Final answer:
Oxytocin, released by the posterior pituitary gland, induces uterine contractions during childbirth and milk ejection through a positive feedback mechanism triggered by cervical and uterine stretching.
Step-by-step explanation:
The hormone oxytocin is secreted by the posterior pituitary gland and plays a crucial role in stimulating uterine contractions during childbirth and milk ejection. Uterine muscles become more sensitive to oxytocin towards the end of pregnancy as the number of oxytocin receptors increases. This hormone functions through a positive feedback mechanism, where the stretching of the cervix and uterus during childbirth triggers additional oxytocin release, intensifying the contractions until delivery is achieved.
Oxytocin also acts on the breast tissue to stimulate the contraction of myoepithelial cells surrounding mammary glands, leading to the forceful ejection of milk, a process also known as the "let-down" reflex. The suckling of a child stimulates the synthesis and release of oxytocin into circulation, enhancing this milk ejection process.
The hormone oxytocin stimulates uterine contractions during childbirth. It is released by the posterior pituitary gland. During pregnancy, the number of oxytocin receptors in the uterus increases, making the uterine smooth muscles more sensitive to oxytocin. Additionally, oxytocin stimulates the contraction of myoepithelial cells around the milk-producing mammary glands, resulting in milk ejection or "let-down" reflex.