Changes

Two hormones directly regulate myometrial contractions:  

Two hormones directly regulate myometrial contractions:  

* '''Oxytocin''': from the posterior pituitary gland (not the corpus luteum) lowers the excitation threshold of muscle cells to increase the likelihood of action potential firing.  Oxytocin also stimulates prostaglandin release.

* '''[[Endocrine_System_-_Pituitary_Gland_-_Anatomy_%26_Physiology#Oxytocin|Oxytocin]]''': from the posterior pituitary gland (not the corpus luteum) lowers the excitation threshold of muscle cells to increase the likelihood of action potential firing.  Oxytocin also stimulates prostaglandin release.

** The uterine Oxytocin receptor is a G protein coupled receptor with a Gαq subinit. Thus the signalling pathway is via a calcium second messenger.  Hence prostaglandin and oxytocin are complementory in action.

** The uterine Oxytocin receptor is a G protein coupled receptor with a Gαq subinit. Thus the signalling pathway is via a calcium second messenger.  Hence prostaglandin and oxytocin are complementory in action.

* '''Prostaglandins''': Stimulate liberation of calcium from intracellular stores to cause the rise in intracellular calcium concentration required for myometrial contraction.

* '''Prostaglandins''': Stimulate liberation of calcium from intracellular stores to cause the rise in intracellular calcium concentration required for myometrial contraction.