Week 4 - Cell Tissue And Injury 3

Front 1

What is fibrosis?

Back 1

Excessive deposition of collagen in the tissue

Front 2

What is the only organ where regeneration occurs? Does scarring occur in the brain?

Back 2

The liver! Scarring is normally suppressed in the brain

Front 3

What are the two elements of tissue repair? How are these defined?

Back 3

Regeneration and scarring (fibrosis). Regeneration of the return of the cell complement or tissue to the state identical to that before injury. Scarring is replacement of the injured tissue with dense connective tissue

Front 4

What structural component is required for regeneration?

Back 4

The basement membrane must be intact in order to serve as a scaffold. This is necessary for regeneration to occur.

Front 5

What are the four stages of tissues repair?

Back 5

1. Formation of temporary barrier
2. Removal of dead tissue
3. Restoration of parenchymal integrity
4. Restoration of epithelial integrity

Front 6

How does cutaneous wound healing work?

Back 6

1. Hemostatic plug formed
- This is the clot
2. Granulation tissue
- macrophages come, which help form the granulation tissue
3. Scar formation
- scar forms and eventually CONTRACTS

Front 7

What happens in the first phase of repair (first 24 hours)?

Back 7

1. Hemostatic plug formed
- this is a barrier which stops bleeding. it works via a protease cascade which eventually turns fibrinogen into fibrin via thrombin. Fibrin serves as a matrix that cells can divide on. Thrombin also sends signals that lead to fibroblast migration proliferation.
2. Inflammation
- Neutrophils, and later macrophages, remove dead tissue and debris. Inflammation brings in proteins that break down fibrin as well

Front 8

What happens in the second phase of repair (3-7 days)?

Back 8

Fibroblasts, macrophages, and new blood vessels migrate in, replace the fibrin matrix with granulation tissue (connective tissue matrix). Epithelial regeneration begins here too

Front 9

From where do new blood vessels arise in angiogenesis?

Back 9

New blood vessels sprout out from old blood vessels

Front 10

What are the triggers for angiogenesis? What important signalling protein is used to stimulate angiogenesis?

Back 10

Cells detect hypoxia and increase transcription of certain genes via HIF. Important: VEGF is secreted from these high HIF cells, which acts on endothelial cells of adjacent capillaries and stimulates angiogenesis

Front 11

What are the phases fibroblasts go through during repair? What signals are associated with these phases? (there is an important one)

Back 11

They undergo migration, proliferation, and collagen synthesis. TGFBeta is associated with collagen synthesis, and PDGF is associated with all three.

Front 12

What is the third phase of repair (weeks to months)? As the scar forms, what happens to the fibroblasts and the inflammatory cells?

Back 12

The third phase is the "remodeling" phase. In this phase, type III collagen is replaced with Type I. The blood vessels are very leaky at this point. Myofibroblasts allow contraction of the skin, and the final tensile strength is 70-80% of normal skin. As time passes, the fibroblasts and the inflammatory cells go away.

Front 13

What do myofibroblasts do?

Back 13

Myofibroblasts, which are associated with phase three (weeks to months), can contract, which is important for scar contraction

Front 14

How does re-epithelialization work?

Back 14

Basal epithelial cells migrate inward until they meet, then start recreating the normal epithelium underneath the scab. Once the epithelium has matured underneath, the scab will fall off on its own

Front 15

What factors impair wound healing?

Back 15

Infection, vascular disease, malnutrition, poor vascularity, foreign bodies, radiation, diabetes

Front 16

What are undesirable consequences of scar formation?

Back 16

Contractures - scar bridging a joint, restricting motion
Adhesions - exudate bridging serosal surfaces (can cause pain)
Strictures - circumferential scar in a tubular structure (the scar can contract, close tube)
Keloid/hypertrophic scar - excessive collagen producing a protruberant scar

Front 17

What is fibrosis?

Back 17

Firbosis is the development of excess collective tissue in an organ, usually due to persistent injury and inflammation. It is probably due to macrophages that keep sending repair signals.
Examples include cirrhosis of the liver, pulmonary fibrosis, scleroderma

Front 18

What is scleroderma?

Back 18

It is an autoimmune disorder where too much collagen is deposited in the skin, so patients can't move their hands very well. It also involves the esophagus and lungs.