Overview Anatomy Epidermis Function: protection, temperature regulation, moisture retention Major cell types: keratinized squamous epithelial cells and melanocytes Layers (top to bottom): stratum corneum stratum lucidum stratum granulosum stratum spinosum stratum basale (contains pluripotent stem cells) "Californians Like Girls in String Bikinis" From basale to corneum, cells mature and lose their organelles and become keratinized Dermis Function: Structure, sensation, wound healing. Contains hair follicles, sebaceous glands, apocrine glands , specialized nerve endings, and vasculature Mostly made up of extracellular matrix: collagen, glycosaminoglycans, proteoglycans, and glycoproteins Major cell types: fibroblasts, langerhans cells, pluripotent stem cells (in hair follicles), endothelial cells Layers (top to bottom) papillary dermis reticular dermis Subcutaneous Tissues Consist of fat, muscle, tendon, ligament, bone, etc. Normal Wound Healing Phases: not discrete, but rather overlapping Hemostasis (1-24h) Endothelial damage leads to exposure of the basement membrane, activation of intrinsic and extrinsic coagulation cascade, and ultimately deposition of fibrin with creation of a platelet plug. Platelets are integral to initiating wound healing. They release cytokines that cause leukocyte migration and chemotaxis into the wound. Inflammation (1-5d) Mast Cells Native cells Initiate the inflammatory phase Secrete cytokines that cause vasodilation and increase vascular permeability Allows influx of neutrophils and macrophages to the wound bed Neutrophils present early in inflammatory phase clear intralesional pathogens prepare the wound bed by removing damaged cells secrete cytokines that stimulate infux of macrophages. Macrophages Present late in inflammatory phase Early on act in coordination with neutrophils to phagocytose bacteria and dead cells Secrete cytokines and growth factors that drive fibroblast proliferation and angiogenesis Also act to downregulate the initial infammatory response Proliferation (3-7d) Fibroblasts lay down type III collagen Myofibroblasts (fibroblasts with contractile filaments) initiate wound contraction Angiogenesis and vasculogenesis lay down new blood vessels Granulation tissue (newly laid collagen with neovascularization) forms Epithelialization occurs from surrounding basal keratinocytes and hair follicle basal cells Maturation (Up to 1 year) Type III collagen remodeled to type I collagen Vessels mature, and excess vasculature involutes Erythema and raised appearance of wound resolves Types of Wound Healing Primary Intention - Wound edges are approximated. Grafts and flaps are considered primary closure. Secondary Intention - Wound edges are left open and allowed to fill in Tertiary Intention - Wound edges are left open and allowed to granulate, and are approximated and closed at a later time. Also known as delayed closure.