Wound healing

Question 1

The process of wound healing in the skin depends on the size of the injury and occurs by what 2 mechanisms?

Answer 1

1. Healing by first intention
2. Healing by secondary intention

Question 2

When can healing by first intention occur?

Answer 2

When the wound edges are opposed, the wound is clean and there is minimal loss of cells and tissue (i.e. surgical incision wound).

Question 3

How is the wound closed in first intention healing?

Answer 3

The wound margins are joined by fibrin deposition, which is subsequently replaced by collagen and covered by epidermal growth.

Question 4

When can healing by secondary intention occur?

Answer 4

When wound margins are not opposed due to extensive tissue damage.

Question 5

How is the wound closed in secondary intention healing?

Answer 5

• Tissue defects fill with granulation tissue.
• Epithelial regeneration to cover the surface.
• Granulation tissue eventually contracts resulting in scar formation; myofibroblasts within granulation tissue are attached to each other and to adjacent extracellular matrix, their contraction draws together the surrounding matrix and thus reduces the size of the defect, but in doing so produces a scar.

Question 6

What are the 4 main stages of acute wound healing?

Answer 6

1. Haemostasis
2. Inflammation
3. Proliferation
4. Remodelling

Question 7

How do bone fractures heal?

Answer 7

Granulation tissue formation with fibrous repair, followed by new bone formation in the fibrous granulation tissue.

Question 8

What are the 5 stages of bone healing?

Answer 8

1. Haematoma formation (Day 1)
2. Organisation (Day 1-7)
3. Callus formation (Weeks 2-3)
4. Remodelling (Weeks 3 - 3 months)
5. Completion

Question 9

During the organisation stage of bone healing, new osteoprogenitor cells (derived from mesenchymal precursor cells) mature into what, which migrates into granulation tissue?

Answer 9

Osteoblasts

Question 10

Bone shows great capacity for healing but what 3 complications can occur?

Answer 10

1. Malunion - poor anatomical alignment.
2. Delayed union - common and defined as 25% longer than average time.
3. Non-union - if union has not occurred within 1 year, the defect is typically filled with fibrous tissue/fibrous ankylosis.

Question 11

Efficient healing requires optimal conditions. Name factors that prevent efficient healing?

Answer 11

Poor apposition of fractured bone ends.
Inadequate immobilisation.
Interposition of foreign bodies or soft tissues.
Infection.
Corticosteroid therapy.
Poor general nutritional status.
Poor blood supply.

Question 12

The regenerative capacity of cells can be categorised in what 3 main ways?

Answer 12

Labile cells
Stable cells
Permanent tissues

Question 13

In tissue regeneration, explain the action of labile cells?

Answer 13

Labile cells are constantly dividing and have a good capacity of regeneration; this allows the replacement of ageing tissue such as the surface epithelia of the skin, gastrointestinal tract and uterus; blood cells are derived from labile cells of the bone marrow.

Question 14

In tissue regeneration, explain the action of stable cells?

Answer 14

Stable cells are in a state of quiescence, meaning that the cells slowly replicate to maintain tissue size; such tissue may rapidly regenerate is stimulated e.g. liver, renal tubular epithelium, endocrine glands

Question 15

In tissue regeneration, explain the action of permanent tissues?

Answer 15

Permanent tissues consist of cells that have left the cell cycle and so are are incapable of division and cannot be regenerated e.g. brain cells, myocardial cells, skeletal muscle cells

Question 16

In the brain, minor injuries related to infective organisms may by what mechanism?

Answer 16

Gliosis - the nervous system equivalent of scarring, by proliferation of astrocytes and the production of fibrillary glial acidic protein.