Skin and its appendages

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detail description of skin, hair and nail.

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Skin and its appendages

  1. 1. Skin and Appendages Dr Laxman Khanal MS-Human Anatomy Batch- 2011
  2. 2. Introduction – our largest organ – Accounts for 12% of body weight…it weighs twice as much as your brain! – Varies in thickness at different parts (< 0.5 mm at eyelids to > 5 mm on middle of upper back) – Divided into three distinct layers • Epidermis • Dermis • Hypodermis – lies deep to the dermis8/5/2012 1212413114 2
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  4. 4. Functions• Barrier against loss of body fluid.• Protection and excretion• Sensory function• Metabolic function• Temperature regulation• Adaptation during edema and pregnancy• Legal and anthropological importance8/5/2012 1212413114 4
  5. 5. Structure of skin8/5/2012 1212413114 5
  6. 6. Epidermis• Primarily made up of keratinized stratified squamous epithelium(keratinocytes)• gives strength to the skin.• Varies in thickness from thick skin to thin skin• It does not have any vascularization, so it relies on the connective tissues deep to it.• Also contain melanocytes, merkel’s cells and Langerhans cell8/5/2012 1212413114 6
  7. 7. Layers of epidermis• Stratum basale (the deepest layer)• Stratum spinosum• Stratum granulosum• Stratum lucidum (only in thick skin)• Stratum corneum (most superficial layer of epidermis8/5/2012 1212413114 7
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  9. 9. STRATUM BASALE • Consists of single layer of basophilic columner or cuboidal cells. • Along with S. spinosum it is component of Malpighian layer • Cells are bound to each other by desmosomes and to basal lamina by hemidesmosomes. • All cells contain intermediate keratin filaments, number of which increases as cells progress upward.8/5/2012 1212413114 9
  10. 10. Stratum Spinosum • Also contain the dividing cells as in basale. • Cells contain bundles of intermediate filament ( tonofilaments) projecting into the processses of cells which give attachment to the desmosomes, so giving spined appearance. • Tonofilaments provide resistant to the abrasion so this layer is thicker in the areas prone to abrasion( thick skin)8/5/2012 1212413114 10
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  12. 12. Stratum Granulosum• Consists of polygonal cells , cytoplasm of which is filled with the basophilic granule , keratohyaline granules. It is rich in phosphorylated histidine and cystine.• Cells contain, lamellated bodies, made up of lipid. It fuses with the cell membrane and it come out of cells and function as a intercellular cement or sealing agent.• This sealing effect is first evolutionary adaptation to terrestrial life.8/5/2012 1212413114 12
  13. 13. Stratum Lucidum • more prominent in thick skin . Cellular organells and nuclei are not prominent. • It is composed of clear non-nucleated cells.• In the palms and soles, the stratum lucidum is present. The tan colored protein blocks the underlying melanocytes from view8/5/2012 1212413114 13
  14. 14. Stratum corneum • The main difference between thick skin and thin skin relates to the thickness of the Stratum corneum. • These are the dead cells, flaking off. The cells lose their nucleus and fuse to form squamous sheets, which are eventually shed from the surface (desquamation). • It takes about 40 50 days days for a cell to move from the stratum basale to the distal edge of the stratum corneum and shed.8/5/2012 1212413114 14
  15. 15. Keratin• Keratin is a waxy protein substance found in the epidermis. It also makes up the nails and hairs.• It can absorb water, so keratin swells when soaking wet.• It makes the skin look wrinkled when you are in the tub too long. The water evaporates when you dry off, and pulls more water out of your body, so soaking in the tub will dry your skin out…unless you put lotion on right away to keep the water in the epidermal and dermal layers. Lotions will not penetrate to the dermis, just water.8/5/2012 1212413114 15
  16. 16. • Icthyosis – excessive keratinisation of the skin with autosomal recessive inheritance pattern.• Grotesque appearance due to icthyosis in fetus- harlequin fetus.8/5/2012 1212413114 16
  17. 17. Melanocytes- neural crest cells •During the first 3 months of development, the epidermis is invaded by cells arising from the neural crest. • These cells synthesize melanin pigment, which can be transferred to other cells of the epidermis by way of dendritic processes.8/5/2012 1212413114 17
  18. 18. Melanin synthesis • Stage 1 – tyrosinase activity in vesicle • Stage 2- melanosome with tyrosinase and filaments of melanin • Stage 3- more filaments of melanin • Stage 4- melanin completely filled the vesicles.8/5/2012 1212413114 18
  19. 19. • Addison disease – adrenal cortex hypo function resulting increased in ACTH production---- increased melanin synthesis.• Albinism – hereditary condition of inability of melanocytes to produce melanin.• Vitiligo- degeneration of entire pool of melanocytes.• Nevus and Malignant melanoma8/5/2012 1212413114 19
  20. 20. Melanin• Tyrosine by the action of tyrosinase converted into the DOPA, which undergo polymerization to form the melanin.• it is located in supranuclear position inside the keratonocytes so that it can prevent the nuclear damage by the UV radiation coming from above.8/5/2012 1212413114 20
  21. 21. Langerhans cells• These are star shaped bone marrow derived cells. Migrated to the skin via blood.• Present in the S. spinosum of the skin• These cells are antigen presenting cells so participate in immune related reaction.• These are component of SALT.8/5/2012 1212413114 21
  22. 22. Merkel’s cell• Neural crest in origin• Found in the basal layer of the thick skin . Has sensory function.• Expanded terminal disc of free nerve endings are found just beneath the merkel’s cell.• These cells also acts as the neuroendocrine function.8/5/2012 1212413114 22
  23. 23. Dermis• It is connective tissue that support the epidermis and attaches the epidermis to the hypodermis.• Its surface consists of many ridges ( dermal papillae) which interdigitate with epidermal ridges.• Dermal papillae are more numerous in the skin that is more prone to pressure and friction.• Has 2 layer - Papillary layer and reticular layer8/5/2012 1212413114 23
  24. 24. Dermoepidermal junction• Dermis is consists of the collagen fibers and elastic fibers which are thicker in reticular layer and thinner in papillary layer.• Special collagen fibers extend from the dermal papillae and inserted in the basal lamina forming the dermoepidermal junction.• Loss of this junction lead to pemphigoid• Loss of intercellular junction lead to pemphigus.8/5/2012 1212413114 24
  25. 25. Papillary layer• Made up of loose connective tissue having thin fibers and many cellular structures.• Has ridges to increase surface area for contact with the epidermis.• Along the ridges sweat gland open at regular interval.• The papillary layer in the dermis is what forms our fingerprints.8/5/2012 1212413114 25
  26. 26. Reticular layer• Dense irregular Connective Tissue• Has bundles of Collagen and Elastic fibers and less number of cells.• Arrangement of bundle in the direction of mechanical force give rise to the cleavage lines of Langer.• strongest layer of the Dermis. Gives the area strength.• Leather is made of this layer.• EDS8/5/2012 1212413114 26
  27. 27. • The dermis is also the area where all the glands of the body are located.• A transdermal patch (nicotine patch, etc) must diffuse all the way from the epidermis into the dermis to reach the blood vessels there.• The blood vessels in the dermis are what give a pink color to Caucasian people.8/5/2012 1212413114 27
  28. 28. Hypodermis• Consists of loose connective tissue which helps in sliding the skin over the deep structure.• Consists of layer of fat according to the nutritional status of the person.• Also called as superficial fascia or panniculus adiposus8/5/2012 1212413114 28
  29. 29. Vessels in skin• Arteries form the 2 plexuses. One at the junction of papillary and reticular layer( sub- papillary plexus) and another at junction of dermis and hypodermis (cutaneous plexus).• Veins form the three plexuses – 2 in same position as for arterial and another in the middle of the dermis.8/5/2012 1212413114 29
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  31. 31. Sensory receptors in skin• Free nerve ending• Merkels cells noncapsulated• Hair follicle receptors• Pacinian corpuscles• Ruffini ending capsulated• Meissener’s corpuscles8/5/2012 1212413114 31
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  33. 33. Skin color1) MELANIN: (dark brown pigment).2) CAROTENE: (a yellowish/orange pigment found only in plants). Accumulates more in the skins of Asians and Native Americans.3) SKIN THICKNESS: blood vessels seen, looks pinker4) HEMOGLOBIN: The DERMIS contains the blood vessels that give Caucasians the pink color to the skin. Even veins are red because blood is red. But when you look at veins through the adipose layer (the hypodermis), they look blue.8/5/2012 1212413114 33
  34. 34. Condition of skin• If you rub the skin, it stimulates cell division = callous• If you rub the skin too hard, the stratum basale tears away from the basement membrane, and causes a gap, which fills with fluid: BLISTER.• The epidermis then dies because it’s too far away from nutrients. That’s why the top of a blister dries up• If the blisters are small (less than 5 mm in diameter), they are known as vesicles; if they are larger (greater than 5 mm in diameter), they are termed bullae8/5/2012 1212413114 34
  35. 35. • Psoriasis – decrease in cell turnover time and increased proliferation of basal layer cells. Results in greater epidermal thickness and rapid renewal of epidermis.• Darkening of the skin to solar radiation- darkens the preexisting melanin and also increase the synthesis of melanin.8/5/2012 1212413114 35
  36. 36. Skin cancer Major types• Squamous cell carcinoma• Basal cell carcinoma• Malignant melanoma8/5/2012 1212413114 36
  37. 37. Appendages of the skin• Hairs• Sebaceous gland• Sweat gland• Nails8/5/2012 1212413114 37
  38. 38. Hair• It is keratinized elongated structure derived from the invagination of epidermis(hair follicle) .• By 3rd month first hairs appear over eyebrow and upper lip.• It acts for thermoregulation, sensory function.• Distribution of hair after puberty possesses distinctive sex differences.• Made up of shaft and root8/5/2012 1212413114 38
  39. 39. Hair• The hair follicle is a tubular structure consisting of five concentric layers of epithelial cells.• At the base, there is a bulbous expansion, the hair bulb, enclosing the hair papilla .• During hair formation inner 3 layer undergo keratinisation and outer 2 layer form epithelial sheath.8/5/2012 1212413114 39
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  41. 41. Stages of Hair growth• Anangen phase- fast growing phase• Catangen phase- involution phase• Telogen phase- rest phaseTypes of hairs• Laungo hairs- foetal hair• Vellus hairs- infant hair and fine hairs of body• Terminal hairs- coarse hair8/5/2012 1212413114 41
  42. 42. Arrector pili muscle • extends from the dermal coat of isthmus of the hair follicle to the papillary layer of the dermis. • Gives gooseflesh appearance. • Cholinergic sympathetic supply8/5/2012 1212413114 42
  43. 43. Nail• Nails are plates of keratinized epithelial cells on the dorsal surface of each distal phalanx.• The nearly transparent nail plate and the thin epithelium of the nail bed provide a useful window on the amount of oxygen in the blood by showing the color of blood in the dermal vessels.• Growth rate 1-3mm/month8/5/2012 1212413114 43
  44. 44. • Nails develop from thickened areas of epidermis at the tips of each digit called nail fields.• Later these nail fields migrate onto the dorsal surface surrounded laterally and proximally by folds of epidermis called nail folds.8/5/2012 1212413114 44
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  47. 47. Beau’s line • Transverse depressions due to disruption of proximal matrix mitotic activity. • Common in coronary artery occlusion, hypocalcemia , malnutrition and trauma.8/5/2012 1212413114 47
  48. 48. Onychomadesis/ nail shedding • Proximal detachment of the nail plate from the proximal nail fold.8/5/2012 1212413114 48
  49. 49. Nail pitting • Punctate depressions of the nail plate surface. • Common in psoriasis8/5/2012 1212413114 49
  50. 50. Onychorrhexis • Longitudinal ridging and fissuring of the Plate. • Common in lichen planus . • Normal in aging process.8/5/2012 1212413114 50
  51. 51. Leukonychia • Because of parakeratotic cells with in ventral portion of nail plate, nail appears whitish. • May be hereditary or associated with congenital disorders.8/5/2012 1212413114 51
  52. 52. Koilonychia / spoon shaped nail • Concave nail due to upward eversion of lateral nail edge. • Common in iron deficiency anemia, PVS8/5/2012 1212413114 52
  53. 53. Splinter hemorrhage • One of the diagnostic sign of infective endocarditis. • Also common in vasculitis.8/5/2012 1212413114 53
  54. 54. Nail clubbing • Schamroths window test is the test to define clubbing. • Lovibond’s angle > 165 degree • Common in heart disease, lung disease and GI disease.8/5/2012 1212413114 54
  55. 55. Sebaceous gland• Holocrine type of branched acinar gland.• Acinus consists of rounded cells filled with lipid.• Cell lost by holocrine secretion are replaced by the proliferation of basal cell of acinus.• Open either with in hair follicle(common) or on the skin surface( rare).• These are not under nervous control.• Pilo-sebaceous apparatus.8/5/2012 1212413114 55
  56. 56. • Gland lies within fibrous sheath of hair follicle. • Glandular epithelium represents the external root sheath. • Discharge their secretion to hair shaft and then to skin surface.8/5/2012 1212413114 56
  57. 57. Eccrine sweat gland• Found everywhere in the skin• Secrets watery secretion –sweat which helps in thermoregulation.• It has 2 component- secretory glandular tissue and duct system . Both are coiled structures.• Secretory part has 3 types of cells- clear cells, dark cells and myoepithelial cells.8/5/2012 1212413114 57
  58. 58. Sweat gland sebaceous gland8/5/2012 1212413114 58
  59. 59. Apocrine gland• Apocrine glands are mainly confined to the areolae of the breasts, axillae and genital regions.• produce a viscid, milky secretion which becomes malodorous after the action of skin commensal bacteria.• Open into the hair follicle.• Matured only after the puberty8/5/2012 1212413114 59
  60. 60. Apocrine gland ….• These are much larger in shape than eccrine glands.• Innervated by adrenergic nerve ending not by cholinergic as in eccrine glands.• Glands of moll of eyelid and ceruminous gland of ear are modified sweat gland.8/5/2012 1212413114 60
  61. 61. References• Basic histology ( 11th edition) by Luiz Carlos Junqueira and Jose Carneiro.• WHEATER’S functional histology(5th edition)• General anatomy – by AK Dutta• Langman Medical Embryology (9th edition)• Various websites.8/5/2012 1212413114 61
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