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About the Pituitary Gland
The human endocrine system is a collection of glands which secrete chemical messengers, called hormones, to perform a variety of functions in many different tissues. Glands lack ducts, so the hormones they produce are released directly into the blood stream.
Located at the junction of the optic nerves, called the optic chiasm, on the bottom of the brain, the pituitary gland is a pea-sized gland comprised of three lobes made of two different tissues. The forward portion, or anterior, is called the adenohypophysis. Adeno- is a prefix meaning “glandular”, and it is formed from glandular tissues. The rear portion, or posterior, is called the neurohypophysis and is made out of neural tissue. The intermediate portion produces and secretes only one hormone.
Called the “master gland” because it controls the function of many other glands, the hypothalamus actually controls pituitary gland function. That aside, the pituitary gland releases several different hormones which control functions throughout the body. These hormones have both primary and secondary effects.
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The anterior lobe produces and secretes growth hormone (GH) as a result of the secretion of growth hormone releasing hormone (GHRH) from the hypothalamus, somatostatin (SS) from the hypothalamus and other tissues and ghrelin from the stomach. Growth hormone's two major functions are the stimulation of the liver to produce insulin-like growth factor 1 (IGF-1); this hormone stimulates the growth and lengthening of bones and the growth of muscle. GH also directly stimulates cartilage cells (chondrocytes) to multiply and divide. It also has several other functions that aid in anabolic processes in the body.
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Following pregnancy and birth, the anterior pituitary releases prolactin (PRL) to prepare the mother for breastfeeding her child. It has two major functions. During pregnancy, it stimulates growth of the alveoli in the mammary glands in preparation for milk production. However, milk production is inhibited by the high levels of progesterone present during pregnancy. Generally, near the end of pregnancy, or just after birth, progesterone levels lower, and then prolactin stimulates the production of milk.
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The anterior pituitary releases adrenocorticotropic hormone (ACTH) in response to the hypothalamus secreting adrenocorticotropin-releasing hormone. Usually during high stress situations ACTH is released; ACTH stimulates secretion of glucocorticoids, such as cortisol. These glucocorticoids have a host of functions that help the body manage trauma, infection and stress.
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In response to thyrotropin-releasing hormone (TRH) from the hypothalamus, the anterior pituitary releases thyroid-stimulating hormone (TSH) in order to stimulate the thyroid gland to secrete thyroxine (T4) and triiodothyronine (T3). These thyroid hormones affect the body's metabolic rate and growth and development.
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The anterior pituitary releases follicle-stimulating hormone (FSH) to aid in the maturation of the reproductive cells, or gametes, in men and women. In women, FSH directly aids in the maturation of the ovarian follicles; late in the follicular phase, FSH levels drop off to ensure that the most mature follicle moves onto ovulation. In men, FSH aids the Sertoli cells, which nurture sperm cells as they mature in the testes.
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The anterior pituitary also produces luteinizing hormone (LH) to work in conjunction with FSH. In women, after the follicle is mature, a surge in LH triggers ovulation; the egg is released, and LH converts the residual follicle into the corpus luteum. The corpus luteum will release progesterone in order to prepare the uterine lining for implantation. In men, LH stimulates Leydig cells in the testes to produce testosterone.
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The only hormone produced by the intermediate lobe of the pituitary gland, melanocyte-stimulating hormone (MSH) affects melanocytes. Melanocytes are cells that produce and release melanin, a pigment responsible for skin and hair color. Exposure to sunlight stimulates release of MSH in humans. Melanin also has effects on appetite and sexual arousal, though the mechanisms of this are less understood.
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The posterior pituitary releases antidiuretic hormone (ADH), also known as vasopressin, to perform several functions which affect the kidneys, cardiovascular system and central nervous system (CNS). Antidiuretic hormone has two main functions, one of which is to conserve water by stimulating the kidneys to retain water from filtrate and concentrate the urine; the other main function is a mild, systemic constriction of arterioles, slightly increasing blood pressure.
In the CNS, ADH has been implicated in several functions such as memory formation and aggression, though, the links are not precisely elucidated.
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Oxytocin is produced in the hypothalamus, as well as a few other tissues. It is however released by the posterior pituitary into the blood stream. The major effects of oxytocin in females are well documented. The “let-down” response allows milk to fill the alveolar sacs in the breast, uterine contraction aids in the birth process and establishment of maternal behaviors are all the major effects. Oxytocin's other effects are far too many to discuss here, but it is implicated in things like social behavior and aggression towards strangers.
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University of Cincinnati Clermont College: Endocrine System
University of Maryland Medical Center: The Pituitary Gland
University of Texas Southwestern Medical Center: The Pituitary Gland
The University of Alabama at Birmingham: Pituitary Gland: Location and Function
University of California Los Angeles Neurosurgery: Pituitary Function & Hormones
University of Pittsburgh Department of Neurological Surgery: What is the Pituitary Gland?
Colorado State University: Growth Hormone
Colorado Sate University: Prolactin
Colorado State University: Adrenocorticotropic Hormone
Colorado State University: Thyroid-Stimulating Hormone
Colorado State University: Luteinizing and Follicle Stimulating Hormones
Colorado State University: Antidiuretic Hormone
Colorado State University: Oxytocin