The lacrimal apparatus consists of the lacrimal gland, which secretes tears, and the lacrimal duct, which excretes tears, including the tear duct, lacrimal duct, lacrimal sac, and nasolacrimal duct. In the inner corner of the eye, near the nose, there is a tear duct that absorbs tears. Tears flow through the eye and collect here and are inhaled, then flow into the nasal cavity through the tear duct, the tear sac and the nasolacrimal duct. Under normal circumstances, tears are continuously secreted in small amounts to maintain the moistening of the conjunctiva of the eye. After the tears are discharged, most of them are evaporated on the surface of the eye, and the rest flows into the nasal cavity via the nasolacrimal duct, mixed in the mucus phlegm on the surface of the nasal mucosa, and evaporated or excreted to the nasopharynx with breathing, because the amount is small and usually does not appear to be runny. When a person cries, sympathetic and parasympathetic nerves stimulate the lacrimal glands to secrete a lot, and part of the tears will flow into the nasal cavity through the nasolacrimal duct, while the nasal mucosal nerves are stimulated and the nasal secretions will increase, so a mixture of tears and nasal mucus will flow out. Generally, the nasal discharge will be reduced or stopped naturally after crying, but when a person is sad and cries for a long time, the nasal discharge will not stop immediately after stopping crying, but it will stop only after the mood is gradually calmed down. If you still have a runny nose after a long time, you may have a cold or a nasal disease, and you need to seek medical examination in time.