Most people are familiar with the term drowning. It has become known as suffocation and death caused by the filling of the lungs with water or other fluid. But the type of fluid a person drowns in has a significant impact on the effects and processes that take place in the body. For example, freshwater and saltwater drowning bring about differing processes within the body even though the end result is death.
In a functioning lung, air enters tiny air sacs called alveoli where the air comes into contact with blood cells in the capillaries. Oxygen is able to cross into the bloodstream and carbon dioxide is able to leave the blood stream and exit through the lungs upon exhalation. When drowning occurs, the lungs fill with water. Instead of air being transferred across the surface of the alveoli, liquids make this transfer, causing damage to the lung. Oxygen is no longer able to reach the bloodstream as it usually would.
The main difference between saltwater and freshwater drowning involves osmosis occurring between the surface of the lung and the blood stream. When freshwater enters the lungs, the low salt content allows the water to cross the membrane of the capillary walls and it will be absorbed into bloodstream. This causes damage to the blood and causes cardiac arrest very quickly.
When salt water enters the lung, the high salt content prevents it from crossing the membranes of the capillaries. Instead it causes blood and water from the bloodstream to cross over the membranes of the capillary walls and into the lungs. This not only prevents oxygen from entering the bloodstream, but also causes the victim to essentially drown in their own fluids.