Extraembryonic Layers: Definition, Meaning, Types, Description, & Facts

Definition Of Extraembryonic Layers

Extraembryonic layers refer to membranes that support the developing embryo but do not become part of the embryo. These tissues play a role in protecting, nourishing, and excreting the developing embryo during its early development.

What Are Extraembryonic Layers?

Extraembryonic layers are tissues formed together with the embryo. They comprise tissues such as the amnion, chorion, yolk sac, and allantois. These membranes help in keeping the embryo alive and thriving in the uterus.

Extraembryonic Layers

The layers are:

Amnion

This membrane envelops the embryo, forming an amniotic cavity that is filled with amniotic fluid. This fluid is what cushions the embryo and surrounds it in a constant environment.

Chorion

The chorion is the outermost layer. It forms the essential component that provides for gas and nutrient exchange between the mother and the developing embryo. It also develops the placenta.

Yolk Sac

This is the sac that provides early nourishment to the embryo before the complete development of the placenta. It also forms blood cells throughout the early development.

Allantois

The allantois acts as a storage sac where waste products are stored and transported. Apart from the umbilical cord, it also forms from this layer and forms part of the chorion which participates in gas exchange.

Functions Of The Extraembryonic Layers

The functions are given below:

Protection

Amnion: this layer cushions the embryo against mechanical shocks and temperature fluctuations.

Nourishment

The yolk sac and subsequently the placenta provide nutrients for the developing embryo.

Waste

The allantois contributes to storing and removing waste products.

Timetable Of Development Of Extraembryonic Layers

The details are given below:

Early Development

Amnion and yolk sacs develop shortly after fertilisation.

Mid-Pregnancy

The chorion becomes more prominent as the development of the placenta takes place.

Late Pregnancy

The allantois mainly contributes to waste and gas exchange as the placenta takes over supplying nutrients.

Clinical Relevance

Understanding extraembryonic layers is very vital in understanding pregnancy and fetal development. Their aberrations can result in miscarriages and developmental disorders.

Conclusion

The extraembryonic layers are very vital for the successful development of the embryo. Protection, nourishment, and waste management are some of the major functions of these layers, securing growth and survival during the early stages of embryonic development.

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