Renal excretion

Renal excretion is the removal of substances from blood into urine by the kidneys. It helps regulate waste levels, fluid volume, and the concentrations of ions and other solutes in blood.

Glomerular filtration: The movement of water and small dissolved substances from glomerular blood into the nephron. It starts urinary removal by filtering plasma while retaining blood cells and most proteins.
Glomerulus: A tuft of capillaries where blood plasma is filtered into the nephron. Its filtration barrier controls which blood components enter the forming urine.
Creatinine clearance: An estimate of glomerular filtration based on creatinine concentrations in urine and blood. It provides a practical measure of kidney filtration and excretory capacity.
Biliary excretion: The elimination of substances from the body through bile released into the digestive tract. It is a major alternative route for substances cleared from blood.
Tubular reabsorption: The transfer of substances from tubular fluid back into the blood. It retrieves filtered substances, reducing their excretion in urine.
Renal tubule: The nephron’s tubular passage, where filtrate is modified before becoming urine. Its transport processes decide what is retained and what is excreted.
Inulin clearance: A measure of glomerular filtration using filtered inulin, which is neither reabsorbed nor secreted. It estimates filtration without the tubular handling that complicates other markers.
Pulmonary excretion: The elimination of volatile substances from the body through the lungs. It contrasts kidney removal with excretion through exhaled air.
Tubular secretion: The transfer of substances from blood into the renal tubule after filtration. It adds selected substances to urine, including some drugs and excess ions.
Homeostasis: The maintenance of relatively stable internal conditions in an organism. Kidney excretion supports stability by adjusting waste, water, and solute levels.

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