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Skin GUCAS Year 1Session Content • Skin functions • Skin structure • Wound healingFunctions of skin • Physical and immunological protection • Physiological regulation – body temp, fluid balance, vit D synthesis • Sensation – heat, cold, touch, painQuestion 1 • What type of epithelium is found in the skin? • A – pseudostratified columnar epithelium • B – non-keratinized squamous epithelium • C – stratified squamous epithelium • D – simple squamous epithelium • E – transitional epitheliumQuestion 1 • What type of epithelium is found in the skin? • A – pseudostratified columnar epithelium • B – non-keratinized squamous epithelium • C – stratified squamous epithelium • D – simple squamous epithelium • E – transitional epithelium Skin has keratinized, stratified, squamous epitheliumSkin Layers Epidermis: • Stratum corneum • Stratum lucidum • Stratum granulosum • Stratum spinosum • Stratum basale Dermis: • Papillary layer • Reticular layer Subcutaneous/hypodermis layer Epidermal Layers Stratum basale: • Cuboidal cells that are mitotically active • Linked to BM by hemidesmosomes • Melanocytes Stratum spinosum: • Polyhedral shape • Rich in desmosomes Stratum granulosum: • Cells start to lose cytoplasm and nucleus and begin to flatten • Contain keratohyalin granules which aggregate keratin filaments to help formation of keratinocytes Stratum lucidum: • Only found in thick skin e.g. palms, soles • Thin layer Stratum corneum: • Flat, densely packed, plate-like cells filled with keratin • Contain lamellar bodies which secrete lipid-rich substance into ECM that provide water barrierQuestion 2 How long would it take for a cell in stratum basale to reach the skin surface? • 1 week • 2 weeks • 3 weeks • 4 weeks • 5 weeksQuestion 2 How long would it take for a cell in stratum basale to reach the skin surface? • 1 week • 2 weeks • 3 weeks • 4 weeks • 5 weeksEpidermis renewalCell types of epidermis Dermis Dense, irregular connective tissue • Upper papillary layer o Loose connective tissue o Fine interlacing collagen fibres o More blood vessels and nerves • Lower reticular layer o Collagen bundles tighter packed o Large elastin fibres o Some blood vesselsDermis • Type 1 collagen fibres, elastin and ‘ground substance’ = connective tissue • Fibroblasts • Blood supply (epidermis is avascular so dermis provides nutrients)Cell types of dermisSubcutis/hypodermis • Shock absorption • Insulation • Energy sourceAdnexal structures – hair,nails,glands Hair: • Invaginations of epidermis (infolding) creates cavities which form follicles, and contain mitotically active cells to give hair • Melanocytes give hair its colour. Nails: • Composed of heavily compacted, highly keratinized cells which replace the stratum corneum and lie on nailbed • Sweat glands – temp control • Abundant on palms, soles, axillae Apocrine gland: • Scent gland Sebaceous gland: • Produce sebum • Formed from hair follicleNerves and skin Free nerve endings: • Papillary dermis and attach with Merkel cells • Act as mechanoreceptors Meissners corpuscles: • Papillary dermis of hands and feet • Mechanoreceptors for touch Pacinian corpuscles: • Subcutis • Detect vibration and pressureWounds A wound by true definition is a breakdown in the protective function of the skin; the loss of continuity of epithelium, with or without loss of underlying connective tissue (i.e. muscle, bone, nerves) Depths of wounds: • Erosion • Ulceration • Partial thickness • Full thicknessQuestion 3 Which stage of wound healing involves formation of type I collagen? • Inflammation • Proliferation • Remodelling • VasodilationQuestion 3 Which stage of wound healing involves formation of type I collagen? • Inflammation • Proliferation • Remodelling • VasodilationW ound healing 3 stages: 1. Inflammation 2. Proliferation 3. RemodellingW ound healing - inflammation Inflammation (24-48 hours) 1. Platelets initiate haemostasis and the healing cascade 2. Attracts neutrophils/macrophages (by chemokines) to site of wound to fight infection and transition to repair 3. Neutrophils and macrophages phagocytose dead tissue and microorganisms o (Characteristic signs of inflammation: red/swelling)W ound healing - proliferation • 2 days – 3 weeks • Re-epithelialization o Epithelial cells loosen adhesions and migrate to wound and cover granulation tissue o Once fully covered by layer of keratinocytes, start to proliferate • Granulation tissue formed o Fibroblasts form type III collagen • Angiogenesis o Endothelial cells proliferate and migrate • Contraction o Myofibroblasts at wound edge contract to make defect smallerW ound healing - remodelling • 3 weeks to 2 years • Granulation tissue -> mature scar tissue o bundles and extensively cross- linked • Type III collagen -> type I collagen • Final strength = 70-80%Question 4 What is the function of IL-6 in wound healing? • ECM formation • Inflammation • Angiogenesis • Attracting neutrophilsQuestion 4 What is the function of IL-6 in wound healing? • ECM formation • Inflammation • Angiogenesis • Attracting neutrophilsSignals involved in wound healing • Epidermal growth factor (EGF) = keratinocyte proliferation and migration • Platelet-derived growth factor (PDGF) = ECM formation and remodelling • Vascular endothelial growth factor (VEGF) = angiogenesis • TNF-α, IL-1, IL-6 = inflammationQuestion 5 Which is NOT a local factor affecting wound healing? • Infection • Vascular supply • Oxygenation • Obesity • Foreign bodyQuestion 5 Which is NOT a local factor affecting wound healing? • Infection • Vascular supply • Oxygenation • Obesity • Foreign body Obesity is a systemic factor affecting wound healingFactors affecting wound healing