Combining mathematics and physiology?
Typically, you will be better off studying mathematics with additional knowledge in X rather than a studying X with additional mathematics. Why? Because you can always enter X as a mathematician, they will welcome you with that. At least for academic jobs. 

Talking about mathematical biology: it is mostly mathematicians who do biology rather than the other way around. Granted, you will also find physicists and computer scientists there. 

A friend of mine claimed that the members of mathematical biology groups get their biology from Wikipedia and then apply their mathematics to it, most of which is settled in analysis of PDE and numerical analysis. He certainly exaggerated a bit, but there is truth in that statement.

Hence my recommendation: if these topic interest you, then pick a math graduate school that feature collaboration with math biology/physiology.