Skin and Body Membranes

Skin and Body MembranesBody MembranesCover surfaces, line body cavities, and form protective (and often lubricating) sheets around organsTwo main categories:Epithelial membranes includes cutaneous, mucous, and serous membranesConnective tissue membranes synovial membranesEpithelial MembranesAlthough they contain an epithelial sheet, it is always combined with an underlying layer of connective tissue actually simple organsCutaneous membrane (skin)Mucous membrane (mucosa)Serous membrane (serosa)Cutaneous membraneThe skinSuperficial epidermis composed of a keratinizing stratified squamous epitheliumUnderlying dermis is mostly dense (fibrous) connective tissueExposed to air dry membraneMucous MembraneMucosaComposed of epithelium resting on a loose connective tissue membrane called a lamina propriaLines all body cavities that open to exterior, such as those of the hollow organs of the respiratory, digestive, urinary, and reproductive tractsMost contain stratified squamous epithelium or simple columnar epitheliumAdapted for absorption or secretionA wet membraneSerous MembraneSerosaComposed of a layer of simple squamous epithelium resting on a thin layer of areolar connective tissueLine body cavities that are closed to exterior except for dorsal body cavity and joint cavitiesMembranes occur in pairs parietal layer lines a specific portion of the wall of the ventral body cavity and folds in on itself to form the visceral layer, which covers the outside of the organs in that cavityLayers are separated by serous fluid, which is secreted by both membranes allows organs to slide easily without frictionSerous MembraneNames depend on location in the bodyPeritoneum serosa lining abdominal cavity and covering its organsPleura serosa surrounding the lungsPericardium serosa surrounding the heartSynovial MembraneComposed of soft areolar connective tissue; contain no epithelial cells at allLine the fibrous capsules surrounding joints, providing a smooth surface and secreting a lubricating fluidLine small sacs of connective tissue called bursae and the tube-like tendon sheaths cushion organs moving against each other during muscle activitySkinAlso called integument, which means coveringInsulates, cushions, keeps water and organs inside body, protects against UV radiation and bacteriaContains many capillaries and sweat glands that play important role in regulating heat lossSynthesizes vitamin DContains receptors that detect touch, pressure, temperature, and painEpidermisOuter layer of skinMade up of stratified squamous epithelium that is capable of keratinizing, or hardeningAvascular

EpidermisFive layers (strata) from inside to outside: stratum basale, spinosum, granulosum, lucidum, and corneumMost cells are keratinocytes, which produce keratin, the fibrous protein that makes the epidermis a tough protective layerStratum basale lies closest to dermis and contains the only epidermal cells that receive adequate nourishment via diffusion and produce new cellsDaughter cells are pushed upward and away

EpidermisStratum lucidum is only found where the skin is hairless and thick, such as the palms of hands or soles of feetStratum corneum is outer most layer, 20-30 layers thick of all epidermal thicknessMelanin = pigment that ranges from yellow to brown to black, produced by melanocytes in stratum basaleExposure to sunlight stimulates melanin production tanningFreckles and moles form where melanin is concentrated in one spotDermisDirectly below epidermisMade up of dense connective tissueUsually firmly connected to epidermis, but sometimes they separate could result in blister

DermisLeather goods = dermis of animalsTwo major regions papillary and reticularPapillary = upper dermal region, uneven with fingerlike projections called dermal papillaeDermal papillae contain capillary loops, pain receptors, and touch receptors form fingerprints and footprintsReticular = deepest skin layer, contains blood vessels, sweat and oil glands, phagocytes, and deep pressure receptorsDermisCollagen and elastic fibers are found throughout dermisCollagen attracts and binds to waterElastic fibers give young skin elasticityAs we age, number of these fibers decreases wrinkles and saggy skinHypodermisAka subcutaneous tissueEssentially adipose tissueHelps anchor skin to underlying organsServes as shock absorber and insulation

Skin ColorThree pigments contribute to skin color:The amount and kind (yellow, reddish brown, or black) of melanin in the epidermisThe amount of carotene (orange-yellow pigment found in orange, yellow, or leafy green veggies) deposited in the stratum corneum and subcutaneous tissueThe amount of oxygen bound to hemoglobin in the dermal blood vesselsLots of melanin = darker skinOxygen-rich hemoglobin is easier to see in people with lighter skinSkin Color IndicationsCyanosis = skin appears blue when hemoglobin is poorly oxygenatedErythema = Reddened skin, may indicate embarrassment, fever, hypertension, inflammation, or allergyPallor (blanching) = pale skin, may indicate emotional stress, anemia, low blood pressure, or impaired blood flowJaundice = yellow skin, usually signifies liver disorder in which bile pigments are absorbed into blood and deposited in body tissuesBruising = black-and-blue marks, reveal sites where blood has escaped from circulation and clotted in tissue spaces hematomas. Excessive bruising can be a sign of vitamin D deficiency or hemophilia, among other thingsSkin appendagesCutaneous glands = exocrine glands (release secretions to skin surface), fall into two groupsSebacious (oil) glands = found all over skin except for palms of hands and soles of feet, ducts usually empty into a hair follicle, produce sebum, a mix of oily substances and fragmented cells. Sebum keeps the skin lubricated, moist, and soft and helps kill bacteria. Blocked sebacious glands result in acne (whiteheads and blackheads)Sweat glands = also called sudoriferous glands, two main kinds: eccrine and apocrineSweat glandsEccrine glands = more numerous, found all over body, produce sweat, a clear secretion that is primarily water plus salts, vitamin C, metabolic wastes, and lactic acid and is usually acidic. Sweat reaches skin through ducts called pores (not to be confused with outlets for hair follicles)Apocrine glands = generally confined to axillary and genital areas of body, usually larger in size with ducts that empty into hair follicles. The secretion contains fatty acids and proteins in addition to substances found in eccrine gland secretions. The secretion is odorless on its own, but when bacteria use its nutrients for growth, it takes on a musky odor. These glands are activated during puberty.Hair and Hair FolliclesServe a few minor protective functions, such as guarding the head against bumps, shielding the eyes (eyelashes and eyebrows), and keeping foreign particles out of respiratory tract (nose hairs)Previously provided insulationHair is produced by a hair follicleThe part of the hair that is enclosed in the follicle is the rootThe part projecting from the surface is the shaftHair and Hair FolliclesHair is formed by the division of the well-nourished stratum basale epithelial cells in the growth zone, or hair bulb matrix, at the inferior end of the follicle.As the daughter cells are pushed farther away from the growing region, they become keratinized and die, thus making the bulk of the hair shaft dead material (almost entirely protein)Each hair consists of a central core called the medulla, which is surrounded by a bulky cortex layer, which is enclosed by a cuticle layer. The cuticle is a single layer of cells that overlap one another like shingles on a roof.

Hair and Hair FolliclesHair pigment is made by melanocytes in hair bulbHair follicles are actually compound structures. The inner epidermal sheath is composed of epithelial tissue and forms the hair. The outer dermal sheath is actually dermal connective tissue, which supplies blood vessels to the epidermal portion and reinforces it.Arrector pili = small bands of smooth muscle cells that connect each side of the hair follicle to the dermal tissue. When they contract, the hair is pulled upright goose bumpsNailsScalelike modification of the epidermis that corresponds to the hoof or claw of other animalsEach nail has a free edge, a body (visible attached portion), and a root (embedded in skin)Borders of nail are overlapped by skin folds, called nail foldsCuticle = thick proximal nail foldStratum basale extends beneath nail as nail bedNail matrix = thickened nail bed responsible for nail growth nail cells become heavily keratinized and dieNails are transparent and nearly colorless, but look pink due to rich blood supply in underlying dermisLunula = white crescent shape at end of nailInfections and AllergiesAthletes foot = itchy, red, peeling condition of the skin between the toes, resulting from fungal infectionBoils and carbuncles = inflammation of hair follicles and sebaceous glands, common on the dorsal neck. Carbuncles are composite boils typically caused by bacterial infection.

Infections and AllergiesCold sores = small fluid-filled blisters that itch and sting, caused by a herpes simplex infection. The virus remains in a cutaneous nerve until it is activated by emotional upset, fever, or UV radiation. Usually found around lips or oral mucosa of mouth.Contact dermatitis = itching, redness, and swelling of skin, progressing to blistering, caused by exposure to chemicals that provoke an allergic reaction.

Infections and AllergiesImpetigo = pink, water-filled, raised lesions, usually around mouth and nose, that develop a yellow crust and eventually rupture. Caused by a highly contagious staph infection, common in elementary school students.Psoriasis = chronic condition characterized by reddened epidermal lesions covered with dry, silvery scales, potentially disfiguring, cause unknown.

BurnsBurn = tissue damage and cell death caused by intense heat, electricity, UV radiation, or certain chemicalsDamage to skin can affect nearly every body system, altering metabolism, immune system, and cardiovascular system.Body loses supply of fluids, dehydration, electrolyte imbalanceRule of nines = helps determine how much fluid is lost, divides body into 11 areas, each accounting for 9% of total body surface area, plus additional area surrounding genitals representing 1%.

BurnsBurned skin is sterile for ~24 hoursAfter that, pathogens such as bacteria and fungi invade areas where skin has been destroyed and multiply in the nutrient-rich environmentPatients immune system becomes depressed within one to two days after severe burn injuryBurnsClassified by severity1st degree burns = only epidermis is damaged, area becomes red and swollen, usually heals in 2-3 days2nd degree burns = damage to epidermis and upper layer f dermis, skin is red and painful, blisters appear, regeneration of epithelium can occur, no scars if care is taken to prevent infection3rd degree burns = destroy entire thickness of skin, burned area appears blanched (grey-white) or blackened, nerve endings destroyed burned area is not painful, regeneration is not possible, skin grafts required

BurnsConsidered critical if:1. Over 25% of the body has second-degree burns2. Over 10% of the body has third-degree burns3. There are third-degree burns of the face, hands, or feetFacial burns are dangerous because of the possibility of burned respiratory passageways, which can swell and cause suffocationSevere burns at joints can result in scar tissue that limits joint mobilitySkin CancerMost skin tumors are benign and do not metastasize to other areas (ex. warts), but some are malignanthttp://video.about.com/dermatology/Skin-Cancer.htm Basal cell carcinoma = least malignant and most common skin cancer, cells of stratum basale proliferate and invade dermis and subcutaneous tissue, appear as shiny, dome shaped nodules which develop central ulcers with pearly beaded edges. Because it is so noticeable and slow-growing, metastasis rarely occurs. When removed surgically, there is a 99% chance for a full cure.

Skin CancerSquamous cell carcinoma = arises from cells in stratum spinosum, lesion appears as a scaly, reddened papule that gradually forms a shallow ulcer with a firm, raised border, usually found on scalp, ears, hands, and lower lip. Grows rapidly and metastasizes to adjacent lymph nodes if not removed, believed to be sun-induced. If caught early and removed, chance of complete cure is good.

Skin CancerMalignant melanoma = cancer of melanocytes, accounts for only 5% of skin cancers, often deadly, can begin anywhere there is pigment, most appear spontaneously, but some develop from moles. Usually appears as spreading brown to black patch that metastasizes rapidly to surrounding lymph and blood vessels, ~50% survival rate, early detection helps, ABCD rule:Asymmetry two sides of pigmented mole do not matchBorder irregularity borders are not smooth, but show indentationsColor pigmented spot contains areas of different colorsDiameter spot is larger than 6 mm in diameter (pencil eraser)

Developmental Aspects of Skin and Body MembranesLanugo = downy type of hair that covers infants during 5th and 6th months of fetal development, usually shed by birthVernix caseosa = white, cheesy-looking substance, produced by sebaceous glands, protects babys skin while it is floating in water-filled sac inside motherMilia = small white spots on baby caused by accumulations in the sebaceous glands, normally disappear by third week after birth

Developmental Aspects of Skin and Body MembranesIn adolescence, the skin and hair become more oily as sebaceous glands are activated acne. This usually subsides by adulthoodSkin begins to visibly change around the 30s as it is constantly exposed to abrasion, chemicals, wind, sun, pollutants, bacteria, etc. causing pores to clog and skin to be irritated pimples, scales, dermatitis

Developmental Aspects of Skin and Body MembranesAging subcutaneous tissue decreases, skin becomes drier, collagen and elastic fibers decrease, skin gets thinnerHair loses its luster, by age 50 the number of hair follicles has dropped by 1/3, resulting in hair thinning or baldnessMale pattern baldness hair follicles have become colorless and tinyGreying hair = usually genetically controlled, amount of melanin deposited decreases or becomes entirely absent, can be caused by stressful events, protein-deficient diets, chemotherapy, etc.