chorionic placenta

biology

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June 24, 2026

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The chorionic placenta is the outermost membrane surrounding an embryo in mammals, developing from an outer fold of the yolk sac. In placental mammals, the chorion becomes rich in blood vessels and forms a close relationship with the uterus's lining, the endometrium. Together, the chorion and endometrium create the placenta, which serves as the embryo's primary organ for respiration, nutrition, and waste removal. This organ is crucial for transferring oxygen and nutrients from the mother's blood to the embryo and removing waste products. The placenta is expelled after birth.12

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animal reproductive system
Provisions for the developing embryo
Chorioallantoic or chorionic placentas represent specializations in a chorionic sac surrounding the embryo. The entire surface of the sac may serve as a placenta (diffuse placenta, as in pigs); numerous separate patches of placental thickenings may develop (cotyledonary placenta, as in sheep); a thickened placental band may…
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Chorioallantoic or chorionic placentas represent specializations in a chorionic sac surrounding the embryo. The entire surface of the sac may serve as a placenta (diffuse placenta, as in pigs); numerous separate patches of placental thickenings may develop (cotyledonary placenta, as in sheep); a thickened placental band may…
Read More