Chapter 6 Skin and the Integumentary System Composed of several tissues Maintains homeostasis Protective covering Retards water loss Regulates body temperature Houses sensory receptors Contains immune system cells Synthesizes chemicals Excretes small amounts of waste

Types of Epithelial Membranes Mucous line tubes and organs that open to outside world lining of mouth, nose, throat, etc. secrete mucus Serous line body cavities that do not open to the outside reduce friction inner lining of thorax and abdomen cover organs of thorax and abdomen secrete serous fluid Cutaneous covers body skin Synovial composed entirely of connective tissue lines joints Secretes synovial fluid

Skin Cells help produce Vitamin D needed for normal bone and tooth development some cells (keratinocytes) produce substances that simulate development of some WBCs

Layers of Skin Epidermis Dermis Subcutaneous layer beneath dermis not part of skin

Epidermis lacks blood vessels keratinized thickest on palms and soles (0.8-1.4mm) melanocytes provide melanin rests on basement membrane stratified squamous

Production of new cells is balanced with the loss of dead cells Protects underlying tissues against water loss, mechanical injury, and the effects of harmful chemicals Epidermal cells keratinize and die as they are pushed to the surface

Epidermis Layers of Epidermis stratum corneum (dead cells) stratum lucidum stratum granulosum stratum spinosum stratum basale (reproduce and grow)

Dermis on average 1.0-2.0mm thick contains dermal papillae binds epidermis to underlying tissues irregular dense connective tissue muscle cells nerve cell processes specialized sensory receptors blood vessels hair follicles glands

Subcutaneous Layer hypodermis loose connective tissue adipose tissue insulates major blood vessels binds skin to underlying organs

Hair Follicles epidermal cells tube-like depression extends into dermis hair root hair shaft hair papilla dead epidermal cells melanin arrector pili muscle

A hair usually grows for a while, rests, and then is replaced by a new hair. Hair color is determined by genes that direct the type and amount of pigment epidermal melanocytes produce A bundle of smooth muscle cells forms the arrector pili muscle and attaches to each hair follicle One or more sebaceous glands are attached to each hair follicle

Nails protective coverings nail plate nail bed lunula made of specialized Epithelial cells that keratinize

Sebaceous Glands usually associated with hair follicles holocrine glands secrete sebum Excess sebum causes acne absent on palms and soles

Sweat Glands sudoriferous glands widespread in skin originates in deeper dermis or hypodermis Types eccrine glands apocrine glands ceruminous glands mammary glands

Eccrine sweat glands Most numerous Found on the forehead, neck, back, palms, and soles Respond to elevated body temp or emotional stress Sweat and sebaceous gland activity decreases with advancing age Sweat is mostly water with salts and waste products

Apocrine Sweat Glands Become active at puberty Located in the axillary regions (armpit), groin, and around the nipples

Ceruminous glands are modified sweat glands that secrete earwax Mammary glands are modified sweat glands that secrete milk

Regulation of Body Temperature Regulation of body temperature is vital because heat affects the rates of metabolic reactions. Normal temperature of deeper body parts is close to a set point of 37°C (98.6°F). Skin plays a key role in body temperature homeostasis.

Heat production and loss Heat is a by-product of cellular respiration. The most active cells are skeletal and heart muscle cells and the liver. If body temperature rises above normal: -more blood enters dermal blood vessels (vasodilation).

If body temperature rises above normal: more blood enters dermal blood vessels (vasodilation). deeper blood vessels contract (vasoconstriction) diverting blood to the surface and the skin reddens

heat is lost to the outside by: radiation - rays move from warmer to cooler surroundings (primary way) conduction - heat moves from warmer objects to cooler objects it is touching convection - heated air moving away from the body evaporation - fluid evaporates from the surface carrying heat away (sweating)

If the body temperature drops below normal: dermal blood vessels constrict, causing the skin to lose color sweat glands become inactive if heat is lost excessively, skeletal muscles involuntarily contract increasing cellular respiration and producing additional heat.

Problems in Temperature Regulation Hyperthermia – abnormally high body temperature Hypothermia – abnormally low body temperature

If the air is saturated with water, sweat may fail to evaporate, and body temperature may remain elevated (hyperthermia) Symptoms may begin with headache, dizziness, nausea, muscle cramping, and may lead to major organ failure Lack of sweating – medical emergency

Hypothermia is lowered body temperature. Symptoms begin with shivering, and leads to mental confusion, lethargy, loss of reflexes and ,consciousness, and eventually major organ failure

Skin Color All humans have about the same number of melanocytes. Skin color differences are due to the amount of melanin produced

Genetic factors Genes that control melanin production are inherited. Dark skin is due to genes that cause large amounts of melanin to be produced Lighter skin is due to genes that cause lesser amounts of melanin to form. Mutant genes may cause a lack of melanin in the skin (albinism).

Environmental factors Sunlight, ultraviolet light, and X rays darken existing melanin and stimulate more melanin production temporarily darkening the skin.

Physiological factors If blood is well oxygenated hemoglobin (blood pigment) is bright red causing the skin of light complected people to appear pinkish. If oxygen content of blood is low hemoglobin is dark red and the skin appears bluish (cyanosis). Dilated blood vessels can cause skin to redden

Constricted blood vessels cause a loss of reddish color. Carotene in the subcutaneous layer may cause the skin to appear yellowish. • Disease may affect skin color.

Healing of Wounds and Burns Skin injuries trigger inflammation. Blood vessels dilate forcing fluids to leave and enter the damaged tissue. The affected area becomes red, warm, swollen, and tender.

Cuts A shallow cut in the epidermis is filled in by reproducing epithelial cells. Deeper cuts into the dermis or subcutaneous layer cause a clot to form. platelets become entrapped in protein fibers (fibrin). tissue fluids seep into the area blood clot and dried fluids form a scab

fibroblasts begin to form new collagenous fibers that bind edges of the wound together blood vessels extend beneath the scab phagocytes remove dead cells a scar where connective tissue replaces skin may appear

granulations (new blood vessel branch & fibroblasts) may form in large open wounds

Healing of Cuts

First degree burns (superficial partial-thickness burn) only burns the epidermis heals quickly with no scarring the area is warm and red.

Second degree burns (deep partial-thickness burn) – destroys some epidermis and dermis blisters appear area becomes moist and firm and varies in color from dark red to waxy white

healing depends on the accessory organs that survive skin usually recovers with no scar tissue unless an infection occurs.

Third degree burns (full-thickness burns) destroys the epidermis, dermis, and the accessory organs of the skin injured skin may appear dry and leathery and varies in color from red to black to white healing only occurs from epithelial cells growing inward from the margin of the burn

may require skin grafting: autograft - thin layer of skin from unburned area is removed and transplanted in injured area homograft - cadaveric skin is used to cover injury skin substitutes - amniotic and artificial membranes human skin cultures - grow in lab and transplant extensive scarring

Rule of Nines

Life Span Changes Melanin production slows Skin becomes scaly Hair thins Number of hair follicles decrease Nail growth becomes impaired Sensory receptors decline Body temperature unable to be controlled Diminished ability to activate Vitamin D Skin becomes scaly Age spots appear Epidermis thins Dermis becomes reduced Loss of fat Wrinkling Sagging Sebaceous glands secrete less oil

Clinical Application Acne Vulgaris most common skin disorder sebum and epithelial cells clog glands produces whitheads and blackheads (comedones) anaerobic bacteria trigger inflammation (pimple) largely hormonally induced androgens stimulate sebum production treatments include antibiotics, topical creams, birth control pills