Chapter 6: Skin and the Integumentary System

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

Layers of skin

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

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

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)

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

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

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

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

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

Accessory glands of skin

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

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

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)

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

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)

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

Other functions of skin

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

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

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)

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

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

Herpes Dermatitis Keloid Alopecia Boil

Psoriasis Mole Eczema Wart