Question

Name the pituitary hormone which stimulates contraction of the uterus during childbirth?

Answer 1

Pituitary gland or hypophysis is located in a bone cavity of the sphenoid bone of the skull called sella turcica. It is attached to the hypothalamus and the hypophysis is divided into adenohypophysis and neurohypophysis.

Complete answer:
Oxytocin is the pituitary hormone which stimulates the contraction of the uterus during childbirth. Oxytocin is secreted by the neurohypophysis or posterior pituitary. The process of childbirth is known as parturition. It is a complex neuroendocrine mechanism and the signal of parturition originates from the fully developed foetus and the placenta which induces mild uterine contractions known as foetal ejection reflex. Oxytocin acts on smooth muscles and stimulates their contraction.
Parturition comprises of three stages:
- Dilation stage
- Expulsion stage
- Stage of after birth
Oxytocin acts on the uterine muscles and causes stronger uterine contractions which stimulate further secretion of oxytocin. The uterine contraction starts from top and occurs after every 30 minutes. These contractions force the foetus forward pushing the fetus's head against the cervix. Dilation of the cervix increases the stimulus for oxytocin secretion and this secretion increases the strength and frequency of contractions (1-3 per minute).

Note: Oxytocin also causes contraction of mammary glands leading to milk ejection. Oxytocin is known as ‘milk ejection hormone’ and ‘birth hormone’. Oxytocin is neurohormone synthesized by hypothalamus and secreted by neurohypophysis.