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