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Pregnancy and Parturition - Horse Anatomy (view source)
Revision as of 17:52, 26 November 2012
, 17:52, 26 November 2012→Parturition
==Parturition==
==Parturition==
The step in the reproductive process that immediately precedes lactation, uterine involution and return to cyclicity. It is initiated by the foetus and involves a complex cascade of endocrine events. Parturition is the process by which the conceptus (foetus, placenta and placental membranes) is expelled from the [[Uterus - Anatomy & Physiology|uterus]]; this requires [[Cervical Softening - Anatomy & Physiology|cervical softening]],[[Uterine Contraction - Anatomy & Physiology|coordinated myometrial contractions]] and contraction of abdominal muscles
The step in the reproductive process that immediately precedes lactation, uterine involution and return to cyclicity. It is initiated by the foetus and involves a complex cascade of endocrine events. Parturition is the process by which the conceptus (foetus, placenta and placental membranes) is expelled from the [[Uterus - Anatomy & Physiology|uterus]]; this requires [[Cervical Softening - Anatomy & Physiology|cervical softening]], [[Uterine Contraction - Anatomy & Physiology|coordinated myometrial contractions]] and contraction of abdominal muscles
to occur.
to occur.
===Stages of Parturition===
===Stages of Parturition===
*Stage 2: The expulsive stage, characterised by the onset of abdominal contractions which together with uterine contractions lead to foetal expulsion. This takes 12-30 minutes.
*Stage 2: The expulsive stage, characterised by the onset of abdominal contractions which together with uterine contractions lead to foetal expulsion. This takes 12-30 minutes.
*Stage 3: Separation and expulsion of the foetal membranes. This takes 1 hour.
*Stage 3: Separation and expulsion of the foetal membranes. This takes 1 hour.
===Placental Changes===
During the last 5 days of gestation, there are changes in the placenta.
* Collaginisation of the placentome.
* Flattening of maternal crypt epithelium.
* Leucocyte migration and increased activity.
* Reduction of binucleate cells in the trophectoderm.
===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.
===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.