Skin Anatomy Coursework Materials

Skin Anatomy Skin Functions Protect body against infection, abrasion, dehydration etc. - Accomplished via the presence of Langerhans within the epidermis, which are a type of fixed macrophages - These phagocyte pathogens -> antigen release -> presented to T-helper cells -> induce immune response Regulate body temperature - Increase in metabolic rate = increase in body temperature - Most heat loss occurs though the skin, whereas a minimal amount of heat is lost through expired air, urine or faeces - Blood vessel constriction and dilation -> control blood flow to skin -> control heat loss - Skeletal muscle shivering Detection of pain, sensation/reception, and pressure - In the dermis there is abundant sensory nerve endings in the dermis - This allows for perception, discrimination, and location of internal and external stimuli - These allow response to changes in the environment Absorption - This function is limited - Allows for absorption of some drugs when applied as transdermal patches, for example nicotine that is used as a way for smoking cessation Excretion Skin Anatomy • Largest organ in the body • 1.5 – 2 square metres • It contains accessory structures: nails, glands, and hair • The skin varies in thickness throughout the body - • The thickest is the skin on the palms and the soles of the feet The skin has two main layers: - Superficial: epidermis ✓ Stratified squamous epithelium ✓ Thin outmost layer ✓ Multiple layers if developing keratinocytes ✓ Functions: secrete glycolipids, prevent water, seeping into/out of the body - Deep: dermis Layers of the epidermis Stratum Basale - Innermost layer - Single columnar stem cell layer -> divide -> produce keratinocytes - Keratinocytes: contains cholesterol precursors which are activated by UVB light -> vitamin D - Contain melanocytes ✓ Determine skin colour ✓ UVB light stimulates melanin secretions -> placed into melanosomes, which are moved up by keratinocytes Stratum Spinosum - Made out of 8-10 keratinocyte cell layers which cannot divide - Proteins on keratinocytes help them adhere together - Dendritic cells seek out invading microbes Stratum Granulosum - Made out of 3-5 keratinocyte layers, which undergo keratinization (flatten out and die) -> form epidermal skin barrier - Have to types of granules: ✓ Keratohyalin granules in keratinocytes which contain keratin precursors -> aggregate and cross link -> keratin bundles ✓ Lamella granules these are also found within keratinocytes, and they contain glycolipids ➢ secreted to the cell surface ➢ glue cell together Stratum Lucidum - Made out of 2-3 layers of dead keratinocyte cell layers that have secreted most of their lamellar granules - Only found in thick skin, such as skin found on palms and soles of the feet Stratum Corneum - Made out of 20-30 dead keratinocyte cell layers which are glued together with glycolipids - Dead keratinocyte produce defensins to flight off pathogens - Cells from stratum lucidum push up -> cells from this layer shed -> skin flakes/dandruff Layers of the dermis • Papillary layer - Contain fibroblasts: ✓ Make collagen ✓ Arranged in papillae • - Contains blood vessels, macrophages, nerve endings (e.g., Meissner’s corpuscles for fine touch, free nerve endings for pain) - Responsible for fingerprints Reticular layer - Fibroblasts ✓ Produce elastin for flexibility - Contain oil, sweat glands, lymphatic, blood vessels, hair follicles, macrophages, nerves (e.g., Pacinian corpuscle for pressure vibration) - Collagen is tightly packed -> increase support - Sweat glands and blood vessels help with temperature regulation ✓ When there is a high temperature: ➢ Blood vessels dilate -> increased blood flow to skin surface -> allow heat loss ➢ Increased sweat gland stimulation ✓ When there is a low temperature: ➢ Blood vessels constrict -> decrease blood flow to skin ➢ Decreased stimulation of sweat glands Hypodermis • Subcutaneous tissue • Inner layer • Contain adipocytes, blood vessels, nerves, lymphatics • Insulates deeper tissues • Provides padding • Anchors skin to underlying muscle with connective tissue (e.g., collagen)