Biological Systems MCAT Practice Exam 2025 – Complete Study Resource

The hormone primarily responsible for causing uterine contractions during labor is oxytocin. This hormone is produced by the hypothalamus and released by the posterior pituitary gland. During labor, oxytocin plays a crucial role in stimulating the smooth muscles of the uterus, leading to rhythmic contractions that help facilitate the process of childbirth.

As labor progresses, increasing levels of oxytocin enhance the intensity and frequency of these contractions, promoting further dilation of the cervix and ultimately helping to push the baby through the birth canal. This feedback loop, where contractions lead to more release of oxytocin, is a key mechanism in the labor process.

Other hormones listed do not have the primary role in inducing uterine contractions. Prolactin is mainly involved in milk production after childbirth, estrogen plays various roles in the menstrual cycle and pregnancy preparation, but not in active contraction during labor, and follicle-stimulating hormone (FSH) is primarily involved in the regulation of reproductive processes, such as the development of egg follicles in ovaries, rather than in labor induction.