Skin & Appendages

1. Skin & Appendages I. General Concepts and Considerations

2. A. Heaviest single organ of body • 16% of total body weight • 1.2 - 2.3 m2 surface area Epidermis Dermis Hypodermis

3. C. Functions of the skin • Protection from injury, desiccation, infection • Regulation of body temperature • Absorption of UV radiation for synthesis of vitamin D • Reception of sensory stimuli • Secretion of protective lipids, milk • Dermis and epidermis interdigitate via dermal papillae - best developed in areas exposed to shearing stress • Classified as thick or thin depending on the thickness of epidermis

4. Skin & Appendages II. Epidermis

5. A. Characteristics • Keratinized stratified squamous epithelium • Regenerated by keratinocytes • Formed by five layers or strata • turnover from basal to superficial varies from site to site • 25-30 days fastest; 40-50 days slowest • Downgrowths produce sweat glands and hair follicles

6. Epidermis

7. B. Stratum Basale • Deepest layer, attached to basement membrane by hemidesmosomes • Keratinocytes, large euchromatic nuclei, mitotically active • Melanocytes and Merkel cells

8. C. Stratum Spinosum • A few layers of prickly keratinocytes • Intercellular bridges formed by desmosomes • Round, euchromatic nuclei, mitotically active • Concentrated tonofilaments in cytoplasm • Upper cells cemented together to waterproof the skin • Langerhans cells & cytoplasmic projections of melanocytes • Psoriasis

9. D. Stratum Granulosum • Cells accumulate keratohyalin granules and bundles of intermediate keratin filaments • All cells produce membrane-coated granules • Keratohyalin granules composed of histidine- & cystine-rich proteins that glue keratin filaments together • Nuclei are present

10. E. Stratum Lucidum • Clear homogenous layer • Nuclei and organelles are not present • Cells contain eleidin

11. F. Stratum Corneum – Thick Skin • Outermost layer, formed of dead cells • Surface cells continuously desquamated

12. F. Stratum Corneum – Thin Skin

13. Langerhans Cell Melanocytes G. Other cellular components • Melanocytes • Langerhans cells • Merkel's cells

14. 1. Melanocytes • structure • derivation • melanosomes • keratinocytes • skin color • distribution • races • tanning

15. 1. Melanocytes

16. 2. Langerhans cells • dendritic-shaped cells derived from the bone marrow • present in all layers but mainly in stratum spinosum • ovid, pale-staining nuclei, cytoplasm with granules, processes • function as APCs • increase in number in chronic inflammatory skin diseases

17. 3. Merkel's cells • found in thick skin; scanty and difficult to find in thin skin • present in stratum basale • contain small dense-core granules • receive afferent nerve terminals, believed to function as sensory - mechanoreceptors

18. H. Types of Skin

19. Epidermis Epidermis H. Types of Skin Thin SkinThick Skin Covers entire body except palms and soles On palms and soles of the feet (0.5 mm on the eyelid, 5 mm on the back) (0.8 mm to 1.5 mm thick) Thin epidermis, dermis can be thick Thick epidermis Hair follicles with sebaceous glands Hairless thus no sebaceous glands Sweat glands Sweat glands

20. Skin & Appendages III. Dermis

21. A. Characteristics • Dense irreg. FECT • Contents • Aging • Blood vessels

22. 400X 40X Epidermal-Dermal Junction • Scalloped margin consisting of epidermal pegs and dermal papillae • Strengthens attachment of epidermis to the underlying dermis Epidermal peg Dermal papilla

23. Dermis

24. Blood Vessels of Dermis

25. B. Layers • Papillary Layer - loose FECT that forms the dermal papillae, loops of small blood vessels and capillaries, nerve endings

26. B. Layers • Reticular Layer - dense irregular FECT that forms bulk of dermis, with blood vessels and a-v shunts, lymphatics and nerves

27. B. Layers • Erector Pili Muscle • bundles of smooth muscle, attached to hair follicles in dermis and papillary layer of dermis • contraction elevates hairs (makes them more vertical) and produces goose bumps

28. 3. Erector Pili Muscle

29. C. Nerve Supply • Sympathetic NS • Afferent fibers • Free nerve endings • Pacinian Corpuscles • Meissner's Corpuscles

30. Paccinian Corpuscle

31. Meisner’s Corpuscle

32. D. Blisters

33. E. Dermatitis

34. Wound Repair

35. Skin & Appendages IV. Glands

36. Eccrine sweat glands • Characteristics • Dark cells • Clear cells • Myoepithelial cells • Ducts • Dermis & epidermis • Produce sweat • Sweat

37. B. Apocrine Sweat Glands Hair follicle Hair follicle Sebaceous gland Sebaceous gland • In axillary, areolar & anal regions • Viscous secretion • Empty into hair follicles

38. C. Sebaceous Glands • Holocrine gland • Hair follicle • Non-hair • Activity • Sebum • Number & size • Locations • Absent • Acne

39. C. Sebaceous Glands

40. Skin & Appendages V. Appendages

41. A. Hair • Derived from epidermal epithelium • Locations • Medulla, cortex, & cuticle • Root of hair, hair bulb, dermal papilla • Rate of growth • Hair color due to melanin

42. B. Nails • Location • Nail plate & nail bed • Eponychium (cuticle) • Hyponychium • Growth

43. B. Nails