Yolk sac placenta

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The yolk sac placenta is an organ that is formed in many vertebrates during embryonic development and that supplies nutrients to the developing embryos in the uterus . The yolk sac placenta is formed from the yolk sac of the embryos and the uterine lining , whereby there are different types in terms of their shape and development (complete, circular, discoidal, row-shaped).

Live birthing sharks , reptiles and mammals usually also form placentas , which in the course of further embryonic development more or less ensure complete nutrition via the maternal bloodstream. In some mammals (e.g. horses , dogs , cats ), however, a real yolk sac placenta also temporarily forms.