Sweat and sebaceous glands, nails and hairs – anatomy, histology and ultrastructural features.
SWEAT GLANDS
Sweat glands, also known as sudoriferous or sudoriparous glands, are small tubular structures situated within and under the skin (in the subcutaneous tissue). They discharge sweat by tiny openings in the surface of the skin.
The sweat is a transparent colorless acidic fluid with a peculiar odor. It contains some fatty acids and mineral matter. It is also called perspiration. Sweating regulates body temperature. The composition of the sweat determines whether body odor is a byproduct of sweating. There are two types of sweat glands, each secreting slightly different products.
- I. Eccrine glands - There are 2–3 million sweat glands distributed all over the body surface but they are most numerous on the palms, soles and axillae. They are coiled glands lying deep in the dermis, with the duct rising up to a pore on the skin surface, where the sweat is released. This type of sweat, released by exocytosis, is hypotonic and composed mostly of water, with some salt, antibodies, traces of metabolic waste, and dermicidin, an antimicrobial peptide. Eccrine glands are a primary component of thermoregulation in humans and thus help to maintain homeostasis.
- II. Apocrine sweat gland - usually associated with hair follicles in densely hairy areas, such as armpits and genital regions. Apocrine sweat glands are larger than eccrine sweat glands and lie deeper in the dermis, sometimes even reaching the hypodermis, with the duct normally emptying into the hair follicle. In addition to water and salts, apocrine sweat includes organic compounds that make the sweat thicker and subject to bacterial decomposition and subsequent smell. The release of this sweat is under both nervous and hormonal control. Most commercial antiperspirants use an aluminum-based compound as their primary active ingredient to stop sweat. When the antiperspirant enters the sweat gland duct, the aluminum-based compounds precipitate due to a change in pH and form a physical block in the duct, which prevents sweat from coming out of the pore.