chapter 4 skin and body membranes biology 112 tri-county technical college pendleton, sc
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Chapter 4 Skin and Body Membranes
Biology 112Tri-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)
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