Contractions in childbirth - a hormone stimulates a nerve, that causes more of the hormone to be produced which increases the contractions.
The process of blood clotting. The loop is initiated when injured tissue releases signal chemicals that activate platelets in the blood. An activated platelet releases chemicals to activate more platelets, causing a rapid cascade and the formation of a blood clot.
Lactation - when a baby suckles there is a nerve response that stimulates more milk to be produced.
Hope this helps!
Answered Sat 1st September, 2012 @ 18:56 by Sophie