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Pregnancy and Parturition - Horse Anatomy (view source)
Revision as of 12:22, 28 November 2012
, 12:22, 28 November 2012→Contractions
* Reduction of binucleate cells in the trophectoderm.
* Reduction of binucleate cells in the trophectoderm.
===Contractions===
===Contractions===
Contractions open endometrial crypts. Foetal villi have shrunk due to the escape of blood from the foetal side of the placenta when the umbillical cord ruptures.[[Uterine Contraction - Anatomy & Physiology|myometrial contractions]] aid exsanguination of the placenta and separation of foetal membranes. The apex of the allantochorionic sac becomes inverted. As the sac is 'rolled' down the uterine horns, foetal villi are drawn out of the crypts. When a large portion becomes detached and inverted, it forms a mass in the maternal pelvis. This stimulates reflex contractions of abdominal muscles and completes expulsion of the allantochorionic sac. The final stage of allantochorionic expulsion lasts 1 hour in the mare.
Contractions open endometrial crypts. Foetal villi have shrunk due to the escape of blood from the foetal side of the placenta when the umbillical cord ruptures.[[Uterine Contraction - Anatomy & Physiology|Myometrial contractions]] aid exsanguination of the placenta and separation of foetal membranes. The apex of the allantochorionic sac becomes inverted. As the sac is 'rolled' down the uterine horns, foetal villi are drawn out of the crypts. When a large portion becomes detached and inverted, it forms a mass in the maternal pelvis. This stimulates reflex contractions of abdominal muscles and completes expulsion of the allantochorionic sac. The final stage of allantochorionic expulsion lasts 1 hour in the mare.
===Placental Expulsion===
===Placental Expulsion===
Expulsion of foetal membranes quickly follows expulsion of the foetus. After the birth of the young, regular abdominal contractions largely cease, but myometrial contractions persist. They are of decreased amplitude, but become more frequent and less regular. This is important for dehiscence and expulsion of foetal membranes. Waves of contractions from uterus to the cervix persist.
Expulsion of foetal membranes quickly follows expulsion of the foetus. After the birth of the young, regular abdominal contractions largely cease, but myometrial contractions persist. They are of decreased amplitude, but become more frequent and less regular. This is important for dehiscence and expulsion of foetal membranes. Waves of contractions from uterus to the cervix persist.