Cells and Hormones of the Anterior Pituitary Gland and Their Physiological Functions

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Cell

Somatotropes

Corticotropes

Thyrotropes Gonadotropes

Lactotropes, Mammotropes IGF, insulin-like growth factor

Hormone

Growth hormone (GH; somatotropin)

Adrenocorticotropic hormone (ACTH;corticotropin)

Thyroid-stimulating hormone (TSH; thyrotropin)

Follicle-stimulating hormone (FSH)

Luteinizing hormone (LH)

Prolactin (PRL)

Chemistry

Single chain of 191 amino acids Single chain of 39 amino acids

Glycoprotein of two subunits, a (89 amino acids) and b (112 amino acids) Glycoprotein of two subunits, a (89 amino acids) and b (112 amino acids) Glycoprotein of two subunits, a (89 amino acids) and b (115 amino acids)

Single chain of 198 amino acids

Physiological Actions

Stimulates body growth;stimulates secretion of IGF-1;stimulates lipolysis; inhibits actions of insulin on carbohydrate and lipid metabolism Stimulates production of glucocorticoids and androgens by the adrenal cortex; maintains size of zona fasciculata and zona reticularis of cortex Stimulates production of thyroid hormones by thyroid follicular cells; maintains size of follicular cells Stimulates development of ovarian follicles; regulates spermatogenesis in the testis

Causes ovulation and formation of the corpus luteum in the ovary; stimulates production of estrogen and progesterone by the ovary; stimulates testosterone production by the testis Stimulates milk secretion and production

Aparato Femenino Maculino

Figure 75-4

Hypothalamic-hypophysial portal system.

rates of secretion of the different hormones (except for prolactin) fall to very low levels.

Secretion from the posterior pituitary is controlled by nerve signals that originate in the hypothalamus and terminate in the posterior pituitary. In contrast, secretion by the anterior pituitary is controlled by hormones called hypothalamic releasing and hypothala-mic inhibitory hormones (or factors) secreted within the hypothalamus itself and then conducted, as shown in Figure 75-4, to the anterior pituitary through minute blood vessels called hypothalamic-hypophysial portal vessels. In the anterior pituitary, these releasing and inhibitory hormones act on the glandular cells to control their secretion. This system of control is discussed in the next section of this chapter.

The hypothalamus receives signals from many sources in the nervous system. Thus, when a person is exposed to pain, a portion of the pain signal is transmitted into the hypothalamus. Likewise, when a person experiences some powerful depressing or exciting thought, a portion of the signal is transmitted into the hypothalamus. Olfactory stimuli denoting pleasant or unpleasant smells transmit strong signal components directly and through the amygdaloid nuclei into the hypothalamus. Even the concentrations of nutrients, electrolytes, water, and various hormones in the blood excite or inhibit various portions of the hypothalamus. Thus, the hypothalamus is a collecting center for information concerning the internal well-being of the body, and much of this information is used to control secretions of the many globally important pituitary hormones.

Figure 75-4

Hypothalamic-hypophysial portal system.

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