Anatomy And Physiology

Anatomy Physiology



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The pituitary gland is divided anatomically into two parts. These are the anterior lobe and the posterior lobe. The anterior lobe of the pituitary gland produces and secretes five types of hormones. All of them are regulated by a positive feedback from hormones in the hypothalamus.

The hormones of the anterior lobe are: first, the growth hormone which is secreted by cells that are called somatotropes. Growth hormone secretion is regulated by two hormones that are produced and secreted by the hypothalamus. These are the growth hormone releasing hormone, in which its secretion increases the level of growth hormone in the blood. The other hormone that is secreted by the hypothalamus is somatostatin. its secretion inhibits the secretion of growth hormone by the pituitary gland.

The anterior lobe is an endocrine gland. It affects target endocrine glands by its hormones except for the growth hormone which does not have specific target organ. It makes its effect on the body tissues all. Growth hormone makes its effect on the body by increasing the blood glucose. This happens by diminishing the uptake of glucose by the cells. In addition growth hormone oversecretion can cause diabetes mellitus because it stimulates also the secretion of excessive amounts of insulin. Thus destroying the islet cells of the pancreas.

People with acromegaly are often likely to develop diabetes mellitus due to the high level of growth hormone in their blood.

The other hormone that is secreted by the anterior pituitary gland is adreno-cortico-tropic hormone ACTH. This hormone makes its effect on cortisol production and secretion by the adrenal cortex. ACTH secretion is regulated by the hormone corticotropin releasing hormone secreted by the hypothalamus. It is secreted by cells that are called corticotropes.

Prolactin is another hormone that is secreted by the anterior pituitary gland. It is secreted by cells that are called lactotropes. It is the only hormone of the pituitary that is regulated by a negative feedback from a hormone that is called dopamine secreted by the hypothalamus.

Drugs that antagonize dopamine action cause hyperprolactinemia due to the lack of the negative feedback of dopamine. Hyperprolactinemia can also be caused by an adenoma of the pituitary gland. The other hormone that is secreted by the anterior pituitary gland is thyroid stimulating hormone. It is regulated by a positive feedback from a hormone in the hypothalamus that is called thyrotropin releasing hormone.

The sex hormones in males and females are regulated both by two hormones of the pituitary gland. These are luteinizing hormone and follicle stimulating hormone. Both are regulated by the hormone gonadotropin releasing hormone secreted by the hypothalamus. The cells that secretes these two hormones are called gonadotropes.

The posterior pituitary gland is not an endocrine gland but a reservoir for two hormonal secretions by the hypothalamus. These are dopamine and oxytocin. Both are peptides that are secreted in response to neural stmulation.

Oxytocin makes its effect on the uterus during child birth by increasing its contraction. It also increases the contraction of the myoepithelial cells in the breast so that milk will be ejected. Dopamine is similar to some extent in structure to oxytocin. Its excess in the blood has the clinical symptoms of psychosis. Therefor drugs that antagonize the action of dopamine are used to treat psychosis. A deficiency of dopamine is responsible for parkinson disease. Parkinson disease is sometimes observed in patients with schizophrenia that are on antipsychotic drugs.

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