Skin and Its Appendages Chapter 6

Integument Skin is the largest organ in the body. Makes up 16% of total body weight. Integumentary system describes the skin and its appendages Hair Nails Skin glands

Structure of Skin Classified as a cutaneous membrane Two primary layers Dermis (inner) Epidermis (outer) Subcutaneous layer Below the dermis rich in fat Thick and thin skin Thick skin- soles and palms (4-5mm thick) Thin skin- covers most of the body (1-3mm thick)

Epidermis

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

Cell Strata (layers) of Epidermis Stratum Corneum (top layer) Dead cells filled with keratin (barrier area) Stratum Lucidum (clear layer) cells filled with keratin precursor called eleidin absent in thin skin. 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 STRATA- epidermis continued 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. 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.

Skin Color Basic determinant is quantity of melanin found in the stratum basale of the epidermis in all races. Melanin is formed from melanocytes using 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)

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

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_nerv16/nerv141.html Movement without injury due to elastic nature of skin Excretion of water, urea, ammonia, and uric acid Vitamin D production (Endocrine Function) Exposure to UV light converts 7 dehydorCHOLESTEROL to cholecalciferol (precusor to vit D) Vitamin D is classified as a hormone once process is complete

Functions of skin Immunity Homeostasis of body temperature Phagocytic cells destroy bacteria Langerhans cells trigger helpful immune reaction with helper T cells. Homeostasis of body temperature Heat production must equal heat lost for temperature to be balanced 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 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, bust 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 scaring 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: 0.5mm 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_nerv16/nerv141.html

Apocrine glands Sweat Glands cont… Located deep in subcutaneous layer Limited distribution- axilla, areola of breast, anus Large 5mm 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 Adult Old age 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