Essentials of Anatomy & Physiology   3/e   Seeley/Stephens/Tate
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Functions of the Integumentary System

The integumentary system separates and protects us from the external environment. Other functions include sensation, vitamin D production, temperature regulation, and excretion of small amounts of waste products.

Hypodermis

• The hypodermis is loose connective tissue that attaches the skin to underlying tissues.

• About half of the body's fat is stored in the hypodermis.

Skin

Dermis

• The dermis is dense connective tissue.

• Collagen and elastic fibers provide structural strength, and the blood vessels of the papillae supply the epidermis with nutrients.

Epidermis

• The epidermis is stratified squamous epithelium divided into strata.

• Cells are produced in the stratum basale.

• The stratum corneum is many layers of dead, squamous cells containing keratin. The most superficial layers are sloughed.

• Keratinization is the transformation of stratum basale cells into stratum corneum cells.

• Structural strength results from keratin inside the cells and from desmosomes, which hold the cells together.

• Permeability characteristics result from lipids surrounding the cells.

Skin Color

• Melanocytes produce melanin, which is responsible for different racial skin colors. Melanin production is determined genetically but can be modified by hormones and ultraviolet light (tanning).

• Carotene, a plant pigment ingested as a source of vitamin A, can cause the skin to appear yellowish.

• Scattering of light by collagen produces a bluish color.

• Increased blood flow produces a red skin color, whereas a decreased blood flow causes a pale skin color. Decreased blood oxygen results in the blue color of cyanosis.

Accessory Skin Structures

Hair

• Hairs are columns of dead, keratinized epithelial cells. Each hair consists of a shaft (above the skin), root (below the skin), and hair bulb (site of hair cell formation).

• Hairs have a growth phase and a resting phase.

Muscles

• Contraction of the arrector pili, which are smooth muscles, causes hair to "stand on end" and produces "goose flesh."

Glands

• Sebaceous glands produce sebum, which oils the hair and the surface of the skin.

• Merocrine sweat glands produce sweat, which cools the body.

• Apocrine sweat glands produce an organic secretion that can be broken down by bacteria to cause body odor.

Nails

• The nail consists of the nail body and nail root.

• The nail matrix produces the nail, which is stratum corneum containing hard keratin.

Physiology of the Integumentary System

Protection

• The skin prevents the entry of microorganisms, acts as a permeability barrier, and provides protection against abrasion and ultraviolet light.

Sensation

• The skin contains sensory receptors for pain, heat, cold, and pressure.

Vitamin D Production

• Ultraviolet light stimulates the production of a precursor molecule in the skin that is modified by the liver and kidneys into vitamin D.

• Vitamin D increases calcium uptake in the intestines.

Temperature Regulation

• Through dilation and constriction of blood vessels, the skin controls heat loss from the body.

• Evaporation of sweat cools the body.

Excretion

• Skin glands remove small amounts of waste products but are not important in excretion.

Effects of Aging on the Integumentary System

• Blood flow to the skin is reduced, the skin becomes thinner, and elasticity is lost.

• Sweat and sebaceous glands are less active, and the number of melanocytes decreases.

The Integumentary System as a Diagnostic Aid

• The integumentary system is easily observed and often reflects events occurring in other parts of the body (e.g., cyanosis, jaundice, rashes).

Burns

• Partial-thickness burns damage only the epidermis (first-degree burn) or the epidermis and the dermis (second-degree burn).

• Full-thickness burns (third-degree burns) destroy the epidermis, dermis, and usually underlying tissues.

Skin Cancer

• Basal cell carcinoma involves the cells of the stratum basale and is readily treatable.

• Squamous cell carcinoma involves the cells immediately superficial to the stratum basale and can metastasize.

• Malignant melanoma involves melanocytes, can metastasize, and is often fatal.

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