In physiology, the<unk>  is the concentration of a substance dissolved in the blood above which the kidneys begin to remove it into the urine. When the<unk>  of a substance is exceeded, reabsorption of the substance by the proximal convoluted tubule is incomplete; consequently, part of the substance remains in the urine.<unk> s vary by substance – the low potency poison urea, for instance, is removed at much lower concentrations than glucose. Indeed, the most common reason for the glucose<unk>  ever being exceeded is diabetes, which is called glycosuria.<unk> s vary by species and by physiological condition; thus an animal may have different<unk> s while hibernating,<unk> s can also be altered by many drugs, and may change in characteristic ways during certain illnesses. Taken together, the collection of a kidney's<unk> s essentially define much of its function in<unk>  physiology. Many tests of kidney function amount to measures of<unk> s for various substances.
Renal threshold
Renal blood flow
Critical closing pressure
Vascular resistance
Effective renal plasma flow
Effective circulating volume
Cardiac reserve
Basal rate