Hypothalamus And Pituitary Gland

As shown in Figure 50-3, endocrine glands are located throughout the body. Two organs, the hypothalamus (HlE-poh-THAL-uh-muhs) and the pituitary (pi-TOO-uh-TER-ee) gland, control the initial release of many hormones.

The hypothalamus is the area of the brain that coordinates many activities of the nervous and endocrine systems. It receives information from other brain regions and then responds to these signals as well as to blood concentrations of circulating hormones. The hypothalmus responds by issuing instructions in the form of hormones to the pituitary gland. As shown in Figure 50-4, the pituitary gland is suspended from the hypothalamus by a short stalk. The hypothalamus produces hormones that are stored in the pituitary gland or that regulate the pituitary gland's activity.

What Cretory

Two hormones—oxytocin (AHKS-ee-TOH-sin) and antidiuretic (AN-TIE-DIE-yoo-RET-ik) hormone (ADH)—are made by nerve cells in the hypothalamus. These nerve cells that secrete hormones are called neurosecretory cells. The axons of the neurose-cretory cells in the hypothalamus extend into the posterior lobe of the pituitary, as shown in Figure 50-4b. Oxytocin and ADH are transported through these axons into the posterior pituitary, where they are stored for eventual release into the bloodstream.

As shown in Figure 50-4b, a special system of blood vessels connects the hypothalamus with the anterior pituitary. Nerve cells in the hypothalamus secrete releasing and release-inhibiting hormones that travel to the anterior pituitary through the blood vessels. Releasing hormones stimulate the anterior pituitary to make and secrete hormones. Release-inhibiting hormones inhibit production and secretion of anterior-pituitary hormones.

Some anterior-pituitary hormones, such as prolactin and growth hormone, are regulated through both a releasing hormone and a release-inhibiting hormone. Other hormones regulated by releasing hormones, such as follicle-stimulating hormone, thyroid-stimulating hormone, and adrenocorticotropic hormone (ACTH), in turn stimulate other endocrine glands. Table 50-1 summarizes the function of the hormones secreted by the pituitary gland.

TABLE 5G-1 Hormones Secreted by the Pituitary Gland

Hormone

Target

Major function

Adrenocorticotropic hormone (ACTH)

adrenal cortex

stimulates secretion of cortisol and aldosterone by the adrenal cortex

Antidiuretic hormone (ADH)

kidney tubules

stimulates reabsorption of water by kidneys, reducing the concentration of solutes in the blood

Follicle-stimulating hormone (FSH)

ovaries in females; testes in males

stimulates egg production in females; stimulates sperm production in males

Growth hormone (GH)

muscle and bone

regulates development of muscles and bones

Luteinizing hormone (LH)

ovaries in females; testes in males

stimulates progesterone and estrogen production; initiates ovulation in females; stimulates testosterone production in males

Oxytocin

uterine muscles and mammary glands

initiates uterine contractions during childbirth; stimulates flow of milk from breasts during lactation

Prolactin (PRL)

mammary glands

stimulates milk production in breasts during lactation

Thyroid-stimulating hormone (TSH)

thyroid gland

regulates secretion of the thyroid hormones—thyroxine and triiodothyronine

Hypothalamus Gland

figure 50-4

Neurosecretory cells in the hypothalamus produce hormones that affect the pituitary gland. The area of the brain where the hypothalamus and pituitary gland are found is circled in (a). The hypothalamus regulates the posterior pituitary through axons and the anterior pituitary through blood vessels, as shown in (b). (Blood vessels in the posterior pituitary have been omitted in order to show axon projections.)

figure 50-4

Neurosecretory cells in the hypothalamus produce hormones that affect the pituitary gland. The area of the brain where the hypothalamus and pituitary gland are found is circled in (a). The hypothalamus regulates the posterior pituitary through axons and the anterior pituitary through blood vessels, as shown in (b). (Blood vessels in the posterior pituitary have been omitted in order to show axon projections.)

Hyoid Epiglottis

figure 50-5

The thyroid gland is located under the larynx and on the trachea.

figure 50-5

The thyroid gland is located under the larynx and on the trachea.

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  • john jones
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    2 years ago

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