The eye's tears are composed of three layers: oil, water and mucous. The outermost oily layer is produced by the meibomian glands which line the edge of the eyelids. The watery portion of the tear film is produced by the lacrimal gland. This gland lies underneath the outer orbital rim bone, just below the eyebrow. The mucous layer comes from microscopic goblet cells in the conjunctiva.
With each blink, the eyelids sweep across the eye, spreading the tear film evenly across the surface. The blinking motion of the eyelids forces the tears into tiny drains found at the inner corners of the upper and lower eyelids. These drains are called puncta (plural for punctum).
The tear film travels from the puncta into the upper and lower canaliculus, which empty into the lacrimal sac. The lacrimal sac drains into the nasolacrimal duct which connects to the nasal passage. This connection between the tear production system and the nose is the reason your nose runs when you cry. Some patients can actually taste eye drops as they drain from the nasal passage into the throat.
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