Objectives • Present a introduction to histology of the skin Normal Skin Histology • Discuss the different cell types in the skin • Cover the reginal variation and artifacts that are seen in the skin Jason Stratton I have no conflicts of interest Duplicate Function Layers 1. Epidermis • Protectionor / mechanical barrier – UV, chemical, thermal insult – Dehydration 2. Dermis • Thermoregulation & electrolyte balance – Prevents & facilitates heat loss • Sensation – Receptors for pressure & pain • Immunologic organ • Sensuality & psychological well-being • Metabolic 3. Subcutaneous Adipose Tissue – Subcutaneous fat for energy – Vitamin D synthesis Distribute Epidermal Cell Function Dermal Cell Function • Immune organ • Supportive – Langerhan cells – antigen presenting cells – Fibroblasts – produce fibers & ground substance – Keratinocytes – produce interleukins, interferons, & growth • Collagen fibers – tensile strength factors • Elastic fibers – retractile properties • Protection UV • Immunologic function – Melanocytes – Dendritic cells, lymphocytes, mast cells, macrophages Not• Produce melanin from tyrosine via tyrosinase & store within • Provides nutrients melanosomes – Vascular networks • Transfer melanosomes to adjacent keratinocytes • Mechanical barrier • Thermoregulation – Keratinocytes – structural integrity via keratin filaments, – Vascular networks Do desmosomes, hemidesmosomes – Nerve supply 1 Epidermis Keratinocytes • Stratified keratinizing squamous epithelium – Continuously renewing itself • Stratified 4/5 layers – Maintains nl thickness via desquamation – Stratum corneum (cornified / horny layer) • Cells (4) • Cornified/keratin – Keratinocytes (80-90%) – Stratum lucidum • Keratin = intermediate filament (tonofilament) • Only palms & soles – Dendritic cells • Melanocytes – Stratum granulosum (granular layer) • Langerhan cells (3-5%) • Thickest on palms & soles – Stratum spinosum (squamous / prickle cell – Merkel cells (neuroendocrine cells) Stratum layer) Malpighi • Also contains – Stratum basalis / germinativum (basal – Opening eccrine ducts (acrosyringium) layer) – Opening hair follicles (acrotrichium) Duplicate Keratinocytes Basal layer (Stratum basalis, germinative layer) • Interface b/w epidermis • Single layeror of mitotically & dermis is irregular active cells above the – Dermal papillae basement membrane that • Upward projections of papillary dermis into give rise to other epidermis keratinocytes – Rete ridges • Basal cells contain melanin • Portion epidermis covering apical surface of separating the dermal papillae nucleus • Attach basement membrane via hemidesmosomes SquamousDistribute Layer Granular Layer (Stratum spinosum) (Stratum granulosum) • Flattened cells •5-10layers keratinocytes •2 to 3cell layers thick – Generally proportional to thickness horny • Maturation layer – Suprabasal cells are polyhedral • Filled with basophilic keratohyalin granules – Form 2 structures with abundant cytoplasm and a • Interfibrillary matrix / filaggrin vesicular nucleus w/ a prominent – Cements keratin filaments together • Marginal band nucleolus – Inner lining of horny cells – ↑ sulfur (cysteine disulfide bonds) → – SuperficialNot cells larger, flattened, strength & stability eosinophilic, oriented parallel • Tonofilaments ↓ sulfhydryl groups → soft & flexible → “soft” keratin • In contrast, hair & nails, which lack • Keratinocytes connected via keratohyaline granules, incorporate disulfide desmosomes (intercellular bonds themselves → “hard” keratin Dobridges) 2 Cornified Layer Basement Membrane Zone (Stratum corneum) • Specialized region at the interface between the • Flattened eosinophillic, anucleated epidermis & dermis • Dead • Homogeneous, • Basket-weave keratin eosinophilic band below pattern (orthokeratotic) Basement membrane (PAS) – Portion horny cytoplasm w/ “Basket-weave” the epidermis disulfide cystine bonds Stratum Corneum shrinks formalin fixation – 1.0 microns thick • Thinnest in eyelid and – Highlighted by periodic genitals acid-Schiff (PAS) stain • Thickest on palms and soles • Continuous around epidermal appendages Duplicate Melanocytes •Origin – Neural crest or • Function – Produce melanin, which protects against non-ionizing ultraviolet irradiation • Histology – Clear peripheral halo surrounding small deep purple ovoid nucleus along basal layer • Ratio of melanocytes to keratinocytes – Normally varies from 1:4 to 1:10 – Does not depend on race (type of melanosome does) • Immunohistochemistry – S-100 protein, Sox-10, Melan-A / MART-1 (Melanoma Antigens Recognized by T cells-1), HMB-45 Melanocytes Melanocytes •EM – Abundant pale cytoplasm – Scattered solitary melanosomes – No tonofibrils / desmosomes Distribute Melanosomes • Stages (4) – Round w/o melanin • I: seen in balloon cell melanoma – Ellipsoidal w/ numerous longitudinal filaments • II: melanin deposits start Not • III: melanin deposits are prominent • IV: fully-packed w/ melanin obscuring internal structures Melanocyte – Transferred to keratinocytes » Epidermal melanin unit = 1 melanocyte : 36 keratinocytes DoMelanocyte 3 Melanosomes Langerhan Cells Lightly Darkly •Origin Pigmented Pigmented – Dendritic cells derived from bone marrow Skin Skin • Function – Antigen presenting cells Melanization Stages II, III Stage IV>III • Important role in cutaneous immunity – Allergic contact dermatitis, allograft rejection & immune tolerance and immune surveillance • Depleted by chronic UVL, steroid application, HIV/AIDS Size 0.3-0.5 0.5-0.8 • Histology microns microns – Clear cells (appear to lie w/i lacunae) in the suprabasal epidermis w/ reniform nucleus Number per <20 >200 • Immunohistochemistry cell – POS: HLA-DR antigen, CD4, S-100 protein, CD1a, langerin – Also positive: Fc & C3 receptors, CD1c (M241), LCA, actin-like & Distribution Groups of 2- Singly vimentin filaments, ATPase, & aminopeptidase – PNA (peanut agglutinin) – stains w/ characteristic halo and/or dot 10 dispersed pattern •EM Degradation Fast Slow – Cerebriform nucleus with Birbeck granules = tennis racquet shaped membrane bound vesicle w/ a dilated end and laminated elongated handle Duplicate or Langerhans Cells Langerhans Cells Langerhan Cells (CD1a) Langerhan Cells (CD1a) Distribute Merkel Cells (Neuroendocrine cells) • Location – Scattered irregularly throughout basal layer – May group together above enlarged terminal sensory nerve fibers • Function – Mediate tactile sensation Not • Histology – Not recognized • Immunohistochemistry – Express a synaptophysin, neuron specific enolase, cytokeratin 20 (and other non-specific low molecular weight cytokeratins such as CK 8, CK 18, & CK 19) Langerhans Cell •EM – Possess membrane-bound electron-dense (neurosecretory) Do granules that vary in size between 80 and 200 nm 4 Merkel Cell Merkel Cells (CK20) Merkel Cells (CK20) Duplicate Dermis • Composition • Layers or – Glycoprotein matrix – Papillary • Ground substance largely • Thin, superficial •c/o finely woven collagen nonsulfated acid fibers mucopolysaccharides such • Periadnexal dermis of as hyaluronic acid similar quality (adventitial – Stains w/ colloidal iron & dermis) digests w/ hyaluronase • Predominantly type III – Type I collagen (90%) collagen • Fine elastic fibers • Eosinophilic fibers in orientated perpendicular birefringent bundles – Reticular – Elastic fibers • Wider, deeper • Wavy, eosinophilic fibers • Coarse thick collagen • Verhoeff Van Gieson bundles elastic staining • Predominantly type I • Orcein / resorcin-fuchsin collagen Dermis stains • Elastic fibers thicker & parallel to the surface epithelium Dermis Distribute Oxytalan Elaunin Not DoElastic Fibers Elastic Fibers Collagen & Fibroblasts 5 Dermal Vessels •Two plexi – Superficial plexus • Located at the papillary & reticular dermal junction – Deep plexus • Located at the dermal & subcutaneous junction • Connected by vertically oriented communicating vessels • Endothelial cells –POS: CD34, CD31, Ulex europaeus lectin, factor VIII-related antigen (vWF) – Contain HLA class I (HLA-A, B, C) & HLA II (HLA-DR) antigens Duplicate Dermal Lymphatics Glomus Body • Specializedor arteriovenous (AV) shunts (Sucquet-Hoyer canal-arterial segment) • Location • Location – Collapsed in normal dermis – Pads & nail beds of fingers & toes, central • May be difficult to distinguish from blood face and ears vessels, unless valve represented • Function – Form a complex network and follow the distribution of the blood vessels – Modified smooth muscle cells that regulate • Histology blood flow and temperature – Lined by a single layer of flattened cells • Histology – Have a thin wall without pericytes – Large cells with uniform, round to oval nuclei – Surrounded by a discontinuous basement and abundant cytoplasm membrane – Surround endothelial lined lumen • Immunohistochemistry • Immunohistochemistry – POS: CD31, D2-40 – NEG: FVIII-related antigen, CD34 – POS: Smooth muscle actin (SMA) Nerves ofDistribute Dermis Pacinian Corpuscle (Vater-Pacini Corpuscle) • Sensory & autonomic nerves • Location – Permeate entire dermis – Travel along course along superficial – Weight-bearing surfaces of & deep plexi deep dermis & subcutis • Sensory (fingers & toes) – Mediate pain, touch, itch, • Function temperature,Not pressure & vibration – Mediates sense of pressure & • Autonomic vibration – Derived from the sympathetic nervous • Histology system – Innervate blood vessels, arrector pili, – Concentrically arranged eccrine and apocrine glands Schwann cells with an axon Do (Onion skin) 6 Meissner Corpsuscle Subcutaneous Tissue • Location (Subcutis, hypodermis)