When a person cries, tear fluid is secreted by the lacrimal gland seen bulging the conjunctiva. This tear passes through numerous ducts into conjunctival sac, aided by ocular muscle contraction From there, it reaches the lacrimal sac and through the lacrimal duct, it is drained into the nasal cavity. (Lacrimal duct is anatomical drainage canal that connects the corner of the eye to the lower surface of the nasal cavity). When there is a sudden discharge of tear, as while crying, the fluid is pooled resulting in congestion.
Another interesting fact is that nature has provided with a flap valve at the terminal part of the canal to prevent tear fluid from being pushed by air, while sneezing or bowling.
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