A blood alcohol concentration (BAC) or blood alcohol level (BAL) reflects the amount of alcohol in the body. Food, type and quantity of beverage, weight, sex, and rate of elimination determine the BAC after the consumption of alcohol.
The process of oxygen transfer in the gills of a fish is a good example of the benefits of countercurrent exchange. As oxygen poor blood meets an opposed flow of oxygen rich water, the oxygen begins to diffuse out of the water and into the blood stream.
Likewise, dolphins, whose thin flippers glide constantly through cool water, seem to be just fine. A special circulatory adaptation called countercurrent heat exchange enables both species to maintain the appropriate body temperature in their extremities. Countercurrent heat exchange is only one of many clever adaptations mammals have to help them to deal with variable temperatures.