Chapter 6: Skin and the Integumentary System

1. Chapter 6: Skin and the Integumentary System

2. Skin: • Largest organ • Otherwise known as cutaneous membrane • Forms barrier between our internal environment and the external world • Vital in maintaining homeostasis • Regulates body temperature • Prevents water loss • Houses sensory receptors • Synthesize biochemicals • Excretes wastes (very small amount) • Makes up integumentary system • Includes skin and accessory organs Introduction

3. Layers of skin

4. Two layers: • 1) Epidermis: • Outer layer • Composed of stratified squamous epithelial tissue • 2) Dermis • Inner layer • Contains: • Connective tissues (collagenous fibers, elastic fibers, blood) • Epithelial tissue • Smooth muscle tissue • Nervous tissue Layers

6. Other layers: • 1) Basement: • Anchors dermis to epidermis • 2) Hypodermis or Subcutaneous: • Beneath skin • Contains masses of loose connective and adipose tissue • Binds skin to underlying organs Layers

7. Characteristics: • Lacks blood vessels • Composed of stratified squamous epithelium tissue • Divides and grow • Pushes older cells away from dermis and towards surface • Become less and less nourished and eventually die • Keratinization: older cells harden and die (cytoplasm fills with keratin protein) • Healthy skin: balances cell division with cell death • Areas of continual wear: causes fast cell division and thickened layers called calluses (hands, soles of feet) and corns (toes) Epidermis

9. Layers of epidermis: • Stratum corneum: • Hardened outer layer (mostly dead, keratinized cells) • Stratum lucidum: • Only present in palms and soles of feet • Hardened, thickened layer • Stratum granulosum: • Very thin layer • Stratum spinosum: • More spacious, numerous • Stratum basale: • Nourished by blood vessels in dermis, newest cells, most nourished, next to basement membrane Epidermis

11. Characteristics, cont.: • Important protective functions • Shields moist underlying tissues against: • Excessive water loss • Mechanical injury • Effects of chemicals, mutagens, pollutants • Pathogens • Contains melanocytes (cells which produces melanin – dark pigment that provides skin color to protect against UV) • Albinism: inability to produce melanin Epidermis

12. Largelydue to amount of melanin • All people have the same average number of melanocytes • Differences in color: come from the AMOUNT of melanin the melanocytes produce • Most genetically determined • Environmental effects: UV (sun and artificial), X-rays • Physiological effects: blood in dermal layer • Red: well-oxygenated; • Blue (very dark red)-deoxygenated • Called cyanosis • Yellow (diet) – yellow vegetables containing B-carotene Epidermis: Skin Color

14. Characteristics: • Contain dermal papillae (projections of the dermis which extend into epidermal spaces) • Fingerprints are as a result of these projections (determined by genes) • Binds epidermis to underlying tissues • Composed of dense connective tissue (includes collagenous and elastic fibers) • Contains blood vessels (supply nutrients to all skin cells, regulate body temperature) • Nerve cells scattered throughout • Contain hair follicles, sebaceous glands, sweat glands Dermis

15. Characteristics: • Otherwise known as hypodermis • Contains loose connective and adipose tissues • Composed of collagenous and elastic fibers (continuous with those of dermis) • No sharp boundary between this layer and dermis • Adipose: • Insulates • Regulates body temp (conserving body heat, not allowing heat to enter) • Contains blood vessels Subcutaneous Layer

16. Accessory glands of skin

17. Characteristics: • Protective coverings • Consists of nail plate (overlies surface of the skin called the nail bed) • White, base of nail (lunula) – covers the most actively growing portion of epidermis • As cells divide here, they keratinize • Then these keratinized cells become scales that become part of nail plate • Thumb: slowest • Middle: fastest Nails

18. Characteristics: • Present everywhere BUT palms, soles, nipples • Hair develops from group of epidermal cells at the base of hair follicle • Follicle extends from surface into dermis • Cells nourished via dermal blood vessels • As cells grow and divide, pushed upward • As push upward, keratinize and die Hair Follicles

19. Characteristics: • Remains become structure of hair (shaft extends outward) • Color: determined by genes (direct color and amount of pigment) • Arrectorpili muscle – smooth muscle, attach to each hair follicle • These muscles can be stimulated to contract (when heat is needed) – produces gooseflesh (goosebumps) Hair Follicles

20. Characteristics: • Otherwise known as oil glands • Closely associated with hair follicles • Holocrine glands (secrete oily mixture of fatty and sebum – cellular wastes) • Secrete mixture through small ducts • Sebum – helps keep hair and skin soft, pliable and waterproof Sebaceous glands

22. Characteristics: • Otherwise known as sudoriferous glands • Exocrine gland • Widespread • Consists of: • Tiny coiled tube laying in subcutaneous layer or deep dermal layer • Most numerous type: eccrine (respond to body temperature changes) • Common forehead, neck and back (produce profuse sweat) Sweat glands

23. Characteristics: • Sweat (fluid) carried away via duct which leads to pore (on surface) • Sweat is mostly water • Contains small amount of salt, wastes (urea, uric acid) • Apocrine glands: • Become active at puberty • Secrete via same mechanism as eccrine glands • Secrete when person is emotionally upset, frightened or in pain • Most numerous in groin and axillary region • Mammary glands: • Modified sweat glands, secrete milk Sweat glands

25. Other functions of skin

26. Humans: Internal temp = 98.6oF (37oC) • Mammals must balance heat gained with heat lost • Skin plays vital role in maintaining this homeostatic mechanism • As body temp drops, nerve impulses stimulate structures in skin to conserve heat • Blood vessels contract, decreasing flow (reduces heat loss) • Sweat glands are inactive • Muscle contract – producing heat Regulate body temperature

27. As body temp rises, nerve impulses stimulate structures in skin to release heat • Blood dilation (more blood enter, heat carries/escapes) • Warm blood reaches hypothalamus (which controls body temperature set point) • Eccrine sweat glands release sweat (as sweat evaporates, heat is carried away from surface) • Hot vs. Cold Regulate body temperature

28. Inflammatory response: • Normal response to injury or stress • Red, painful, warm, swollen • Becomes red when blood vessels dilate and become more permeable (forces fluids to leave vessels and enter tissue) • Advantage: Provides tissue with more nutrients and oxygen (aid in healing process) Healing Wounds

30. Shallow cut • Epithelium will divide rapidly, filling in gap • Deep cut • Blood vessels break, clot forms • Clot and tissues form scab (protect underlying tissues) • Fibroblasts migrate to injury and begin forming new collagenous fibers (bind edges of wound together) • Scar: forms when connective tissue appears on surface Healing Wounds

31. Skin Disorders

32. Herpes Alopecia Dermatitis Keloid Boil

33. Psoriasis Mole Eczema Wart