Microscopic Anatomy and Enzyme Histochemistry of the Canine Anal Canal

Abstract

AbstractThe microscopic anatomy of the anal canal was studied using routine histological methods and the light microscope in male and female dogs ranging from six months to 10 years of age. Precise anatomical boundaries were established for the zona columnaris, the zona intermedia, and the beginning of the zona cutanea. In an effort to clarify conflicting terminology concerning the anal canal, the term “anal sinus” (sinus anales) is applied to the shallow troughs located between the longitudinal mucosal ridges or columns (columnae anales) characteristic of the canine and human zona columnaris; and the term “anal crypt” is used to represent and distinguish the terminal blind pockets of anal sinuses which extend into the lamina propria of the zona intermedia.Anal glands were identified routinely in the z. columnaris and z. intermedia of the anal canal; dilated excretory ducts of the anal glands were frequently encountered, often filled with inflammatory cells. PAS‐positive but Sudan Black‐negative secretion was demonstrated in these ducts as well as within the secretory acini. Sebaceous, circumanal and apocrine sweat glands were restricted to the z. cutanea. Moderate to high alkaline phosphatase activity in the basement membrane of circumanal glands may suggest the presence of myoepithelial cells.