Anatomy And Physiology

Anatomy Physiology



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Pituitary gland disorders are predominantly  manifested as hypersecretion or hyposecretion of one or more of its hormone.  Oversecretion of all its hormones is called panhyperpituitarism.  Hypersecretion of the pituitary gland usually occurs  due to an adenoma of the gland or due to hyperplasia.  In rare instances the hypersecretion is caused by a cancer of the gland.

Hyposecretion on hormones from the pituitary usually is occured due to a surgery of the pituitary which would eliminate part of the gland.  Thus reducing its size and consequently reducing its secretion of hormones into the blood.

The pituitary gland is divided into an anterior and a posterior part.  The anterior part secretes 6 hormones while the posterior part secretes only 2 hormones to the  circulation. 

The most important hypersecretion of the anterior pituitary gland is the secretion of the hormone prolactin and growth hormone.  Their secretion often occurs together but also isolated hypersecretion occurs in some cases. 

Hyperprolactinemia can occur due to an adenoma of the anterior part of the pituitary gland.  It can also occur due to administration of drugs which are dopamine antagonists. 

Dopamine antagonists are usually administered to control psychotic symptoms in schizophrenic patients.  Drugs that antagonize the action of dopamine such as resperidone allow for oversecretion of prolactin due to the lack of feedback inhibition that dopamine makes usually on the secretion of prolactin.

Growth hormone oversecretion also due to an adenoma can cause gigantisism in children and acromegaly in adults.  It can also predispose to diabetes mellitus in adults due to its action of stimulating glucose level in the blood to be higher than usual causing hyperglycemia.

Adrenocorticotropic hormone is another important hormone that can be oversecreted in adenoma of the pituitary gland.  Its excessive secretion can cause hypercortisolism due to its function in stimulating the synthesis and secretion of cortisol by the adrenal cortex. 

Adrenocorticotropic hormone also stimulates the proliferation of melanin producing cells.  Thus one of the symptoms of ACTH excess is hyperpigmentation of the skin.  This condition is called cushing disease.  This is in contrast to cushing syndrome which is caused by excess cortisol that is inherent to the adrenal cortex itself.

Adenomas that secrete follicle stimulating hormone and luteinizing hormone are not identified readily clinically due to the fact that these two hormones are secreted in a pulsatile manner in small quantities.  When the tumour of the pituitary gland becomes significantly large enough to cause neurological symptoms such as impaired vision by pressing the optic nerve.  Only then the clinical symptoms are alerting to the presence of a pituitary tumour.

Thyroid stimulating hormone oversecretion by the anterior pituitary gland is a rare cause of hyperthyroidism and oversecretion of the thyroid hormones. 

The posterior pituitary gland secretes two important hormones that are very similar in structure.  Both are polypeptides that are composed of 10 amino acids. 

The first one is called antidiuretic hormone or ADH and the second is called oxytocin.  Oxytocin is a hormone which functions by stimulating the myoepithelial cells of the breast muscle.  Thus causing its contraction.  The result is enhanced milk ejection from the breast in females.  Oxytocin also stimulates the contraction of the uterus during childbirth.

ADH has two distinct clinical disorders.  These are hyposecretion and hypersecretion of the antidiuretic hormone.  Pituitary gland ADH functions usually by stimulating the conservation and reabsorption of water in the kidney tubules. Thus helping in water homeostasis in the body. 

Its excessive secretion occurs in adenomas of the posterior part of the pituitary gland.  The clinical manifestations of ADH excess is hyperconsevation of water in the kidney tubules.  Thus causing edema and hypertension. 

The treatment to this disorder is by administering antagonists to the action of ADH or by surgery to remove part of the pituitary gland that is affected by the adenoma. 

In hyposecretion of ADH by the posterior part of the pituitary gland which is usually caused by due to surgery of the pituitary gland the secretion of ADH is not sufficient to maintain homeostasis. 

The clinical picture of this disorder is the presence of polyurea due to the lack of concentration mechanism of water by ADH.  The treatment to this condition is to administer ADH analogues.  

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