Wound Healing & Skin Flashcards
Define parenchyma and stroma
Parenchyma = organ specific cells related to function Stroma = background tissue providing structure, mechanical and nutritional support
What are the 4 stages of wound healing?
Haemostasis (<24 hrs)
Inflammation (0-4d)
Proliferation (1-14d)
Remodelling (day 21+)
Outline tissue regeneration
Complete restoration of damaged tissue, driven by growth factors (PDGF, VEGF, TGF-B)
Only occurs in labile/stable tissues
Broadly, what do growth factors do?
Stimulate entry of cells into cell cycles
Bind to cellular receptors
Produced mainly by macrophages/lymphocytes at site of injury
Proteins that stimulate cell survival and proliferation
What’s granulation tissue?
New connective tissue + new blood vessels = pink granular tissue
Laying down of new connective tissue: migration and proliferation of fibroblasts (FGF) and deposition of ECM proteins
What are labile and stable tissues? What’s the 3rd type of tissue? Give organ examples
Labile = cells continuously proliferating in order to replace dead/sloughed off cells (skin, GI, salivary gland)
Stable = cells normally exist in a non-dividing state but enter cell cycle in response to stimuli (growth factors) (liver, kidney, pancreas)
Permanent tissue = non-dividing cells that lead to scar tissue when damaged (bone, cardiac, skeletal)
Outline the process of remodelling
Collagen is remodelled to 80% of its normal tensile strength
Matrix metalloproteases degrade collagen/ECM components (balance between ECM protein synthesis and degradation)
If weak, opportunity of wound reopening is likely
What local and systemic factors affect tissue repair?
Local: infection, mechanical factors, foreign bodies, size of wound, location, type of wound
Systemic: nutritional status, metabolic status, circulatory status, hormones, age, collagen disorders
What causes fibrosis?
Excessive deposition of collagen and other ECM components
= sign of organ failure
What are some key factors delaying healing?
Infection is main factor - prolongs inflammation and potential tissue injury
Nutrition - collagen synthesis inhibited by vitamin C deficiency
Poor perfusion - diabetes/arteriosclerosis
Foreign bodies - fragments of steel, glass, bone
Mechanical variables - increased local pressure cause dehiscence (wound pulls apart)
What are 3 complications of tissue repair?
Inadequate formation (dehiscence, evisceration, ulceration)
Excessive formation (keloid scar formation/excessive granulation tissue which hinders re-epithelialisation)
Contracture formation (myofibroblasts)
What’s the difference between first and second intention healing?
First intention: clean cut to skin, epithelial regeneration is main focus of repair (only focal disruption to epithelial membrane)
Second intention: more chronic wounds, requires lots of granulation tissue, ECM tissue and scar formation (complex repair)
Outline the stages of fracture healing
Haematoma
Granualtion tissue formation (replaces haematoma)
Callus (bridges between bone ends)
Woven bone (OPGs strengthen callus)
Lamellar bone (replaces woven bone)
Remodelling (osteoblasts and osteoclasts)
Which growth factor converts fibroblasts -> myofibroblasts?
TGF-B
Outline healing by first intention
Fibrin clotted scab Neutrophils migrate towards fibrin clot Acute inflammation at site of injury Epithelial cells from both edges migrate towards each other and proliferate along dermis Neutrophils replaced by macrophages Angiogenesis Pink granular tissue Continued collagen accumulation and fibroblast proliferation = scar maturation
Outline haemostats -> inflammation -> proliferation -> remodelling
Haemostasis: wound closed by coagulation, platelets and fibrin adhere to site, thrombus formation
Inflammation: platelets control bleeding, macrophages prevent infection, neutrophils control inflammation
Proliferation: angiogenesis, epithelialisation, contraction and fibrous tissue formation to close wound
Remodelling: restored to normal function, collagen remodelled to normal tensile strength
What are the 5 functions of skin?
Sensation Thermoregulation Metabolic function (vitamin D) Protection (abrasion and impermeable, prevents dehydration and microorganism entry) Psychosocial
What’s the macroscopic structure of skin?
Epidermis
Basement membrane
Dermis: papillary then reticular layers
Subcutis
What’s the microscopic structure (layers) of the epidermis?
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum corneum
What’s the extra epidermal layer in thick skin?
Stratum lucidum (between corneum and granulosum)
What are lamellar bodies and keratinohyaline granules?
Involved in formation of keratin
Contain water repellent glycophospholipid to bind keratin flakes (in stratum corneum)
What are some different skin appendages?
Sebaceous glands Eccrine sweat glands Apocrine hormonal glands in axilla/groin Nails (dense keratin on nail bed) Hair follicles (made of keratin and associated with sebaceous glands)
What’s the circulation of the skin?
Subpapillary superficial plexus in dermis
Cutaenous deep plexus in subcutis
Form anastomoses to regulate heat loss/preservation and supply epidermis/appendages with nutrition
In which layer are melanocytes founds?
Stratum basale
