1. Chapter 6: Skin and the Integumentary System

2. Introduction Makes up integumentary system 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

3. Layers of skin

4. Layers Two layers: 1) Epidermis: 2) Dermis 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

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

7. Epidermis 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)

9. Epidermis Layers of epidermis: Stratum corneum: Stratum lucidum:
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

11. Epidermis 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

12. Epidermis: Skin Color Largely due 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

14. Dermis 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

15. Subcutaneous Layer 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

16. Accessory glands of skin

17. Nails 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

18. Hair Follicles 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

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

20. Sebaceous glands 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

22. Sweat glands 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)

23. Sweat glands 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

25. Other functions of skin

26. Regulate body temperature
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

27. Regulate body temperature
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

28. Healing Wounds 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)

30. Healing Wounds Shallow cut Deep 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

31. Skin Disorders Disorder Name Description Acne
Disease of sebaceous/oil glands
Alopecia
Hair loss
Birthmark
Congenital blemish, visible at birth
Boil
Bacterial infection in hair follicle
Dermatitis
Inflammation of skin
Eczema
Noncontagious skin rash, itching, blistering, scaling
Herpes
Caused by herpes simplex virus, recurring formations of small sores
Keloid
Elevated, enlarged scar tissue
Mole
Fleshy skin tumor, usually pigmented
Psoriasis
Chronic skin condition, red patches
Wart
Flesh-color, raised area, viral infection

32. Herpes
Dermatitis
Keloid
Alopecia
Boil

33. Psoriasis
Mole
Eczema
Wart