Which autonomic innervation drives eccrine sweat secretion during thermal stress?

• A Sympathetic adrenergic fibers acting on alpha 1 receptors
• B Parasympathetic cholinergic fibers acting on muscarinic receptors
• C Sympathetic adrenergic fibers acting on beta 2 receptors
• D Sympathetic cholinergic fibers acting on muscarinic receptors ✓

Explanation

Eccrine sweat glands receive postganglionic sympathetic fibers that release acetylcholine rather than norepinephrine, making them sympathetic cholinergic. The signal acts on muscarinic receptors, which explains why muscarinic agonists produce sweating and why atropine causes dry skin. Apocrine glands in axilla and groin are instead supplied by ordinary sympathetic adrenergic fibers responding to emotional stimuli. This exception to the rule of sympathetic noradrenergic transmission is repeatedly tested and also underlies the treatment of hyperhidrosis with anticholinergics.

Reference: Ganong's Review of Medical Physiology, 26th ed.

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