Final answer:
Oxytocin stimulates uterine contractions during childbirth, leading to the expulsion of the fetus and placenta from the uterus.
Step-by-step explanation:
Oxytocin is a hormone that stimulates uterine contractions during childbirth. As the baby pushes toward the cervix, stretch-sensitive nerve cells in the cervix send messages to the brain, causing the release of oxytocin from the pituitary gland. Oxytocin then causes stronger contractions of the uterine wall muscles. This process continues in a positive feedback loop, with increased contractions leading to more oxytocin release and further contractions.