An Activity Model to Demonstrate Countercurrent Exchange

Abstract

Countercurrent exchange for the efficient movement of molecules across biological membranes is one of the most intriguing of the physiological adaptive mechanisms. At least one example of a countercurrent exchange mechanism was found in each of six college-designated textbooks examined. Although these textbooks are used in many advanced high school classes, the mechanism was presented in only one of 11 high school textbooks inspected (BSCS 1990). The most commonly presented example is the counter flow of the blood and water in fish gills (Audesirk & Audesirk 1996; BSCS 1990; Campbell 1996; Gould & Keeton 1996; Purves et al. 1995; Raven & Johnson 1996; Solomon et al. 1996). Heat exchange between arterial and venous blood to conserve heat as blood flows into the extremities of animals in a cold environment is the next most common example (Campbell 1996; Gould & Keeton 1996; Purves et al. 1995; Raven & Johnson 1996). The countercurrent multiplier system in the loop of Henle in the kidney was utilized by three of the authors (Campbell 1996; Purves et al. 1995; Raven & Johnson 1996). Counter flow of air and blood in the air sacs of birds is also cited in three texts (BSCS 1990; Gould & Keeton 1996; Raven & Johnson 1996). Only Gould & Keeton (1996) present countercurrent flow of air and blood in the nasal passages as a mechanism for cooling and moistening the air to prevent damage to lung tissue in hot arid environments and to remove heat from the blood traveling to the brain in panting animals. These authors also discuss the countercurrent exchange