Accessory Structures of the Skin: Sweat Glands

Eccrine and apocrine sweat glands are the two main types. Eccrine glands are distributed throughout the skin, secrete hypotonic sweat composed mainly of water and electrolytes, and function in thermoregulation. Apocrine glands are associated with hair follicles in areas like armpits, secrete thicker sweat containing fats and proteins, and activate at puberty in response to emotional stimuli and male sex hormones.

Eccrine sweat glands secrete water-based sweat directly onto the skin surface. When this water evaporates, it absorbs heat energy from the body, cooling the skin and regulating overall body temperature. Eccrine glands can secrete up to 600 milliliters of sweat daily, making them the primary component of thermoregulation in humans.

Eccrine sweat is hypotonic and composed mostly of water with some salt, antibodies, traces of metabolic waste, and dermcidin, an antimicrobial peptide. This composition allows eccrine sweat to cool the body through evaporation while also contributing to the excretion of metabolic waste products like urea and ammonia.

Sweat glands are small, coiled tubular structures located in the dermis, the middle layer of skin. Eccrine glands lie deep in the dermis with ducts rising to pores on the skin surface. Apocrine glands lie deeper in the dermis or hypodermis, with ducts opening into hair follicles rather than directly to the skin surface.

Apocrine sweat appears milky and contains fats and proteins. When bacteria on the skin degrade these organic compounds, they produce a generally unpleasant smell that renders the body its characteristic odor. This process differs from eccrine sweat, which is primarily composed of water and produces minimal odor.

Most commercial antiperspirants use aluminum-based compounds as their primary active ingredient. When the antiperspirant enters the sweat gland duct, the aluminum compounds precipitate due to a pH change and form a physical block in the duct, preventing sweat from exiting the pore and reaching the skin surface.

Beyond thermoregulation, sweat glands contribute to excretion by removing metabolic waste products such as urea and ammonia from the body. However, excessive sweating can disrupt electrolyte balance. Overall, sweat glands are essential in maintaining both thermoregulation and excretion processes, keeping the body cool and maintaining internal homeostasis.