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Oxytocin is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. [4] Present in animals since early stages of evolution, in humans it plays roles in behavior that include social bonding, love, reproduction, childbirth, and the period after childbirth.
Many nonhuman studies can be used as both potential models for humans and to show the phylogenetic conservation of some endocrine signals. [1] Estrogen and progesterone released by ovaries during pregnancy make oxytocin receptors more sensitive in female rats [8] and is associated with the onset of maternal behaviors in other species as well.
Oxytocin's uterine-contracting properties were discovered by British pharmacologist Henry Hallett Dale in 1906. [9] Oxytocin's milk ejection property was described by Ott and Scott in 1910 [44] and by Schafer and Mackenzie in 1911. [45] Oxytocin was the first polypeptide hormone to be sequenced [46] or synthesized.
By the 1970s, home birth rates fell to approximately 1%. [167] In the United States, the middle classes were especially receptive to the medicalisation of childbirth, which promised a safer and less painful labour. [166] Accompanied by the shift from home to hospital was the shift from midwife to physician.
An increase in levels of oxytocin, glucocorticoids, estrogen and prolactin occur in the paternal brain. [13] [59] These hormonal changes occur through the father's interaction with the mother and his offspring. [1] Oxytocin levels are positively correlated with the amount of affection the father displays towards the child. [60]
A low level of estrogen can lead to a non-conception cycle, and a high level of estrogen when LH is at its peak, can lead to lower live birth rates and other complications. [13] During pregnancy, estrogen plays a role in supporting placentation through the modulation of angiogenic factor expression. [13]
Replacement fertility is the total fertility rate at which women give birth to enough babies to sustain population levels, assuming that mortality rates remain constant and net migration is zero. [10] If replacement level fertility is sustained over a sufficiently long period, each generation will exactly replace itself. [10]
Oxytocin contracts the smooth muscle of the uterus during and after birth, and during orgasm(s). After birth, oxytocin contracts the smooth muscle layer of band-like cells surrounding the alveoli to squeeze the newly produced milk into the duct system. Oxytocin is necessary for the milk ejection reflex, or let-down, in response to suckling, to ...