What to know about Hypothalamus and Pituitary Glands

Hypothalamus and Pituitary Gland 
The hypothalamus, located beneath the thalamus in the lower walls and floor of the third ventricle of the brain, helps regulate the body's internal environment. For ex­ample, the hypothalamus helps control heart rate, body temperature, and water balance, as well as the activity of the pituitary gland.
The pituitary gland is small-about 1 centimeter in diameter-and lies just inferior to the hypothalamus. It has two portions: (1) the anterior pituitary, or hypophysis, and (2) the posterior pituitary.
Posterior Pituitary 
The posterior pituitary is connected to the hypothalamus by means of a stalklike structure. The hormones released by the posterior pituitary are made by neurosecretory cells in the hypothalamus. The hormones then migrate through axons that terminate in the posterior pituitary.
Antidiuretic (an"ti-di"u-ret'ik) hormone (ADH), also called vasopressin, promotes the reabsorption of water from the kidneys, thereby preventing dehydration. The hypo­thalamus is believed to contain cells that are sensitive to blood solute concentrations. When these cells detect that the blood lacks sufficient water, ADH is produced by spe­cial neurosecretory cells and is transported by their fibers to the posterior pituitary, where it is released. As the blood becomes more dilute, the hormone ceases to be produced and released.
Inability to produce ADH causes diabetes insipidus (watery urine), in which a person produces copious amounts of urine with a resultant loss of electrolytes from the blood. The condition can be corrected by the adminis­tration of ADH.
Oxytocin is another hormone made in the hypothala­mus and released by the posterior pituitary. Oxytocin causes the uterus to contract and can be used to artificially induce labor. It also stimulates the release of milk from the breast when a baby is nursing.
Anterior Pituitary 
The hypothalamus controls the anterior pituitary by pro­ducing hypothalamic-releasing and release-inhibiting hormones, which are transported to the anterior pitu­itary by the blood within a portal system. Each of these hypothalamic hormones causes the anterior pituitary ei­ther to secrete or to stop secreting a specific hormone. The anterior pituitary produces several different hor­mones.
Growth hormone (GH), or somatotropin, produced by the anterior pituitary, affects the physical appearance dramatically since it determines an individual's size and height. If little or no GH is secreted by the anterior pituitary during childhood, a person can become a pituitary dwarf, characterized by perfect proportions but small stature. If too much GH is secreted, a person can become a giant. Giants usually have poor health, primarily because GH has a secondary effect on the blood sugar level pro­moting an illness called diabetes mellitus.
GH is produced in greatest quantities during child­hood and adolescence, when most body growth is occur­ring, but is still produced (though in lower quantities) in adults to aid in continued protein synthesis and normal cell division and replacement. If GH production increases in an adult after full height has been obtained, only the bones of the jaw, eyebrow ridges, nose, fingers, and toes re­spond. When these bones begin to grow, the person ac­quires a slightly grotesque look, with huge fingers and toes. This condition is called acromegaly.
Prolactin (PRL) is produced by the anterior pituitary only after childbirth. It causes the mammary glands in the breasts to develop and produce milk.
The anterior pituitary also secretes the hormones that follow.

• Since these hormones have an effect on other en­docrine glands, the anterior pituitary is sometimes called the master gland.
• Thyroid-stimulating hormone (TSH), which stimu­lates the thyroid to produce thyroxine 
• Adrenocorticotropic (ad-re"no-kor"te-ko-trop'ik) hormone (ACTH), which stimulates the adrenal cor­tex to produce and secrete hormones 
• Gonadotropic (gon"ah-do-trop'ik) hormones, which stimulate the gonads-the testes in males and the ovaries in females-to secrete sex hormones 

A three-tiered relationship exists between the hypo­thalamus, anterior pituitary, and other endocrine glands. The hypothalamus produces releasing hormones that con­trol the anterior pituitary, which produces hormones that control the thyroid, adrenal cortex, and gonads.

Posted in Human Anatomy and Physiology