TISSUE RESPONSE TO INJURY

INTRODUCTION Healing is a changing continuum however, to try and understand the healing process researchers have divided the events into three different phases. INFLAMMATION PROLIFERATION REMODELLING

TIMESCALE TISSUE HEALING

INJURY This stage represents tissue trauma at the time of injury, before the inflammatory process is activated The body attempts to stabilise the injured site by rushing chemicals and cells to the area. This has a two fold effect firstly, momentarily VASOCONSTRICTION VASODILATION

VASODILATION This is the moment inflammation starts. Blood and its products now slowly flow to the injured area. As they accumulate chemicals are released along with other cells that are attracted into the area. The following stages take place;

STAGES CONTINUED Fibronectin binds together FIBRIN and Collagen in a X like formation this acts as a plug to stop the bleeding. Plug is fragile but gives the wound its only strength and is eventually replaced. Lymph vessels also damaged therefore fluid accumulates. Once area becomes stable FIBRINOLSIN is released. Plug replaced type 3 collagen.

ONSET INFLAMMATION First few hours body tries to remove debris from injured area. This process started by Neutrophils or Polymorphonucleur Leukocytes (PMN’s) After 5/6hours, the neutrophils begin to be replaced by other cells namely, Mononuclear Phagocytes which predominate cells at injury site within 24/48hrs. Fibrinolysin is an enzyme that converts fibrin from in-soluable to a soluable protein to promote absorption of fibrin plug which allows lymph vessels to perform normal function – draining excess fluid. Monocytes and Macrophages

INFLAMMATION CONT’D PMN’s and macrophages act as phagocytes to remove dead tissue/debris. This is necessary if healing to continue. They also release several Growth Hormones and can trigger termination of tissue growth when healing process is complete. What then are the signs of inflammation. Macrophages are vital to the healing process.

SIGNS & SYMPTOMS HEAT – due to this increased blood flow REDNESS – Vessels enforced and dilated SWELLING – due to movement of a fluid into restricted area, possibly a haematoma PAIN – caused by swelling that has put pressure on the nerve endings. Also a protection mechanism of the body. Not just a feature soft tissue injury. Can last 10 minutes – several days.

PROLIFERATION PHASE Transition from removal of debris to formation of new blood vessels and granulation tissue. Angiogenesis happens at a rapid rate during this phase which is important for scar tissue formation as it requires vascular production and supply for further healing to take place. Fibroblasts responsible for this new growth and number increases 3/5 days post injury. Can identify stage of healing by increased number fibroblasts to decrease number or non-existent PMN’S INFL- PROF

WHAT NEXT Growth factors enter into the area and: Causes local migration of fibroblasts, myofibrils and endothelial cells. Above cells are responsible for development of new capillaries and matrix Matrix consists of two components fibrous and non-fibrous. Combination of these fibres provides tensile strength and some resilience to stresses applied to the tissue. Non-fibrous = the ground substance and fills in the spaces between fibrous elements of matrix and reduces friction between fibres when stressed. COLLAGENASE = enzyme prevents over production of above which is important process to help prevent excessive scar tissue forming.

REMODELING PHASE A number of activities start to recede as area becomes more stable. Capillaries produced during proliferation to promote tissue growth now longer need eventually start to disappear. Cellular changes = visible changes colour returns to skin, swelling goes + sensitivity. As collagen converted to type 1 becomes more insoluble less resistant to destruction

CONT’D Produce more x links strengthening scars structure. Collagen strength is enhanced by the arrangement of these fibres and when aligned in organised parallel fashion = optimal strength. External forces required to change the arrangement.