tonicity vs. osmolarity

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So my question is, what is the difference between tonicity & osmolarity? I cant find an adequate explanation in my PR book or online. Any help?

Thanks in advance!

 

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So my question is, what is the difference between tonicity & osmolarity? I cant find an adequate explanation in my PR book or online. Any help?

Thanks in advance!

From what I remember, tonicity is only affected by non-permeating (NP) solutes whereas osmolarity considers NP and penetrating solutes. They both basically measure concentration. I believe osmolarity also measures dissociated species, so 1 mol NaCl has i=2 and 1 mol glucose has i=1. If you have the Silverthorn Human Physiology book, it gives an excellent explanation.