The effects of thermal stimulation on the ultrastructure of the fundus and duct of the equine sweat gland.

Sweating in the horse had little effect on the ultrastructure of the glandular duct, other than on the lumen which enlarged. The fundus secretory cells, which in the resting gland were packed with vesicles, gradually lost them as sweating progressed until, after 4 hours of activity, few remained. Sweat appeared to be largely the product of secretion (a) by fluid transport, probably involving a region of complex cellular interdigitations adjacent to the basement membrane and (b) by exocytosis of vesicles, although a secondary mechanism of vesicle loss by micro-apocrine secretion may occur. However, the products of cell death also contribute to sweat formation. The myoepithelium appeared contracted throughout. The function of the lower duct body, where complex basal infoldings of the luminal cells penetrated to the basement membrane, may differ from that of the upper portion. Dendritic Langerhans cells were found between the epithelia throughout the duct and fundus.