Skin and Its Appendages Chapter 6 Integument Skin

Skin and Its Appendages Chapter 6

Integument �Skin is the largest organ in the body. Makes up 16% of total body weight. �Approximately 1. 6 -1. 9 m 2 in the average sized adult �Integumentary system describes the skin and its appendages �Hair �Nails �Skin glands

Structure of Skin �Classified as a cutaneous membrane �Two primary layers- dermis and epidermis joined by a dermal epidermal junction �Subcutaneous layer- hypodermis or superficial fascia lies beneath the dermis �Thick and thin skin �Thick skin- soles and palms (4 -5 mm thick) �Thin skin- covers most of the body (1 -3 mm thick)

Epidermis

Epidermis- Cell types �Keratinocytes- make up 90% of cells present- principal structural element of outer skin �Melanocytes- pigment producting cells (%5 of total) give color and filter UV light �Langerhans cells- play a role in immune response

Cell Layers of Epidermis 1. Stratum Corneum (top layer) �Dead cells filled with keratin (barrier area) 2. Stratum Lucidum (clear layer) cells filled with keratin precursor called eleidin absent in thin skin. 3. Stratum granulosum (granular layer) cells arranged 2 -3 layers and filled with keratohyalin granules that contain a high # of lysosomes ( to digest the cytoplasm as it is replaced with keratin)

Cell layers- epidermis continued 4. Stratum Spinosum (spiny layer) cells arranged in 8 -10 layers with prominent desmosomes (strong connections between cells appear spiny in microscope): Rich in RNA which is necessary for the protein synthesis of Keratin. 5. Stratum basale (base layer) single layer of columnar cells: only these cells undergo mitosis and then migrate through the other layers until they are shed.

Layers of the epidermis

Epidermal growth and repair �Turnover or regeneration time refers to time it takes for cells to go from base layer to corneum. This takes about 35 days �Shortened turnover time can be created with abrasion. However prolonged abrasion of an area that stimulates mitotic division results in a callus (increased stratum corneum) �Normally 10 -12% enter mitosis daily in the stratum basale.

Dermis Epidermis junction �A definite basement membrane, specialized fibrous elements and a polysaccharide gel serve to “glue” the epidermis to the dermis. �The junction serves as a partial barrier to the passage of some cells and large molecules

Dermis “TRUE SKIN” �Much thicker �Gives strength to the skin �Reservoir storage area for water and electrolytes �Contains specialized sensory receptors, muscle fibers hair follicles, sweat and sebaceous glands and blood vessels.

Dermis cont… �Rich vascular supply plays a critical role in the regulation of body temperature. �As the body senses an increase in temperature the blood vessels of the skin dilate and heat radiates out of the blood vessels through the dermis (vasodilation) �As the body senses a decrease in temperature the blood vessels will constrict (vasoconstriction). This keeps warmer blood circulating deeper in the tissue in more “critical” areas.

Layers of the Dermis �Papillary layers- composed of dermal papillae that project into the epidermis; contains fine collagenous and elastic fibers; contains the dermal epidermal junction ; forms a unique pattern that gives individual fingerprints

Layers of dermis cont… �Reticular layer- contain dense, interlacing white collagenous fibers and elastic fibers to make the skin tough yet stretchable; when processed from animal skin it produces leather.

Dermal Growth and Repair �The dermis does not continually shed and regenerate itself as does the epidermis �During wound healing the fibroblasts begin forming and unusually dense mass of new connective fibers; if not replaced by normal tissue, this mass remains a scar. �Langer’s cleavage lines patterns formed by the collagenous fibers of the reticular layer of the dermis. Important for surgeons �If the elastic fibers of the dermis are stretched too much as in obesity or pregnancy or rapid growth phases the result is tiny linear markings or stretch marks- actual tears in the elastic

Skin Color �Basic determinant is quantity of melanin, found in the stratum basale of the epidermis in all races. �Melanin is formed from melanocytes from the amino acid tyrosine. �Albinism- congenital absence of melanin.

Skin color cont… �Process of skin coloration is regulate by tyrosinase(enzyme that breaks down tyrosine) , exposure to sunlight, and certain hormones including ACTH (adrenocorticotropic hormone) that regulates aging. �Carotene (yellowish color) can also contribute to skin color �Color changes also occur as a result of changes in blood flow to skin and circulating levels of unoxygenated hemoglobin. (bluish to pale appearance)

Functions of the skin �Protection �Prevent dehydration �UV barrier through melanin �Surface film- sweat, oil, epithelial cells that are shedding �Antibacterial, antifungal activity �Lubrication �Hydration of skin surface �Buffer caustic agents �Blockade of toxic agents

Functions of skin cont. �Sensation- sophisticated sense organ �Able to detect temperature, pressure, touch , pain and other general senses. http: //www. innerbody. com/image_nerv 16/nerv 141. h tml �Movement without injury due to elastic nature of skin �Excretion of water, urea, ammonia, and uric acid �Vitamin D production �Exposure to UV light converts 7 dehydor. CHOLESTEROL to cholecalciferol (precusor to vit D) �Vitamin D is classified as a hormone once process

Functions of skin �Immunity �Phagocytic cells destroy bacteria �Langerhans cells trigger helpful immune reaction with helper T cells. Homeostasis of body temperature 1. Heat production must equal heat lost for temperature to be balanced 2. Heat production- metabolism of foods in skeletal Muscle and liver. Chief determinant is the amount of muscular work being done.

Function of skin: homeostasis of body temp � 3. Heat Loss- approximately 80% of heat loss occurs through the skin; remaining 20% occurs through the skin mucosa of the respiratory, digestive, and urinary tracts. �Evaporation- to evaporate fluid from skin energy must be expended (sweat) �Radiation- heat loss in cool environmental conditions �Conduction-very small amounts of heat loss �Convection- transfer of heat away from skin by movement of air (sitting under a fan or air conditioner) �Fig 6 -6 pg 173

Homeostatic regulation of heat loss � Heat loss is controlled by a negative feed back loop �Hypothalamus senses temperature change from its “set point” �If too high- signal sent to sweat glands and blood vessels �If too low- to muscles to shiver to create frictional heating �Once temperature is returned to set point nervous response is inhibited.

BURNS- figure 6 -9 p 176 �Injury or death to skin cells caused by heat, UV, electrical current or corrosive chemical �Severity is determined by depth of lesion and % of body surface burned �Estimating burn area �RULE OF PALMS- palm is approximately 1% of body surface �Lund-Browder Charts- more accurate with children due to the difference in proportions of head to body.

Burns- Rule of NINES �Head/neck - 9% �Each arm - 9% �Anterior thorax - 18% � Posterior thorax 18% �Each leg - 18% �Perineum - 1%

First degree burn �Minor pain – no significant tissue destruction �Some reddening of the skin �No blistering, but some peeling of surface occurs �No scarring �Typical sunburn �Partial thickness burn

Second degree burn �Severe pain �Damage or destruction of epidermis and upper dermal layers �Blisters form with swelling and edema (fluid in the tissue) �Dermal tissue death not complete but scarring common �Partial thickness burn

Third degree burn- full thickness burn �Total destruction of both epidermis and upper dermal layers �Tissue death extends below level of hair follicles and sweat glands �No immediate pain; nerve endings are destroyed �Burning may involve deep tissues , including muscle and bone �Scarring is a serious problem

Burns

Appendages of the Skin �Hair �Papilla- capillaries clustered under follicle �Root- tip of hair embedded in follicle �Shaft- visible part of hair �Medulla- inner core of hair: Cortex- outer portion �Color- results from the different amounts of melanin in cortex of hair �Growth- periods of growth and rest. Grows about 5 inches per year. �Sebaceous glands- oil glands that secrete sebum into follicle �Male pattern baldness

Appendages cont… � Nails �Epidermal cells converted to hard keratin �Nail body – visible part of each nail �Root- part of nail in groove hidden by fold of skin, cuticle �Lunula- moon-shaped white area of nearest root �Nail bed- layer of epithelium under nail body- abundant blood vessels �Growth average: 0. 5 mm per week or 1 inch per year

Appendages cont. . . SKIN GLANDS �Two types of sweat glands �Eccrine glands �Most numerous sweat glands, quite small �Over total body surface �Simple coiled tubular glands �Function entire life �Help body maintain temperature �http: //www. innerbody. com/image_nerv 16/nerv 141. html

Sweat Glands cont… �Apocrine glands �Located deep in subcutaneous layer �Limited distribution- axilla, areola of breast, anus �Large 5 mm in diameter �Simple branched tubular glands �Function at puberty �Secretion cyclic changes in female with menstrual cycle

Skin Glands- Sebaceous glands �Secrete sebum- oily substance that keeps hair and skin soft and pliant; prevents water loss �Lipid components have antifungal activity �Simple branched glands �In dermis except for palms and soles �Secretion increases in adolescence forming pimples, blackheads

Ceruminous glands �Modified apocrine sweat glands �Simple coiled, tubular glands �Empty contents into external ear canal alone with sebaceous glands �Mixed secretions result in ear wax �Functions to protect area from dehydration. �Excess production can block ear canal and cause loss of hearing

Cycle of Life: skin � Children �Smooth skin, elasticity, and flexibility �Few sweat glands �Rapid healing � Adult �Activation of sweat and sebaceous glands �Increased sweat and body odor �Increased sebum production (oil)= acne � Old age �Decreased sweat and sebaceous activity �Wrinkling �Decreased in the body’s ability to cool itself