extend out side its confines.

Prolactin is secreted in response to both stress and TRH, and plasma concentration also depends on estrogen status. It is therefore difficult to define an upper limit of normal for plasma prolactin, less than 400mUlLis probably normal and more than 600Mu/Lis abnormal. Slightly elevated concentrations of prolactin are less likely to be of significance in well oestrogenized women. Prolactin-secreting tumors>10 mm diameter are usually associated with plasma prolactin concentrations >5000Mu/L. lower concentrations in patients with large pituitary tumours are usually a result of disruption of the delivery of dopamine to the pituitary. Because prolactin-secreting tumours often respond rapidly to medical treatment, urgent measurement of prolactin may be required in a patient with a large pituitary tumour associated with visual failure.

Numerous dynamic tests have been proposed to aid in the diagnosis of suspected prolactin- secreting tumours. The most widely used is the measurement of prolactin response to TRH, which diminished in most patients with prolactinomas. However, this is not a consistent, nor a specific, finding and neither the TRH nor any other dynamic test is of established value in the diagnosis of prolactinomas.

If a tumour is diagnosed, patients must be tested for deficient secretion of other anterior pituitary hormones .

Usually with small tumours other functions are normal.The majority of patients with small prolactin secreting tumours respond to treatment with (a dopamine agonist e.g. BROMOCRIPITINE or CABERGOLINE).Prolactin concentration usually falls to normal and many women regain fertility.Long term treatment is usually necessary although in some patients hyperprolactinaemia dose not recur on withdrawal of the drug.

Patients who do not respond to or are intolerants of medication retreated by trans-sphenoidal surgery.

Medical treatment reduces prolactin secretion and causes tumour shrinkage in the majority of patients with large tumours. Surgery is some times required but tends to be less successful than with small tumours. External irradiation may be helpful in some cases.

Clinical featuresFemales:

Oligomenorrhoea , amenorrhoeaInfertilityGalactorrhoeaMales:Impotence.Infertility.Gynaecomastia.

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