Brent Cornell

    
The process of childbirth is called parturition and occurs via positive feedback under hormonal control

Positive feedback involves a response that reinforces the change detected (it functions to amplify the change)

• In the case of childbirth, fetal growth eventually causes stretching of the uterine walls, which is detected by stretch receptors
• This triggers the release of hormones (oxytocin) that induce uterine muscles to contract, further reducing space in the womb
• This causes more stretching and hence more contraction until the origin stimulus (the foetus) is removed (i.e. birth)

The Role of Positive Feedback in the Birth Process

Hormonal Control

The chemical regulators of the birthing process include oxytocin, oestrogen, progesterone and prostaglandin

• After 9 months, the baby is fully grown and stretches the walls of the uterus – placing a strain on both mother and infant
• This stress induces the release of chemicals which trigger a rise in the levels of estrogen (estriol in particular)
• Estriol prepares the smooth muscle of the uterus for hormonal stimulation by increasing its sensitivity to oxytocin
• Estriol also inhibits progesterone, which was preventing uterine contractions from occurring while the foetus developed
• Now that the uterus is primed for childbirth, the brain triggers the release of oxytocin from the posterior pituitary gland
• Oxytocin stimulates the uterine muscles to contract, initiating the birthing process (it also inhibits progesterone secretion)
• The foetus responds to this uterine contraction by releasing prostaglandins, which triggers further uterine contractions
• As the uterine contractions trigger the release of chemicals that cause further contractions, a positive feedback loop ensues
• Contractions will stop when labour is complete and the baby is birthed (no more stretching of the uterine wall)

Hormonal Regulation of the Birth Process