Regulations of intakes: clearances

1) Intakes of substances (oxygen, food) are related to availability or concentration of the substance that is being taken from the environment. This removal accords with dimensions of clearance. 2) Intakes from limited sources, as gut or pocket, also vary with the concentrations there. 3) Reabsorptions of selected substances during excretion are intakes into body. 4) Intakes respond to bodily deficits of materials (water, sodium, heat). Wherever plasma or other concentrations are measured, intake clearances may be computed. These four relations allow quantitative comparisons of the mechanisms and regulations for transport of various substances into body or cells. Kinetic "constants" can be estimated.