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Block 4: Anatomy + Physiology > Wound healing > Flashcards

Wound healing Flashcards

1
Q

What is parenchyma?

A

Organ-specific cells related to the function (e.g. parenchyma of the kidneys = epithelial tissue)

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2
Q

What is stroma?

A

‘Background’ tissue providing structure, mechanical and nutritional support to the organ

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3
Q

Define healing

A

Process of returning to health

Restoration of structure and function of injured or diseased tissue

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4
Q

Define tissue repair

A

The restoration of structure and function of damaged tissue (through regeneration or scar formation)

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5
Q

What are the stages of wound healing?

A
  1. Haemostasis process (first 24 hours): wound closed by coagulation process, adherence of platelets and fibrin to site, formation of thrombus
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6
Q

Define regeneration

A

Healing in which new growth completely restores portions of damaged tissue to their normal state

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7
Q

What are the stages of wound healing?

A
  1. Haemostasis process (first 24 hours)
  2. Inflammatory process (0-4 days)
  3. Proliferative process (1-14 days)
  4. Remodelling process (Day 21 - years)
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8
Q

What does the haemostasis phase of wound healing involve?

A

Wound closed by coagulation process
Platelets and fibrin adhere to site
Thrombus formed

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9
Q

What does the inflammatory phase of wound healing involve?

A

Platelets control bleeding; macrophages prevent infection; neutrophils involved in inflammation

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10
Q

What does the proliferative phase of wound healing involve?

A

Angiogenesis (formation of new blood vessels)
Epithelialisation (formation of granulation tissue)
Contraction
Fibrous tissue formation

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11
Q

What does the remodelling phase of wound healing involve?

A

Maturation phase

Collagen is remodelled and becomes realigned

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12
Q

What aids regeneration?

A

Growth factors (e.g. PDGF, VEGF, TGF-Beta, ECM)

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13
Q

What are labile tissues?

A

Tissue that is continuously proliferating in order to replace dead or sloughed-off cells

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14
Q

What are some examples of labile tissues?

A

Skin, GI, Salivary gland

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15
Q

What is stable tissue?

A

Cells that normally exist in a non-dividing state but may enter the cell cycle in response to certain stimuli (e.g. cell injury)

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16
Q

What are some examples of stable tissue?

A

Parenchymal cells of the liver, kidneys and pancreas

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17
Q

What is permanent tissue?

A

Non-dividing cells leading to scar formation

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18
Q

What are some examples of permanent tissue?

A

Cardiac and skeletal tissue

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19
Q

What are growth factors?

A

Proteins that stimulate survival and proliferation of particular cells
Can also promote migration and differentiation

20
Q

Where are growth factors produced?

A

By macrophages and lymphocytes at the site of injury as part of the inflammatory process
Can also be produced by parenchymal cells or stromal cells in response to cell injury

21
Q

What is the role of growth factors?

A

Stimulate entry of a cell into the cell cycle

22
Q

How do growth factors work?

A

Produced in response to an external stimulus and act by binding to cellular receptors

23
Q

What is the role of the extracellular matrix in regeneration?

A

Stores and presents growth factors

Acts as a scaffold to which migrating cells can adhere

24
Q

What is scar formation?

A

Replacement of damaged parenchymal cells with connective tissue leading to incomplete restoration of architecture and function

25
Q

When does scar formation occur?

A

In severe or chronic injuries that result in damage of parenchymal cells AND connective tissue
Also occurs in permanent non-dividing tissues

26
Q

What is angiogenesis?

A

New blood vessel development (sprouting from existing vessel) via endothelial cell proliferation and migration

27
Q

When does angiogenesis occur?

A

Healing at injury sites

Development of collateral circulations at sites of ischaemia

28
Q

How does the formation of granulation tissue occur?

A
  1. Migration and proliferation of fibroblasts into the site of injury
  2. Deposition of ECM proteins produced by these cells

[Derived by growth factors]

29
Q

What is granulation tissue?

A

New connective tissue with new blood vessels

[Have pink, granular appearance]

30
Q

How does skin wound healing occur?

A

[Involves epithelial regeneration and the formation of a connective tissue scar]

Can occur by:

  1. First intention (primary union)
  2. Second intention (secondary union)
31
Q

What are examples of when first intention skin wound healing should occur?

A

Healing of a clean, uninfected surgical incision (approximated by sutures)

32
Q

What is the main mechanism of repair in first intention healing?

A

Epithelial regeneration

Causes small scar with minimal wound contraction

33
Q

How does first intention healing occur?

A
  1. Incisional space fills with fibrin-clotted blood (a scab)
  2. Within 24 hours, neutrophils seen at incision margin, migrating towards fibrin clot (acute inflammation)
  3. Within 24-48 hours, epithelial cells from both edges begin to migrate and proliferate along dermis
  4. By days 3-7, neutrophils largely replaced by macrophages and angiogenesis peaks - granulation tissue invades incisional space
  5. By week 2, there is continued collagen accumulation and fibroblast proliferation (scar maturation)
  6. Remodelling of scar continues for months to increase wound tensile strength
34
Q

What is an example of second intention healing?

A

Large wounds at sites of abscess formation, ulceration and infarction

35
Q

How do first intention and second intention healing differ?

A

Secondary healing has:
Larger clot/ scab
More intense inflammation
Greater volume of granulation tissue (and therefore greater mass of scar tissue)
Wound contraction (reducing original size of defect within approx. 6 weeks)

36
Q

How does fracture healing differ between cortical and trabecular bone?

A

Trabecular bone tends to have a better blood supply and therefore less necrosis than cortical bone

37
Q

What are the stages of fracture healing?

A
  1. Haematoma (bleeding from ruptured vessels, inflammatory reaction)
  2. Granulation tissue replaces haematoma (cell proliferation in response to GF/ cytokines)
  3. Callus formation (irregular swelling that bridges gap between bone ends - made up of fibrocellular material and cartilage initially)
  4. Woven bone (osteoprogenitor cells proliferate and move into area forming woven bone strengthening callus)
  5. Lamellar bone (replaces woven bone gradually)
  6. Remodelling (by osteoclasts and osteoblasts into appropriate form, excess callus resorbed and medullary cavity re-established)
38
Q

What is fibrosis?

A

Excessive deposition of collagen and other ECM components in tissue
(Scar and fibrosis often used interchangeably, fibrosis usually refers to deposition of collagen in chronic diseases)

39
Q

What local factors affect tissue repair?

A

Infection (prolongs inflammation)
Mechanical factors (e.g. increased local pressure or torsion can cause wounds to pull apart/ dehisce)
Foreign bodies
Size/ location of wound
Type of wound (injury to tissue composed of permanent cells, rather than stable/ labile cells, results in scarring)

40
Q

What systemic factors affect tissue repair?

A

Nutritional status (e.g. protein deficiency, vitamin C deficiency - inhibit collagen synthesis)
Metabolic status
Circulatory status (poor perfusion impairs healing)
Hormones
Age
Collagen disorders

41
Q

What are the possible complications of tissue repair?

A

Inadequate formation
Excessive formation
Formation of contracture

42
Q

What is the consequence of inadequate tissue formation?

A

Dehiscence/ rupture
Evisceration
Ulceration

43
Q

What is dehiscence?

A

Separation of layers of surgical wound

44
Q

What is evisceration?

A

Extrusion of viscera outside the body through a surgical incision

45
Q

What is ulceration?

A

Lesion through the skin or a mucous membrane resulting from loss of tissue, usually with inflammation

46
Q

What is the consequence of excessive tissue formation?

A 
Keloid formation (formation of excess collagen giving rise to raise, prominent scarring - common in Africans) 
Generation of excess granulation tissue (protruding above level of surrounding skin and hindering re-epithelialisation)
47
Q

What are contractures?

A

Fibrosis of connective tissue in skin, fascia, muscles or a joint capsule that prevents normal mobility of the related tissue or joint (e.g. in severe burns)

Block 4: Anatomy + Physiology (12 decks)

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