10.03 Positive feedback

Good examples of positive feedback are with oxytocin, a hormone released from the posterior pituitary. In the process of child birth, oxytocin is release from the posterior pituitary of both the mother and foetus.The oxytocin stimulates its receptors on the uterus to cause contraction (Figure 10.5). Oxytocin also stimulates its receptors on the placenta to stimulate the production of prostaglandins. Prostaglandins alsostimulate receptors on the uterus to cause contraction. Thus, when both oxytocin and prostaglandins are produced, vigorous contractions of the uterus occur, leading to childbirth (Figure 10.5).

Figure 10.5 Oxytocin and uterine contraction (Copyright Sheila Doggrell, QUT)

Oxytocin also controls the positive feedback whereby suckling by a baby leads to milk release. Thus, suckling leads to a sensory nerve input to the hypothalamus, and the release of oxytocin from the posteriorpituitary (Figure 10.6). Oxytocin has a positive feedback on the breast leading to stimulation of milk release for the baby to drink (Figure 10.6).

Figure 10.6 Oxytocin and milk release (Copyright Sheila Doggrell, QUT)