Oxytocin is a nine amino acid peptide hormone synthesized in the hypothalamus and released by the posterior lobe of the pituitary gland. Oxytocin is a hormone produced in the posterior lobe of the pituitary gland. It is peptide chain composed of nine amino acids that is synthesized in hypothalamic neurons and then carried through a support of axons to the posterior lobe of the pituitary gland to be distributed into the bloodstream.
An important function of this oxytocin hormone is executed when a women has reached the end of gestation, when she is in labor. In order to deliver the fetus, the women must undergo contractions when the smooth muscles of the uterus/uterine wall contract. In order for the uterus to contract for a prolonged period of time, oxytocin must be produced. So, as the fetus stimulates the cervix and vagina during labor, an enhanced amount of oxytocin receptors form on the uterine smooth muscle cells and larger amounts of oxytocin are released in order to deliver the baby. The fetus moves further down towards the cervix and vagina as oxytocin reacts with the hormone receptors on the smooth muscle uterine wall. As more oxytocin is released, the fetus is pushed steadily downward.
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.
Oxytocin may also facilitate bonding of young to their mother by promoting pup attachment to the nipple. Oxytocin is very concentrated in the milk of lactating rats. Washing the belly of a rat mother removes an important olfactory cue for pup attachment. Topical oxytocin administration on the mother has been reported to re-instate nipple attachment within minutes, even in the absence of milk ejection. It is known that more receptors for oxytocin are present in the fetal rat brain compared to the adult rat brain. Perhaps oxytocin from the mother is triggering affiliative behavior in pups by binding to olfactory areas of the brain, thus setting off a signaling cascade to stimulate feeding.
Oxytocin is responsible for uterine contractions, both before and after delivery. The muscle layers of the uterus (myometrium) become more sensitive to oxytocin near term. Towards the end of a term pregnancy, levels of progesterone decline, and contractions that were previously suppressed by progesterone begin to be more frequent and stronger. This change in the oxytocin/progesterone ratio is believed to be one of the initiators of labor.
Oxytocin is responsible for the contractions that bring about delivery, by thinning and dilating the cervix, and applying pressure that helps the baby descend in the pelvis. It is also important after delivery, as it continues to cause the myometrium to contract. These contractions help constrict the blood vessels that are sending blood to the uterus at the time of childbirth at the rate of a liter a minute!
Oxytocin is also responsible for milk ejection during breastfeeding, by contraction of the myoepithelial cells in the lactating mammary gland. The uterine "cramping" that often occurs with breastfeeding is a signal that oxytocin is still causing the uterus to contract after delivery. These contractions help the uterine muscle to continue to constrict the uterine blood vessels, and bring about a decrease in the amount of vaginal bleeding after delivery.