Electron microscopic study on the innervation of the human lower respiratory tract: evidence of adrenergic nerves

Samples of human lung were studied electron microscopically after fixation with glutaraldehyde and osmium tetroxide. Three different types of nerve profiles were found in the human lower respiratory tract. Type I nerve profiles contained small agranular vesicles 30-50 nm and large granular vesicles ranging from 60 nm to 210 nm. Type II nerve profiles contained small granular vesicles 30-50 nm and a few large granular vesicles ranging from 60 to 120 nm. Type III nerve profiles contained predominantly large irregular vesicles ranging from 60 to 210 nm, and only a few small agranular vesicles. The present electron microscopic results indicate that the smooth muscle layer of human bronchial tree receives adrenergic nerves.