Integument PDF

Overview of the Skin\ Largest organ of the body (16% of body weight)\ Two layers\ -- epidermis\ keratinized stratified squamous epithelium\ contains 4-5 layers\ -- dermis\ connective tissue layer\ Rests on subcutaneous layer or hypodermis\ Normal thickness of 1-2 mm, up to 6 mm Epider...

Overview of the Skin\ Largest organ of the body (16% of body weight)\ Two layers\ -- epidermis\ keratinized stratified squamous epithelium\ contains 4-5 layers\ -- dermis\ connective tissue layer\ Rests on subcutaneous layer or hypodermis\ Normal thickness of 1-2 mm, up to 6 mm Epidermis\ Epithelium on basement membrane over dermis\ No blood vessels in epidermis, gets supply through diffusion\ Top cells are dead\ 4-5 layers\ 4 cell types Dermis\ Composition\ -- collagen, elastic & reticular fibers, fibroblasts &\ accessory structures such as hair follicles and glands\ Dermal papillae\ Layers\ -- papillary layer\ -- reticular layer Hypodermis\ Known as subcutaneous tissue\ Has more white adipose cells than dermis\ Functions\ -- energy reservoir\ -- thermal insulation\ Hypodermic injections\ -- into subcutaneous tissue since highly vascular Skin Colors (Pigmentation)\ Hemoglobin is red pigment of red blood cells\ -- visible through dermal collagen fibers\ Carotene (we pick up from our diet which turns adipose a light yellow) is yellow pigment of vegetables, fruits & egg yolks\ -- concentrates in stratum corneum & subcutaneous fat\ Melanin pigment produced by melanocytes\ -- pigment synthesis stimulated by UV radiation from sunlight\ -- produces yellow, brown, black and reddish hues Abnormal Skin Coloration\ Cyanosis -- lack of blood flow (bluish)\ Erythema -- increased blood flow\ Jaundice -- high levels of bilirubin in blood (yellow)\ Pallor -- decreased blood flow\ Albinism - a genetic variation, have melanocytes that aren't producing melanin\ Hematoma -- bruise Skin Markings\ Freckles and moles (moles are raised and have more melanin)\ Stretch marks- tears in dermal tissue, hard to go away because connective tissue heals slowly\ Hemangioma (true birthmark)\ -- Benign capillary tumor\ -- Strawberry birthmarks disappear soon after birth (close to surface)\ -- Cavernous hemangiomas disappear after about a year (bluish and deeper in skin)\ -- Port-wine stains remain for life Skin Functions\ Barrier to water, UV light\ Vitamin D synthesis\ -- UV converts a form of 7-dehydrocholesterol in the blood into Vitamin D\ Absorption\ -- We actually bring in 1-2% of the oxygen we need directly through the skin\ -- Lipid-soluble vitamins (vitamin E, A/steroids/hydrocortisone) Skin Functions\ Sensory functions\ -- Temperature, touch, pressure, vibration, pain\ Thermoregulation (temperature control)\ -- Sweating, constriction & dilation of blood vessels\ Social functions\ -- Facial expressions / nonverbal communication Characteristics of Human Hair\ Stratum corneum of the skin contains soft keratin\ Hair and nails are composed of hard keratin\ -- toughened by disulfide bridges between molecules\ Hair found almost everywhere on the body\ 3 different body hair types\ -- lanugo \-- fine, unpigmented fetal hair\ -- vellus \-- fine, unpigmented hair\ -- terminal hair \-- coarse, long, pigmented hair Structure of Hair and Follicle\ Hair is filament of keratinized cells\ -- Shaft: parts above skin\ -- Root: parts below within follicle\ -- Follicle: epidermal invagination into dermis\ -- Bulb: swelling in base where hair originates\ -- Papilla: vascular tissue in bulb All cells in sweat glands are epithelial Structure of Hair Follicle\ Epithelial root sheath is an extension of the epidermis\ Connective tissue root sheath is derived from the dermis\ Hair receptors entwine each follicle\ Arrector pili muscle Hair Structure\ Hair in cross section\ -- Cuticle (very outside)\ -- Cortex (in between cuticle and medulla)\ -- Medulla (center, middle) Hair Color\ Two types of Melanin, pigments can vary in shade\ Eumelanin: Brown-black\ Pheomelanin: Red-yellow Melanocyte stimulating hormone binds to a receptor to make melanin - Lots of agouti protein (also binds to same receptor) makes hair redder and lighter Hair Growth\ Growth initiated in hair bulb\ A hair grows about 1 mm every 3 days for several years\ Then it goes dormant for up to several more years\ Then it gets pushed out by a new hair\ Eyelashes and eyebrows\ -- Growth: \~ a month\ -- Dormant: \~ 3 months Hair Growth\ Cells become keratinized and push each other\ upward, forming the new hair\ At some point, the old hair gets pushed out Hair Growth Process: 1. Anagen: active growing stage 2. Catagen: transitions (to club hair/stops growing) 3. Telogen: resting phase (dermal papilla fully separates from follicle) 4. Return to Anagen Phase Nails\ Clear, hard derivative of stratum corneum\ -- densely packed cells filled with hard keratin\ Flat nails allow for fleshy, sensitive fingertips\ Growth rate is 1 mm per week\ -- new cells added by mitosis in the nail matrix\ -- nail plate is visible part of nail Cutaneous Glands\ Sweat glands\ -- merocrine\ -- apocrine\ Sebaceous glands\ Ceruminous glands\ Mammary glands Sweat Glands\ Filtrate of plasma\ -- 500 ml of perspiration/day\ Merocrine gland -- simple tubular gland\ -- millions of them\ -- cool the body\ Apocrine glands -- sweat contains fatty acids\ -- found only near hair follicles & respond to stress & sex\ -- body odor produced by bacterial action on fatty acids Sebaceous Glands\ Oily secretion called sebum that contains broken-\ down cells\ -- lanolin in skin creams is made from sheep's sebaceous glands when you sheer their wool\ Flask-shaped gland with duct that may open into hair\ follicle Ceruminous Glands\ Modified sweat gland\ Found only in external ear canal (ear wax)\ Their secretion combines with sebum to produce earwax\ -- waterproof keeps eardrum flexible Mammary Glands\ Breasts of both sexes rarely contain glands\ -- Secondary sexual characteristic of females\ -- Glandular tissue - only during lactation and pregnancy\ similar in origin to apocrine sweat gland Mammary Glands\ Mammals typically have two rows of\ mammary glands, called milk lines\ Humans have one from each line but can\ occasionally develop additional rudimentary\ nipples (milk lines) Diseases of the Skin\ Most vulnerable organ to injury & disease\ Skin cancer\ -- caused by UV light; common in fair-skinned &\ elderly\ -- basal cell carcinoma\ arises from cells of the stratum basale\ treated by surgical removal, rarely metastasizes\ -- squamous cell carcinoma\ arises from the stratum spinosum\ if neglected, metastasis to the lymph nodes\ -- malignant melanoma (most deadly cancer)\ arises from melanocytes, 25% from preexisting mole\ ABCDE\--asymmetry, border irregular, color mixed,\ diameter over 6 mm, & evolving\ -- merkel cell carcinoma\ arises from merkel cells, weakened immune system\ shiny nodule, rapid growth, 2nd to Mel for death (least common) Burns\ In lethal burns, the cause of death is usually fluid\ loss, infection, or complications resulting from\ tissue death 1st-degree burn\ Affect only the epidermis\ Most sunburns are 1st-degree\ Typically don\'t leave scars 2nd-degree\ Involve the epidermis and part of the dermis but leave at least some of the dermis\ intact\ Blisters\ May leave scars 3rd-degree\ Completely destroy the dermis\ Typically require skin grafts\ Less painful than 2nd- degree because nerves are destroyed 4^th^ degree - Goes into hypodermis - Destroys muscle and tendons (possible bones)