Chapter 4 Skin and Body Membranes

Biology 110Tri-County Technical CollegePendleton, SC

Membranes and more… Body membranes cover surfaces, line

body cavities, & form protecting (often lubricating) sheets around organs fall into TWO major groups

EPITHELIAL membranes include the CUTANEOUS, MUCOUS, and SEROUS membranes All contain epithelial sheet always combined

with underlying connective tissue These membranes are actually simple

organs

Membranes, cont. CONNECTIVE tissue membranes

represented by SYNOVIAL membranes

Two major categories of body membranes, EPITHELIAL and CONNECTIVE are classified in part according to their tissue makeup

Cutaneous Membranes Cutaneous membrane is the SKIN Its superficial EPIDERMIS

composed of keratinizing stratified squamous epithelium

Underlying DERMIS is mostly dense (fibrous) connective tissue

Unlike other epithelial membranes, CUTANEOUS membrane is exposed to air and is a DRY MEMBRANE

Mucous Membranes Mucous membrane (mucosa) composed

of epithelium resting on loose connective tissue membrane called LAMINA PROPRIA

Lines ALL body cavities open to the exterior Hollow organs of respiratory, digestive,

urinary, and reproductive tracts Stratified squamous (mouth and

esophagus) or Simple columnar (rest of digestive tract)

Mucous Membranes, cont. “WET” or moist membranes

continually bathed in secretions Urinary mucosa bathed with urine

Mucosa epithelium adapted for ABSORPTION/SECRETION

Mucosa of respiratory/digestive tracts secrete large amounts of protective, lubricating mucus

Urinary tract DOES NOT secrete mucus

Serous Membranes Composed of layer of simple squamous

resting on thin layer of areolar connective tissue

Line ALL body cavities closed to exterior (except for dorsal body cavity and joint cavities)

SEROUS membranes occur in PAIRS PARIETAL LAYER lines specific portion of

wall of ventral body cavity then folds back on itself to form VISCERAL LAYER which covers outside of organs in cavity

Serous membranes, cont. In body, serous membranes

separated by thin, clear fluid called SEROUS FLUID that is secreted by both membranes

Allows organs to slide easily across cavity walls and one another without friction

Extremely important when mobile organs such as pumping heart and churning stomach are involved

What’s in a name? Specific names of serous

membranes depend on their locations

PERITONEUM is serous lining abdominal cavities and covering its organs

PLEURA is serosa lining the lungs PERICARDIUM is serosa lining

around the heart

Connective Membranes Composed of connective tissue and contain

NO epithelial cells Line fibrous capsules surround joints Provide smooth surface and secrete

lubricating fluid called SYNOVIAL FLUID Also line small sacs of CT called BURSAE

and tubelike TENDON SHEATHS Both of these cushion organs moving

against each other during muscle activity (movement of tendon across a bone’s surface)

Skin and more… Skin is major organ of integumentary

system Insulates, cushions, & protects from

mechanical damage (bumps/cuts), chemical damage (acids/bases), thermal damage (heat/cold), UV radiation (sunlight), and bacteria

Uppermost (outermost) layer full of KERATIN and CORNIFIED (hardened) to prevent water loss from body surface

Skin, cont. Capillary network and sweat glands play

role in regulating heat loss from body surface

Acts as mini-excretory system: urea, salts, and water lost via sweat

Manufactures several proteins important in immunity and synthesizes vitamin D

CUTANEOUS sensory receptors (NS) located in skin

Tiny sensors include touch, pressure, temperature, and pain receptors

Skin Structure Skin composed of two kinds of tissue Outer EPIDERMIS=stratified squamous

capable of keratinizing (becoming hard/tough) Underlying DERMIS=dense connective tissue Epidermis and dermis firmly connected

Burn causes separation = blister Epidermis composed of 5 layers called STRATA From inside out: stratum BASALE, SPINOSUM,

GRANULOSUM, LUCIDUM, and CORNEUM

Skin Structure, cont. DERMIS composed of 2 zones or layers From inside out: RETICULAR LAYER and

DERMAL PAPILLAE Deep to dermis is the SUBCANTANEOUS

TISSUE (HYPODERMIS) which is essentially adipose tissue NOT considered part of the skin Serves as shock absorber and insulates deeper

tissues Responsible for curves that are more a part of a

woman’s anatomy than a man’s

De layer…de layer STRATUM BASALE is deepest layer of

epidermis Lies closest to the DERMIS

Contains the ONLY epidermal cells that receive adequate nourishment (diffusion) of nutrients from dermis

Cells in this layer constantly undergoing mitosis Also called stratum germinativum

Millions of new cells produced DAILY

Stratum Spinosum Stratum spinosum layer situated above

stratum basale and means “spiny layer”

Consists of 8 to 10 layers of cells, mostly KERATINOCYTES (most abundant epithelial cells) bound together by desmosomes

Begin to become flatter and increasingly full of keratin

Cells in this layer continue to divide

Stratum Granulosum “Grainy” layer superficial to stratum

spinosum 3-5 layers of keratinocytes that have

stopped dividing Become more flatter and produce

copious amounts of keratin Cell membrane thickens, nuclei and

organelles disintegrate Cells die and dehydrate creating

tightly interlocked layer of keratin fibers surrounded by KERATOHYALIN

Stratum Lucidum This layer occurs ONLY where skin

is hairless and extra thick Palms of hands and soles of feet

Glassy stratum lucidum (clear layer) covers stratum granulosum

Cells in this layer are flattened, densely packed, and filled with keratin

Doomed because NOT able to get adequate nutrients and oxygen

Stratum Corneum Found at surface of thick and thin skin

Normally 15-20 layers of keratinized cells Keratinization (cornification) occurs in exposed

skin surfaces except anterior surfaces of the eye OMG, Darling, you are very beautiful…but Dead cells within each layer remain tightly

interconnected by desmosomes Shed as large sheets rather than single cells Layer is water-resistant but not waterproof Journey from stratum basale to stratum

corneum takes about 15-30 days Dead cells remain in stratum corneum for about

2 weeks before being shed or washed away

Melanin and the Body Beautiful Melanin is a pigment that ranges from

yellow to brown to black Produced by special cells called

MELANOCYTES Melanocytes found primarily in stratum

basale Skin exposed to sunlight, melanocytes

stimulated to produce more melanin = tanning

Pigment umbrella Freckles/moles are seen where melanin

is [ ]ed in one spot

Dermis and beyond Dermis is strong, stretchy envelope that

helps hold body together Dense fibrous connective tissue making up

dermis consists of two major regions PAPILLARY LAYER is upper dermal region Uneven with fingerlike projections from its

superior surface called DERMAL PAPILLAE which indent epidermis above

Many dermal papillae contain capillary loops which supply nutrients to epidermis

Dermis, cont. Other dermal papillae house pain receptors

(free nerve endings) and touch receptors (Meissner’s corpuscles)

On palms of hand and soles of feet, papillae arranged in definite pattern that forms looped and whorled ridges on epidermal surface that increase friction and enhance gripping ability of fingers and feet

Ridges of fingertips covered with sweat pores and leave identifying film of sweat called FINGERPRINTS on nearly everything they touch

Dermis, cont. RETICULAR LAYER of dermis is deepest skin

layer Contains blood vessels, sweat and oil glands,

and deep pressure receptors (Pacinian corpuscles)

Many phagocytes found in reticular layer Both collagen and elastic fibers found with layer Collagen = toughness of dermis but also

attracts and binds water Elastic = skin elasticity during youth Aging decreases # of collagen and elastic

fibers, skin begins to sag and wrinkle…tell me about it!!!!

Sidebar on Skin Colors Three pigments contribute to skin color

Melanin, carotene, and hemoglobin Amount and kind of melanin (yellow, reddish

brown, or black) in the epidermis (basale) Amount of carotene deposited in stratum

corneum and subcutaneous tissue (yellow-orange pigment)

Amount of oxygen bound to hemoglobin (pigment in RBCs) in dermal blood vessels

Example: lots of melanin = brown skin tone

Skin Colors, cont. Light skinned people, crimson color of

oxygen-rich hemoglobin in dermal blood supply shows through = “rosy glow”

Large amounts of carotene-rich food consumed, skin takes on yellow-orange cast

CYANOSIS-occurs when hemoglobin is poorly oxygenated and blood/skin of Caucasians appear BLUE

ERYTHEMA (redness)-name given reddened skin and may indicate embarrassment, fever, hypertension, inflammation, or allergy

Skin Colors, cont. PALLOR (blanching)-certain types of emotional

stress (fear, anger, & others) cause some people to become PALE Pale skin may also signify anemia, low blood

pressure, or impaired blood flow to area JAUNDICE (yellow cast)-name given abnormal

yellow skin tone; usually signifies liver disorder Excess bile pigments absorbed into blood and

deposited in body tissues Bruises/Black and blue marks-reveal sites

where blood has escaped from circulation and clotted in tissue spaces Such clotted masses called HEMATOMAS Unusual tendency to bruise may be indicate

deficiency of vitamin C or hemophilia

Skin Appendages Skin appendages are cutaneous

glands, hair and hair follicles, and nails Each arises from epidermis and plays

unique role in maintaining homeostasis

CUTANEOUS GLANDS Are all EXOCRINE glands that release

their secretions to skin surface via DUCTS

Are two groups of cutaneous glands: Sebaceous glands and sweat glands

Sebaceous glands These “oil glands” are found all over body

except on palms of hands and soles of feet Ducts usually open into hair follicles but

some open onto skin surface SEBUM is lubricant that keeps skin soft and

moist and prevents hair from becoming brittle Also contains chemicals that kill bacteria

Sebaceous glands become very active when male sex hormones produced in > amounts (in both sexes) during adolescence

Sebaceous glands, cont. Skin becomes oilier during this period of life Sebaceous gland’s duct becomes clogged =

whitehead Accumulated material oxidizes and dries =

blackhead ACNE is active infection of sebaceous glands

accompanied by “pimples” on skin SEBORRHEA (cradle cap) in infants caused

by overactivity of sebaceous glands Scalp turns pink, raised lesions gradually form

yellow to brown crust that sloughs off as oily dandrull

Sweat of one’s brow… Two types of sweat glands: eccrine and

apocrine ECCRINE sweat glands most numerous and

are found all over the body Produce SWEAT-clear secretion that is

primarily water plus some salts (sodium chloride), vitamin C, traces of metabolic wastes (ammonia, urea, & uric acid), and lactic acid (attracts mosquitoes)

Sweat is usually acidic (pH 4-6) helping inhibit growth of bacteria

Eccrine Sweat glands, cont.

Typically sweat reaches skin via duct opening externally as funnel-shaped pore

Eccrine glands play important part of body’s heat regulating equipment

Supplied with nerve endings that cause them to “sweat” when external temp or body temp is high

As sweat evaporates, carries large amounts of body heat with it

Can lose 7 liters of body water a day in very hot temps

Heat regulating functions important to maintaining life

Apocrine Glands Apocrine glands largely confined to axillary

and genital areas of body Usually > than eccrine glands and their ducts

empty into hair follicles Secretions contain fatty acids and proteins as

well as “stuff” in eccrine gland secretion Secretion is “odorless” but bacterial growth

may impart musky, unpleasant odor Begin to function at puberty (androgens) Play minimal role in thermoregulation Activated by nerve fibers during pain, stress,

and/or sexual foreplay/activity

Neither “hair” nor there HAIR is produced by a root follicle and is

flexible epithelial structure HAIR ROOT is part of hair enclosed in follicle HAIR SHAFT is part projecting from surface

of skin or scalp Hair formed by division of well-nourished

cells in stratum basale epithelial cells in growth zone (hair bulb matrix)

Bulk of hair shaft, like bulk of epidermis, is dead material

Goose bumps…or whatever

Small bands of smooth muscle cells called ARRECTOR PILI connect each side of hair follicle to dermal tissue

When these muscles contract (cold, frightened, …not going there), hair is pulled upright

Dimples skin surface with “goose bumps”

If I had a hammer… NAIL is scalelike modification of epidermis

similar to hoof/claw of other animals EACH nail has FREE EDGE, BODY (visible,

attached portion), and ROOT (embedded in the skin)

Borders of nail over overlapped by skin folds called nail folds

Thick, proximal nail fold is called the CUTICLE

STRATUM BASALE of epidermis extends beneath nail as the NAIL BED

Nails, cont. Nail’s thickened proximal area that is

responsible for nail growth is called the NAIL MATRIX

LUNULA is white crescent over the thickened nail matrix

Nails, like hair and the stratum corneum cells, are mostly nonliving material

Infectious Disorders of the Skin

TINEA PEDIS (athlete’s foot)-itchy, red peeling condition of skin between toes from fungus infection

BOILS-inflammation of hair follicles and sebaceous glands, common on dorsal neck

CARBUNCLES-composite boils typically caused by bacterial infections (Staphylococcus aureus)

COLD SORES-small fluid-filled blisters that itch/sting caused by herpes simplex virus Localizes in cutaneous nerve where dormant until

activated by emotional upset, fever, or UV radiation Usually occur around lips/oral mucosa of mouth

Skin disorders, cont. CONTACT DERMATITIS-itching, redness and

swelling of skin, progressing to blisters Caused by exposure of skin to chemicals (poison

ivy, etc.) that promote allergic responses in sensitive individuals

IMPETIGO-pink, water-filled lesions (around mouth/nose) that develop yellow crust and rupture Caused by highly contagious staphylococcus

infection Common in elementary school children

Skin Disorders, cont. PSORIASIS-chronic condition

characterized by reddened epidermal lesions covered with dry, silvery scales

If severe, may be disfiguring Cause unknown, but heredity seems to be

implicated Attacks often triggered by trauma,

infection, hormonal changes, and stress

Three Types of Burns BURN is tissue damage and cell death

caused by intense heat, electricity, UV radiation, or certain chemicals

Burns are classified according to their severity

FIRST-DEGREE-only epidermis is damaged Area becomes red and swollen Temporary discomfort but “usually” NOT serious Heal in 2-3 days without any special attention Sunburn is “usually” a first-degree burn

Burns, cont. SECOND DEGREE-involve injury to

epidermis and upper region of dermis Skin red/painful and BLISTERS appear Sufficient numbers of epithelial cells still

present, regrowth (regeneration) of epithelium can occur

Normally, no permanent scarring results IF infection prevented

First- and Second-degree burns referred to as PARTIAL-THICKNESS BURNS

Burns, cont. THIRD-DEGREE-destroy entire thickness of

skin and are called full-thickness burns Burned areas appear blanched (gray-white) or

blackened Nerve endings in area destroyed so burn area

NOT painful NO regeneration is possible so skin grafting

required to cover underlying exposed tissues Considered CRITICAL if over 25% of body

has second-degree burns or if over 10% of body has third-degree burns OR if there are third-degree burns of face, hands, or feet

Rule of Nines Burns result in two life-threatening problems

Body loses supply of fluids containing proteins and electrolytes as they seep from burned surface

This dehydration/loss of electrolytes can lead to shut down of kidneys and CIRCULATORY SHOCK (inadequate circulation of blood due to low blood volume)

Volume of fluid loss can be estimated indirectly by determining how much of surface has been burned using the RULE OF NINE

Rule of Nine, cont. Method divides body into 11 areas

each accounting for 9 percent of total body surface

Additonal area surrounding genitals (perineum) = 1 percent

Types of Skin Cancers Skin cancer most common cancer in

humans BASAL CELL CARCINOMA-least malignant

and most common skin cancer Cells of stratum basale, altered so can no longer

form keratin, no longer honor boundary between epidermis and dermis

Proliferate & invade dermis and subcutaneous tissue

Occur most often on face as shiny, dome shaped nodules that later develop central ulcer with “pearly” beaded edge

Skin Cancers, cont.

Slow-growing and seldom metastasizes before discovery

Cure rate is 99% (surgical removal) SQUAMOUS CELL CARCINOMA-arises from

cells of stratum spinosum Lesion is scaly, reddened papule (small, rounded

elevation) that gradually forms shallow ulcer with firm, raised border

Appears on scalp, ears, dorsum of hands, lower lip Metastasizes rapidly to lymph nodes if not removed Believed to be ‘sun-induced” but recovery rate

good if caught early (surgery/radiation)

Skin cancers, cont. MALIGNANT MELANONA-is cancer of

melanocytes Accounts for 5% of skin cancers, rate is

rising, and CAN be deadly Can begin anywhere there is pigment (some

begin at pigmented mole) Usually appear as spreading brown/black

patch that metastasizes rapidly to lymph nodes and blood vessels

Survival rate is about 50%

The ABCD Rule for Melanomas

A (asymmetry)-two sides of pigment spot or mole do NOT match

B (border irregularity)-borders of lesion are not smooth but exhibit indentations

C (color)-pigmented spot contains areas of different colors (blacks, browns, tans, and sometimes blue and reds)

D (diameter)-spot is larger than 6 mm in diameter (size of pencil eraser)