Sweat Gland

Sweat Gland

Sweat glands, or sudoriferous glands, are small tubular structures of the skin that produce sweat. There are two kinds of sweat glands:

• Eccrine sweat glands are found only in primates and reach their greatest development in humans. They are distributed all over the body (except for the lips, tip of penis and clitoris) although their density varies from region to region. Humans utilize eccrine sweat glands as primary form of cooling. The human thermal eccrine system has evolved in concert with bipedalism and development of smooth hairless skin.
• Apocrine sweat glands are larger, have different mechanism of secretion, and are limited to axilla (armpits) and perianal areas in humans. Although apocrine glands contribute little to cooling in humans, they are the only effective sweat glands in hoofed animals such as the donkey, cow, horse, and camel. Most other mammals, such as cats, dogs and pigs, rely on panting or other means for thermal regulation.

Domestic animals have apocrine glands at the base of each hair follicle but eccrine glands only in foot pads and snout. Their apocrine glands, like those in humans, produce an odorless oily milky secretion evolved not to evaporate and cool but rather coat and stick to hair so odor-causing bacteria can grow on it. Eccrine glands on their foot pads, like those on palms and soles of humans, didn't evolve to cool either but rather increase friction and enhance grip.

Both apocrine and eccrine sweat glands contain myoepithelial cells (from Greek myo-, "muscle"), specialized epithelial cells located between the gland cells and the underlying basal lamina. Myoepithelial cell contractions squeeze the gland and discharge the accumulated secretions. The secretory activities of the gland cells and the contractions of myoepithelial cells are controlled by both the autonomic nervous system and by the circulating hormones.

Ceruminous glands, which produce ear wax, and mammary glands, which produce milk, are frequently considered to be modified sweat glands, but they are not. Both ceruminous and mammary glands are true apocrine glands.