Germ layers

Definition

Germ layers are the primary cell layers formed during embryonic development in animals. They give rise to all tissues and organs in the body.

5 Must Know Facts For Your Next Test

1. Germ layers are established during the process called gastrulation.
2. Animals typically have two or three germ layers: ectoderm, mesoderm, and endoderm.
3. The ectoderm gives rise to the nervous system and skin.
4. The mesoderm forms muscles, bones, and the circulatory system.
5. The endoderm develops into the digestive tract and associated organs.

Review Questions

• What are the three primary germ layers in animal embryos?
• Which germ layer is responsible for forming the nervous system?
• During which developmental process do germ layers form?

Related terms

Ectoderm: The outermost germ layer that forms structures such as skin and the nervous system.

Mesoderm: The middle germ layer that gives rise to muscles, bones, and the circulatory system.

Endoderm: The innermost germ layer that becomes the lining of the digestive tract and other internal organs.