anatomy

1. 5.8 Functions of Skin
• Skin is first and foremost a barrier
• Its main functions include:
– Protection
– Body temperature regulation
– Cutaneous sensations
– Metabolic functions
– Blood reservoir
– Excretion of wastes
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2. Protection
• Skin is exposed to microorganisms, abrasions, temperature
extremes, and harmful chemicals
• Constitutes three barriers:
– Chemical barrier
– Physical barrier
– Biological barrier
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3. Protection (cont.)
• Chemical barrier
– Skin secretes many chemicals, such as:
• Sweat, which contains antimicrobial proteins
• Sebum and defensins, which kill bacteria
• Cells also secrete antimicrobial defensin
– Acid mantle: low pH of skin retards bacterial multiplication
– Melanin provides a chemical barrier against UV radiation damage
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4. Protection (cont.)
• Physical barrier
– Flat, dead, keratinized cells of stratum corneum, surrounded by
glycolipids, block most water and water-soluble substances
– Some chemicals have limited penetration of skin
• Lipid-soluble substances
• Plant oleoresins (e.g., poison ivy)
• Organic solvents (acetone, paint thinner)
• Salts of heavy metals (lead, mercury)
• Some drugs (nitroglycerin)
• Drug agents (enhancers that help carry other drugs across skin)
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5. Protection (cont.)
• Biological barriers
– Epidermis contains phagocytic cells
• Dendritic cells of epidermis engulf foreign antigens (invaders) and present
to white blood cells, activating the immune response
– Dermis contains macrophages
• Macrophages also activate immune system by presenting foreign antigens
to white blood cells
– DNA can absorb harmful UV radiation, converting it to harmless
heat
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6. Body Temperature Regulation
• Under normal, resting body temperature, sweat glands produce about
500 ml/day of unnoticeable sweat
– Called insensible perspiration
• If body temperature rises, dilation of dermal vessels can increase
sweat gland activity to produce 12 L (3 gallons) of noticeable sweat
– Called sensible perspiration; designed to cool body
• Cold external environment
– Dermal blood vessels constrict
– Skin temperature drops to slow passive heat loss
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7. Cutaneous Sensations
• Cutaneous sensory receptors are part of the nervous system
– Exteroreceptors respond to stimuli outside body, such as
temperature and touch
– Free nerve endings sense painful stimuli
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8. Figure 5.1 Skin structure.
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Hair shaft
Dermal papillae
Epidermis
Papillary
layer
Subpapillary
plexus
Sweat pore
Appendages of skin
• Eccrine sweat gland
• Arrector pili muscle
• Sebaceous (oil) gland
• Hair follicle
• Hair root
Dermis Reticular
layer
Hypodermis
(subcutaneous
tissue; not part
of skin)
Cutaneous plexus
Nervous structures
• Sensory nerve fiber
with free nerve endings
• Lamellar corpuscle
• Hair follicle receptor
(root hair plexus)
Adipose tissue

9. Metabolic Functions
• Skin can synthesize vitamin D needed for calcium absorption in
intestine
• Chemicals from keratinocytes can disarm some carcinogens
• Keratinocytes can activate some hormones
– Example: convert cortisone into hydrocortisone
• Skin makes collagenase, which aids in natural turnover of
collagen to prevent wrinkles
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10. Blood Reservoir
• Skin can hold up to 5% of the body’s total blood volume
• Skin vessels can be constricted to shunt blood to other organs,
such as an exercising muscle
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11. Excretion
• Skin can secrete limited amounts of nitrogenous wastes,
such as ammonia, urea, and uric acid
• Sweating can cause salt and water loss
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12. 5.9 Skin Cancer and Burns
• Skin can develop over 1000 different conditions and ailments
• Many internal diseases reveal themselves on skin
• Most common disorders are infections
• Less common, but more damaging, are:
– Skin cancer
– Burns
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13. Skin Cancer
• Most skin tumors are benign (not cancerous) and do not spread
(metastasize)
• Risk factors
– Overexposure to UV radiation
– Frequent irritation of skin
• Some skin lotions contain enzymes that can repair damaged
DNA
• Three major types of skin cancer
– Basal cell carcinoma
– Squamous cell carcinoma
– Melanoma
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14. Skin Cancer (cont.)
• Basal cell carcinoma
– Least malignant and most common
– Stratum basale cells proliferate and slowly invade dermis and
hypodermis
– Cured by surgical excision in 99% of cases
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15. Skin Cancer (cont.)
• Squamous cell carcinoma
– Second most common type; can metastasize
– Involves keratinocytes of stratum spinosum
– Usually is a scaly reddened papule on scalp, ears, lower lip, or
hands
– Good prognosis if treated by radiation therapy or removed
surgically
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16. Skin Cancer (cont.)
• Melanoma
– Cancer of melanocytes; is most dangerous type because it is highly
metastatic and resistant to chemotherapy
– Treated by wide surgical excision accompanied by immunotherapy
– Key to survival is early detection: ABCD rule
• A: asymmetry; the two sides of the pigmented area do not match
• B: border irregularity; exhibits indentations
• C: color; contains several colors (black, brown, tan, sometimes red or blue)
• D: diameter; larger than 6 mm (size of pencil eraser)
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17. Burns
• Tissue damage caused by heat, electricity, radiation, or certain
chemicals
– Damage caused by denaturation of proteins, which destroys cells
• Immediate threat is dehydration and electrolyte imbalance
– Leads to renal shutdown and circulatory shock
• To evaluate burns, the Rule of Nines is used
– Body is broken into 11 sections, with each section representing 9% of
body surface (except genitals, which account for 1%)
– Used to estimate volume of fluid loss
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18. Figure 5.11 Estimating the extent and severity of burns using the rule of nines.
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Totals
41⁄2%
Anterior and posterior
head and neck, 9%
Anterior and posterior
upper limbs, 18%
41⁄2%41⁄2%
Anterior
trunk, 18%
Anterior and posterior
trunk, 36%
9% 9%
Perineum, 1%
Anterior and posterior
lower limbs, 36%
100%

19. Burns (cont.)
• Burns can be classified by severity
– First-degree
• Epidermal damage only
– Localized redness, edema (swelling), and pain
– Second-degree
• Epidermal and upper dermal damage
– Blisters appear
– First- and second-degree burns are referred to as partial-thickness burns
because only the epidermis and upper dermis are involved
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20. Burns (cont.)
• Burns can be classified by severity (cont.)
– Third-degree
• Entire thickness of skin involved (referred to as full-thickness burns)
• Skin color turns gray-white, cherry red, or blackened
• No edema is seen and area is not painful because nerve endings are
destroyed
• Skin grafting usually necessary
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21. Figure 5.12 Partial-thickness and full-thickness burns.
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1st-degree
burn
3rd-degree
burn
2nd-degree
burn
Skin bearing partial-thickness
burn (1st- and 2nd-degree burns)
Skin bearing full-thickness
burn (3rd-degree burn)

22. Burns (cont.)
• Burns are considered critical if:
– >25% of body has second-degree burns
– >10% of body has third-degree burns
– Face, hands, or feet bear third-degree burns
• Treatment includes:
– Debridement (removal) of burned skin
– Antibiotics
– Temporary covering
– Skin grafts
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23. Developmental Aspects of the Integumentary
System
• Fetal: by end of 4th month, skin of fetus is developed
– Lanugo coat: delicate hairs in 5th and 6th month
– Vernix caseosa: sebaceous gland secretion that protects skin of
fetus while in watery amniotic fluid
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24. Developmental Aspects of the Integumentary
System
• Infancy to adulthood: skin thickens and accumulates more
subcutaneous fat; sweat and sebaceous gland activity increases,
leading to acne
– Optimal appearance during 20s and 30s
– After age 30, effects of cumulative environmental assaults start to
show
– Scaling and dermatitis become more common
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25. Developmental Aspects of the Integumentary
System
• Aging skin
– Epidermal replacement slows; skin becomes thin, dry, and itchy
(decreased sebaceous gland activity)
– Subcutaneous fat and elasticity decrease, leading to cold
intolerance and wrinkles
– Increased risk of cancer due to decreased numbers of melanocytes
and dendritic cells
– Hair thinning
• Ways to delay aging:
– UV protection, good nutrition, lots of fluids, good hygiene
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