Muscle sphincters of visceral and superior mesenteric artery walls of domestic pig

A microscopic study was carried out on 10 specimens of visceral and superior mesenteric arteries and their branches, taken from domestic pigs. Some thickenings in the middle tunic of the visceral artery and its main branches were observed. The thickenings appeared at intervals of about 2 cm and were even several centimetres long. The structure of the thickenings was similar. Besides numerous circularly arranged elastic fibres, it contained clusters of modified myocytes located under the stratifying internal elastic membrane. In cross-sections, the myocytes, lying perpendicularly to the proper muscle layer, looked like epithelial cells, and due to that, they were defined as epithelial muscle cells. They formed a distinct ring around the vessels (superior mesenteric artery). They may play the regulatory function in relation to the circularly arranged myocytes.