What would happen to a person blood osmolality when drinking seawater?

Answer 1

When you drink seawater, a high concentration of salt finds its way into your blood vessels. As a result, you have a higher concentration of solutes (salt molecules, in this case) on the outside of your blood cells than in your blood cells-- there is a hypertonic solution on the outside of the blood cells. Your body wants to keep solutions isotonic across the membranes-- that means your body wants the same amount of free water molecules on the inside of the blood cells as the outside-- so water molecules move out of the blood cells in order to keep the balance of free water molecules. The water moving out of the blood cells cause them to "crenate," or shrink, which is of course not very good for your cells.