Pituitary Gland and Hormone Secretion
From Encyclopedia of Sex and Sexuality
A small endocrine gland located at the base of the brain that functions as the regulator of the endocrine system, responding to signals from the central nervous system and passing them on to the rest of the endocrine glands. The endocrine gland secretes hormones, the molecules that regulate growth, development, and reproduction and help maintain many metabolic functions of the body.
The central nervous system (CNS) and the endocrine system cooperate in controlling the internal environment of the body in a process known as homeostasis. The CNS receives information about the external environment, such as changes in temperature or day length, and is aware of conditions within the body, such as how the respiratory or digestive system are functioning, and changes in metabolic activity. This information is previewed and relayed to the pituitary through the hypothalamus, a small area of the brain near the pituitary. The messages are changed to chemical, or hormonal, messages. The pituitary then sends out these hormonal messages, and they stimulate other endocrine glands or somatic cells to regulate their activity. Each hormone stimulates a specific endocrine gland, called the target organ, and a specific response within the target organ.
The pituitary has two lobes: the anterior (front) lobe and the posterior (rear) one. The anterior pituitary produces trophic hormones. The response may be secretion of hormones, or increased protein production or metabolic activity. The reproductive trophic hormones are called gonadotropins; they control activity of the gonads (ovaries or testicles) and stimulate gamete (egg or sperm) production. There are two gonadotropins, luteinizing hormone (LH) and follicle stimulating hormone (FSH). LH stimulates hormone-producing cells in both the female ovaries and male testes; FSH stimulates development of the sperm cells, or gametes. Other trophic hormones are thyroid stimulating hormone (TSH), which stimulates the thyroid, and adrenocorticotropin (ACTH), which acts on the adrenal gland. Growth hormone, secreted especially during childhood, regulates the ultimate height of an individual. Prolactin, which stimulates milk production, is also produced by the anterior pituitary.
The trophic hormones and other hormones from the pituitary are secreted in response to changing concentrations in the blood of hormones produced by target organs. For instance, hormones from the gonads—testosterone from the male and estrogens from the female—inhibit secretion of the gonadotropins, maintaining homeostasis. Estrogen and testosterone levels are detected by the hypothalamus of the brain. It then signals the pituitary to increase or decrease gonadotropin secretion, depending on the needs of the system. This control mechanism is known as negative feedback. In this way the endocrine system maintains a balance in body functions and systems. In the reproductive system, it helps to regulate the menstrual cycle in the female and sperm production in the male (see also Menstruation; Testicles).
The posterior lobe of the pituitary produces hormones that regulate water retention and uterine contractions at the time of birth.