Endocrine System Part II

Hypothalamus

The hypothalamus (pronounced: hi-po-THA-luh-mus), a collection of specialized cells that is located in the lower central part of the brain, is the main link between the endocrine and nervous systems. Nerve cells in the hypothalamus control the pituitary gland by producing chemicals that either stimulate or suppress hormone secretions from the pituitary.

Pituitary

Although it is no bigger than a pea, the pituitary (pronounced: puh-TOO-uh-ter-ee) gland, located at the base of the brain just beneath the hypothalamus, is considered the most important part of the endocrine system. It's often called the "master gland" because it makes hormones that control several other endocrine glands.

The production and secretion of pituitary hormones can be influenced by factors such as emotions and changes in the seasons. To accomplish this, the hypothalamus provides information sensed by the brain (such as environmental temperature, light exposure patterns, and feelings) to the pituitary.

The tiny pituitary is divided into two parts: the anterior lobe and the posterior lobe. The anterior lobe regulates the activity of the thyroid, adrenals, and reproductive glands. The anterior lobe produces hormones such as:

• growth hormone, which stimulates the growth of bone and other body tissues and plays a role in the body's handling of nutrients and minerals
• prolactin (pronounced: pro-LAK-tin), which activates milk production in women who are breastfeeding
• thyrotropin (pronounced: thy-ruh-TRO-pin), which stimulates the thyroid gland to produce thyroid hormones
• corticotropin (pronounced: kor-tih-ko-TRO-pin), which stimulates the adrenal gland to produce certain hormones

The pituitary also secretes endorphins (pronounced: en-DOR-fins), chemicals that act on the nervous system and reduce feelings of pain. In addition, the pituitary secretes hormones that signal the reproductive organs to make sex hormones. The pituitary gland also controls ovulation and the menstrual cycle in women.

The posterior lobe of the pituitary releases antidiuretic(pronounced: an-ty-dy-uh-REH-tik) hormone, which helps control the balance of water in the body. The posterior lobe also produces oxytocin (pronounced: ahk-see-TOE-sin), which triggers the contractions of the uterus in a woman having a baby.