Anterior Lobe or Adenohypophysis

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Because of its role in the control of other endocrine glands, the pituitary is often called the "master gland of the body." This designation is more appropriately applied to the pitu-itary's anterior lobe than it is to the posterior lobe, as the adenohypophysis manufactures and secretes hormones that regulate the body's most important glands (e.g., the adrenal glands, the thyroid gland, the gonads). In fact, the prefix "adeno-" means gland.

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Figure 1. Schematic drawing showing the relationship of the posterior lobe (neurohypophysis) to the hypothalamus. The anterior lobe (adeno-hypophysis) is functionally connected to the hypothalamus by blood vessels (not shown).

The anterior lobe of the pituitary is derived from skin cells from the roof of the mouth, and the surgical approach to the pituitary is through the roof of the mouth, which will give you a better appreciation of the gland's location in your head. Although it is not in direct neural contact with the brain, the activities of the adenohypophysis are regulated by the hypothalamus, which secretes neurochemicals termed "releasing factors" that travel to the anterior lobe through a system of blood vessels called the hypothalamo-hypophysical portal system.

The releasing factors are peptides and they modulate the secretion of anterior lobe hormones such as somatotro-pin, thyrotropin, adrenocorticotropin, lactogenic hormone, and the gonadotropins. Each will be discussed briefly.

Somatotropin (STH) is a growth-promoting hormone and, in fact, is usually called growth hormone. Its presence at appropriate developmental periods is essential for normal growth. Too much can produce a distorted growth problem called acromegaly; too little results in dwarfism.

Thyrotropin (TSH or thyroid-stimulating hormone) acts on the thyroid gland to promote the synthesis, storage, and release of the thyroid hormones thyroxine (T4) and triiodothyronine (T3). Thyroid hormones are involved in the regulation of the body's metabolism.

Adrenocorticotropin (ACTH or adrenocorticotropic hormone) stimulates the production and release of hormones by the adrenal cortex (the adrenal glands are above the kidneys). ACTH triggers the release of glucocorticoids (e.g., cortisol), which are important in carbohydrate metabolism and in the body's resistance to stress. ACTH itself is released in response to physical or emotional stress.

Lactogenic hormone (LTH or prolactin) acts on the mam mary glands to promote milk secretion. Prolactin may also be important for the display of parental behaviors in vertebrates.

The gonadotropins (luteinizing hormone and follicle stimulating hormone) act on the gonads. Luteinizing hormone (LH) is necessary for ovulation in females. In males, LH acts on cells in the testes to cause them to produce testosterone.

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