The integumentary system consists of the skin, hair, glands, and nails.
Functions of the Integumentary System
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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Contraction of the arrector pili, which are smooth muscles, causes hair to "stand on end" and produces "goose flesh."
- 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.
- The nail consists of the nail body and nail root.
- The nail matrix produces the nail, which is stratum corneum containing hard keratin.
- Protection
- The skin prevents the entry of microorganisms, acts as a permeability barrier, and provides protection against abrasion and ultraviolet light.
- The skin contains sensory receptors for pain, heat, cold, and pressure.
- 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.
- Through dilation and constriction of blood vessels, the skin controls heat loss from the body.
- Evaporation of sweat cools the body.
- Skin glands remove small amounts of waste products but are not important in excretion.
- 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 is easily observed and often reflects events occurring in other parts of the body (e.g., cyanosis, jaundice, rashes).
- 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.
- 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.