The anatomy and innervation of the sphincter of oddi in the dog and cat

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Abstract
The fine morphology of the choledocho‐duodenal junctions of dogs and cats was studied by means of microdissection, classical histological staining techniques and by demonstrating in serial sections non‐specific cholinesterases, which stain the smooth muscle components excellently. The inbuilt cholinergic nervous apparatus was studied in serial sections by demonstrating acetylcholinesterase. By combining these methods, the three‐dimensional structural arrangement of the intrinsic cholinergic innervation system, with reference to the various substructures to be innervated, could be studied and mapped in detail.The most important features in the morphology, with respect to the function, were the tapering of the terminal ductus choledochus into a nozzle, the existence of concentric retrograde saccules around the ampulla and the intramural part of the bile duct, and the complex construction of the sphincters. Normally such a structure makes possible an active suction‐pressure pumping for evacuation of bile and pancreatic juice, being at the same time effective in preventing regurgitation of the duodenal fluid. On the contrary, if the orificium of the ampulla is obstructed, this structural arrangement probably facilitates regurgitation, especially into the pancreatic duct.The intrinsic cholinergic nervous apparatus of the choledocho‐duodenal junction was extremely rich, especially if compared with the cholinergic innervation of the muscular layer of the gut wall. This can probably be considered as an indication of complex motor (and possibly associated sensory) functions of the sphincters, in contrast to only slow gross contractions of the gut.To summarize: both morphological and neuroanatomical bases seem to be provided for rhythmic suction‐pressure pumping as well as for sensitive protective reflex functions in the choledocho‐duodenal junctions of the dog and cat. The finely graded complex interactions of the various muscle components are regulated by connecting and integrating neural elements between the individual smooth muscle units.