Pituitary Gland and the HypothalamusThe pituitary gland, also called the hypophysis is a pea-sized gland located in a depression of the sphenoid bone. It is attached to the undersurface of the hypothalamus by a short stalk called the infundibulum. The pituitary contains two main parts: the anterior pituitary gland and posterior pituitary gland.The secretions of both the anterior and posterior lobes of the pituitary gland are dependent upon the hypothalamus.The secretion of the anterior pituitary gland is controlled by the hypothalamic secretion of hormones called releasing hormones and release-inhibiting hormones—they either stimulate or inhibit the secretion of anterior pituitary hormones.Prolactin-inhibiting hormone (PIH), secreted by the hypothalamus, inhibits the secretion of prolactin by the anterior pituitary gland.The hypothalamus secretes its hormones into a network of capillaries (tiny blood vessels) that connect the hypothalamus with the anterior pituitary gland.These connecting capillaries are called the hypothalamic–hypophyseal portal system. Thus, hormones secreted by the hypothalamus flow through the portal capillaries to the anterior pituitary.Anterior Pituitary GlandThe anterior pituitary gland is composed of glandular epithelial tissue and is also called the adenohypophysis.The anterior pituitary gland secretes six major hormones.
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These hormones control other glands and affect many organ systems. In fact, the anterior pituitary affects so many other glands that it is often called the master gland. The hormones of the anterior pituitary include thyroidstimulating hormone (TSH), ACTH, growth hormone (GH), the gonadotropins, and prolactin (PRL).PROProlactinATHletesACTHGotGonadotrophins (FSH,LH)ToTSHGROWGrowth HormoneGrowth HormoneGrowth hormone (GH) is also called somatotropin or somatotropic hormone. Its primary effects are on the growth of bones, cartilage, and skeletal muscles.GH also exerts powerful metabolic effects. It causes amino acids to be built into proteins and fats to be broken down and used for energy. It also stimulates the conversion of protein to glucose (gluconeogenesis),especially during periods of fasting between mealsGH thus causes blood glucose levels to rise. GH also affects electrolyte balance: it stimulates the kidneys to reabsorb sodium (Na + ), potassium (K+ ), and chloride (Cl −) and the digestive tract to absorb dietary calcium.These electrolytes then become available to growing tissue. In additionto the direct effects of GH on tissue growth, it also stimulates growth indirectly. GH stimulates the liver to produce growth stimulants called insulin-like growth factors (or somatomedins). GH is secreted during periods of exercise, sleep, and hypoglycemia.
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