Introduction- Chapter 6

3. Introduction- Chapter 6 Skin (integument) is body’s largest organ Approximately 1.6 to 1.9 m2 in average-sized adult Integumentary system describes the skin and its appendages— the hair, nails, and skin glands

4. Structure of the Skin • Skin classified as a cutaneous membrane • Two primary layers—epidermis and dermis; joined by dermal-epidermal junction • Hypodermis lies beneath dermis

5. Structure of the Skin • Thin and thick skin • “Thin skin”—covers most of body surface • 1 to 3 mm thick • “Thick skin”—soles and palms • 4 to 5 mm thick • Makes fingerprints • No hair

6. Structure of the Skin • Epidermis • Cell types • Keratinocytes • Melanocytes • Langerhans cells

7. Keratinocytes • constitute over 90% of cells present • principal structural element of the outer skin • Arranged in strata, or layers

8. Melanocytes • pigment-producing cells (5% of the total) • contribute to skin color • filter ultraviolet light – decrease the amount of UV light that can penetrate into the deeper layers of the skin

9. Langerhans cells they play a role in immune response Originate in the bone marrow Function with specialized leukocytes called helper T cells, to trigger immune response

10. Structure of the Skin • Epidermis • Cell layers- 5 Layers (deep  superficial) • Stratum germinativum (growth layer)—describes the stratum spinosum and stratum basale together • Stratum basale (base layer) • Stratum spinosum (spiny layer) • Stratum granulosum (granular layer) • Stratum lucidum (clear layer) • Stratum corneum (horny layer)

11. Structure of the Skin • Epidermis • The cells form in the basale layer and degenerate and fill with keratin as they move up to the surface • This is keratinization

12. section reveals epidermis containing basal, spinous, granular keratinocytes and stratum corneum. Dermis contains numerous viable fibroblasts. 400X)

13. 1. Stratum basale (base layer- deepest) • single layer of columnar cells • only these cells undergo mitosis  migrate through the other layers until they are shed The renewal of the human epidermis takes about 3 to 4 weeks.

14. 2. Stratum spinosum (spiny layer) cells arranged in 8 to 10 layers with desmosomes (bridges) that pull cells into spiny shapes cells rich in RNA  protein synthesis to produce keratin

15. 3. Stratum granulosum (granular layer) cells arranged in two to four layers filled with granules  makes keratin contain high levels of lysosomal enzymes  they’re starting to degenerate Nuclei absent May not be in regions of thin skin

16. 4. Stratum lucidum (clear layer) Closely packed and clear keratinocytes cells filled with eleidin (ay lee din)  blocks water penetration or loss (eventually makes keratin) absent in thin skin (in thick skin- hands and feet) Nuclei absent

17. 5. Stratum corneum (horny layer) • Dead, squamous cells • most superficial layer • dead cells filled with keratin water-repellent protein • Cell membranes are thick and chemically resistant • Also called barrier area because it functions to prevent water loss

18. Structure of the Skin Thin Skin Thick Skin

19. Wrinkled Fingers and Toes • FYI: • dead cells in stratum corneum absorb water • (deeper layers do NOT) • When swollen water-filled cells expand over the normal sized cells below, the skin wrinkles

20. Structure of the Skin • Epidermis • Epidermal growth and repair • Turnover or regeneration time refers to time required for epidermal cells to form in the stratum basale and migrate to the skin surface— about 35 days • Shortened turnover time will increase the thickness of the stratum corneum and result in callus formation

21. Structure of the Skin • Epidermal growth and repair continued • Normally 10% to 12% of all cells in stratum basale enter mitosis daily • Each group of 8 to 10 basal cells in mitosis with their vertical columns of migrating keratinocytes is called an epidermal proliferating unit, or EPU

22. Structure of the Skin Specific staining of the indicated protein is displayed as a red band localized at the dermal/epidermal junction. • Dermal-epidermal junction • Definite basement membrane • “glues” the epidermis to the dermis below • Partial barrier to the passage of some cells and large molecules

23. Blisters • FYI: • Caused by injury to cells in epidermis OR • From separation of dermal-epidermal junction

24. Structure of the Skin Sunburn cell formation in EpiDerm-FT following solar UV-irradiation. H&E stained paraffin sections were prepared from EpiDerm-FT 24 hr after irradiation. Sunburn cells are indicated by arrows. • Dermis (corium) • Sometimes called “true skin”—much thicker than the epidermis and lies beneath it • Gives strength to the skin

25. Structure of the Skin • Dermis (cont.) • Contains various structures: • Arrector pili muscles and hair follicles • Sensory receptors • Sweat and sebaceous glands • Blood vessels • Rich vascular supply plays a critical role in temperature regulation homeostasis

26. Structure of the Skin • Dermis (cont.) • 2 Layers of dermis: • Papillary layer • Reticular layer

27. Dermis-Papillary Layer • composed of dermal papillae that project into the epidermis  fingerprints- used for grasping and gripping tools • contains loose connective and elastic fibers • contains the dermal-epidermal junction • Like egg crate foam mattress pad

28. Dermis- Reticular Layer • contains interlacing collagenous fibers and elastic fibers  make the skin tough yet stretchable • when processed from animal skin, produces leather • Attachment point for muscle fibers (smooth and skeletal) • Contains arrector pili muscles

30. Arrector pili muscles Bundle of smooth muscles on each hair follicle Makes the hair “stand on end” Occurs due to fright or cold Causes erection of nipples and elevation of testes

31. Where are the arrector pili? • Where is the adipose tissue? • Is adipose deep or superficial to the stratum lucidum?

32. Dermis • Dermal growth and repair: • The dermis does NOT continually shed and regenerate • During wound healing, begins forming a dense mass of new connective fibers  scar • If elastic fibers in dermis stretch too much, they TEAR and form  stretch marks • Eventually lose color- NOT due to cocoa butter

33. FYI • If an incision “cuts across” cleavage lines (Langer’s lines), stress tends to pull the cut edges apart and may retard healing. • Surgical incisions parallel to cleavage lines are subjected to less stress and tend to heal more rapidly.

34. Hypodermis • Also called subcutaneous layer or superficial fascia • Deep to the dermis • forms connection between the skin and other structures • NOT part of the skin

35. Skin Color • Melanin • Basic determinant of skin color • Melanin formed by melanocytes • Albinism— congenital absence of melanin

37. Functions of the Skin (Table 6-1 Page 171) • Protection • Physical barrier • Prevents dehydration • Sensation • Pain • Heat and cold • Pressure and touch

38. Functions of the Skin cont’d (Table 6-1 Page 171) • Movement & growth • Imagine moving without elastic skin • Endocrine (hormones) • vitamin D production • Excretion (minor role) • Water & Urea/ammonia/uric acid

39. Functions of the Skin cont’d (Table 6-1 Page 171) • Immunity • Phagocytic cells (“phago”- to eat) (-”cyte”- cell) • Langerhans cells • Temperature Regulation • Heat loss or retention

40. Temperature Regulation- Vasodilation • Heat loss—approximately 80% of heat loss occurs through the skin • Increased blood flow to epidermis • Decreased blood flow to organs • Redness after exercise

41. Temperature Regulation- Vasoconstriction • Heat retention • Decreased blood flow to skin • Increased blood flow to organs • Turning white • Vasoconstriction

42. How do we sense touch? • MANY receptors in our skin (mostly dermis) allow for different “touch” stimuli • Meissner’s corpuscle- detects light touch- superficial dermis • Pacinian corpuscle- detects pressure- deep dermis Receptors send signals to the brain (those signals were called?)

43. Somatosensory Cortex in Brain • Receptors send action potentials to specialized part of brain  somatosensory cortex (“soma”- body) (“cortex”- outermost, superficial) • Each part of the body corresponds with a particular area in the cortex • Also a corresponding Motor cortex

44. Homunculi (Page 394) • Both sensory & motor cortex have “homunculi” (little man) • Hands and face- large part of cortical area • Most important for survival

45. Two point discrimination The density of receptors varies If the hands and the face have the most cortical area, where do you think the densest area of receptors will be?

46. Skin Glands • 3 Types: • Sweat (2 types) • Sebaceous • Ceruminous

47. Skin Glands- Sweat Glands • Eccrine glands • Most numerous sweat glands; very small • Distributed over total body surface except a few places (ear canal, lips) • Simple, coiled, tubular glands • Secrete sweat  constant core temperature

48. Skin Glands- Sweat Glands 2. Apocrine glands • Located deep in subcutaneous layer • Limited distribution—axilla (armpit), areola of breast, and around anus • Large (> 5 mm in diameter) • Connected to hair follicle • Begin to function at puberty

49. Skin Glands Stages of acne. (A) Normal follicle; (B) open comedo (blackhead); (C) closed comedo (whitehead); (D) ; (E) pustule v • Sebaceous glands • Secrete sebum (oil) • Hair and skin • prevents excessive water loss from the skin • antifungal activity • dermis except in palms and soles • Secretion increases in adolescence • Oxidated sebum accumulations  blackheads

50. Blackhead Whitehead Papules