Stem Cells

Stems cells are the building block of the human body

The stem cells inside an embryo will eventually develop into all the different cells, tissues and organs in the foetus's body

When it divides, it can make any one of the 220 different cells in the human body

Stem cells have two main capacities:

• Endless self-renewal: a stem cell can divide endlessly to produce more stem cells

• Potency: the capacity to differentiate along different pathways to become specialised

During embryonic development cells gradually commit to particular pathways of differentiation

Embryonic stem cells change from being totipotent to pluripotent

Stem cells that remain in the adult body are more restricted in potential and can only differentiate into several types

Totipotent: stem cells which can form all types of cells of the body

Only found in very early-stage embryo (5-days, morula)

Pluripotent: can form cells of the body (early, embryo up to 7 days, blastocyst)

Multipotent: can form a specialised lineage of cells that give rise to a tissue or organ

Only found in stem cell niches in an adult organism (after day 7)

Embryonic stem cells: found only in early embryo tissues up until about 3-5 days after fertilisation (blastocyst)

Cord blood stem cells are not embryonic stem cells

Single cell embryo = totipotent

5-7 day embryo = embryonic stem (ES) cells pluripotent

Adult stem cells: they can found in juvenile (after day 5 embryo) and adult tissues in the brain, heart, bone marrow, lungs and other organs for repair

Cord blood stem cells = multipotent

Placental stem cells = multipotent

Infant + adult = 'adult stem cells' multipotent