Amnion

Definition

The amnion is a membranous sac that surrounds and protects the embryo in reptiles, birds, and mammals. It creates an aquatic environment necessary for embryo development on land.

5 Must Know Facts For Your Next Test

1. The amnion is one of the four extraembryonic membranes in vertebrates.
2. It is filled with amniotic fluid, which cushions the developing embryo.
3. The presence of an amnion is a key feature distinguishing amniotes (reptiles, birds, and mammals) from amphibians and fish.
4. Amniotic fluid plays a critical role in preventing desiccation and providing mechanical protection.
5. The development of the amnion allowed vertebrates to reproduce away from water.

Review Questions

• What is the primary function of the amnion?
• How does the amnion contribute to the evolutionary success of reptiles?
• What are some key differences between amniotes and non-amniotes regarding their embryonic development?

Related terms

Chorion:

The outermost membrane surrounding embryos in reptiles, birds, and mammals that contributes to gas exchange.

Allantois:

A sac-like structure involved in respiration and waste storage during embryonic development.

Yolk Sac:

The membranous sac attached to an embryo that provides early nourishment through yolk material.