Tonicity Can Be Expressed in Multiple Ways

Abstract

We have provided a definition for tonicity 1 to eliminate many issues with the concept 2-4 in physiology education and proposed that there are multiples ways to express tonicity 1 . In this abstract, we prove this hypothesis using logical reasoning. OC 0 (the initial osmotic concentration in a solution compartment (S) before osmosis occurs) 5 is the key term to be used. If person A and B are playing a game and score 12 and 8 points, respectively, there are many ways (narrative or quantitative) to express the result of the game, such as “A won the game,” “B lost the game,” “A earned 4 more points than B,” “B had 4 points less than A,” “12 to 8” or “3 to 2.” Osmosis in an osmosis system (S 1 -m-S 2 ) can be viewed as a water-competing game between OC 0 (S 1 ) and OC 0 (S 2 ) across the membrane (m). If OC 0 (S 1 ) and OC 0 (S 2 ) equal 300 and 250 (mOsm/L), respectively, then the tonicity between S 1 and S 2 can be expressed as “S 1 is hypertonic to S 2 .” This also means that any expressions that mean “S 1 is hypertonic to S 2 ” are alternate ways to express tonicity, including 300:250, 6:5, Δ OC0 = 300 – 250 = 50 (mOsm/L), π (S 1 ): π (S 2 ), and Δ π = π (S 1 ) - π (S 2 ). These multiple expressions are not exclusive. Among these ways, “00:250” is most informative. Just like A and B can only own their points (12 and 8) and the score (12 to 8) can only be owned by the game, as we have addressed previously 1 , S 1 and S 2 own their points (OC 0 (S 1 ) and OC 0 (S 2 )) and the owner of the water-competing game (S 1 -m-S 2 ), not any solution owns tonicity. A tiny difference between the scores of “12:8” and “300:250” or “ Δ π ” is the following: “12:8” shows the result of the game, “300:250” predicts the result of osmosis or “ Δ π ” shows the result of osmosis. In fact, Δ π is the only accurate definition in a list of inconsistent, elusive definitions of tonicity in the literature we presented in a past work 2 . As long as the truth of tonicity is clear, the multiple expressions of it can be developed without confusion. Hence, it is incorrect to refer to “a solution’s tonicity” or “the tonicity of a solution,” as is commonly seen in the literature and causes great confusion 1 .