What are the amnion, chorion, yolk sac and allantois?

Question

What are the amnion, chorion, yolk sac and allantois and what is their function during development in mammals?

Answer 1

One of the membranous structures which surround the embryo during its developmental period. Since such membranes are external to the embryo proper, they are called extraembryonic membranes. They function in the embryo's protection, nutrition, respiration, and excretion.

There are four fetal membranes—the amnion, chorion, yolk sac, and allantois. In the course of development, the chorion becomes the outermost, and the amnion the innermost, membrane surrounding the developing embryo. As the allantois increases in size, it expands and becomes closely associated, if not fused, with the chorion. The two membranes together are known as the chorioallantoic membrane.

The amniotic cavity within which the embryo is enclosed becomes filled with an aqueous fluid which gives osmotic and physical protection to the embryo during the remainder of its fetal existence. Smooth muscle fibers in the amnion spontaneously contract and gently rock the embryo before it develops the capacity for spontaneous movement.

As the stored nutrients of the yolk are depleted during development, the yolk sac gradually decreases in size and is eventually incorporated into the midgut of the embryo. The yolk sac in the nonyolky eggs of placental mammals is vestigial. It has evolutionary but essentially no functional significance.

At the time of birth or hatching, the embryo becomes completely separated from the amnion and chorion and from the major portion of the allantois. The proximal portion of the latter remains within the embryo, however, as the urinary bladder.

This is a more specific definition of each of the words:

Allantois: A membranous sac that develops from the posterior part of the alimentary canal in the embryos of mammals, birds, and reptiles. It is important in the formation of the umbilical cord and placenta in mammals.

Amnion: A thin, tough, membranous sac that encloses the embryo. It is filled with a serous fluid in which the embryo is suspended.

Chorion: The outer membrane enclosing the embryo in reptiles, birds, and mammals. In placental mammals it contributes to the development of the placenta.

Yolk sac: A membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals and functioning as the circulatory system of the human embryo before internal circulation begins.

Answer 2

This Site Might Help You.

RE:
What are the amnion, chorion, yolk sac and allantois?
What are the amnion, chorion, yolk sac and allantois and what is their function during development in mammals?

Answer 3

Yolk sac in the development of mammals?

Answer 4

For the best answers, search on this site https://shorturl.im/LVGwZ

They are basically protective extraembryonc membranes. Chorioallantoic membrane forms placenta for achoring to the uterine wall and draws nutrition from the mother. Allantois serves as foetal urinary bladder.

Answer 5

Allantois