Complex sentence: The largest quantities of lacritin is produced by the lacrimal gland while smaller quantities are also produced by the meibomian gland, and also by epithelial cells of the conjunctiva and cornea.
Split into simpler sentences: The largest quantities of lacritin is produced by the lacrimal gland. Some lacritin also is produced by the meibomian gland, and also by epithelial cells of the conjunctiva and cornea.