Tissue Homeostasis
Stem Cell’s Role in Homeostasis
At the tissue level, a stem cell is a cell that continuously renews turning over new
tissue (blood, skin, germ cells) undergoing regeneration after injury (muscle,
pancreas, and liver). Some differentiated cells are so highly specialised they lack a
nucleus and so cannot replenish themselves and some cells (in the immune
system) lose DNA sequences during differentiation.
Proliferated Growth
A process characterised by the rapid multiplication or expansion of cells or
tissues. If a mutation forms it gives the cell a growth advantage which generates a
cancer. Stem cells are a solution to this. They divide very slowly and are immortal.
They generate very fast dividing daughter cells which have a limited lifespan. The
final differentiated cell is non-proliferative and has a limited lifespan.
The cell biological definition of a stem cell is a cell that has a choice to divide and
give rise to an exact copy of itself or a differentiated cell.
In stem cells there are two distinct pattern of cell division which dictate how stem
cells contribute to tissue growth:
Tissue Homeostasis 1
, In Symmetrical Growth both daughter cells resulting from a stem cell have the
same fate. This can result in two stem cells (maintaining the stem cell pool) or
two differentiated cells (contributes to tissue formation but depletes the stem
cell pool).
In Asymmetrical Growth both daughter cells have different fates. One remains
a stem cell (ensuring the self-renewal of the stem cell pool) and one
differentiates (forming specialised cells). Asymmetry can be generated
through external (neighbouring cells, ECM, and morphogens) and internal
mechanisms (localised cell components).
Existence and Role of Haematopoietic Stem Cells (HSCs):
When irradiated mice were transplanted with a mix of marked and unmarked
bone marrow cells the scientists observed spleen colonies. The question was
whether these colonies arose from: mixed populations of donor cells (multiple
cells contributing to each colony) and single donor cells (each colony derived
from a single cell dividing and differentiating).
The initial experiments couldn’t rule out the possibility that donor cells didn’t
mix completely, leading to colonies appearing "pure" by chance. To address
this, they needed a way to uniquely identify cells derived from individual
donors. Radiation-induced chromosomal breaks served as unique markers.
Tissue Homeostasis 2
Stem Cell’s Role in Homeostasis
At the tissue level, a stem cell is a cell that continuously renews turning over new
tissue (blood, skin, germ cells) undergoing regeneration after injury (muscle,
pancreas, and liver). Some differentiated cells are so highly specialised they lack a
nucleus and so cannot replenish themselves and some cells (in the immune
system) lose DNA sequences during differentiation.
Proliferated Growth
A process characterised by the rapid multiplication or expansion of cells or
tissues. If a mutation forms it gives the cell a growth advantage which generates a
cancer. Stem cells are a solution to this. They divide very slowly and are immortal.
They generate very fast dividing daughter cells which have a limited lifespan. The
final differentiated cell is non-proliferative and has a limited lifespan.
The cell biological definition of a stem cell is a cell that has a choice to divide and
give rise to an exact copy of itself or a differentiated cell.
In stem cells there are two distinct pattern of cell division which dictate how stem
cells contribute to tissue growth:
Tissue Homeostasis 1
, In Symmetrical Growth both daughter cells resulting from a stem cell have the
same fate. This can result in two stem cells (maintaining the stem cell pool) or
two differentiated cells (contributes to tissue formation but depletes the stem
cell pool).
In Asymmetrical Growth both daughter cells have different fates. One remains
a stem cell (ensuring the self-renewal of the stem cell pool) and one
differentiates (forming specialised cells). Asymmetry can be generated
through external (neighbouring cells, ECM, and morphogens) and internal
mechanisms (localised cell components).
Existence and Role of Haematopoietic Stem Cells (HSCs):
When irradiated mice were transplanted with a mix of marked and unmarked
bone marrow cells the scientists observed spleen colonies. The question was
whether these colonies arose from: mixed populations of donor cells (multiple
cells contributing to each colony) and single donor cells (each colony derived
from a single cell dividing and differentiating).
The initial experiments couldn’t rule out the possibility that donor cells didn’t
mix completely, leading to colonies appearing "pure" by chance. To address
this, they needed a way to uniquely identify cells derived from individual
donors. Radiation-induced chromosomal breaks served as unique markers.
Tissue Homeostasis 2
