Chapter 44 - Regulation of sweating

Abstract

Regulation of sweating plays an important role in thermoregulation. There are two types of human sweat glands, apocrine and eccrine. The full complement of eccrine sweat glands is present at birth and undergoes a gradual reduction in numbers with increasing age. Sweat glands are morphologically complex. Sweat glands are primarily innervated by sympathetic cholinergic nerve fibers although in utero innervation is adrenergic and undergoes an adrenergic to cholinergic innervational switch during development. Cholinergic and adrenergic innervation of sweat glands is of M3 receptors although human eccrine sweat glands are also innervated by vasoactive intestinal peptide, CGRP, and substance P fibers. The density of human sweat glands varies greatly, being most dense around the palms with a rostral to caudal gradient. There are sex differences in sweat glands with larger volume in males compared to females although absolute number of sweat glands is similar. Sweat glands may hypertrophy with repeated stimulation. With denervation, preganglionic or postganglionic, sweat gland size and function become greatly reduced and undergo significant atrophy. Transynaptic degeneration may also occur. Denervation and atrophy of sweat glands may manifest with disorders of hypohidrosis or anhidrosis while excessive stimulation may manifest as hyperhidrosis (see Sweating Disorders Chapter 125).