Introduction to the Integumentary System

1. Introduction to the Integumentary System • The integument is the largest system of the body • 16% of body weight • 1.5 to 2 m2 in area • The integument is made up of two parts • ______________________membrane (skin) • Accessory structures (hair, nails, exocrine glands)

2. Introduction to the Integumentary System Fig 5–1

3. Introduction to the Integumentary System • Origin • Ectoderm • Cells that respond to FGF2 turn into nervous tissue. Cells that don’t turn into skin • Connections • Cardiovascular system • Blood vessels in the papillary layer of the dermis • Nervous system • Sensory receptors for pain, touch, and temperature

4. Introduction to the Integumentary System • Functions of Skin • Protectsunderlying tissues and organs (U.V., invaders) • Excretes salts, water, and organic wastes (glands) • Maintains body temperature (insulation and evaporation) • Synthesizes vitamin D3 • Stores lipids • Detects touch, pressure, pain, and temperature

5. Epidermis • The most abundant cells of the epidermis are ____________. • Contain large amounts of keratin • Epidermis is avascular stratified squamous epithelium • Nutrients and oxygen diffuse from capillaries in the dermis • Thin Skin: Covers most of the body • Has four layers of keratinocytes • Thick Skin: Covers the palms of the hands and soles of the feet • Has five layers of keratinocytes • Lacks hair and sebaceous glands

6. Epidermis The S. coreum would be thinner in thin skin. The S. lucidum is found only in thick skin. Fig 5-3

7. Epidermis • Stratum Germinativum (Stratum Basale) • The “germinative layer” • Has many germinative (stem) cells or basal cells • Is attached to basal lamina by hemidesmosomes • Forms a strong bond between epidermis and dermis • Forms ____________________(e.g., fingerprints) • Dermal papillae (tiny mounds) • Increase the area of basal lamina • Strengthen attachment between epidermis and dermis

8. Epidermis Fig. 5-2 Fig 5-4 Dermal papilla: Tiny mounds that (1) increase the area of the basal lamina and (2) strengthen the attachment between the epidermis and the dermis

9. Epidermis • Specialized Cells of Stratum Germinativum • ______________________(1% of cells in the skin) • Found in hairless skin (sensory function) • Respond to touch (trigger nervous system) • ______________________ (3% of cells in the skin) • Contain the pigment melanin • Scattered throughout stratum germinativum

10. Epidermis • Stratum Spinosum • The “spiny layer” • Produced by division of stratum germinativum • Eight to ten layers of keratinocytes bound by desmosomes • Cells shrink until cytoskeletons stick out (spiny) • Continue to divide, increasing thickness of epithelium • Contain dendritic (______________) cells, active in immune response

11. Epidermis • Stratum Granulosum • The “grainy layer” • Cells stop dividing, produce protein fibers, dehydrate, and die • Keratin: • a tough, fibrous protein • makes up hair and nails • Keratohyalin : • dense granules • cross-link keratin fibers

12. Epidermis • Stratum Lucidum • The “clear layer” • Found only in thick skin • Covers stratum granulosum

13. Epidermis • Stratum Corneum • The “horn layer” • Exposed surface of skin • 15 to 30 layers of keratinized cells • Water resistant • Shed and replaced every 2 weeks

14. Epidermis • Keratinization • The formation of a layer of dead, protective cells filled with keratin • Occurs on all exposed skin surfaces except eyes • Skin life cycle • It takes 15–30 days for a cell to move from stratum germinativum to stratum corneum

15. Dandruff is caused by excessive shedding of cells from the outer layer of skin in the scalp. Thus dandruff is composed of cells from which epidermal layer? • Stratum germinativum • Stratum spinosum • Stratum corneum • Stratum granulosum

16. Skin Color • Skin color is influenced by • Two pigments • ______________________: • orange-yellow pigment • found in orange vegetables • accumulates in epidermal cells and fatty tissues of the dermis • can be converted to vitamin A • ______________________: • yellow-brown or black pigment • produced by melanocytes from tyrosine in the stratum germinativum • stored in transport vesicles (melanosomes) • transferred to keratinocytes • Blood circulation (red blood cells)

17. Skin Color (contains melanin) (in melanosome) Fig 5-5

18. Skin Color • Function of Melanocytes • Melanin protects skin from sun damage • Ultraviolet (UV) radiation • Causes DNA mutations and burns that lead to cancer and wrinkles • Production of cholecalciferol (Vit. D3) within epidermal cells • Stimulates secretion of melanocyte stimulating hormone from keratinocytes (this gives you a tan) • Skin color depends on melanin production (bigger melanosomes), ____________ number of melanocytes

19. Skin Color • Localized differences in rates of melanin production by melanocytes: • Freckles: • Small pigmented areas with irregular borders on relatively pale skin. • Most abundant on surfaces with greater exposure to the sun (e.g., face). • Lentigos: • Similar to freckles, but have regular borders and contain abnormal melanocytes. • Senile lentigos (liver spots/age spots): • Variable pigmented areas on sun-exposed skin in older individuals with pale skin.

20. Skin Color • Capillaries and Skin Color • Oxygenated red blood contributes to skin color • Blood vessels dilate from heat, skin reddens • Blood flow decreases, skin pales • Cyanosis • Bluish skin tint • Caused by severe reduction in blood flow or oxygenation

21. Skin Color • Illness and Skin Color • Jaundice • Buildup of bile produced by liver • Yellow color (i.e., yellow pigment accumulates in body fluids) • Addison disease • A disease of the pituitary gland • Skin darkening (i.e., secretion of large qunatities of ACTH, a hormone structurally similar to MSH) • Vitiligo (1% of population) • Loss of melanocytes (attacked by lymphocytes) • Loss of color

22. Skin Cancer • Basal cell carcinoma = most common. • Squamous cell carcinomas = restricted to areas of sun-exposed skin. • Malignant melanomas = metastasize through the lymphatic system. • A = Asymmetry • B = Border • C = Color • D = Diameter

23. Why does the skin of a fair-skinned person appear red during exercise in hot weather? 1. Sunlight stimulates erythrocyte production in skin. 2. Blood is diverted to the superficial dermis to eliminate heat. 3. Sunlight bleaches fair skin, allowing blood to be seen. 4. Heat stimulates cutaneous blood vessels, causing leaks.

24. Vitamin D3 • Vitamin D3 • Epidermal cells in s. spinosum and s. basale produce cholecalciferol (vitamin D3) • In the presence of UV radiation • Liver and kidneys convert vitamin D3 into calcitriol • To aid absorption of calcium and phosphorus • Essential for bone maintenance and growth • Insufficient vitamin D3 • Can cause __________________ in children and osteomalacia in adults.

25. Vitamin D3 Fig 5-7

26. In some cultures, women must be covered completely, except for their eyes, when they go outside. Explain why these women exhibit a high incidence of problems with their bones. 1. UV light prevents calcium deposition in bones. 2. Melanin production is necessary for bone growth. 3. Cloth prevents oxygen from diffusing into skin and bones. 4. UV light is necessary to produce the hormone cholecalciferol (vitamin D3).

27. Epidermal Growth Factor (EGF) • Is a powerful peptide growth factor • Is produced by glands (salivary and duodenum) • Is used in laboratories to grow skin grafts • Functions of EGF • Promotes division of germinative cells • Accelerates keratin production • Stimulates epidermal repair • Stimulates glandular secretion

28. The Dermis • The Dermis • Is located between epidermis and subcutaneous layer • Anchors epidermal accessory structures (hair follicles, sweat glands) • Has two components • Outer papillary layer • Deep reticular layer

29. The Dermis • The Papillary Layer • Consists of areolar tissue • Contains smaller capillaries, lymphatics, and sensory neurons • Has dermal papillae projecting between epidermal ridges • The Reticular Layer • Consists of dense irregular connective tissue • Contains larger blood vessels, lymph vessels, and nerve fibers • Contains collagen and elastic fibers • Contains connective tissue proper

30. The Dermis • Dermatitis • An inflammation of the papillary layer • Caused by infection, radiation, mechanical irritation, or chemicals (e.g., poison ivy) • Characterized by itch or pain (due to abundance of sensory receptors in skin.

31. The Dermis • Dermal Strength and Elasticity • Presence of two types of fibers • Collagen fibers: • very strong, resist stretching but bend easily • provide flexibility • Elastic fibers: • permit stretching and then recoil to original length • limit the flexibility of collagen fibers to prevent damage to tissue • Properties of flexibility and resilience Skin turgor:

32. Skin Damage (dermal level) • Sagging and wrinkles (reduced skin elasticity) are caused by: • Dehydration (loss of skin turgor) • Age • Hormonal changes • UV exposure • Stretch Marks (Thickened tissue resulting from excessive stretching of skin due to): • Pregnancy • Weight gain/loss • Note: Tetinoin (Retin-A), a derivative of Vit. A, increases blood flow to dermis and stimulates dermal repair leading to a decrease in wrinkles.

33. The Dermis • Lines of Cleavage • Collagen and elastic fibers in the dermis • Are arranged in parallel bundles • Resist force in a specific direction • Lines of cleavage establish important patterns • A parallel cut remains shut, heals well • A cut across (right angle) pulls open and scars Fig 5.8

34. The Hypodermis • The __________________ layer or hypodermis • Lies below the integument • Is connected to the reticular layer of integument by connective tissue fibers • Is made of elastic areolar and adipose tissues • (Subcutaneous fat deposits can be reduced by lipoplasty) • Has few capillaries and no vital organs (only the superficial region or reticular layer of the dermis has large arteries and veins. • Is the site of subcutaneous injections using hypodermic needles

35. Hair • Hair, hair follicles, sebaceous glands, sweat glands, and nails • Are integumentary accessory structures • Appendages of the skin that represent specializations of keratinocytes that extend from the connective tissue to the skin • Are derived from embryonic epidermis • Are located in dermis • Project through the skin surface

36. Hair • The Hair Follicle • Is located deep in dermis • Produces nonliving hairs • Is wrapped in a dense connective tissue sheath • Base is surrounded by sensory nerves (root hair plexus)

37. Hair • Hair Shaft Structure • Medulla • The central core • Cortex • The middle layer • Cuticle • The surface layer Cross-Section Through a Hair Follicle Fig 5.10

38. Hair • The human body is covered with hair, except • Palms • Soles • Lips • Portions of external genitalia • Functions of Hair • Protects and insulates • Guards openings against particles and insects • Is sensitive to very light touch

39. Hair • Accessory Structures of Hair • _______________________ • Involuntary smooth muscle • Causes hairs to stand up • Produces “goose bumps” • ________________________ • Lubricate the hair • Control bacteria Fig 5.10

40. Hair • Hair Color: • Produced by melanocytes at the hair papilla • Determined by genes • Alopecia Areata: • Ability to produce hair is gone (2% of population) • Due to immune system attack on the hair follicles • Male Pattern Baldness: • Hair growth is inhibited by testosterone receptor alterations (50% of men over 50) • Rogaine can stimulate production of growth factors that stimulate weakened hair follicles to create larger amounts of hair

41. Which two events are possible results of the contraction of the arrector pili muscle? 1. Goose bumps/release of sebum 2. Sweating/contraction of underlying muscles 3. Goose bumps/localized increase in blood flow 4. Localized pallor/release of sebum

42. Sebaceous Glands and Sweat Glands • Exocrine Glands in Skin • Sebaceous glands (oil glands) • Simple branched alveolar glands are associated with hair follicles • Holocrine glands • Secrete sebum (lipids and other stuff that lubricate and protect the epidermis while inhibiting bacteria) • Sweat glands • Two types: apocrine glands and merocrine (eccrine) glands • Watery secretions

43. Clinical Correlations • Folliculitis: • Local inflammation of hair follicle as a result of a bacterial infection. • Furuncle or “boil”: • Abscess from blockage of a gland’s duct. • Acne: • Due to increased concentration of sex hormones during puberty. • Seborrheic dermatitis: • Inflammation around abnormally active sebaceous glands • Sebaceous glands and sweat glands

44. Sebaceous Glands and Sweat Glands • ____________________ sweat glands • Found in armpits (axillae), around nipples, and groin • Secrete products into hair follicles • Produce sticky, cloudy secretions • Break down and cause odors • Surrounded by myoepithelial cells • Squeeze apocrine gland secretions onto skin surface • In response to hormonal or nervous signal

45. Sebaceous Glands and Sweat Glands • __________________ (Eccrine) sweat glands • Widely distributed on body surface • Especially on palms and soles • Coiled, tubular glands • Discharge directly onto skin surface • Sensible perspiration (water is excreted by sweat glands) • Water, salts, and organic compounds • Functions of merocrine sweat gland activity • Cools skin • Excretes water and electrolytes • Flushes microorganisms and harmful chemicals from skin

46. Other Integumentary Glands • Mammary glands: • Anatomically related to apocrine sweat glands • Sexual and pituitary hormones control their development and secretion • Produce milk • Ceruminous glands: • Modified sweat glands in external ear • Produce cerumen (earwax) • Protect the eardrum

47. Control of Glandular Secretions • Control of Glands • Autonomic nervous system • Controls sebaceous and apocrine sweat glands • Works simultaneously over entire body • Merocrine sweat glands • Are controlled independently • Sweating occurs locally • Thermoregulation • Is the main function of sensible perspiration • Works with cardiovascular system • Regulates body temperature

48. What are the functions of sebaceous secretions? 1. Inhibits the growth of bacteria 2. Lubricates and conditions the surrounding skin 3. Lubricates and protects the keratin of the hair shaft 4. All of the above

49. Nails • Nails protect fingers and toes • Made of dead cells packed with keratin • Metabolic disorder can change nail structure, shape or appearance Fig 5-13

50. Nails (Cuticle) Fig 5-13