Skin and Body Membranes Chapter 4 Skin and Body Membranes

Body Membranes Cover surfaces, line body cavities, form protective sheets 2 groups – classified according to tissue

Epithelial membranes Aka covering and lining membranes Do contain some connective tissue Considered simple organs (1) Cutaneous membrane – Skin Dry membrane

(2) Mucous membranes (mucosa) Epithelium on top of lamina propria Lines any cavity w/ an exterior opening Wet (moist) membranes Continuously covered by secretions Ex. Respiratory, digestive, urinary, reproductive tracts Adapted for absorption or secretion

(3) Serous membranes (serosa) Simple squamous epithelium on areolar tissue Line cavities closed to exterior Occur in pairs Parietal layer – wall of ventral body cavity Visceral layer – covers organs in the cavity

Serous fluid – btw layers – secreted by both layers Allows organs to move w/out friction (heart,stomach) Name depends on location Abdominal cavity – peritoneum; lungs – pleura; heart - pericardium

Connective membranes Aka synovial membranes Areolar tissue – no epithelial Line fibrous capsules around joints Smooth surface Secrete lubricating fluid

Line bursae (small sacs of connective tissue) and tendon sheaths Cushion organs that move against each other

Integumentary System Cutaneous membrane Aka integument – “covering” 2 layers – epidermis & dermis – usually very close Burns/friction may cause separation = blister Functions Insulates and cushions deeper organs Regulates body temp – capillaries, sweat glands Mini excretory system – urea, uric acid, salts, water released w/ sweat Synthesizes immunity proteins Synthesizes vitamin D Contains cutaneous receptors – touch, pressure, temp, pain

Epidermis Avascular Keratinocytes – majority of cells – produce keratin (tough, protective, waterproofing) May have up to 5 strata (layers)

(1) Stratum basale Deepest Best nourished via diffusion Aka stratum germinativum because they are continually dividing Daughter cells are pushed upward Contains melanocytes – produce melanin (pigment) Sunlight stimulates production Concentrated in 1 spot = freckles, moles

(2) Stratum spinosum (3) Stratum granulosum (4) Stratum lucidum Dead – unable to get nutrients and oxygen Occurs in hairless, extra thick areas – palms, soles of feet (5) Stratum corneum 20-30 cell layers (3/4 of epidermis) Dead – completely filled w/ keratin Aka cornified cells (corno = horn) Rubbed/flakes off and is replaced by lower cells Cycle 25-45 days

Dermis Hide – leathergoods Strong, stretchy envelope that holds body together 2 layers (1) Papillary layer Upper dermal Dermal papillae – projections on superior surface Contain capillary loops which provide nutrients May have Meissner’s corpuscles – touch receptors Form ridges - fingerprints

(2) Reticular layer Deepest skin layer Contains blood vessels, sweat/oil glands, Pacinian corpuscles (pressure receptors) Both layers contain phagocytes that work to prevent bacteria from going deeper If blood supply is restricted = cell death = skin ulcers (bed sores) Ex. Decubitus ulcers – found in bedridden patients

Collagen fibers – provide toughness Attract/bind water – keep skin hydrated Elastic fibers – give skin elasticity # of fibers decreases – allows wrinkles Blood vessels help maintain temp To release heat – vessels swell To conserve heat – vessels constrict, may bypass capillaries

Hypodermis Subcutaneous tissue – adipose tissue Not part of skin Acts as an anchor, shock absorber, insulator

Skin Color 3 pigments Melanin – yellow, brown, black Carotene – yellow-orange Oxygen-rich hemoglobin – red/pink Emotional stimuli or disease affect color Redness (erythema) Blushing, fever, inflammation, allergy

Pallor (blanching) – become pale Anemia, low blood pressure, fear Jaundice (yellow cast) Liver disorder – bile deposited in tissues

Bruises (hematomas) Where blood has left vessels and clotted in tissue space May be vitamin C deficit or hemophilia

Cyanosis Bluish cast due to low oxygen Common in people with breathing disorders