Integumentary System

1. Integumentary System BIOL241 INTERCONNECTEDNESS

2. Outline • Structure and function of integument • Epidermis • Dermis • Hypodermis • Skin color • Skin cancer • Accessory structures of Integument • Temperature regulation • Aging • Skin Injury and regeneration

3. Integumentary System (skin)

4. Skin (Integument) • Consists of three major regions • Epidermis – outermost superficial region • Dermis – middle region these two together make up the cutaneous membrane) • Subcutaneous region (aka Hypodermis or (superficial fascia) – deepest region • Also includes all the accessory structures found in the skin (hair, glands, etc.)

5. What are some of the functions of skin? • Protection • Excretion (salts, water, wastes) • Maintenance of body temperature • Metabolism (Vitamin D3) • Storage (lipids, blood reserve) • Detection of sensation • Note: skin keeps water in as well as keeping it out

6. Hair shaft Pore Dermal papillae (papillary layer of dermis) Epidermis Meissner's corpuscle Free nerve ending Reticular layer of dermis Sebaceous (oil) gland Arrector pili muscle Dermis Sensory nerve fiber Eccrine sweat gland Pacinian corpuscle Artery Hypodermis (superficial fascia) Vein Adipose tissue Hair root Hair follicle Eccrine sweat gland Hair follicle receptor (root hair plexus) Figure 5.1

7. Parts of the Cutaneous Membrane • Outer epidermis: • superficial epithelium (epithelial tissues) Composed of keratinized stratified squamous epithelium, consisting of four distinct cell types and four or five layers • Cell types include keratinocytes, melanocytes, Merkel cells, and Langerhans’cells • Outer portion of the skin is exposed to the external environment and functions in protection • Inner dermis: • connective tissues (what are they?)

8. Epidermis • Avascular stratified squamous epithelium • Nutrients and oxygen diffuse from capillaries in the dermis to lower layers of epidermis

9. Cells of the Epidermis • Keratinocytes – produce the fibrous protein keratin • Melanocytes – produce the brown pigment melanin; cell bodies in upper dermis that have extensions into the epidermis • Langerhans’ cells – epidermal macrophages that help activate the immune system • Merkel cells – function as touch receptors in association with sensory nerve endings

10. Organization of the Epidermis: Figure 5–2

11. Layers of the Epidermis Figure 5.2b

12. Thin Skin Covers most of the body Has 4 layers of keratinocytes Thick skin Covers the palms of the hands and soles of the feet Has 5 layers of keratinocytes The thick of it

13. Layers of the epidermis are known as “strata”

14. Layers of the Epidermis Top: Free surface of skin - stratum corneum - stratum lucidum - stratum granulosum - stratum spinosum • stratum germinativum Bottom: Basal lamina

15. 1. Stratum Germinativum (Basale) • The “germinative layer” (or basal layer): • Deepest epidermal layer firmly attached to the basal lamina and dermis via hemidesmosomes • Consists of a single row of the youngest keratinocytes along with projections of melanocytes • Cells undergo rapid division,

16. Structures of Stratum Germinativum • Epidermal ridges – • cause the pattern of your fingerprints; • created by presence of: • Dermal papillae (tiny mounds): • increase the area of basal lamina • Function?

17. Fingerprints are epidermal ridges • Which themselves are negative images of the dermal papilla Figure 5–4

18. 2. Stratum Spinosum • “spiny layer” • 8-10 cells (keratinocytes) thick • Immature keratinocyte cells continue to divide, then shrink until cytoskeletons stick out (spiny), a system of intermediate filaments attached to desmosomes • Melanin granules and Langerhans’ cells are abundant in this layer

19. 3. Stratum Granulosum • “grainy layer” • Consists of 3-5 cell layers of keratinocytes • Cells stop dividing in this layer, dehydrate and produce tons of proteins: • Keratohyaline • Keratin

20. 4. Stratum Lucidum • The “clear” layer • Only found in thick skin • Covers granulosum • Consists of a few rows of flat, dead keratinocytes filled with keratin • The layer appears, ironically, very thin in slides • Probably functions to hold on the thicker corneum layer above

21. A note on thick vs. thin skin • Thick skin has an extra layer (lucidum) but that is NOT the reason that it is thicker than thin skin. • The reason is the other layers are thicker in thick skin than in thin skin, esp. s. corneum

22. 5. Stratum Corneum • The “horn layer”: • exposed surface of skin • 15 to 30 layers of keratinized cells • Accounts for ¾ of epidermal thickness • water resistant (not water proof!) • Protects from abrasion and penetration • shed and replaced every 2 - 4 weeks Skin is often called a cornified epithelium

23. Skin Life Cycle • It takes 15–30 days for a cell to move from stratum germinosum to stratum corneum

24. Layers of the Epidermis Figure 5.2b

25. Dermis consists of connective tissue

26. The Dermis • Deeper part of cutaneous layer • Located between epidermis and subcutaneous layer • Anchors epidermal accessory structures (hair follicles, sweat glands) • Contains strong, flexible connective tissue • Cell types include fibroblasts, macrophages, and occasionally mast cells and white blood cells • Has 2 components: • outer papillary layer • deep reticular layer

27. The Papillary Layer • Consists of areolar tissue with collagen and elastic fibers • Contains smaller capillaries, lymphatic vessels, and sensory neurons • Has dermal papillae projecting between epidermal ridges

28. The Reticular Layer • Consists of dense irregular connective tissue • Accounts for approximately 80% of the thickness of the skin • Contains larger blood vessels, lymph vessels, and nerve fibers • Collagen fibers in this layer add strength and resiliency to the skin • Elastin fibers provide stretch-recoil properties Contains collagen and elastic fibers

29. The Subcutaneous Layer • Subcutaneous layer(superficial fascia or hypodermis): • loose connective tissue - areolar and adipose • connected to the reticular layer of dermis by connective tissue fibers • stabilizes the skin • allows separate movement • Insulates and stores energy • location of hypodermic injections

30. Skin Color • Skin color depends on three pigments: • Melanin -yellow to reddish-brown to black pigment, responsible for dark skin colors • Freckles and pigmented moles – result from local accumulations of melanin • Produced by melanocytes just below stratum germinativum • Stored in transport vesicles (melanosomes) • Projections extend up into epidermal layers • Some transferred to keratinocytes • Hemoglobin in red blood cells • Carotene (minor factor)

31. Melanocytes Figure 5–5

32. Function of Melanocytes • Ultraviolet (UV) radiation: • causes DNA mutations and burns which lead to cancer and wrinkles • Melanin protects skin from sun damage • Pigment molecules absorb UV and diffuse it, preventing it from penetrating to the DNA of cells in the strata germinativum and spinosum

33. Melanocytes • Skin color depends on amount of melanin production per melanocyte, not number of melanocytes.

34. Capillaries and Skin Color • Oxygenated red blood contributes to skin color: • blood vessels dilate from heat, skin reddens • blood flow decreases, skin pales • corpses appear pale and lighter because they lack this coloration

35. Cyanosis • Bluish skin tint • Caused by severe reduction in blood flow or oxygenation • The veins appear blue when blood is deoxygenated but deoxegenated blood is NOT blue – it is darker red

36. Illness and Skin Color • Jaundice: • buildup of bile produced by liver • yellow color • Addison’s disease: • and other diseases of pituitary gland • skin darkening • Vitiglio: • loss of melanocytes • localized loss of color

37. Vitamin D • The “sunshine vitamin” • Epidermal cells produce cholecalciferol(vitamin D3) in the presence of UV radiation • Liver and kidneys convert vitamin D into calcitriol which aids in absorption of calcium and phosphorus at the intestines • Insufficient vitamin D: • can cause rickets • Symptoms?

38. Skin Damage • Sagging and wrinkles (reduced skin elasticity) are caused by loss (or decresed production) of collagen and elastin by fibrolasts, due to: • dehydration • age • hormonal changes • UV exposure

39. Skin Cancer Figure 5–6

40. Skin Cancer • The three major types of skin cancer are: • Basal cell carcinoma (s. germinativum) • Squamous cell carcinoma (s. spinosum) • Melanoma • The vast majority of all skin cancers are of the first two types (basal and squamous) • They rarely metastasize and can be taken care of by excision; thus they are not included in most cancer statistics

41. Melanoma • Cancer of melanocytes is the most dangerous type of skin cancer because it is: • Highly metastatic • Resistant to chemotherapy • Kind of ironic because they evolved to protect basal cells, but basal cell cancer has a much better prognosis

42. Skin Cancers Figure 5.7a–c

43. Skin color tradeoff? • Vitamin D is necessary for bone strength, but if there is not much UV (high latitudes), individuals with a lot of melanin have trouble getting enough Vitamin D. But when UV is plentiful, they are better protected from skin cancer. • On the other hand, in places with a lot of UV (low latitudes), people with very little melanin are at high risk of skin cancer. But they are more likely to get enough UV from the sun in low UV regions.

45. Use Protection!

46. Accessory Structures of the Integument • Are of epidermal lineage (cells are modified epithelial cells) • “Originate” in the dermis (this is where you look to find them) • Extend through the epidermis to skin surface: • Hair ad follicles • nails • multicellular exocrine glands (sebaceous, sweat)

47. The Hair Follicle • Is located deep in dermis • Is made of epidermal tissue • Produces nonliving hairs • Is wrapped in a dense connective-tissue sheath • Base is surrounded by sensory nerves

48. Structures of Hair and Follicles Figure 5–9a

49. Structures of Hair • Arrectorpili: • involuntary smooth muscle • causes hairs to stand up • produces “goose bumps” • Sebaceous glands: • lubricate the hair • control bacteria

50. Properties of hair • As hair is produced, it is keratinized: • middle medulla contains flexible soft keratin • outer cortex and cuticle contain stiff hard keratin • Hair Color • Produced by melanocytes at the hair papilla (base) • Determined by genes