Accessory Organs of the Skin

Hair Function and Distribution

• Hair is distributed over the entire skin surface except:

• Palms, soles, and lips

• Nipples and portions of the external genitalia

Hair Follicle• Individual hairs develop from cells at the base of the

hair follicle, an invagination of the lower epidermis that dips down into the dermis

• As new cells are formed, old cells are pushed outward and become keratinized, forming the hair shaft

• A bundle of smooth muscle cells, called the arrector pili muscle, is attached to each hair follicle

• Hair color is determined by genetics; melanin from melanocytes is responsible for most hair colors, but red hair also contains the pigment trichosiderin

Hair Function and Distribution

• Functions of hair include:

• Helping to maintain warmth

• Alerting the body to presence of insects on the skin

• Guarding the scalp against physical trauma, heat loss, and sunlight

Sebaceous Glands (Oil Glands)

• Simple ~alveolar glands found all over the body

• Soften skin when stimulated by hormones

• Secrete an oily secretion called sebum

Sweat Glands• Different types prevent overheating of the body;

secrete cerumen~ and milk

• Eccrine sweat glands – found in palms, soles of the feet, and forehead. Respond to body temperature

• Apocrine sweat glands – found in axillary and anogenital areas. Respond to body temperature, stress, & sexual arrousal

• ~Eruminous glands – modified apocrine glands in external ear canal that secrete cerumen (wax)

• ~Mammary glands – specialized sweat glands that secrete milk

Structure of a Nail

• Scalelike modification of the epidermis on the distal, dorsal surface of fingers and toes

• Consist of epithelial cells overlying the nail bed, with the lunula as the most actively growing region of the nail root

• As new cells are produced, older ones are pushed outward and become keratinized.

Functions of the Integumentary System: Regulation of Body Temperature

• Body temperature regulation is accomplished by:

• Dilation (cooling) and constriction (warming) of dermal vessels

• Increasing sweat gland secretions to cool the body

• Excessive cooling: inactivates sweat glands, shivering

Healing of Wounds &

Burns

Wounds•Inflammation, in which blood vessels dilate and become more permeable, causing tissues to become red and swollen, is the body’s normal response to injury.•Superficial cuts are filled in by reproducing epithelial cells.•Deeper cuts are closed off by clots, covered by scabs, and eventually filled in by fibroblasts, making connective tissue. Blood vessels extend into the area, injured tissues are replaced, and the scab falls off.•Large wounds leave scars and healing may be accompanied by the formation of granulations.

Burns

• First-degree – only the epidermis is damaged– Symptoms include localized redness, swelling, and

pain• Second-degree – epidermis and upper regions

of dermis are damaged– Symptoms mimic first degree burns, but blisters also

appear• Third-degree – entire thickness of the skin is

damaged– Burned area appears gray-white, cherry red, or black;

there is no initial edema or pain (since nerve endings are destroyed)