In the steady state, our total body water content and salt content remain constant. An increase or decrease in water and salt intake is paralleled by an equivalent change in renal water and salt excretion1 . Fluid homeostasis is achieved through the process of glomerular filtration of plasma to produce an ultrafiltrate. The tubules then process this ultrafiltrate so that the final urine flow rate and solute excretion meet the homeostatic needs of the body.
This is a companion discussion topic for the original article at https://patient.info/doctor/investigations/osmolality-osmolarity-and-fluid-homeostasis