Comparative and medical physiology: a theme with three variations

Abstract.

The aim of this essay is to show how a comparative approach, by adding new variables, might shed unexpected light on some well-known problems of general physiology. In my first example I describe how a classic study of the energetics of Na reabsorption in canine kidneys leads to new insights if kidney size is introduced as a co-variable. The second example demonstrates that if the maximum rate of ATP production does not suffice to meet the ATP-demand of a particular physiological function, the deficit metabolic fuel could be supplied by the ATP spared by the suppression of another function. In evidence I draw attention to the high metabolic cost of growth in larval fish, although any mammalian organ with high energy requirements could run into the same problem under energy limiting conditions. In the third example, I suggest that the experimentally determined degree of sensitivity of cellular functions to hypoxia could be used to make predictions about the ecology of the biological system studied. This inference would be valid irrespective of whether the term "ecology" refers to the external environment of different species or to the internal environment of different organs in the human body.