Oxytocin is a hormone released from the pituitary gland in the brain, which stimulates uterine contractions and also controls the production of milk in the mammary glands of the breast (a process called lactation). Synthetic oxytocin is sometimes given to women in labor to induce labor.
The mechanism that prompts the secretion of oxytocin from the pituitary during labor is thought to be initiated by the pressure of the fetus's head against the cervix, the opening of the uterus. As the fetus's head presses against the cervix, the uterus stretches, and relays a message along nerves to the pituitary, which responds by releasing oxytocin. The more the uterus stretches, the more oxytocin is released.
Science EncyclopediaScience & Philosophy: Bilateral symmetry to Boolean algebraBirth - Viviparous Animals, Maternal Progesterone, Oxytocin, History Of Childbirth, Types Of Childbirth Preparation, Types Of Anesthesia - How does birth begin?, Fetal endocrine control, Birth in humans