The eccrine gland is the primary type of sweat gland found in human skin. These exocrine glands produce and secrete a watery substance directly onto the skin surface via a duct, making them indispensable for maintaining internal temperature stability. Their activity is a physiological response to internal and external temperature changes. The eccrine gland system is widespread and efficient, forming the largest exocrine gland organ of the body by aggregate weight.
Structure and Distribution
Each eccrine gland is a simple, coiled tubular structure composed of a secretory coil and a duct that leads to the skin surface. The secretory coil is located deep within the dermis or hypodermis, where it generates the initial sweat fluid from surrounding interstitial fluid. This coiled section is supported by myoepithelial cells, which provide structural integrity against the pressure of sweat production.
The duct extends upward through the dermis and epidermis, opening onto the skin surface through a sweat pore, or acrosyringium. These glands are distributed across virtually the entire human body, totaling between two and four million. They are most densely concentrated on the palms and soles, where density can reach up to 620 glands per square centimeter. Although less dense on the trunk and limbs, their large number ensures coverage across the entire body surface.
Primary Role in Thermoregulation
The primary function of the eccrine gland is thermoregulation, the body’s mechanism for stabilizing its core temperature. When internal body temperature rises, specialized centers in the hypothalamus recognize the change and initiate a cooling response. This response involves the sympathetic nervous system, which sends signals to the eccrine glands.
The glands are innervated by cholinergic sympathetic nerve fibers, which release acetylcholine to stimulate sweat production. Once secreted, the watery sweat spreads across the skin, where it undergoes evaporative cooling. As the sweat evaporates, it draws heat energy away from the skin’s surface, effectively lowering the body temperature. Under intense heat stress, the eccrine system is highly efficient and capable of producing several liters of sweat per hour.
Chemical Composition of Eccrine Sweat
The fluid secreted by eccrine glands is a sterile, odorless, clear solution that is approximately 98 to 99% water. The initial fluid produced in the secretory coil is nearly isotonic with blood plasma. As this fluid travels up the duct toward the skin surface, the duct acts as a reabsorptive unit.
The duct’s function is to reabsorb sodium and chloride ions back into the body tissue. This process, which occurs mostly in the proximal part of the duct, minimizes the loss of electrolytes. The resulting final sweat that reaches the skin is hypotonic, meaning it has a lower salt concentration than the initial fluid and the body’s plasma. Minor components include potassium, urea, ammonia, lactic acid, metabolites, and antimicrobial peptides like dermcidin.
Conditions Related to Eccrine Gland Dysfunction
Dysfunction of the eccrine glands can lead to two primary categories of conditions: excessive sweating and insufficient sweating. Hyperhidrosis is characterized by excessive sweating that goes beyond what is physiologically required for normal temperature maintenance. This condition can be localized to specific areas, such as the palms, soles, or armpits, or it can be generalized across the entire body.
Conversely, anhidrosis or hypohidrosis describes the reduced or complete inability to generate sweat when the body needs to dissipate heat. Anhidrosis severely impairs the body’s ability to cool itself. This impairment can rapidly lead to hyperthermia, heat exhaustion, or heat stroke, especially during physical activity or in hot environments. The underlying causes of eccrine dysfunction can range from problems with the central nervous system to physical obstructions or damage within the gland itself.