Structure of the paralacrimal gland

The traditional view is that the paralacrimal gland is an uninervated exocrine gland that secretes mainly the aqueous component of the basal tears, whereas the main lacrimal gland is innervated and independently undertakes reflex and cardiac tear secretion. Many scholars have challenged the idea that the paralacrimal gland is not innervated by indirect evidence, but no strong morphological basis has been seen. It was not until 1994 that Seifert et al. published the first electron micrographs of the presence of innervation in the paralacrimal gland, but further in-depth studies have been lacking to date.

Numerous unmyelinated nerve fibers of varying thickness were observed in the tissue interstitium of the paralacrimal gland. A varying number of axons were wholly or partially encapsulated in longitudinal grooves formed by depressions on the surface of the ceviche cells. The axons ranged from 200 nm-1 μm in diameter, and mitochondria, microtubules, neurofilaments, and vesicles containing neurotransmitters were seen in the axoplasm (axoplasm). There are two main types of vesicles, round clear synaptic vesicles with a diameter of 20-50 nm and large granular vesicles with a diameter of 80-100 nm. The granular vesicles have a dense nuclear core in the center and the core is surrounded by clear.

The axon terminals form "synaptic structures" with myoepithelial cells. The axon terminals were completely exposed without the cytomembrane of the Schwann cells and were located in the shallow groove formed by the depression of the cytomembrane of the myoepithelial cells or in parallel with the cytomembrane of the myoepithelial cells, and the synaptic gap between the two was 10-30 nm, and there was no obvious dense band in the presynaptic and postsynaptic membranes, and the surface of the axon membrane, which did not participate in the formation of synapses, was overlaid with the basement membrane. Mitochondria, a large number of round bright synaptic vesicles and a small number of large granular vesicles were seen in the presynaptic axon terminal expansion (varicosity).