Wound Healing and Repair Pathophysiology PDF

Wound healing and repair Dr Ronak Reshamwala, MBBS, MMST, PhD NIISQ Senior Research Fellow In-charge of translational and clinical research in Spinal Injury Project Griffith University...

Wound healing and repair Dr Ronak Reshamwala, MBBS, MMST, PhD NIISQ Senior Research Fellow In-charge of translational and clinical research in Spinal Injury Project Griffith University Slide Courtesy: A/Prof. Dr. Neelam Maheshwari Bond University  Learning outcomes Case: Osteoporosis LO: Describe the pathophysiology of wound healing and repair  Session objectives 1. Wound healing (Tissue repair) a) Background b) Definition c) Elements: Cells (types), Growth factors (GF) and Extracellular matrix (ECM) d) Mechanism of healing(or Reaction) e) Stages of healing f) Special tissues healing 2. Differentiate between types of wound healing: Primary/ Secondary / Tertiary Intention 3. What is the process of scar formation. 4. Identify the factors affecting wound repair 5. Examples of dysfunctional wound repair 6. Summary Case based and Moulage Simulation Learning Background: Outcomes of Acute Inflammation  What is wound healing (Tissue repair) ? Definition – Restoration of tissue architecture and function after an injury Need: critical for survival – To eliminate the agent (stimulus) inflicting injury e.g.: pathogen/toxin / autoimmune complexes…. – To retain the structural morphology and function to normalcy Several terminologies Repair=Healing, Regeneration, Restoration, Restitution Damaged tissue= wound  Elements of tissue repair Cells Cytokines & Growth factors (GF) Extracellular matrix (ECM) Balanced interplay between all above host elements decides the adequacy and type of tissue repair Along with environment and stimulus (triangle)  Cell development Stem cells – Labile and stable cells – Examples Skin : basal layer adjacent to BM, in hair follicles and sebaceous glands ( split skin graft) Emergence Intestinal mucosa : crypt bottoms Liver : cells of Ito Cell population homeostasis  Cell types: Proliferative capacity Labile – Tissues with high turnover and good proliferative capacity – Continuous replacement by stem cell proliferation Stable – Slow and or limited proliferation rate – Only when injured Permanent – Non proliferative or minimally proliferative, terminally differentiated cells – Not sufficient to replace the lost tissue Can you think of some examples of each cell type?  Growth factors Produced transiently by the stimulus (VINDICATE-inflammation/injury) Polypeptide proteins secreted by cells-mainly lymphocytes, macrophages, platelets, endothelial cells, keratinocytes, fibroblasts, smooth muscle cells, activated by inflammatory process. Bind to target cell receptors where damage has occurred Stimulate growth control genes (proto-oncogenes) that leads to cell proliferation, survival, migration, differentiation, stimulation of angiogenesis and fibrinogenesis Examples: Table Robbins as below Growth factor Secreted by cell Function  ECM ECM is a meshwork of proteins that surround cells 2 basic components: Interstitial matrix and Basement membrane Provides turgidity, strength & scaffold for tissue repair. It supports cells migration, adhesion and acts as reservoir of growth factors Cross linking of collagen is Vitamin C dependent Intact or preserved ECM is important for regeneration otherwise healing occurs by scar formation (fibrosis)  How does tissue repair occur: Two mechanisms / Significant tissue loss 1. 2. =Re-epithelialisation =Fibrosis Depends on : 1. Cell type: Ability to regenerate/proliferate 2. Severity of injury Labile cells, minor injury, clean/sutured cuts Stable or permanent cells, large defects, Stem cells /residual cells proliferate to contaminated wounds replace the damaged cells Fibrous tissue to fill the defect: Scar formation Return to normal or near normal state. Enough structural strength but loss of function No /minimal residual damage Skin , fetal tissue, GIT, endometrium, bone marrow Liver, kidney, brain, muscle, bone  1. Healing by Regeneration-Normal repair, no or 2. Healing by scarring–Complex repair minimal scarring Wound margins Wound margins far away apposed Dehisced , large Clean apposed cuts defects + of clot/FB Contact Inhibition Intense inflammation, Minimal inflammation abundant granulation and tissue scarring Angiogenesis Myofibroblasts cause Minimal or no wound wound contraction and contraction and strength strength over mo-yrs over days-weeks Quiz! 1. Primary Intention Types of healing – Minor, clean, sharp cuts or sutured incisions – Closely apposed edges – Superficial cuts, most surgical incisions – Re-epithelialisation  scarring 2. Secondary intention – Large defects e.g.: gingivectomy, tooth extraction sockets compound fractures, venous ulcers, pressure sores – Wound kept open to granulate, slow healing, – Re-epithelialisation moderate and more scarring – Packed with gauge/VAC/drains to enhance healing process 3. Tertiary intention (Delayed primary closure ) – Too large defect and contaminated – Wound is cleaned, edges debrided and kept open for 4-7 days: Secondary healing – Then edges brought close when granulation appears (pink healthy base): Delayed Primary closure E.g.: Tissue grafting sites, highly contaminated/infected, ischaemic/necrotic, dehisced surgical wounds OR burst abdomen Stages of wound repair Day 0 Day 1-2 Day 3-5 Day 7 This is for superficial non complicated wound Angiogenesis: Day 3 onwards Development of new blood vessels esp. venules from existing damaged vessels at the site of injury Growth factors: VEGF/FGF-2,PDGF, TGF-β ( See table on slide 8) Inflammation causes vasodilation (Nitric oxide), increased vascular permeability induced by VEGF from mesenchymal cells causes outgrowth from residual endothelium-new vessel sprouts, migration and proliferation of endothelial cells –formation of capillary tubes, recruitment of pericytes to form mature vessel wall – suppression of endothelial proliferation and deposition of BM. ECM enzymes (MMPs) matrix metalloproteinase allows extension of vascular tubes and sets the platform for ECM remodelling Seen as granulation tissue ( by naked eyes in the wound) Granulation tissue Pink granular tissue at the wound base (floor) Granularity is due to new vessel buds felt as knobs and blood flow gives pinkish red color to the tissue New thin vessels are fragile hence leaky –serum in oedematous loose ECM ( swelling around wound d1-4) Pink base with some serous ooze – moist wet wound ( Happy surgeons)  Scar formation: In 2 stages 1. Laying of connective tissue On the granulation tissue/loose ECM scaffold Myofibroblasts migrate and proliferate Deposition of ECM Inhibit collagen degradation – Cells: macrophages, mast cells and granulation tissue cells – Growth factors: TGF-β, PDGF, FGF-2 and – Cytokines: IL 1, IL-13 2. Remodelling of connective tissue = Wound strengthening and type of wound repair – Balance between MMPs (collagen degrader=remodelling/strengthening) and TIMPS ( inhibit collagen degradation=excess fibrosis) regulates repair process – Matrix metalloproteinase secreted by fibroblasts, macrophages, polymorphs, synovial cells – Degrade the excess collagen and ECM resulting into a well balanced ECM – MMPs activity is tightly controlled and shut down by tissue inhibitors of MP (TIMPs) secreted by mesenchymal cells When can I lift /go back to heavy work? Wound strengthening time period: Wounds that heal by Primary intention Wounds that heal by Secondary/Tertiary intention 10% strength - 1 week Takes months-a year 80% strength by 3 month 80% strength over many years  Extra slide: MMPs- Matrix metalloproteinases Proteases family by Jerome Gross and Charles Lapierre 1962, with enzymatic activity to degrade collagen triple helix ( excess laid collagen ) Zinc and Calcium ion dependent endopeptidases Secreted by fibroblasts, macrophages, polymorphs, synovial cells MMPs – 1-3=Interstitial collagenases – 2 & 9=gelatinases – 3,10,11=stromelysins Major role in to control repair process : cell proliferation, migration, adhesion, differentiation, angiogenesis, apoptosis, and Degrade the excess collagen and excess ECM deposited. Inhibitors: Tissue inhibitors of MP (TIMPs) secreted by mesenchymal cells stop the collagen breakdown when repair is complete Steroids inhibit MMPs: weak /delayed ECM repair Doxycycline antibiotic, inhibits high levels of MMPs in chronic wounds and enhance their repair  Interactive activity Moulage simulations – Stimulate students to think the wound type and healing types Case studies What stage and day is it? What stage and day is it? Is it a normal ? What stage and day is it? What stage ? What day is it? What changes are seen and stage?  Healing of special structures GIT – Gastric erosions (picture) : primary intention – Gastric ulcers heal by mix of primary and secondary intention  Healing of damaged liver Preservation of ECM is the key for normal repair Normal Liver : Gross and histology Cirrhotic liver: Gross and Histology Secondary healing as ECM not preserved Silver stain : Fibrosis causing nodular formation of disturbed hepatic architecture  Healing of bone fracture Y2 femur fracture case -SGL Problems with fracture healing Mal-union Ongoing movement Interposed soft tissue Infection Delayed union Osteo myelitis Pre existing bone disease Pathological fracture Irregular woven cartilage islands Abnormal healing: Malunion or Non union  Factors influencing wound healing and repair Healing depends on 1. Tissue type 2. Wound type 3. Wound contamination- Infection, foreign body, faeces 4. Age of the patient 1. Infants: Impaired as proliferation, migration and tissue differentiation at peak 2. Childhood: Rapid wound healing 3. Old age : Impaired/Slow: connective tissue elasticity & collagen bonding weak, weak bones, poor microcirculation, co morbidities 5. Nutrition status: Important for collagen synthesis a) Scurvy (Vit. C deficiency) : impaired proline hydroxylation –weak collagen –weak wound strength, weak capillaries b) PEM : antibody deficiency -- impaired resistance , methionine for collagen synthesis c) Iron , Copper, Zinc, Calcium, Mg, Mn 6. Tissue vascularity: Insufficiency= ischemia, infarction, haemorrhage, varicose Hypoxia and compromised cellular components. Abnormal or Delayed healing. Clot acts as an excellent culture media for bugs 7. Denervation : Poor mediation of inflammatory response, prone to infection as poor sensations ( e.g.: diabetics, leprosy, peripheral neurological disorders, stroke ) 8. Excessive steroids: Cushing’s syndrome : impair macrophage & fibroblast migration, inhibit release of plasminogen activator - poor granulation tissue 9. Co-morbidities : Diabetics (polymorph dysfunction, high tissue glucose conc. ) Immunosuppressive states- Neoplasia , PEM  Next up: Examples of dysfunctional wound healing Considering each stage/step of healing Secondary Infection Proud flesh: Excessive granulation tissue Nail bed lump-A Tissue biopsy-B Wound dehiscence/gapping 5-10 days after suturing paradoxically when collagen synthesis is at peak Predisposing factors: Haemorrhage, Infection, Too much inflammation, Weak abdominal muscles, Obesity Serous discharge and distension of abdomen at 5-10 d is the clue VAC therapy : Wound dehiscence management  Delayed wound healing Oral cavity Diabetic foot infection Hypertrophic scar- Collagen overproduction Hypertrophic scar: raised scar due to collagen overproduction but scar remains within the boundaries of the wound  Keloid raised scar due to collagen overproduction but scar extends outside the boundaries of the wound Wound contractures-Abnormal Fibrous bands post operative causing intestinal obstruction  Summary 1. Wound healing depends on Wound type Cell/Tissue type: Proliferative capacity Growth factors 4. Stages of wound healing Preservation of ECM Healing factors Nutritional status Balanced interplay between all elements 2. Two mechanisms of wound healing. Regeneration (Re-epithelialisation) Scar formation (Fibrosis) 3. Three types of wound healing. Primary intention Secondary intention Tertiary intention Open the wound dressing and examine it thoroughly: Look, listen and feel and if needed, swab the right area for lab sampling. Thank you! Questions??