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Oxytocin: Hormones
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Oxytocin is a mammalian hormone that ... acts as a neurotransmitter in the brain. In women, it is released mainly after distension of the cervix and vagina during labor facilitating birth, and also after stimulation of the nipples helping breastfeeding. Oxytocin is released during orgasm in both sexes. In the brain, oxytocin is involved in social recognition and bonding, and might be involved in the formation of trust between people. Injected oxytocin analogues are used to induce labour and support labour in case of non-progression of parturition. It has largely replaced ergotamine as the principal agent to increase uterine tone in acute postpartum haemorrhage.
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Oxytocin is a peptide hormone that is actually produced in two discrete groups of neurons in the brain of all mammals. One group of oxytocin-producing neurons projects to the posterior pituitary, which is an endocrine gland located at the base of the brain. From the pituitary, oxytocin is released into the bloodstream, whereby it exerts the well-known peripheral effects like uterine contraction and milk let-down. The other group of oxytocin-containing neurons projects directly to specific brain areas that are known to mediate maternal behaviors. By acting locally as a chemical messenger in these brain areas, oxytocin acts as a regulator or controller of maternal behaviors.
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Oxytocin holds the distinction of being the first naturally-occuring peptide hormone to b synthesized, a feat for which du Vigneaud received the Nobel prize in 1955. Immunostaining techniques have been used to show that oxytocin is synthesized mainly in specialized magnocellular neurons in the supraoptic and paraventricular nucleus of the hypothalamus, separate from the vasopressin-synthesizing neurons (Zimmerman & Defendini, 1977). Fibers from the paraventricular nucleus course to the level of the supraoptic nucleus where they are joined by fibers from this nucleus as well. Both sets of fibers then travel down the median eminence to the posterior pituitary.
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Oxytocin means "rapid birth." It is a synthetic hormone named for the natural posterior pituitary hormone. It stimulates uterine smooth muscle contractions indirectly and helps expedite the normal contractions of spontaneous labor. As in all significant uterine contractions, there is a transient reduction in uterine blood flow. Oxytocin ... stimulates the mammary glands to increase lactation without increasing the production of milk. The drug is administered in the prehospital setting to control postpartum bleeding.
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Oxytocin was discovered almost a century ago. It is produced in the brain and has long known to be a hormone that favors contraction of the uterus during childbirth as well as the secretion of milk whilst breast-feeding. Indeed, hospitals still make use of oxytocin to stimulate lazy uteri during labor. It ... seems to be involved in reproductive behaviors such as a female’s sexual appetite, fidelity and maternal instinct. Furthermore, its role in social cohesion such as the recognition of a familiar partner have led scientists to form the hypothesis that defects in the hormone’s metabolism could lead to psychiatric illnesses associated with relational deficiencies such as autism.
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Oxytocin was discovered in 1909 when Sir Henry H. Dale found that an extract from the human posterior pituitary gland contracted the uterus of a pregnant cat. (The hormone is found unchanged in every mammalian species.) Dale named the unknown substance oxytocin, using the Greek words for "quick" and "birth." As early as 1911, physicians began using the pituitary extract to stimulate childbirth contractions. Dale subsequently found that the same extract facilitates the release of mother's milk. Oxytocin contracts the smooth-muscle cells surrounding the mammary glands to move milk into the nipple--called milk "let-down."
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