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In the alveoli, oxygen from the air is absorbed into the blood. Carbon dioxide, a waste product of metabolism, travels from the blood to the alveoli, where it can be exhaled. Between the alveoli is a thin layer of cells called the interstitium, which contains blood vessels and cells that help support the alveoli.
having the same tonicity or osmotic pressure as blood. lacrimal fluid. aqueous fluid secreted by the lacrimal glands; called also tears. fluid line. in radiographs, the interface between fluid and gas, as in the gastrointestinal tract, will show as a straight line.fluid loss. by vomiting, diarrhea, polyuria, water deprivation.t is composed of three layers: (1) The deepest and densest is the mucin layer (or mucous layer) which derives from the conjunctival goblet cells, as well as some secretion from the lacrimal gland. (2) The watery lacrimal fluid is the middle layer, called the lacrimal (or aqueous layer).