How does your body heal itself?
Updated: Dec 7, 2022
The Healing Process consists of four highly integrated and overlapping phases:
Tissue Remodelling (Maturation/Resolution).
For your body to heal, all four phases and their physiological functions must occur in the proper sequence. These phases are precise and highly programmed to happen at a specific time whilst continuing for a specific duration at an optimal intensity.
These four phases overlap. i.e. the next phase commences before the previous phase is fully complete.
In subsequent articles, I will discuss some of the factors that can interfere with one or more phases of this process. When these factors are present they can cause improper or impaired healing.
A brief summary of the Healing Process
When soft tissue is damaged, the blood vessels contract and clots are formed to restrict blood flow.
Then the blood vessels dilate/expand to allow white blood cells and other cells to migrate to site of injury to fight possible infection and clear up damaged tissue. The oedema/swelling also acts like a splint to immobilise the site of injury.
Next new tissue is laid down to repair and replace damaged soft tissue, blood vessels and skin.
Finally remodeling starts to shape the site of injury back to how it was originally.
How the body heals itself: each stage explained
platelet aggregation, fibrin formation (thrombus), and degranulation.
When an injury occurs the first thing the body does is to rapidly make the blood vessels diameter smaller (vascular constriction) at the site of the injury. This helps to stem the flow of blood and fluids.
Next, substances move to the site of injury to form blood clots (fibrin clots). Fibrin formation is called thrombus. The aim of fibrin clots is to stop bleeding at the site of injury. Some of the substances that form fibrin clots are:
Platelets (thrombocytes) are small, colourless cell fragments that are formed in our bone marrow and float in our blood
Thrombin an enzyme
Various messenger adhesive substances (ligands) such as von Willebrand factor, fibrinogen, and fibronectin.
To prevent infection, your immune system responds by moving specialised cells called Mast Cells to the area of injury. When these cells arrive, they burst open releasing granules (degranulation) that go to work eliminating bacteria, viruses and other foreign cells in your body. Vascular constriction is a short-lived process that is soon followed by making the blood vessels diameter larger (vascular dilation) which allows the influx of white cells and more platelets leading to the Inflammatory phase of the Healing Process.
monocyte infiltration and differentiation to macrophage
Once bleeding is controlled, inflammatory cells migrate into the wound and promote the inflammatory phase.
The swelling (oedema) of the Inflammation phase can also act as a splint to prevent strain and further injury, to wall off and isolate the site of injury to deal with any threat of infection, and to prevent the rest of the body from being infected. As well as visible signs of oedema (swelling); erythema (reddening of the skin), heat and pain is often present. The white blood cells that make up the oedema include the following cells:
Leukocytes such as neutrophils. Their job is to destroy microbes (bacteria, viruses, etc) and remove cellular debris around the site of the injury.
Macrophages. Their job is to attract more leukocytes such as neutrophils. As the neutrophils finish their job, the macrophages clear up the neutrophils and secrete growth factors and proteins that attract immune system cells such as keratinocytes, fibroblasts, and angiogenesis to promote tissue regeneration leading to the next phase, Proliferation.
Lymphocytes. Their job is to maintain tissue integrity, defend against pathogens, and regulate inflammation.
Inflammation usually is at its peak between 24 to 48 hours after injury and starts to reduce after 3 days.
The Proliferative phase follows and overlaps with the Inflammatory phase.
This stage generally starts between 5 and 7 days after injury. This is the original rebuilding phase that includes laying down a framework to repair the site of injury, rebuilding linings of vessels and other small cavities, repairing the skin and the area under the skin, and developing new blood vessels. The framework is called the extracellular matrix (ECM). Cells called fibroblasts that produce collagen (collagen synthesis) are major components of the extracellular matrix (ECM formation) as well as glycosaminoglycans and proteoglycans. The extracellular matrix provides structural support between cells and is responsible for cell communication, cell growth, cell migration as well as cell proliferation and differentiation. Initially, this is a fine layer but over time cells called epithelial cells lay down a thicker and more durable layer of cells that bridge the site of injury. (re-epithelialisation) If the skin or dermis has been damaged, cells called keratinocytes play multiple roles essential for skin repair and restoration of the epidermal barrier. Neurovascularisation is a name to describe the restoration of blood supply. This occurs through both forming new blood vessels from existing vessels (angiogenesis), and forming brand new vessels (vasculogenesis) from endothelial progenitor cells (EPCs).
The Proliferative phase does not occur at a discrete time, but is ongoing all the time in the background.
The Proliferative phase often lasts anywhere from four to 24 days.
vascular maturation and regression.
The final phase is called Remodelling where seeming miracles take place as the site of injury returns to normal. This phase can last from 21 days to years depending on the extend of injury and subsequent repair.
Below are some of the processes that take place in this phase:
Collagen is laid down in the process of new tissue formation in the proliferation phase. In the remodelling phase this is where any excess collagen is broken down to help the new tissue resemble its original state. Collagen is the main building block of soft tissue and the most abundant protein in your body.
The original injury may cause the tissue to be pulled apart, and in this phase the tissue contracts back close to its original size . This is thought to be done by substances called myofibroblasts that are also involved in remodelling of the extracellular matrix (ECM).
ECM re-models to an architecture that approaches that of normal tissue. The ECM is a moist, pliable framework that cells attach, communicate, and live within.
Regression of many of the newly formed capillaries (small blood vessels) occurs, so that vascular density of the wound returns to normal.
The four phases of the healing process are highly integrated, overlapping and dependant on each other. Before one phase completes the next phase has commenced. Gentle stretching and massage help to optimise the process by supporting the movement of fluids in and out of the injury site as well as reducing scar formation and adhesions as the new tissue is laid down and then remodelled towards its original shape/structure.