eli5: How do we produce tears when we cry?

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Obviously we have glands that do that. When we are crying and making a lot of tears that fast, how do the glands get the water so quickly and where do they pull it from?

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They get water form the same place every other gland does-your blood. Blood contains a lot of water. Basically, what glands do is pump ions (salts) from one place to another. They take salt ions from the blood, and put them in the ‘lumen’ (the space in the gland where the tears or whatever collect) The water then follows the salts by osmosis.The average person is made up of like 50 liters of water, So a few ml of tears is no problem to get so quickly.