Define the control of tear production.
Control of Tear Production
The lacrimal secretary system was initially thought to be comprised of two parts, basic secretors and reflex secretors. Basic secretion corresponds to the accessory glands of Krause and Wolfring and reflex secretion to the main lacrimal gland.
Now, it is thought that all lacrimal glands respond as a single unit. The aqueous Eyelids, Lacrimal and Tear Film portion of tear fluid consists of reflex and basic secretois. Basic secretion occurs under sympathetic control (by blood flow regulation through the gland). Reflex secretion is controlled by the main lacrimal gland under parasympathetic control. There are two types of reflex secretion-peripheral and central reflex. Peripheral reflex occurs by stimulation of 5th nerve in the cornea. Central reflex occurs by the stimulation of the retina or psychogenic events. The aqueous component functions in hydration, lubrication, and oxygenation of the tear film. The lipid portion of tear fluid is secreted by the meibomian glands and functions in lubrication and prevents evaporation. The mucus layer is secreted by goblet cells and converts the corneal epithelium from a hydrophobic to a hydrophilic layer.