An ultrastructural study of the smooth muscle cells and nerve endings of the human stomach.

The circular muscle layer of the human stomach was studied with the electron microscope. The smooth muscle cells differ structurally according to their location. In fact, the circular muscle layer of the fundus is made up of large, irregularly shaped smooth muscle cells, with long, thick, dense bands, and immersed in an abundant, elastic supporting connective tissue. In the circular muscle layer of the corpus (the two curvatures and the corpus between), those located in the outermost zone are identical to that commonly described in the alimentary tract, but are gradually substituted, first by larger irregularly shaped cells, and then, towards the innermost area, by flattened cells richer in sarcoplasmic reticulum, with thick and continuous dense bands on their submucosal surface. The smooth muscle cells of the antrum are all identical to the outermost located corporal ones. The gap junctions are absent in the fundus and in the innermost area of the corporal circular muscle layer, are present in the other areas, particularly frequent in the antrum and in the outermost area of the greater curvature. The number of the nerve endings is similar in the fundus, greater curvature and antrum, while it is two-three times more in the other parts of the corpus. They are located at the periphery of the muscle bundles in the fundus, antrum and greater curvature, sparsely scattered among the smooth muscle cells in the other areas of the corpus and contain small agranular and large granular synaptic vesicles, often mixed in the same axon. These nerve endings lie distant from the smooth muscle cells in the fundus, antrum and greater curvature and directly contact the smooth muscle cells in the other parts of the corpus.