Histology LC 2: Skin and Its Appendages PDF

○ SENSORY COURSE OUTLINE – Largest sensory organ of the body; has many receptors for sense of I. SKIN...

○ SENSORY COURSE OUTLINE – Largest sensory organ of the body; has many receptors for sense of I. SKIN AND FUNCTION touch, pressure, pain and II. EPIDERMIS temperature. Three basic cell types of ○ HOMEOSTASIS/THERMOREGULATION epidermis – Thermoregulation by fatty layer or Epidermal water barrier adipose tissue or subcutaneous Layers of the epidermis tissue, as well as the head on hair. Heat conservation or heat loss. III. BASEMENT MEMBRANE ZONE 4 major basement ○ METABOLIC membrane zone – Through the action of UV light, cells components of the of skin synthesize Vit.D3, needed for basement membrane zone calcium metabolism and bone formation. IV. THREE MAJOR TYPE OF SKIN – Stores energy in the form of fat. CANCER Squamous cell carcinoma ○ SECRETION (ENDOCRINE/EXOCRINE) Basal Cell Carcinoma OR EXCRETION Melanoma – Has the sebaceous gland, sweat gland and apocrine gland. V. DERMIS Parts of dermis ○ WOUND REPAIR/ REGENERATION Composition of dermis – Skin has elastic fibers that can Subcutaneous tissue/ expand rapidly to cover swollen hypodermis/panniculus areas. Self-renewing throughout life. VI. APPENDAGES ○ SEXUAL SIGNALING Hair – Physical appearance- pigmentation Sebaceous glands – Pheromones- produced by apocrine sweat glands and other Sweat glands skin glands. Imparts factors in Apocrine glands attraction. Nails Blood supply 3 MAIN LAYERS: Innervation / Nerve Endings VII. REFERENCE I. SKIN AND FUNCTION Largest organ of the body base on surface area 1.5 -4.0-mm thick. (Thinnest = lower eyelids, Thickness = sole of the feet) Figure 1. skin layers Epidermal layer point basis in classifying thin or EPIDERMIS thick skin ○ Avascular ○ “Thin” – with hair ○ Stratified squamous keratinizing epithelium ○ “Thick” – without hair (sole of feet and (ectodermal) palm) ○ Note: Anatomically (actual/ entire skin DERMIS thickness), the thickest skin is at the ○ Vascular upper portion of the back where the ○ Dense irregular C.T. (mesodermal) dermis is exceedingly thick, but epidermis ○ Upper layer (adjacent to epidermis): is thin. papillary dermis. – layer of ridges adhering dermis to the FUNCTIONS: epidermis ○ PROTECTIVE ○ Reticular layer: deep layer – Physical barrier (pathogens, thermal and mechanical insults) – Immunoregulatory or ultraviolet protection 1 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. HYPODERMIS/ SUBCUTIS A. CELLS OF THE EPIDERMIS (3 Basic Cell ○ Varying amounts of adipose conn.tissues Types) Keratinocytes Note: Dermal papillae: projection at the junction Melanocytes between epidermis and dermis layer (helps to the Langerhans cells adhesion) Additional cell types ○ Merkel cell ○ Indeterminate dendritic cells A1. KERATINOCYTES Squamous cells 80% of cells Ectodermal origin Production of keratin ○ Surface coat of the epidermis ○ Structural protein of hair and nai EPIDERMAL WATER BARRIER Figure 2. Dermal papillae lI. EPIDERMIS Figure 4: Illustration of Epidermal Water Barrier Functions: ○ For body homeostasis (two-factor) ○ Insoluble proteins on the inner surface ○ Lipid layer attached to the outer surface Lamellar bodies (membrane-coating granules; lipid-producing granules) Tubular or ovoid-shaped membrane-bound organelle Figure 3. Dermal papillae Unique to mammalian epidermis Outermost layer Probarrier lipids + lipid-processing enzymes. Keratinized, stratified squamous epithelium ○ Assembled into lamellar bodies 0.4 to 1.5 mm thick Organized lamellae forms the epidermal water Cells renew 15-30 days (depending on age, barrier region of the body and other factors) Cornification (formation of the outermost A2. MELANOCYTES dead layer of the skin - stratum corneum) ○ Synthesis of lamellar granules & distinctive proteins (keratins, filaggrin, involucrin) ○ Alterations of nuclei, cytoplasmic organelles, plasma membranes, & desmosomes Cornification/keratinization ○ Basal cells divide by mitosis and as they move upward the cells flatten and nucleus disappears ○ Takes place within 28 days Figure 5: Melanocyte BATCH 2028 1C 2 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. Neural crest origin Long, irregular cytoplasmic and dendritic extensions Between stratum basale and spinosum Production of MELANIN Epidermal melanin unit ○ 1 melanocyte : 4 basal keratinocytes (face, shins, genitalia) ○ 1 melanocyte:10 basal keratinocytes (limbs) Activity of melanocytes increases with Figure 8: Albinism exposure to X-rays and UV light MELANIN ○ FRECKLES ○ Synthesized from tyrosine - increased production of melanin by ○ Linked in a protein matrix normal number of melanocytes ○ Accumulate to vesicles until it forms (hyperpigmentation) MELANOSOMES ○ Dark color of the skin ○ Protects the skin from the damaging effects of UV radiation SKIN COLOR (PIGMENTATION) ○ Number, size and distribution of MELANOSOMES = pigment granules within the keratinocyte ○ Vascular pigments (oxyhemoglobin and deoxyhemoglobin) ○ Dietary pigments (carotene and lycopene) Figure 9: Freckles Clinical Correlation ○ NEVUS ○ ADDISON’S DISEASE - Benign proliferation of melanocytes - ACTH elevation, insufficient cortisol (moles or benign melanocytic nevi) - Dysplasia (uncontrolled proliferation) turn into malignant melanoma Figure 6: Addison’s disease ○ VITILIGO - Destruction of melanocyte - Depigmentation of the skin due to lessened activity of melanocytes Figure 10: Nevus A3. LANGERHANS CELL Figure 11: Langerhans cell Star shaped cells with numerous dendritic processes found in stratum spinosum; Figure 7: Vitiligo represent 2-8% of the epidermal cells The skin macrophages (monocytes in origin) ○ ALBINISM that are responsible in immune response - Normal number of melanocytes but By E/M: indented nucleus, well developed RER unable to synthesize melanosomes and Golgi complex, clear cytoplasm with rodlike - Hypopigmentation due to lack of inclusion: Birbeck granules (Rod/Racquet tyrosinase (enzyme for tyrosine) inclusions) BATCH 2028 1C 3 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. Potent stimulators of T-cell mediated B3. Stratum Granulosum (Granular Cell Layer) immunoreactions 3-5 layers of flattened cells Consists of filaggrin A4. MERKEL CELLS (additional cell) Filled w/ coarse, basophilic (keratohyalin) Found in stratum germinativum in association granules with intraepithelial nerve endings Secretory granules not surrounded by a Palms, soles, infundibula, epithelium of nail membrane beds, oral mucosa, genital regions KERATOHYALIN GRANULES EM: possess distinctive electron-dense ○ Hygroscopic granules w/in their cytoplasm ○ Repeated cycles of hydration and Mechanoreceptors (gentle touch) dehydration ○ Results in the soft and flexible keratin B. LAYERS OF THE EPIDERMIS Clinical Correlation: ○ ICHTHYOSIS VULGARIS - Absent or diminished granular layer; hard and rigid keratin Figure 12: Tissue layer of epidermis Stratum basale - single layer of tall columnar cells Stratum spinosum - polyhedral cells with Figure 14: Ichthyosis Vulgaris "intercellular bridges" Stratum lucidum - non-nucleated cells with B4. Stratum Lucidum eleidin granules (palms/soles) Palms and soles Stratum corneum - layer of dead cornified Translucent and barely visible cells Flat cells Stratum malpighii: stratum granulosum + Densely packed keratin filaments stratum spinosum + stratum basale B5. Stratum Corneum (Cornified Layer) Anucleate, flattened, dead cells filled with soft keratin filaments (birefringent) 15-20 layers of squamous keratinized cells During keratinization they increase in mass with filaggrin and other proteins End of keratinization=cell with amorphous, fibrillar protein with lipid-rich plasma membrane Cornified cells (squames) continuously shed (desquamation) at the outermost layer as desmosomes and lipid-rich cell membrane breakdown. Figure 13: Stratum malphigi Clinical Correlation: B1. Stratum Basale / Germinativum (Basal Cell ○ PSORIASIS Layer) - Accelerated differentiation of Single layer, columnar to cuboidal cells; keratinocytes causing sped up histologic stain: basophilic in H&E stain desquamation and keratinization Germinative cells (Increased mitotic activity) Desmosomes (cell junctions) Hemidesmosomes (attachment to the basement membrane zone) B2. Stratum Spinosum (Prickle Cell Layer) 4-6 rows of cells Thickest layer of the epidermis Numerous cytoplasmic extensions/ spines Figure 15: Psoriasis ○ Sites of desmosomes anchorage to tonofilaments ○ Tonofilaments - Cell cohesion - Resistance to abrasions BATCH 2028 1C 4 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. ○ SQUAMOUS CELL CARCINOMA 2. Lamina lucida - Atypical keratinocytes - Electron-lucent region that lies beneath basal keratinocytes - Portion of papillary dermis 3. Lamina densa - Electron-dense plate below lamina lucida & above papillary dermis - Basal lamina 4. Sublamina densa - Below the lamina densa Figure 16: Squamous cell carcinoma - Fibrous components: 4.1 Anchoring fibrils III. BASEMENT MEMBRANE ZONE 4.2 Dermal microfibrils 4.3 Collagen fibers BASEMENT MEMBRANE ZONE (BMZ)- aka. B. COMPONENTS OF DERMAL-EPIDERMAL dermo-epidermal junction (DEJ) - junction BASEMENT MEMBRANE between epidermis & dermis Figure 17: basement membrane zone FUNCTIONS: Figure 19: Components of the basement membrane zone ○ Attaches the epidermis to the dermis ○ Separates components of the epidermis Components: and dermis ○ TYPE IV COLLAGEN - component of the ○ Provides resistance against external basal lamina, This Collagen is found only shearing forces in basement membranes. ○ Maintains tissue architecture ○ TYPE VII COLLAGEN - component of the anchoring fibrils. For structural support and A. Basement Membrane Zone (BMZ) 4 zones: stability to BMZ. Found in lamina densa and sublamina densa. ○ LAMININ - large glycoprotein networks held together by transmembrane proteins. 2 Major Hemidesmosomal Proteins: ○ BP230 (Antigen 2) ○ BP180 (Antigen 1 or Type XVII Collagen) Clinical Correlation ○ BULLOUS (BLISTERING) PEMPHIGOID - Antibodies against BP230 and BP180 Figure 18: 4 layers of the basement membrane zone 1. Hemidesmosomes - Plasma membrane of the basal keratinocytes that constitute the upper boundary of the interface Figure 20: Bullous Pemphigoid BATCH 2028 1C 5 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. ○ EPIDERMOLYSIS BULLOSA ACQUISITA - Antibodies against collagen V. DERMIS Derived from mesenchyme Composition: collagen (70%), elastin, ground substance (proteoglycans) Contains sweat glands, sebaceous glands, and hair follicles Highly vascular Two parts: ○ Papillary dermis ○ Reticular dermis Figure 21: Epidermolysis bullosa acquisita A. Parts of Dermis A1. Papillary Dermis (Papillary Layer) Thin zone immediately beneath the epidermis IV. THREE MAJOR TYPE OF SKIN Haphazardly arranged collagen bundles CANCER Highly irregular Accounts for the whorls, loops and arches that constitute fingerprints or footprints Delicate branching elastic fibers Plentiful fibrocytes Abundant ground substance Highly developed circulation made mostly of capillaries A2. Reticular Dermis (Reticular layer) Thick collagen bundles arranged in orthogonal pattern Collagen fibers have parallel orientation (Cleavage lines or Langer's lines) Elastic fibers course along collagen bundles Figure 22. Tissue illustration of the three major types of skin fewer fibrocytes, blood vessels & ground cancer substance A. Squamous cell carcinoma Second most common. Develop as a small painless nodule or patch Surrounded by areas of inflammation. Disrupted basement membrane is responsible for tumor spread via lymph nodes. B. Basal Cell Carcinoma Most common Originate from stratum basale, slow growing and does not metastasize. Arises from follicular vouch in outer root Figure 23: Papillary and Reticular sheath. B. Composition of Dermis C. Melanoma B1. Collagen Most serious skin carcinoma. Major structural protein for the entire body Begins at an early age Synthesized by fibroblast ○ Originates from melanocytes, aggregates Type 1 Collagen – major component of the in nests or scattered from entire dermis epidermis. Stress-resistant material of the skin that ○ Early stage: With time, melanoma provides integrity, firmness, elasticity undergoes radial growth phase where B2. Dermal blood supply melanocytes grow in all directions. Two major plexuses ○ After 1-2 years: melanocytes with dead ○ Subpapillary plexus: between the spots exhibit mitotic activity. And enter a papillary and reticular dermal layer vertical growth phase where melanocytes ○ Deep plexus: lies near the interface of the display little or no pigment and dermis and the subcutaneous layer. metastasize to regional lymph nodes. Thermoregulatory function - Arteriovenous anastomoses or shunts. (Decrease/increase blood flow in the papillary layer to minimize or facilitate heat loss) BATCH 2028 1C 6 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. - Decreased elastin synthesis Figure 24: Dermal blood supply Figure 27: Cutis laxa B3. Elastic tissue ○ SKIN AGING 2 - 4% of dermis - Loss of collagen (wrinkling) and For retractile properties of the skin elastin (sagging) Also synthesized by fibroblasts ELASTIN – amorphous protein; fiber matrix component Papillary dermis: thin and run at right angles to the skin surface Reticular dermis: thicker and oriented parallel to skin surface Demonstrated by van-Gieson stain Clinical Correlation ○ KELOID - Excessive collagen deposition Figure 28: Skin aging C. Subcutis/ Panniculus Deepest layer, derived from mesenchyme Lobules of adipocytes separated by fibrous SEPTA ○ Collagen ○ Blood vessels FUNCTIONS ○ Repository of energy ○ Endocrine organ ○ LEPTIN (body weight regulation) Figure 25: Keloid ○ Conversion of androstenedione to estrone ○ STRIAE - Decreased expression of collagen, Clinical Manifestation stretching of the epidermis. Rapid ○ PANNICULITIS change in weight (gain or loss). - Inflammation of the adipose tissue Associated with endogenous or exogenous corticosteroids Figure 29: Panniculitis ○ LIPODYSTROPHY - Selective loss of body fat Figure 26: Striae ○ CUTIS LAXA Figure 30: Lipodystrophy BATCH 2028 1C 7 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. Opposite side of the follicle (3rd bud) gives rise to the eccrine gland VI. SKIN APPENDAGES THREE VERTICAL SEGMENTS: A. Hair B. Sebaceous gland C. Sweat glands D. Apocrine glands E. Nails FUNCTION: ○ Reserve epidermis (re-epithelialization) ○ Keratinocyte migration from the adnexal epithelium to the skin surface ○ E.g. face and scalp re-epithelialize more rapidly than the back A. HAIR Figure 33: Inferior segment of hair follicle HAIRS - Regulate body temperature HAIR FOLLICLE - hair production and growth INFUNDIBULUM HAIR BULB - stem cells, differentiation of ○ Uppermost portion various cell types ○ Surface opening to the entrance of the sebaceous duct ISTHMUS ○ Below the infundibulum ○ Between the sebaceous duct and the insertion of arrector pili muscle ○ IRS fully keratinized and sheds within this portion INFERIOR SEGMENT ○ Where hair bulb is located Figure 31: Hair HAIR FOLLICLE MORPHOGENESIS Mesenchymal cells in the fetal dermis collect immediately below the basal layer of the epidermis Epidermal buds grow down into the dermis Developing follicle forms at an angle to the skin surface and continues its downward growth At the base, the column of cells widens forming the bulb and surrounds small collections of mesenchymal cells Figure 34: Anatomy of Hair Follicle 3 Major Parts of the Hair Follicle: ○ Hair cuticle Figure 32: Stages of Hair follicle morphogenesis ○ Cortex A.1 HAIR FOLLICLE - Along one side of the fetal ○ Medulla follicle, 2 buds are formed: UPPER - develops into sebaceous gland Tubular structure: LOWER - becomes an attachment for the ○ formed of perifollicular connective tissue arrector pili muscle and epithelium Pilosebaceous unit (hair follicle, sebaceous ○ invagination of the epidermis gland and arrector pili muscle) BATCH 2028 1C 8 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. ○ surrounded by external and internal root sheaths (ERS and IRS) A.2. HAIR BULB Base, bulbous expansion Highly vascularized and contains melanocytes MATRIX CELLS ○ Produce the hair shaft, IRS and ERS Undergoes cycles of involution and regeneration throughout life As hair follicles grow, they are pushed towards the skin surface from the hair bulb and the 5 epithelial layers form. The inner epithelial layers undergo keratinization to form the hair shaft while the outer layers form an outer root sheath and an IRS. 0.37mm/day or 1cm/month- normal hair growth A.3 HAIR SHAFT Extending beyond the surface of the skin contains melanin pigment Composed of: ○ HAIR CUTICLE - thin, pale-stained. Figure 35: Anatomical parts of a hair follicle Surrounds the pigmented CORTEX and pale MEDULLA. External Root Sheath (ERS) ○ CORTEX - located peripherally to the ○ separated from the CT tissue sheath by medulla. Contains cuboidal cells which the glassy membrane undergo differentiation into keratin filled ○ Homogenous cells. ○ Separates the hair follicle from the dermis ○ MEDULLA - forms the central part of the ○ Covers the internal root sheath and shaft and contains large vacuolated cells. extends all the way to the epidermis Usually present only in thick hairs Internal Root Sheath (IRS) ○ Eosinophilic (keratohyalin) granules ○ Completely surrounds the initial part of the hair root but degenerates at the level of the attached sebaceous glands Figure 37: Parts of hair shaft TYPES OF HAIR LANUGO - fetal/newborn hair Figure 36: Internal and external root sheath Figure 38: Lanugo hair INTERNAL ROOT SHEATH LAYERS: HENLE LAYER VELLUS - fine, light colored, narrow hair shaft, ○ Thin, pale epithelial stratum thin inner root sheath ○ Composed of a single layer of cuboidal cells and these cells are in direct contact with the outermost part of the hair follicle which represents a down growth to the epidermis and is designated to the external root sheath HUXLEY LAYER ○ thin, granular epithelial stratum. Figure 39: Vellus hair ○ single or double layer of flattened cells that formed the middle plate of the IRS BATCH 2028 1C 9 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. Terminal Hairs – coarse, thick, dark (except blondes) OVAL ○ Pubic hair, facial hair and eyelashes ○ Scalp hair (African descent, usually curly hair) Figure 43: Oval hair Figure 40: Terminal hair HAIR COLOR Degree of melanization STAGES OF HAIR GROWTH Distribution of melanosomes within the hair It occurs in cyclical manner shaft each follicle functions as an independent unit Colors: (humans do not shed synchronously) ○ BLACK HAIR - large melanosomes 3 stages: ○ BLONDE HAIR - Smaller melanosomes 1. Anagen aggregated within membrane-bound ○ active growth phase complexes ○ long mitotic growth ○ RED HAIR - Spherical melanosomes 2. Catagen ○ GRAY HAIR - Loss of melanosomes ○ transition phase ○ brief period of arrested growth and regression of the hair bulb 3. Telogen ○ resting phase ○ final long period of inactivity during which part of the hair will shred Figure 44: Black hair Figure 45: Blonde hair Figure 41: Stages of hair growth ANAGEN HAIRS ○ Scalp: 0.37 mm/day ○ Pigmented bulb in IRS CATAGEN HAIRS Figure 46: Red hair Figure 47: Gray hair ○ Many apoptotic cells in the ORS TELOGEN HAIRS Clinical Correlation: ○ Eyelashes: short anagen, long telogen ○ ALOPECIA AREATA ○ Nonpigmented bulb - Autoimmune, peribulbar lymphocytic infiltrates anagen phase HAIR SHAPE - the dimensions and curvature of the inner root sheath ROUND - scalp hair (Caucasian) Figure 48: Alopecia Areata Figure 42: Round hair BATCH 2028 1C 10 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. ○ TELOGEN EFFLUVIUM ○ SEBORRHEIC DERMATITIS - Premature termination of anagen - Form of eczema, found in areas rich phase, increase in telogen phase in sebaceous glands Figure 49: Telogen Effluvium B. SEBACEOUS GLANDS Associated with hair follicles (pilosebaceous Figure 52: Seborrheic dermatitis unit) Lateral protrusions from the hair follicle ARRECTOR PILI MUSCLE Simple or branched alveolar in morphology Part of the pilosebaceous unit appearing like a bunch of grapes Oblique bands of smooth muscle inserted into HOLOCRINE GLAND - total disintegration of middle of hair follicle secretory cells with sebum Controlled by the autonomic nervous system Basal layer of flattened epithelial cells on the Contraction: "goose flesh appearance" basal lamina Sebocytes - filled Figure 50: Sebaceous Gland Found everywhere on the body except the palms and soles More abundant in the scalp, face, midline of the back, perineum and orifices of the body Figure 53: Arrector pili muscle Eyelids: Meibomian glands Buccal mucosa and vermilion of lip: Fordyce spots Areola of women: Montgomery glands Labia minora and glans: Tyson glands SEBUM mixture of lipids (wax esters, squalene, cholesterol and triglycerides) increases at puberty Figure 54: goose flesh appearance by arrector pili muscle stimulated by androgens helps maintain the stratum corneum and hair C. SWEAT GLANDS shaft Eccrine Sweat Glands weak antibacterial and antifungal properties ○ Found in palms, soles and foreheads ○ Merocrine/eccrine in type Clinical Correlation: ○ Secretion discharged by exocytosis simple ○ ACNE VULGARIS coiled tubular in morphology - Inflammation of the pilosebaceous ○ Stimulus is heat, under control of unit, common skin condition hypothalamic thermostat: SWEAT ○ Duct opens into epidermis as sweat pore, reabsorb sodium without water Figure 51: Acne vulgaris BATCH 2028 1C 11 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. - Stimuli: emotional stress, sympathetic discharge (adrenergic nerve endings vs. cholinergic fibers in eccrine) Figure 55: Eccrine sweat gland Figure 57: Apocrine gland SECRETORY COIL Clinical Correlation: Shows only one distinct layer composed of ○ HYPERHIDROSIS secretory cells - Excessive sweating (eccrine glands) 3 Distinct Cell Types: ○ CLEAR CELLS (SECRETORY) - Produce sweat - Transports interstitial fluid from the dermis ○ DARK CELLS (MUCOID) - Eosinophilic granules at the lumen → merocrine secretion ○ MYOEPITHELIAL CELLS Figure 58: Hyperhidrosis - At the basal lamina - Contract to move watery substance ○ BROMHIDROSIS to the duct - Offensive odor from apocrine gland secretions when associated with DERMAL DUCT foreign bacteria Double layer (2 layers of acidophilic cells) Eosinophilic lumen Na+ reabsorption Merges with the stratum basale to form the sweat pore Figure 59: Bromhidrosis E. NAILS Figure 56: Eccrine sweat gland Dorsal surfaces of terminal phalanges Plates of keratinized cells containing hard D. APOCRINE/ODORIFEROUS SWEAT GLAND keratin Nail apparatus: Found in axilla, mammary areola, labia majora ○ 1. Nail plate and circumanal region ○ 2. Specialized epithelia: Larger than eccrine glands – Proximal Nail Fold - covers the nail Opens into a hair follicle root Coiled and tubular – Nail Matrix Wider and dilated lumen – Nail Bed – contains only basal and Myoepithelial cells more numerous spinous epidermal layers Non-functional until puberty – Hyponychium Found in the dermis Low cuboidal secretory cells Viscous secretion - Initially odorless → unpleasant odor (bacterial decomposition) BATCH 2028 1C 12 HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. LUNULA Crescent-shaped white area Opaque nail matrix and immature nail plate below it Figure 60: Parts of the nail (External view) Figure 64: Lunula NAIL PLATE Dense keratinized appendage Hard keratin Rests on a stratified squamous epithelium, the NAIL BED NAIL BED Figure 61: Parts of the nail (Sagittal section) Contains only basal and spinous epidermal layers NAIL ROOT HYPONYCHIUM proximal part of the nails Distal end of the plate covered by a fold of skin (PROXIMAL NAIL FOLD) → CUTICLE/ EPONYCHIUM forms the NAIL MATRIX Figure 65: Structure of the nail Figure 62: Nail root Clinical Correlation ○ NAIL PITTING NAIL MATRIX - Abnormal keratinization of the nail nail growth matrix a semilunar area of proliferative cells on proximal ventral surface of nail groove 3 mm/month (fingernails) and 1 mm/month (toenails) Responsible for nail growth and differentiation of epithelium Figure 66: Nail pitting Figure 63: Nail matrix BATCH 2028 1C 13  HISTOLOGY LC 2: SKIN AND ITS APPENDAGES DR. DE GRANO, A.P. ○ MELANONYCHIA Figure 68: Meissner (left) and Pacinian (right) - Melanin production in the nail matrix VIII. THICK VS THIN SKIN THICK SKIN ○ Palms of hands, fingers, soles, toes ○ Thickness of epidermis considerable ○ Abundant sweat glands ○ No pilosebaceous follicles ○ Grooves and ridges prominent because of tall dermal papillae ○ Numerous arterio-venous anastomosis Figure 67: Melanonychia F. BLOOD SUPPLY CUTANEOUS PLEXUS: between the dermis and subcutis with larger blood vessels SUBPAPILLARY OR SUPERFICIAL PLEXUS: between the papillary and reticular dermis, Figure 69: Thick skin capillaries, end arterioles, venules GLOMUS BODIES: special type of THIN SKIN arteriovenous anastomosis for temperature ○ Other regions except palms, soles, regulation; fingers, toes and nails fingers, toe SMALL ARTERIES (deep vascular plexus) ○ Thin epidermis and ARTERIOLES (dermis) possess three ○ Small number of sweat glands layers: ○ Presence of pilosebaceous follicles ○ INTIMA ○ Lacks ridges and grooves with checkered - Composed of endothelial cells and network of lines absent or few an internal elastic lamina arterio-venous anastomosis ○ MEDIA - Contains collagen, elastic fibers, & several concentric layers of smooth muscle cells bounded by an external elastic lamina (in arteries) ○ ADVENTITIA - Composed of fibrocytes, collagen, & elastic fibers ○ Walls of veins generally are thinner than those of arteries and less clearly divided into the three classic layers Figure 70: Thin skin G. INNERVATION AND NERVE ENDINGS Both efferent and afferent nerve supplies Free nerve endings ○ pain, itch and temperature VII. REFERENCES specialized encapsulated nerve endings ○ MEISSNER: mechanoreceptors Wheather’s Functional Histology – A text and colour - Prominent in the papillary dermis of atlas, 6th edition the pain receptor, soles and palms ○ PACINIAN: deep pressure and vibration Junqueira’s Basic Histology, 15th edition Andrews Diseases of the skin: Clinical dermatology, 10th edition BATCH 2028 1C 14