Transcript skin
Integument: -skin, hair, sweat glands, sebaceous glands Skin: - protection against injury, dessication, bacteria - regulates body temp. - sensory organ - excretion - UV absorption for vitamin D synthesis Skin -regions Epidermis - stratified squamous keratinized Dermis - dense irregular CT - dermal papillae Hypodermis - loose CT - adipose tissue Keratinocytes of the epidermis: Five zones: Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum Stratum Corneum 1. Stratum basale - above the basal lamina - cells have hemidesmosomes - many intermediate filaments - mitotic figures 2. Stratum spinosum - cells polyhedral to flat - “prickle cell appearance” because of desmosomes - keratinocytes have lots of if (tonofilaments) containing cytokeratin - membrane-coating granules (lamellar) 3. Stratum granulosum - flattened keratinocytes - basophilic keratohyalin granules - lots of membrane coating granules, oily content released by exocytosis - very thin in thin skin 4. Stratum lucidum - lightly stained cells - only in thick skin - no nuclei or organelles - yes keratin filaments and keratohyaline prduct (eleidin) 5. Stratum Corneum - flattened keratinized cells with thickened plasmalemma - very thick in thick skin Other cells of the epidermis: Langerhans Cells - antigen presenting cells Merkel Cells - indented - have cytokeratin - have dense core vesicles - form synapses onto sensory fibers - may be mechanoreceptors Melanocytes: - from neural crest cells - cell body in the dermis - processes between keratinocytes - contain melanin within melanosomes - cytocrine secretion - ? Tips of the melanocytes end up in keratinocytes Dermis - Papillary Layer - loose CT - capillaries - encapsulate nerve endings, Meissner’s Corpuscles - Reticular Layer of the Dermis - dense, irregular collagenous CT - sweat glands - sebaceous glands - arrector pilli muscles - Pacinian corpuscles Eccrine sweat glands - simple coiled tubular glands - dark (mucoid) cells - clear cells with watery secretion - myoepithelial cells - secretory duct Apocrine sweat glands - armpits, nipple, anal region - larger than eccrine sweat glands - secretory portion in dermis, opens to follicle - secretion becomes odorous when metabolized by bacteria - in some species, secrete pheromones Sebaceous glands - sebum - secrete into follicles - holocrine secretion Pacinian corpuscles - encapusulated nerve endings - Hair • • • • Keratinzied filaments Cuticle – from periphery of matrix Cortex – from slight periphery of matrix Medulla – large vacuolated cells from center of matrix Hair follicle • External root sheath – outer layers of follicular epithelium • Matrix – surrounds the dermal papilla, contains proliferating cells that will make the keratin filaments Hair follicle • Glassy mb – separates the dermis from the epithelium of the hair follicle • Hair root – expansion of the hair follicle with matrix cells, like stratum basale. And external root sheath is outer layer. • Dermal papilla – inside the hair root has bv, inductive factors. • Hair bulb = hair root + dermal papilla Hair follicle • External root sheath • Internal root sheath (ends at subaceous gland/follicle interface) – Outer single row of cuboidal cells, Henle’s layer – Flattened cells, Huxley’s layer – Cuticle of root sheath, overlapping scale-like cells with free ends projecting to base of the hair follicle