Oxytocin is a mammalian hormone that has many functions, the most notable having to do with pregnant or lactating mammals. In this capacity, some of the hormone’s main functions are preparing a female’s body for childbirth, stimulating milk “let-down” so that a baby can properly feed, and facilitating the bond between a mother and a newborn infant. The hormone is also thought to play a role in sexual arousal and orgasms in females who are not pregnant or lactating, as well as in males. In nonsexual human relationships, the hormone is credited with increasing trust, generosity, and cooperation. It can also stimulate a nurturing aspect within males and females who are not mothers.
One of the main roles of oxytocin is to prepare a pregnant woman for childbirth. During the last months of pregnancy, the woman’s uterus develops more and more receptors for this hormone. These receptors allow the smooth muscle of the uterus to react to the hormone when it is released. When the fetus is ready to be born, it releases oxytocin, which starts a process that causes the mother’s pituitary gland to release more of the hormone. Once the hormone is released, it causes the uterus to contract, which in turn helps push the baby out.
Once the baby is born, the hormone helps to encourage the mother-child bonding. In many mammals, oxytocin released during the birthing process affects not only the uterus, but also the brain. The hormone stimulates the nurturing and maternal instincts in a mother to her child, helping to ensure that she will take care of her baby instead of letting it die from neglect. In those who are not mothers, this hormone can also help establish a bond among social groups. It may also play a role in the display of aggression against those that are viewed as outsiders of a group.
This hormone also plays a role in milk expression, a process also known as milk let-down. In a lactating woman’s breast are milk-producing glands surrounded by myeopithelial cells. The milk-producing glands make milk, but the milk does not leave the glands until an infant suckles. This stimulates the mother’s hypothalamus to produce oxytocin, which causes the myeopithelial cells to contract and force the milk down. This also causes the uterus to contract until it shrinks back to a near-normal size.