The ultrastructure of the sweat gland duct of the ox, sheep and goat before and during sweating.

The duct of the cow, sheep and goat can be divided into two main parts, the intrafollicular region and the intradermal region. Three sub-regions, namely the perifollicular zone, the duct body and the duct/fundus transition zone, can be distinguished within the latter. In the outer portion of the hair follicle, the luminal surface was keratinized but the presence, in the cow and sheep, of surface microvilli with closely associated vesicles deeper within this layer suggested the possibility of a reabsorptive role. The intradermal duct had junctional complexes at the luminal extremity throughout its length. Gap junctions were observed between basal cells only in the lower part of the duct body. Dovetailing between luminal cells in the intradermal duct was barely noticeable in the cow but prominent in the goat. In the duct/fundus transition zone of all three species there was evidence of cell differentiation, the potential significance of which is discussed. There was little change in the ultrastructure of the duct in any of the three species, other than an increase in lumen size, as a result of heat exposure and sweating activity.