Drowning is often the introduction of outside water into the alveoli, yet some water is normally present in alveoli. Why is water normally present in the alveoli? What is present in alveolar fluid, besides water, that aids in respiration? What properties of water are detrimental to respiration? What causes drowning? While extremely rare, there have even been documented cases of people walking

Question

away from recreational swimming only to die later, on dry land, as a result of drowning (termed "delayed" or "secondary" drowning). Propose an explanation for delayed drowning.

What will be an ideal response?

Answer 1

Water is present everywhere in living tissues, because all living cells require water as a diffusion medium for
solutes. Alveolar fluid is present in only a thin layer because it contains surfactant, preventing it from collapsing
the alveoli due to surface tension. Oxygen has low solubility in water, but the large total surface area of alveoli
combined with the thinness of the water layer in the alveoli allows for sufficient oxygen to enter the blood.
Inhalation of water increases the amount of water and decreases the relative amount of surfactant. Less oxygen will
reach the alveolar membranes, and alveoli will collapse. Alveolar collapse combined with the low solubility of
oxygen in water will lead to hypoxemia and will trigger cardiovascular and respiratory reflexes. Delayed drowning
likely results from tissue damage in the lungs and malfunction in other organs resulting from hypoxemia and
reflexes related to the water inhalation.