Oxytocin: A hormone secreted by the posterior pituitary gland which targets the smooth muscle of the uterus and mammary glands, stimulating uterine contractions amd the letdown of milk.
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Hormones: Complex molecules produced by the body which act as chemical messengers to the body's cells. They are made by the endocrine glands of various organs, including the pituitary gland, parthyroid gland, thyroid gland, pancreas, hypothalamus, adrenal glands, stomach, small intestine, and gonads (males). These proteins, in response to the proper signal, are secreted and then exert influence on they are carried through the bloodstream to exert influence of target tissues, which may be a great distance away. They act by chemically stimulating a cell to increase or decrease its functional activity or to increase or decrease the secretion of another hormone.
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When Hans Selye was experimenting on rats by inflicting stress them either by injecting them with hormones or chemicals, making surgical incisions or exposing them to extreme temperatures, he noticed that the rats were all displaying the same group of symptoms. At first he believed that he had discovered a new hormone1; however, several years of further testing by injecting the rats with other substances, such as formaldehyde, revealed the same results. Even exposure to cold, cutting their spinal cords and forced exercise produced the same effects. The effects occurred in a predictable sequence that is now known as the General Adaptation Syndrome2 (GAS).
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Cortisol is the primary member of a family of glucocorticoids, and is considered the main catabolic hormone. Corticosterone is the other glucocorticoid, but is thought to be much less potent than cortisol (accounting for approximately 4-5% of total glucocorticoid activity). Cortisol is made and secreted from the adrenal cortex, via the hypothalamic-pituitary-adrenal (HPA) axis, with a small amount also derived from the conversion of cortisone.
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