Inflammation & healing

Question 1

What are the 4 main stages of inflammation & healing? What are their ‘normal’ timescales?

Answer 1

Bleeding - 0-72 hours (usually 6-8 hours)

Inflammation - immediate start, can last up to 2 weeks. Reaches peak on day 2-3.

Proliferation - Quick onset (24 hours). Peak retraction around 2-3 weeks post injury

Remodelling - 2-3 weeks post injury - can continue for months to years

Question 2

What occurs in the vascular phase of inflammation (0-72 hours)?

Answer 2

• Damaged tissue BLEEDS - blood is leaking into surrounding tissues
• Vasodilation of surrounding capillaries = slower blood flow.
  White blood cells marginate in the capillaries
• Causes the capillary membrane to become more permeable = diapedesis of WBCs & other substances (movement into damaged tissue through cell membrane)
• Fluid being drawn out of intact capillaries into interstitial fluid causes osmotic pressure changes. The fluid is now called exudate = SWELLING / OEDEMA

Question 3

What occurs in the cellular phase of inflammation (0-72 hours)?

Answer 3

As well as bleeding, the damaged tissue releases chemical mediators that release chemicals that:

1) cause and maintain VASODILATION of surrounding tissues.
2) Cause chemotaxis (attract WBCs to area - macrophages & neutrophils to initiate the immune response)
NB dead WBCs & waste = pus

These chemicals include:

• Histamine & seratonin
• Complement proteins
• Prostoglandins
• Kinins = Bradykinin

The vasodilation increases the permeability of the surrounding tissues.

Question 4

What does oedema do?

Answer 4

• Exudate (swelling inside tissue) dilutes concentration of bacteria
• The fluid contains:
  WBCs (immune response) & other substances - including platelets (produce fibrin = clotting)
• Can create pressure on nerve endings = pain = loss of function / stop moving = forced rest

Question 5

What does chemotaxis do?

Answer 5

Brings neutrophils & macrophages to the area. They have several actions:

1) Macrophages engluf and destroy bacteria through phagocytosis to prepare the site for healing
2) Release interleukin 1 = causes local or systemic temperate increase (fever = pyrexia). This increase in temperature increases cell metabolism. Excessive heat can also kill bacteria.
3) Secrete chemical mediators which cause:
- Angiogenesis (growth of new blood vessels)
- Brings fibroblasts to begin healing.

Question 6

Describe the proliferation phase of healing?

Answer 6

1) As macrophages clear the debris away they secrete chemical mediators which cause angiogenesis & bring fibroblasts to the area.

Fibroblasts lay down Type 3 collagen, elastin and ground substance. Collagen is laid down in a disorganised pattern.

This forms granulation tissue (GT) - a loose form of connective tissue that bridges the wound (2nd intention healing).

The new blood vessels bring oxygen to the area.

2) Organisation occurs once the gap is closed.
The fibrous element of new tissue gets laid down more orderly.
Fibroblasts become myofibroblasts - which scar and initiate wound contraction

Question 7

Describe the remodelling phase?

Answer 7

• The tissue becomes less vascular and more cellular
• Collagen accumulates and converts to type 1 at a steady rate
• The process peaks around 2 -3 months
• Tensile strength of the wound increases for many months or even years.

Question 8

What is 1st intention and 2nd intention healing?

Answer 8

1st Intention -
- Edges of the wound are close together, clean and are clearly defined at the edge

2nd Intention -
Edges of the wound are far apart, so requires granulation tissue to ‘fill in’ the wound. May benefit from surgical intervention.

Question 9

What are some of the complications of wound healing?

Answer 9

• Ulceration = common where blood supply is poor, such as, diabetes
• Deficient scar formation resulting in wound dehiscence
• Excessive scar formation (keloid healing) = can be cosmetically undesirable or lead to organ blockage