Stem cells are biological cells found in all multicellular organisms, that can divide
(through mitosis) and differentiate into diverse specialized cell types and can
self-renew to produce more stem cells. In mammals, there are two broad types of
- embryonic stem cells, which are isolated from the inner cell mass of blastocysts,
and adult stem cells, which are found in various tissues. In adult organisms, stem
- progenitor cells act as a repair system for the body, replenishing adult tissues.
In a developing embryo, stem cells can differentiate into all the specialized cells
(these are called pluripotent cells), but also maintain the normal turnover of
regenerative organs, such as blood, skin, or intestinal tissues.
Properties of Stem Cells:
The classical definition of a stem cell requires that it possess two properties:
- Self-renewal: the ability to go through numerous cycles of cell division while
maintaining the undifferentiated state.
- Potency: the capacity to differentiate into specialized cell types. In the strictest
sense, this requires stem cells to be either totipotent or pluripotent—to be able
to give rise to any mature cell type, although multipotent or unipotent progenitor
cells are sometimes referred to as stem cells. Apart from this it is said that stem
cell function is regulated in a feed back mechanism.
Two mechanisms exist to ensure that a stem cell population is maintained:
1. Obligatory asymmetric replication: a stem cell divides into one father cell
that is identical to the original stem cell, and another daughter cell that is
2. Stochastic differentiation: when one stem cell develops into two
differentiated daughter cells, another stem cell undergoes mitosis and
produces two stem cells identical to the original.
Umbilical Cord Blood:
Umbilical cord blood is blood that remains in the placenta and in the attached
umbilical cord after childbirth. Cord blood is collected because it contains stem
cells, which could be used to treat hematopoietic and genetic disorders.
Perinatal hypoxia-ischemia refers to exposure to low oxygen (hypoxia) and
decreased blood flow (ischemia) prior to, during, or after birth and is regarded
as a dominant cause of neurologic deficits in term and preterm infants. Potency Definitions:
Potency specifies the differentiation potential (the potential to differentiate into