A & P – Chapter 4: Skin and Body Membranes (Integumentary System)
Body membranes, which cover surfaces, line body cavities and form protective (and often lubricating) sheet
around organs.
Classification of Body Membranes
 Epithelial membranes
* Cutaneous (skin) – dry membranes that are exposed to air
* Mucous – (mucosa) – lines body cavities that open to the exterior (ex. Respiratory, digestive,
urinary and reproductive systems)
- Mucosa only refers to the location of the epithelial membranes, not their cell makeup
* Serous – lines body cavities that are closed to the exterior except for the dorsal and joint
cavities
- Serous fluid – allows organs to slide easily across the cavity walls and one another
without friction as they carry out their functions
- Peritoneum – lining of the abdominal cavity and covering of its organs
- Pleura – around the lungs
- Pericardium – around the heart
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Connective tissue membranes
* Synovial membranes – composed of connective tissue – they line the fibrous capsules
surrounding joints, also secrete a lubricating fluid
- Bursae – sacs of connective tissue
- Tendon sheaths – tube-like structures Cushion organs moving against
each other during muscle activity
Integument – covering
Skin – the largest organ and is called the cutaneous membrane
- Plays a role in maintaining water balance and temperature
- Upper most layer of skin is full of keratin (tough, insoluble protein) and cornified (or hardened) to
prevent water loss from the body surface
- Can keep water and precious molecules in the body and also keep water out (ex. Swimming – not
becoming “water-logged”)
- Acts as a mini-excretory system – urea, salts, and water are lost when we sweat.
- Cutaneous sensory receptors (actually part of the nervous system) are found in the skin and provide
us with information about our external environment (bumps and tissue-damaging factors) – sense
touch, pressure, temperature, and pain
Functions of the Skin
– Protection
• Chemical damage (acids and bases)
• Bacterial damage
• Ultraviolet radiation (sunlight) – contains melanin
• Thermal damage (heat/cold) – contain heat/cold/pain receptors
• Desiccation (drying out) – contains waterproofing substance called keratin
– Insulation – controlled by the nervous system
• heat loss (activating sweat glands and allowing blood to flush into skin capillary beds)
• heat retention (not allowing blood to flush into skin capillary beds
– Cushion
• Mechanical damage (bumps)
– Excretion
– Sensation – controlled by the nervous system
– Production of Vitamin D – modified cholesterol in skin converted by sunlight
Layers of the Skin
 Epidermis – (outer layer) – avascular (has no blood supply of its own)
- keratinocytes – keratin cells – make up most of the epidermis
- has 5 layers called strata:
* stratum basale – deepest cell layer (closest to the dermis) – contains melanin – pigment that
ranges from yellow to brown to black and is produced by cells called melanocytes
- Freckles and moles are seen where melanin is concentrated in one spot
- Despite melanin’s protective effects, excessive sun exposure eventually damages skin
- causes elastic fibers to clump, leading to leathery skin
- depresses the immune system
- Overexposure to the sun can also alter DNA and lead to skin cancer; black people
seldom have skin cancer due to melanin’s effectiveness as a natural sunscreen.
* stratum spinosum
More superficial layers
* stratum granulosum
* stratum lucidum – clear, flatter, more keratinized; occurs where skin is hairless and extra thick
(palms of hands and soles of feet)
* stratum corneum – outermost layer – 20-30 cell layers thick; accounts for about ¾ of
epidermal thickness
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Dermis – (middle layer) – your “hide” – sensory receptors, blood vessels, and glands
2 Major Regions
• Papillary Layer – upper dermal region – uneven and has fingerlike projections from its
superior surface that indent the epidermis above; gives us our fingerprints and enhances
gripping ability – papillary patterns are genetically determined
• Reticular Layer – deepest skin layer – contains blood vessels, sweat/oil glands, and deep
pressure receptors
- Any restriction of normal blood supply to the skin results in cell death and if
severe enough, skin ulcers.
- Bedsores – decubitus ulcers – occur in bedridden patients who are not turned
regularly or who are dragged or pulled across the bed repeatedly –
permanent damage to the superficial blood vessels and tissue eventually
results in degeneration and ulceration of the skin
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Hypodermis or Subcutaneous tissue – (inner layer) – contains adipose tissue (fat); anchors skin to
underlying organs; serves as shock absorber and insulation for deeper tissues; responsible for your
“curves”
Skin Color
• Skin color is determined by:
– The amount and kind of pigment
• Yellow
• Reddish brown
• Black
– Amount of carotene deposited in the stratum corneum and subcutaneous tissue
• Carotene is an orange-yellow pigment found in carrots and other orange, deep yellow, or
leafy green vegetables
– The amount of oxygen bound to hemoglobin in the dermal blood vessels
• Hemoglobin – pigment in red blood cells; oxygen carrier
• Skin Color Alterations:
– Cyanosis – when Caucasian skin appears blue – due to poorly oxygenated hemoglobin;
common during heart failure and severe breathing disorders – apparent in the nail beds and
mucous membranes of black skin
– Erythema – redness – may indicate embarrassment (blushing), fever, hypertension,
inflammation, or allergy
– Blanching – (or pallor/paleness) – emotional stress (fear, anger, and others), may signify
anemia, low blood pressure, or impaired blood flow into the area
– Jaundice – yellow cast – signifies a liver disorder in which excess bile pigments are absorbed
into the blood, circulated throughout the body and deposited in body tissues
– Bruises – black/blue marks – reveal sites where blood has escaped from the circulation and has
clotted in the tissue spaces, also called hemotomas.
• An unusual tendency to bruising may signify a deficiency of vitamin C or hemophilia
(bleeder’s disease).
Appendages of the skin
 Cutaneous glands (sweat glands)
 Hair
 Nails
Cutaneous Glands (exocrine glands)
 Sebaceous – (oil glands) – found all over the skin except the palms of the hands and soles of the feet
The product of sebaceous glands is sebum – lubricates and keeps the skin soft and prevents hair
from becoming brittle
Sudoriferous – (sweat glands)
- Eccrine – more numerous
- Aprocrine – axillary and genital areas
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Hair
– Protective Functions:
• Guarding head against bumps
• Shielding the eyes (eyelashes)
• Help keep foreign particles out of the respiratory tract (nose hairs)
– Produced by a hair follicle
• Flexible epithelial structure
• Root – encloses the hair in the follicle
• Hair bulb matrix – growth zone at the inferior end of the follicle
– As daughter cells are pushed farther away from the matrix, they become
keratinized and die
– Hair pigments made by melanocytes are found here
• Shaft – the part projecting from the surface of the scalp or skin
– The bulk of the shaft is dead material and almost entirely protein
– Shape of the shaft determines sizes and shape
» Oval – smooth and silky
» Flat/ribbonlike – curly or kinky
» Perfectly round – straight and tends to be coarse
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Humans are born with as many hair follicles as they will ever have
Hormones account for the development of “hairy” regions
– “Goose bumps” are the flexing action of the arrector pili muscle attached to the hair follicle.
• The process to make goose bumps starts in the sympathetic nervous system.
• The raised bumps make human skin somewhat resemble the skin of a plucked goose.
• Factors that cause goose bumps:
• Cold
- The hair standing on end in such a manner raises body temperature allowing less
heat to escape in furrier animals.
• Fever
- Sometimes the body sweats or has chills with fever; natural reaction to high fever.
• Fright/Excitement
- Rush of adrenaline causes the nervous system to react.
Nails
– A nail is a scale-like modification of the epidermis; similar to a hood or claw of other animals
– Nail matrix is responsible for nail growth
• As nail cells are produced by the matrix, they become keratinized and die; so like hair,
most is nonliving material
– Transparent and colorless, but look pink due to the rich blood supply in the underlying dermis
Homeostatic Imbalances of the Skin
• When anything goes wrong with the skin, it is quite visible.
• The skin is only about as thick as a paper towel, so when it is severely damaged, nearly every body
system suffers.
• The skin can develop more than 1000 different ailments.
• Most common skin disorders result from:
– Allergies
• Contact dermatitis – caused by exposure to chemical that provoke allergic responses
(example: poison ivy, bee stings)
– Infections
• Bacterial
– Boils and carbuncles – inflammation of hair follicles and sebaceous glands;
often caused by staphylococcus aureus
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Impetigo – (in-fan-ti-go) – pink, water0filled, raised lesions (commonly around
mouth and nose) that crust and rupture; also called “hand, foot and mouth
disease”; caused by a highly contagious staphylococcus infection
» Most common in elementary-aged children
Viral
– Cold sores (fever blisters) – herpes simplex virus localized in the cutaneous
nerve
Fungal
– Athlete’s Foot – tinea pedis – itchy, red, peeling condition
A common skin problem is acne – affects 80% of teenagers
Tiny inhabitants that can live primarily on the secretions of the skin (example: hair mites, bed bugs)
Psoriasis – chronic condition characterized by reddened epidermal lesions covered with dry, silvery
scales; caused is unknown, may be hereditary in some; attacks often triggered by trauma, infection,
hormonal changes, and stress
Burns
• A burn is tissue damage and cell death caused by intense heat, electricity, UV radiation (sunburn), or
certain chemicals (such as acids).
• When the skin is burned and its cells are destroyed, two life-threatening problems result.
– 1st – the body loses its supply of fluids
• Dehydration and electrolyte imbalance follow and can lead to a shutdown of the kidneys
and circulatory shock
• Volume of fluid lost is determined by how much of the body surface is burned – Rule of
Nines
– The body divided into 11 areas, each accounting for 9% of the total body surface
area and the genital area accounting for 1%
– 2nd – infection becomes the most important threat and is the leading cause of death in burn
victims
• Burned skin is sterile for 24 hours
• After that, infection sets up easily where the skin has been destroyed and rapidly
multiplies in the nutrient-rich dead tissues
• Burns are classified according to severity:
– Partial-thickness Burns
• First-degree burns – only epidermis is damaged; area is red and swollen
• Second-degree burns – injury to the epidermis and upper region of the dermis; skin in
red and painful and blisters appear
• Regeneration occurs and no permanent scars result if care is taken to prevent infection
– Full-thickness Burns
• Third-degree burns – entire thickness of the skin is destroyed; area appears blanched or
blackened; nerve endings are destroyed and burned area is not painful
– Regeneration is not possible and skin grafting must be done to cover the
underlying exposed tissues
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Burns are critical if only one of the following applies:
– Over 25% of the body has 2nd degree burns
– Over 10% of the body has 3rd degree burns
– There are 3rd degree burns of the face, hands, or feet
Skin Cancer
• Numerous types of tumors arise in the skin.
• Most are benign (non-cancerous) and do not metastasize (spread)
– Example: wart
• A neoplasm caused by a virus
• Some skin tumors are malignant (cancerous) and ten to invade other body areas
• Skin cancer is the single most common type of cancer in humans.
• What are the risk factors for melanoma?
– Skin cancer is more common in fair-skinned people - especially those with blond or red hair,
who have light-colored eyes. However, no one is safe from skin cancer. Almost half of all
Americans who live to age 65 will be diagnosed with skin cancer at some point in their lives,
according to the National Cancer Institute. Other risk factors include:
• Family history of melanoma.
• Sun exposure/overexposure to UV radiation - The amount of time spent unprotected in
the sun directly affects your child's risk of skin cancer.
• Early childhood sunburns - Research has shown that sunburns early in life. Increase a
child's risk for skin cancer later in life. Sun exposure early in life is the major
contributing factor to developing skin cancer.
• Many freckles.
• Many ordinary moles (more than 50).
• Dysplastic nevi (Atypical mole)
• Infections
• Chemicals
• Physical Trauma
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Types of Skin Cancer
– Basal Cell Carcinoma – least malignant; most common (Basal cell carcinoma accounts for
approximately 75 percent of all skin cancers. This highly treatable cancer starts in the basal cell layer of the
epidermis (the top layer of skin) and grows very slowly. Basal cell carcinoma usually appears as a small,
shiny bump or nodule on the skin - mainly those areas exposed to the sun, such as the head, neck, arms,
hands, and face. It commonly occurs among persons with light-colored eyes, hair, and complexion.)
– Squamous Cell Carcinoma – grows rapidly and metastasizes to adjacent lymph nodes if not
removed (Squamous cell carcinoma accounts for about 20 percent of all skin cancer cases. Although more
aggressive than basal cell carcinoma, this cancer is highly treatable. Squamous cell carcinoma, may appear
as nodules or red, scaly patches of skin, and may be found on the face, ears, lips, and mouth. Squamous
cell carcinoma can spread to other parts of the body. This type of skin cancer is usually found in fairskinned people.)
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Arises from the cells of the stratum spinosum; lesion appears as a scaly, reddened papule
that gradually forms a shallow ulcer with a firm, raised border
Appears most often on the scalp, ears, dorsum of the hands, and lower lip
Believed to be sun-induced
If caught early and removed surgically or by radiation therapy, the chance of complete
cure is good
– Malignant Melanoma – cancer of the melanocytes (Although less common, this type of skin cancer
is the most deadly, accounting for approximately 79 percent of all skin cancer deaths. Malignant melanoma
starts in the melanocytes - cells that produce pigment in the skin. Malignant melanoma usually begins as a
mole that then turns cancerous. This cancer may spread quickly. Malignant melanoma most often appears
on fair-skinned men and women, but persons with all skin types may be affected.)
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Incidences are on the rise
Often deadly
Can begin wherever there is pigment
Most appear spontaneously, but some develop from pigmented moles
– Usually appears as a spreading brown to black patch that metastasizes rapidly to
surrounding lymph and blood vessels
– Chance for survival is about 50%
– Early detection is a must
– ABCD Rule:
» Asymmetry
» Border Irregularity
» Color
» Diameter
– Usual therapy is wide surgical excision along with immunotherapy (chemo)
Developmental Aspects of Skin
• In young people, the skin is extensible and elastic. As a person grows older, the skin becomes thinner,
fat disappears from the subcutaneous tissue and wrinkles appear
– Sunlight can speed up the loss of elasticity
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– Although there is no way to stop skin from aging, good nutrition, plenty of fluids and
cleanliness help to delay the process.
Balding and/or graying occurs with aging.
– Genetically controlled by a “delayed-action” gene.
– By age 50 the number of hair follicles drops by 1/3 and may continue to decline.
– The amount of melanin deposited in the hair decreases or becomes totally absent, resulting in
gray-to-white hair.
– Both are genetically determined, but other factors can influence:
• Drugs/medication
• Hair treatments (chemical alterations, overstyling)
• Emotional stress/anxiety
• Hormonal changes
• Diseases/sickness
• Insufficient diet/poor nutrition
– If the cause of balding is not genetic, usually the problem is temporary.
• When to see a doctor about Balding:
- Talk to your doctor if you notice sudden or patchy hair loss or more
than usual hair loss when combing or washing your hair. Sudden hair loss
can signal an underlying medical condition and may require medical
treatment.
- No cure is available for permanent hair loss or baldness. However, you
can talk to your doctor about medical treatments to slow the rate of hair
loss or to hide hair loss.
Alopecia – baldness due to degeneration of hair follicles; may occur in women also
– Permanent Hair Loss:
• Male-pattern baldness (androgenetic alopecia) - pattern baldness can begin early, even in
the teens or early 20s. It's typically characterized by a receding hairline at the temples
and balding at the top of the head. The end result may be partial or complete baldness.
• Female-pattern baldness (androgenetic alopecia) - Women with permanent hair loss
usually have hair loss limited to thinning at the front, sides or crown. Women usually
maintain their front hairline and rarely experience complete baldness.
• Cicatricial (scarring) alopecia - This rare condition occurs when inflammation damages
and scars hair follicles, causing permanent hair loss. Sometimes the patchy hair loss is
associated with itching or pain.
– Temporary Hair Loss:
• Alopecia areata - Hair loss usually occurs in small, round, smooth patches about the size
of a quarter. Usually the disease doesn't extend beyond a few bare patches on the scalp,
but it can cause patchy hair loss on any area that has hair, including eyebrows, eyelashes
and beard. In rare cases, it can progress to cause hair loss over the entire body. If the hair
loss includes your entire scalp, the condition is called alopecia totalis. If it involves your
whole body, it's called alopecia universalis. Soreness and itching may precede the hair
loss, but symptoms are often minimal
• Telogen effluvium - This type of temporary hair loss occurs suddenly, most often after a
significant illness or major life stress. Handfuls of hair may come out when combing or
washing your hair or may fall out after gentle tugging. This type of hair loss usually
causes overall hair thinning and not bald patches.
• Traction alopecia - Bald patches can occur if you regularly wear certain hairstyles, such
as pigtails, braids or cornrows, or if you use tight rollers. Hair loss typically occurs
between the rows or at the part where hair is pulled tightly.
• Anagen effluvium - In this type of hair loss, actively growing hairs in the anagen state
are affected most often by chemotherapeutic drugs given to fight cancer or lymphoma.
Hair loss starts soon after beginning therapy and is more extensive than in the telogen
effluvium state. In the weeks after the therapy has been completed, the hair cycles reestablish themselves, although the hair may not return as thickly as before
chemotherapy.
male pattern baldness
traction alopecia
female pattern baldness
alopecia areata