Accessory Structures of the Integument: Hair, Nails, and Glands

Accessory Structures of the Integument

Hair

The hair is a filamentous structure composed primarily of dead, keratinized epithelial cells. It is found on most body surfaces and serves several important functions.

• Structure: Each hair consists of a shaft (visible part), a root (embedded in the skin), and a hair follicle (the structure from which the hair grows). The base of the follicle contains the hair bulb, where cells divide and produce new hair.

• Function: Hair provides protection (e.g., scalp hair protects against UV radiation), sensory input (via hair root plexuses), and helps reduce friction (e.g., in the axillary and pubic regions).

• Example: Eyelashes protect the eyes from debris, while nasal hairs filter inhaled air.

Nails

Nails are hard, keratinized plates covering the dorsal surfaces of the distal phalanges of the fingers and toes.

• Structure: The nail consists of the nail plate (visible part), nail bed (underlying skin), nail matrix (site of nail growth), and the lunula (whitish crescent at the base).

• Function: Nails protect the distal tips of fingers and toes, enhance fine touch sensation, and aid in grasping small objects.

• Example: Fingernails help manipulate small objects and provide support for the tips of the fingers.

Sweat Glands

Sweat glands are exocrine glands that produce sweat, playing a key role in thermoregulation and excretion.

• Types: There are two main types: eccrine (or merocrine) glands, which are widely distributed and open directly onto the skin surface, and apocrine glands, which are found in specific areas (e.g., axillae, groin) and open into hair follicles.

• Structure: Sweat glands are coiled tubular glands located in the dermis or subcutaneous layer.

• Function: Eccrine glands help regulate body temperature through evaporative cooling, while apocrine glands are associated with scent production.

Sebaceous Glands

Sebaceous glands are holocrine glands associated with hair follicles that secrete an oily substance called sebum.

• Structure: These glands are branched alveolar glands typically connected to hair follicles.

• Function: Sebum lubricates and waterproofs the skin and hair, and has mild antibacterial properties.

• Example: Overproduction of sebum can lead to acne, especially during adolescence.

Composition and Function of Sweat and Sebum

• Sweat: Composed mainly of water, salts (especially sodium chloride), and small amounts of metabolic waste (e.g., urea, ammonia). Its primary function is to cool the body and excrete waste products.

• Sebum: A mixture of lipids (triglycerides, wax esters, squalene), cellular debris, and fatty acids. Sebum keeps the skin and hair moisturized and provides a barrier against pathogens.