Stem Cells

Embryo

An organism in the early stages of development following fertilization.

Morula

A solid ball of 16–32 undifferentiated cells formed a few days after fertilization.

Blastocyst

A hollow ball of cells with an inner cell mass that will develop into the fetus.

Gastrula

An early embryo stage with three distinct tissue layers (germ layers) formed through cell movement.

Mesoderm

The middle germ layer; forms muscles, bones, the circulatory system, and the heart.

Endoderm

The inner germ layer; forms the linings of the digestive tract and respiratory system.

Ectoderm

The outer germ layer; forms the skin, hair, and nervous system (brain/spinal cord).

Stem Cells

Undifferentiated cells capable of dividing indefinitely and turning into specialized cell types.

Totipotent

Stem cells that can differentiate into any cell type plus placenta/extra-embryonic tissues (e.g., zygote).

Pluripotent

Stem cells that can differentiate into any body cell type except placenta (e.g., embryonic stem cells).

Multipotent

Stem cells that can only differentiate into a limited family of related cells (e.g., blood stem cells).

Unipotent

Stem cells that can only differentiate into one single specific cell type (e.g., muscle stem cells).

Embryonic Stem Cell

Pluripotent stem cells harvested from the inner cell mass of a 5-day-old blastocyst.

Adult Stem Cell

Multipotent stem cells found in mature tissues (like bone marrow) used for ongoing repair and replacement.