Which hormone released by the pituitary gland causes contraction of the uterus, indicating the beginning of labour?

The hormone released by the pituitary gland that causes contraction of the uterus, indicating the beginning of labor, is Oxytocin. Oxytocin is a peptide hormone that plays a crucial role in childbirth and is often referred to as the "love hormone" because it also has roles in social bonding and reproductive behaviors.

During labor, the release of oxytocin increases uterine contractions, helping to dilate the cervix and facilitate the delivery of the baby. The secretion of oxytocin is triggered by various factors, including the physical pressure of the baby's head against the cervix, which signals to the brain to release more oxytocin, creating a positive feedback loop that intensifies contractions. This process is essential for the effective progression of labor and ensuring the delivery of the infant.

In summary, Oxytocin's role in labor is vital as it promotes the necessary uterine contractions that lead to childbirth.