Integumentary SystemSkin

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Skin• surface area of 1.2-2.2 square

meters• weighs 9-11 lbs• 7% of total body weight

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Functions of Skin1. 3 types of barriers2. Chemical, Physical, Biological

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Chemical1. skin secretions2. melanin

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Skin Secretions1. Acid mantle2. Sebum3. Human defensin4. Cathelicidins

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Melanin1. Provides a chemical pigment

shield to protect from UV damage

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Physical1. continuity of skin2. hardness of the keratinized cells3. If too thick, lose suppleness and

agility4. If too thin, not as protective5. Waterproofing glycolipids

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Physical1. Lipid soluble items can penetrate2. oxygen, carbon dioxide, fat-soluble

vitamins, steroids3. certain plant chemicals (poison oak and

poison ivy)4. organic solvents (acetone, dry-cleaning

fluid, paint thinner5. salts of heavy metals (lead and mercury), &

drug agents

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Biological Barriers1. Langerhans' Cells2. active elements of the immune system3. for immune response to be activated,

the antigens must be presented to lymphocytes (WBCs)

4. the Langerhans' cells play this role in the epidermis

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Biological Barriers1. Macrophages in the dermis2. DNA molecules3. electrons absorb radiation and

transfer it to the nuclei, which heat up and vibrate to dissipate heat to surrounding water molecules

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Other Functions

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Body Temperature• regulates temperature within

homeostatic limits• as long as air is cooler than

internal temperature, the skin surface loses heat to the cooler objects in its environment

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Body Temperature• Sweat continuously, just

unnoticeable• when body temp rises, so does

sweat production• can lose up to 12L of water per day• evaporation of sweat cools the body

to prevent overheating

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Body Temperature• when the external environment is

cold, blood vessels constrict, this causes the warm blood to bypass the skin temporarily

• this slows passive heat loss, to conserve heat within the body

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Cutaneous Sensation• richly supplied with cutaneous

sensory receptors (part of the nervous system)

• Meissner's corpuscles• Merkel discs• Pacinian corpuscles• Hair Follicle Receptors

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Merkel’s Disc

Metabolic Functions•When sunlight bombards the skin, modified

cholesterol molecules circulating through blood vessels in the dermal layer are converted to a vitamin D precursor• These are transported via the blood to

other body areas to play various roles in calcium metabolism•Calcium cannot be absorbed from the

digestive tract without vitamin D

Blood Reservoir•Can hold large volumes of blood within the

dermal layer•About 5% of the body’s entire blood volume•When other organs need a greater blood

supply, the dermal vessels constrict, restricting the blood flow to the skin and shunting it to the needed areas

Excretion• Limited amounts of nitrogen-containing

wastes are eliminated though sweat (although most are excreted through urine)•Profuse sweating is an important avenue for

water and salt loss