Fetal membrane

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Definition

noun, plural: fetal membranes

A membrane surrounding the embryo or fetus and is involved in nutrition, respiration, excretion, and protection of the developing offspring (within the uterus or the egg)


Supplement

Fetal membranes are the membranes surrounding the embryo or fetus. These membranes are the amnion, the chorion, the allantois, and the yolk sac. The chorion is a membrane comprised of four layers, particularly the cellular layer, the reticular layer, the basement membrane, and the trophoblast layer. The trophoblast is the outermost layer. The chorion and the amnion form the amniotic sac. The amniotic sac filled with a fluid referred to as amniotic fluid. The fluid serves as a cushion to the developing fetus. The amnion is a membrane that lies next to the chorion. It is a thin and tough membrane. It lines the amniotic cavity. It is comprised of two cell layers, i.e. the epiblast-derived extraembryonic ectodermal layer and the thin non-vascular extraembryonic mesoderm. The allantois is a sac-like or diverticulum from the ventral wall of the hindgut. It forms a part of conceptus (i.e. the embryo and its appendages or adjunct parts or associated membranes) of amniotes. The allantois helps in gas exchange and movement of liquid waste. The yolk sac is a membrane formed by the hypoblast. It is associated with early embryonic blood supply and the formation of the primordial gut.


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