The human body has approximately 2 million sweat glands. The eccrine sweat gland consists of a single tubule, opening onto the epidermis at one end and closed at the other. The proximal half of the tubule is the secretory coil and the distal half the reabsorptive duct. The sweat secreted onto the skin is the original tubular secretion minus the substances which are, further up the tubule, reabsorbed; from the isoosmotic fluid secreted by the coil most of the major electrolytes (Na+, Cl_, HCO3, and lactate) are transported out of the duct back into the extracellular fluid in excess of water. The final sweat secreted onto the skin is therefore hypotonic with respect to body fluids.
Was this article helpful?