Final answer:
Cervical stretching during birth increases the release of oxytocin from the posterior pituitary gland, leading to stronger uterine contractions and the eventual delivery of the baby.
Step-by-step explanation:
During parturition (birth), the action of cervical stretching feeds back and causes increases in levels of the hormone oxytocin. As the baby engages with the cervix, it stretches, which sends nerve impulses to the hypothalamus. The hypothalamus then signals the posterior pituitary to release oxytocin, which increases the contractions in the smooth muscle of the uterus.
This process of increasing oxytocin levels continues due to a positive feedback mechanism, where the more the cervix stretches, the more oxytocin is released, leading to stronger uterine contractions. This cycle repeats until the baby is delivered.