Inner cell mass

Definition

The inner cell mass (ICM) is a cluster of cells inside the blastocyst, which forms during early embryonic development. These cells give rise to the embryo proper and eventually differentiate into all the tissues and organs of the body.

5 Must Know Facts For Your Next Test

1. The ICM is formed around days 4-5 after fertilization in humans.
2. The ICM will differentiate into two layers: the epiblast and hypoblast.
3. Only cells from the ICM are pluripotent, meaning they can give rise to any cell type in the body.
4. The outer layer of the blastocyst, called the trophoblast, surrounds and protects the ICM.
5. The ICM's differentiation is crucial for forming both embryonic stem cells and extraembryonic structures like the amniotic sac.

Review Questions

• What stage of development does the inner cell mass form?
• Which parts of the body do cells from the inner cell mass ultimately develop into?
• How does the inner cell mass differ from the trophoblast in terms of function?

Related terms

Blastocyst: A structure formed in early development consisting of an outer trophoblast layer and an inner cell mass.

Trophoblast: The outer layer of cells in a blastocyst that contributes to forming the placenta.

Pluripotent Cells: Cells that have the ability to develop into nearly all types of cells in an organism.