On the functional morphology of the equine large intestinal mucosa with special regard to its epithelium

The mucous membrane of the caecum and colon ascendens of adult horses was f irst studied using light and transmission electron microscopy. In the surfa ce epithelium there was an inconspicuous constellation of organelles, other wise there was a lot of mitochondria as a source of energy for absorptive p erformances. Moreover, enlarged intercellular spaces exist as an indication of an increased uptake of water and electrolytes. In the basal region of L ieberkuhn's crypts there were single enteroendocrine cells and numerous gra nules in the apical epithelial cytoplasm. The functional meaning of these g ranules is contrarily discussed in the literature. There was no epithelial activity of alkaline phosphatase. Against that a small positive reaction of adenosine triphosphatase was observed at the lateral plasmalemmata of the epithelial cells. The sense of these findings with regard to the transport of substances in the equine large intestine is discussed.