2.4 - Cell Differentiation

What are the different stages of embryonic cell development?

1. Zygote

2. Morula

3. Blastocyst

4. Embryo

5. Fetus

What is a zygote?

a diploid cell resulting from the fusion of two haploid gametes; a fertilised ovum. (The stage at which the sperm and egg begin to fertilise). Zygotes are totipotent as it is still able to become any form of cell.

What is a morula?

Collection of ~12-32 cells in the early stage of development. Morulas are totipotent as they are able to become any form of cell.

What is a blastocyst?

A hollow ball of cells in which some differentiation within the cell has occurred. A blastocyst is pluripotent as it can only become forms of cells within the embryo.

E.g. Muscle, brain, skin (not placenta or umbilical cord)

What is an embryo?

an unborn or unhatched offspring in the process of development.

What is a fetus?

an unborn offspring of a mammal, in particular an unborn human baby more than eight weeks after conception.

What are the three sections of an embryo?

Ectoderm (outer)

• Nervous system

• Skin

Mesoderm (Middle)

• Muscle

• Skeleton

• Kidneys

• Reproductive system

Endoderm (inside)

• Lungs

• Digestive tract

• Liver

What are stem cells?

Unspecialised cells that are yet to be assigned a function to the body. The 'potency' of a cell is its ability to change into different types of cells (the more potent, the more it can change into). All cells are different because most of the time, one of the genes will be 'switched off', which is where differentiation comes from.

What are the different potencies of stem cells?

Totipotent: Can differentiate into any type of cell throughout the body, including the cells that make up the embryo and external growth cell bodies (placenta).

E.g. Zygotes, morulas

Pluripotent: Can differentiate into germ line layers (ecto, meso, endo) - can specialise into anything EXCEPT FOR EXTERNAL GROWTH CELL BODIES like the placenta.

E.g. Blastocysts

Multipotent: Can divide into any type of cell in a specific lineage (depending on the area they come from) - only into a small group of tissue within the region.