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The primary function of the pituitary gland is to secrete and store the chemical messages known as hormones and to regulate other glands within the body’s endocrine system. The pituitary is often referred to as the “master gland” because of its influence on other hormone-secreting glands of the endocrine system. There are three lobes in the pituitary gland — the anterior, intermediate and posterior lobes — and they each control different types of hormones.
Although all vertebrates have a pituitary gland, its structure and size can vary wildly depending on the species, though the main function of the pituitary gland remains fairly uniform among all organisms. In humans, the pituitary gland is no larger than a pea and is located at the base of the brain, between the optic nerves and attached by nerve cells to the hypothalamus. From this position at the brain’s base, the function of the pituitary gland is to regulate the distribution of hormones throughout the body, to control the hormone secretion of other endocrine system glands — such as the thyroid and adrenal glands — and to stimulate the body’s reproductive organs.
The anterior, or frontal, lobe of the pituitary gland is responsible for producing growth hormone and prolactin, which is responsible for milk production in mammals following birth. It also produces the hormones responsible for stimulating the adrenal glands, called adrenocorticotropic hormone; the thyroid gland; and the ovaries and testes, called follicle-stimulating hormone and luteinizing hormone. Another function of the pituitary gland's anterior lobe is to release hormones such as endorphins, which can contribute to a feeling of well-being.
The intermediate, or middle, lobe is not present in all animals and varies greatly in size from organism to organism. In humans, this lobe consists of only a thin layer of cells that produce melanocyte-stimulating hormone. This hormone stimulates the production of melanin, which is responsible for changes in skin and hair coloration.
The posterior, or rear, lobe of the pituitary gland is primarily responsible for the storage and release of antidiuretic hormone and oxytocin. Antidiuretic hormone regulates the body's use of water and is essential for the proper functioning of the kidneys. Oxytocin controls uterine contractions during labor, in addition to helping to stimulate milk production and breastfeeding in mammals.