Sweat is produced by eccrine glands as an isotonic precursor fluid. As it moves through the duct, it becomes hypotonic. Which mechanism is responsible for making sweat hypotonic by the time it reaches the skin surface?

• A Active secretion of water from the duct lumen
• B Reabsorption of Na+ and Cl- in the duct exceeding water reabsorption ✓
• C Osmotic equilibration with the interstitial fluid
• D Active secretion of K+ into the duct lumen

Explanation

The eccrine gland secretory coil produces a fluid isotonic to plasma. As this fluid passes through the duct, Na+ and Cl- are actively reabsorbed while the duct is relatively impermeable to water, resulting in hypotonic sweat at the skin surface. Aldosterone enhances Na+ reabsorption in the duct. Active water secretion does not occur in sweat ducts.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.