Fine structure of a neuroendocrine complex in the mucosa of the appendix.

The fine structure of a neuroendocrine complex within the lamina propria of the human appendix is described. This complex contains four types of neurosecretory cells, occasional neurons, Schwann cells, and numerous nerve processes, including axons with varicose swellings. Few of the axons form true synapses, but many make some junctional contact with the neurosecretory cells and with other nerve processes. From the morphology of their vesicles, most of the nerve fibers appear to belong to the peptidergic component of the enteric nervous system. The mucosal neuroendocrine complex appears to be an integral part of the mucosal nervous plexus.