Volume accommodation by distension of gastric fundus (rabbit) and gastric corpus (cat).

In attempts to identify the structures of the proximal stomach responsible for volume accommodation, the dimensions of a herbivore (rabbit) were compared to those of a carnivore (cat) stomach at various degrees of filling. The total gastric surface area was similar in both species, but the proximal stomach of cats consisted primarily of the segment between the incisura angularis and the cardia (gastric corpus), while the proximal stomach of the rabbit was represented largely by the true fundus (segment orad to cardia). In both species, the muscle coat of the proximal stomach was thinner than that of the distal stomach, but this difference was more prominent in rabbits than in cats. In both species, the length and the angulation of the lesser curvature were little affected by filling of the stomach. Most length increases of the greater curvature occurred proximal to the cardia in the rabbit and proximal to the incisura angularis in the cat. Filling the stomach increased the length of the gastric circumference more steeply in the cat than in the rabbit. In both species, the stomachs shortened in their longitudinal axis in response to a drug that excites gastric smooth muscle (carbachol). A drug that inhibits gastric smooth muscle (isoproterenol) gave the stomach a more elongated shape. Cat stomachs ruptured at higher volumes and intragastric pressures than rabbit stomachs. In the cat, volume accommodation takes place in the transverse axis of the stomach, and parallel to the circular muscle fibers of the gastric corpus. In the rabbit, volume unfolds the gastric fundus in the longitudinal and transverse axes in parallel to the radiating course of the oblique muscle fibers.