Tissue Repair

When continuous tissues like the skin, mucosae, and blood vessels are broken, the body initiates the inflammatory response.1. Injured cells and certain white blood cells

release inflammatory hormones (e.g. histamines).

2. Nearby capillaries dilate and become leaky. 3. Clotting proteins in the blood form a scaffold

that traps platelets, leading to a clot. (stops bleeding and isolates pathogens)

4. White blood cells attack pathogens, dead cells, and other debris.

Tissue Repair

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Even as the clot is forming, tissue repair begins immediately. Depending on the tissue, and severity of injury, tissues will regenerate or be replaced by scar tissue (or both).

• Regeneration = Replacement of destroyed tissue by the same kind of cells

• Fibrosis = Repair by dense fibrous connective tissue (scar tissue)

Tissue Repair

Tissue RepairTissue Regeneration1. Blood clot is replaced by granulation tissue.

• Capillaries grow in from nearby areas, forming new capillary bed.

• Fibroblasts produce growth factors (encourage mitosis) and collagen fibers.

• Some fibroblasts even help to pull the wound together.2. Large white blood cells digest clot.3. Granulation tissue is replaced either by original tissue type.

Fibrosis 4. Same as above, except granulation tissue is replaced by fibrous

connective tissue.5. Always occurs in cuts, scrapes, punctures, burns to some extent.

May be visible at surface or not. 6. Over time scar tissue might be replaced by original tissue type.7. Pure infections rarely lead to fibrosis. (only occurs in destructive

infections)

Regeneration of Tissues· Tissues that regenerate easily:

Epithelial tissue, fibrous connective tissue, areolar tissue, bone, blood-forming tissue

· Tissues that regenerate moderately:

Smooth muscle, dense regular connective tissue

· Tissues that regenerate poorly:

Skeletal muscle, cartilage· Tissues that are replaced largely with scar

tissue:

Cardiac muscle, nervous tissue within the brain and spinal cord

Sometimes, the body goes overboard with tissue repair. This can lead to hypertrophic scars AKA keloids.

Tissue Repair