Inflammation & Tissue Healing

When the body is injured a sequence of events is initiated that leads to the eventual repair of the injury site. The first stage in this process is inflammation which is followed by tissue healing and repair.

Inflammation

What is the Inflammatory Response?

The inflammatory response is the body's natural response that occurs immediately following tissue damage. It's main functions are to defend the body against harmful substances, dispose of dead or dying tissue and to promote the renewal of normal tissue.

What are the signs of Inflammation?

The inflammatory reaction is normally characterized by 5 distinct signs, each of which is due to a physiological response to tissue injury.

  • Pain (due to chemicals released by damaged cells).
  • Swelling or Edema (due to an influx of fluid into the damaged region).
  • Redness (due to vasodilatation- the widening of blood vessels and bleeding in the joint or structure).
  • Heat (due to an increase in blood flow to the area).
  • Loss of function (due to increased swelling and pain).

What are the stages of the Inflammatory reaction?

The inflammatory reaction is the combination of a number of overlapping reactions within the body. Although a lot of these occur simultaneously a certain order of events may be seen:

1. Tissue Injury

Tissue damage may occur from trauma such as a tackle, collision or from an awkward fall. However, quite commonly tissue injury is as a result of overuse, commonly known as microtrauma.

2. Release of Chemicals

When tissue cells become injured they release a number of chemicals that initiate the inflammatory response. Examples of these are kinins, prostaglandin and histamine. These chemicals work collectively to cause increased vasodilation (widening of blood capillaries) and permeability of the capillaries. This leads to increased blood flow to the injured site. These substances also act as chemical messengers that attract some of the body's natural defense cells- a mechanism known as chemotaxis.

Although highly beneficial to the body's defense strategies some chemicals also increase the sensitivity of the pain fibres in the area and so the area becomes painful.

3. Leukocyte Migration

Chemotaxis leads to the migration of certain white blood cells (leukocytes) to the damaged area. Two types of leukocyte are predominant in the inflammatory response- macrophages and neutrophils. Neutrophils are first to the injured site and function by neutralizing harmful bacteria. Macrophages aid the healing process by engulfing bacteria and dead cells and ingesting them so that the area is clear for new cells to grow. They arrive at the injured site within 72 hours of the injury and may remain in the area for weeks after the injury.

Tissue Healing

1. Collagenation

Wound healing occurs towards the end of the inflammatory process, however the two processes overlap considerably. Macrophages work tirelessly to clear the damaged area and make space for the regeneration of new tissue. After a number of days fibroblasts (collagen producing cells) begin to construct a new collagen matrix which will act as the framework for new tissue cells

2. Angiogenesis

Once sufficient cleansing of the area has been achieved the damaged area begins to sprout new capillaries to bring blood to the region- this is known as angiogenesis or revascularization. When blood flow has been re-introduced to the area specific tissue cells begin to re grow- for example in a muscle tear muscle cells will repopulate the area.

3. Proliferation

The proliferation phase lasts up to 4 weeks. In cases where the injury sustained has been more severe the affected area may be composed of a mixture between specific tissue cells (such as muscle cells) and other tissue known as granulation tissue. If this granulation tissue is not removed it will remain and form scar tissue, which can lead to a decreased functional ability of the tissue.

4. Remodeling

The stage of remodeling now occurs where by the new cells mould into their surroundings to once again produce a functioning tissue. This process of remodeling can take months even years, altering the new tissue slowly. The new cells and protein fibres become arranged in a way that is best suited to the stresses imposed on the tissue. Hence when a tissue is healing it is important to stretch it in the correct direction so to optimize the strength of the new tissue.

Tissue Healing

1. Collagenation

Wound healing occurs towards the end of the inflammatory process, however the two processes overlap considerably. Macrophages work tirelessly to clear the damaged area and make space for the regeneration of new tissue. After a number of days fibroblasts (collagen producing cells) begin to construct a new collagen matrix which will act as the framework for new tissue cells

2. Angiogenesis

Once sufficient cleansing of the area has been achieved the damaged area begins to sprout new capillaries to bring blood to the region- this is known as angiogenesis or revascularization. When blood flow has been re-introduced to the area specific tissue cells begin to re grow- for example in a muscle tear muscle cells will repopulate the area.

3. Proliferation

The proliferation phase lasts up to 4 weeks. In cases where the injury sustained has been more severe the affected area may be composed of a mixture between specific tissue cells (such as muscle cells) and other tissue known as granulation tissue. If this granulation tissue is not removed it will remain and form scar tissue, which can lead to a decreased functional ability of the tissue.

4. Remodeling

The stage of remodeling now occurs where by the new cells mould into their surroundings to once again produce a functioning tissue. This process of remodeling can take months even years, altering the new tissue slowly. The new cells and protein fibres become arranged in a way that is best suited to the stresses imposed on the tissue. Hence when a tissue is healing it is important to stretch it in the correct direction so to optimize the strength of the new tissue.