4. Healing and Repair Flashcards
(39 cards)
What is regeneration?
The replacement of dead or damaged cells by functional, differentiated cells derived from stem cells.
What is the key difference between regeneration and repair?
In regeneration, the normal structure is restored, in repair, the normal structure is permanently altered.
What is repair?
Response to injury involving both regeneration and scar formation.
Define unipotent.
Can only produce one type of differentiated cell, like epithelia.
Define multipotent.
Can produce several types of differentiated cell, like haematopoietic.
Define totipotent.
Can produce any type of cell, like embryonic stem cells.
Where are the two checkpoints in the cell cycle and what do they check for?
Between G1 and S - checks that there’s no DNA damage.
Between G2 and M - checks no DNA rampage after synthesis.
What are labile cells?
Normal state is active cell division. Usually has rapid proliferation.
What are stable cells?
Resting state is G0 but it can enter the cell cycle so its speed of regeneration is variable.
What are permanent cells?
Unable to divide as permanently in G0. They therefore can’t regenerate.
Are the following cells labile, stable or permanent?
a. epithelia
b. cardiac myocytes
c. hepatocytes
d. osteoblasts
e. neurones
f. fibroblasts
g. haematopoietic cells
a. labile
b. permanent
c. stable
d. stable
e. permanent
f. stable
g. labile.
What are the key features controlling regeneration?
Growth factors, and contact between basement membrane and adjacent cells
How do growth factors control regeneration?
They promote proliferation in the stem cell population and expression of genes controlling cell cycle.
How does contact between basement membrane and adjacent cells control regeneration?
Signalling through adhesion molecules. It inhibits proliferation in intact tissue - contact inhibition. Loss of contact promotes proliferation, this happens in a deranged way in cancer.
What is fibrous repair?
The replacement of functional tissue by scar tissue.
What are the key components of fibrous repair?
Cell migration, blood vessels (angiogenesis), and extracellular matrix production and remodelling.
What are the cell types and their roles in fibrous repair?
Inflammatory cells: neutrophils and macrophages - phagocytosis of debris, lymphocytes and macrophages - chemical mediators.
Endothelial cells: angiogenesis.
Fibroblasts/myofibroblasts: collagen - extracellular matrix proteins, wound contraction.
Why is angiogenesis needed in fibrous repair?
For wound healing, provides access to the wound for inflammatory cells and fibroblasts, also delivers oxygen and other nutrients.
What initiates angiogenesis?
Proangiogenic growth factors like VEGF (vascular endothelial growth factor).
What is the process of angiogenesis?
Endothelial proteolysis of basement membrane.
Migration of endothelial cell via chemotaxis.
Endothelial proliferation.
Endothelial maturation and tubular remodelling.
Recruitment of periendothelial cells.
What is the function of extracellular matrix in fibrous repair?
Supports and anchors cells, separates tissue compartments, sequesters growth factors, allows communication between cells, and facilitates cel migration.
What are the fibrillar collagen types?
I-III. Uninterrupted triple helices.
What are the amorphous collagen types?
IV-VI. Triple helical domains are interrupted and have breaks, so they form sheets instead of fibrils.
How are fibrillar collagens synthesised?
Polypeptide alpha chains synthesised in ER.
Enzymatic modification steps, vitamin C dependent hydroxylation.
Alpha chains align and cross link to form procollagen triple helix.
Soluble procollagen is secreted.
Procollagen cleaved to tropocollagen.
Tropocollagen polymerises to form fibrils.
Bundles of fibrils form fibres.
Slow remodelling by specific collagenases.
