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WEEK 8:
Histology of Skin
| Question | Answer |
|---|---|
| layers of the skin | epidermis dermis hypodermis/ subcutis |
| epidermis (epithelium) | Stratified squamous epithelium (keratinised): keratinocytes |
| dermis (connective tissue) | Dense irregular connective tissue: fibroblasts, collagen I, elastin, blood vs, nerves and receptors. Divided into papillary and reticular dermis |
| hypodermis/ subcutis (fascia) | Adipose tissue and main blood supply |
| epidermis cells | Keratinocytes Melanocytes Langerhans cells Merkel cells |
| epidermis structure | variable thickness and avascular |
| layers of the epidermis/ epidermal strata | Stratum corneum Stratum lucidum Stratum granulosum Stratum spinosum Stratum basale |
| barriers in the epidermal strata | Tight junctions (prevent paracellular diffusion) Desmosomes and hemidesmosomes (mechanical and shear) Keratin (microbes) Phospholipid (waterproof) |
| stratum basale | single layer cuboidal/ columnar cells on BM with intense mitotic activity hemidesmosomes (in basal cell membranes to join cells to basal lamina) desmosomes (joins cells in lateral and upper surfaces) keratinocytes melanocytes merkel cells |
| derivatives of basal cells | keratinocytes melanocytes merkel cells |
| stratum spinosum | polyhedral cells with central nuclei and prominent nucleolus containing keratinocytes and epidermal dendritic cells (langerhans) |
| keratinocytes | Keratin filaments assemble into tonofibril bundles Tonofibril converge and terminate at desmosomes Cells extend around tonofibrils on either side of desmosomes: spiny appearance |
| stratum granulosum | 3-5 layers of flattened cells cells undergo terminal differentiation via keratinisation keratohyaline (Filaggrin mass) enrichment lamellar granular (L)- exocytosis to form lipid rich impermeable layer (skins barrier againt water loss) |
| skin sealant made of (2) | keratinisation and lipid layer |
| stratum lucidum | found only in thick skin- is a thin translucent layer of eosinophilic keratinocytes held together by desmosomes with no nuclei or organelles with cytoplasm packed with keratin |
| stratum corneum | 15-20 laters of squamous keratinised cells, amorphous dead flattened anucleated cells kertain filled which protects against friction and water loss where squamous continuously shed at epidermal surface |
| skin cell types | keratinocytes and melanocytes |
| keratinocytes | Stratified squamous keratinising epithelial cells Produce keratin |
| melanocytes | Pigment-synthesising cells responsible for skin and hair colour Neural crest-derived cells lying in the stratum basale Melanosomes in cytoplasm contain melanin and are passed to keratinocytes – scattering of UV light |
| langerhans cells | All layers and upper dermis, prominent in spinosum Bone marrow-derived Dendritic, antigen-presenting cells, migrate to regional lymph nodes and communicate with the immune system |
| merkel (tactile) cells | Clear cells in stratum basale Low-threshold mechanoreceptors Plentiful in touch areas Connected to keratinocytes and afferent nerves Neuroendocrine function |
| thin skin | Most locations. This epidermis, less well-defined rete ridges, thinner keratin layer, lots of eccrine glands |
| thick skin | Fingertips, palm and soles of feet Characterised by thick epidermis and thick keratin layer, well developed rete ridges, lots of eccrine glands. No hair. No sebaceous gland |
| hairy skin | Scalp, axilla and groin Thin epidermis. Lots of hair follicles and sebaceous glands. Oblique follicles in curly hair. Lots of apocrine glands in the axilla and groin. |
| dermis | Contains hair and glands Highly vascular Largely dense irregular connective tissue: collagen 70% papillary later reticular layer |
| papillary layer in dermis | Loose connective tissue Types I and III collagen Fibroblasts Leucocytes Type VII collagen inserts into basal lamina |
| reticular layer in dermis | Thicker with dense irregular connective tissue Mainly type I collagen Elastic fibres provide elasticity |
| interdigitation between epidermis and dermis increase | SA |
| what adhere epidermis to dermis | hemidesmosomes |
| basement membrane sits between epidermis and dermis composed of | Sheets of matrix at interface of parenchyma and support tissue Composed mainly of type IV collagen, glycoproteins (Laminin secreted by epithelial cells & Fibronectin from fibroblasts) and GAGs |
| function of basement membrane | adhesion, barrier (permeability), organisation of cells (controlling growth and differentiation) |
| hair follicles | Produce hair shafts (keratin) for thermoregulation and display. Arrector pili muscle |
| sweat glands (2) | Eccrine: dermal-subcutis junction of all skin, produce sweat. Ducts open onto skin surface (thermoregulation) Apocrine: Localised (axilla/groin) scent production. Open into hair follicles above sebaceous duct. Functional at puberty |
| sebaceous glands | Majority associated with hair follicles. Secrete lipid mixture - sebum into hair follicle (waterproofing) |
| eccrine sweat glands | dermal-subcutis junction of all skin, produce sweat. Ducts open onto skin surface (thermoregulation) |
| apocrine sweat glands | Localised (axilla/groin) scent production. Open into hair follicles above sebaceous duct. Functional at puberty |
| major nutritive plexus of vessels | cutaneous plexus and papillary plexus |
| pacinian corpuscle | in reticular dermis/ hypodermis providing deep pressure vibration |
| meissner corpuscle | in papillay dermis providing light touch/ low frequency stimuli |
| free nerve endings | in papillary dermis providing pain itch and temperature |
| root hair plexuses | in base of hair follicles in reticular dermis and detects movement of hairs |
| merkel cells (tactile corpuscle) | associated with expanded nerve endings |
| krause end bulbs | for light vibration sensation in skin of clitoris and penis |
| ruffini corpuscles | for sensing cutaneous tension and torsion |
| efferent nerve endings (sympathetics) | Regulate vessel diameter and blood flow Carry information to sweat glands and erector pili muscles |
| psoriasis | caused by overactive T lymphocytes trigger autoimmune reaction in skin -> inflammation redness irritation itching scaling with defective skin barrier |
| moles or naevi | melanocytes proliferate in skin to make moles (benign melanocytic nevi) normally and changes in size or appearance of moles sometimes indicate of dysplasia that can progress further to malignant melanoma |
| epidermolysis bullosa (EB) | A group of hereditary diseases of the skin characterized by blister formation following minor trauma to the skin caused by defects in keratinocyte intermediate filaments which anchor fibrils |
| bullous pemphigoid | A blistering disorder due to autoimmune damage of proteins at the dermo-epidermal junction |
Created by:
kablooey
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