Comparative cytology of hydrochloric acid secreting cells

A comparative study of the oxyntic cells of the stomach of Vertebrates is presented. A system of membranous tubules which is apparently inter-convertible with the luminal plasma membrane is described as an important structural feature in all classes. In all Vertebrates with the sole exception of Mammals, this system shares a common cell with the structures involved in the secretion of zymogen. In Mammals it becomes segregated into a specialized cell type, the parietal cell, characterized in addition by the presence of a long tortuous intracellular canaliculus, which serves as its secretory pole. The hypothesis is presented and discussed that the parietal cell is capable of achieving a higher efficiency in hydrochloric acid secretion by the existence of the intracellular canaliculus which makes the immediate surroundings of the secretory pole independent of the contents of the gastic lumen. In Birds (whose gastric glands do not possess parietal cells) a corresponding effect can be achieved only by complex structures such as the compound gastric glands. An explanation is hereby offered for the unique features of the Avian stomach.