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Primary urine

German: Primärharn

1 Definition

Primary urine is the fraction of blood plasma which is filtered out by renal corpuscles.

While passing through the renal tubule, resorption and secretion take place which produces urine that is ready to be excreted.

see also: Modification of primary urine

2 Details

Due to the massive blood supply to the kidneys and the large number of glomerular filtration units (approximately 1 million nephrons per kidney), the body produces about 180 liters of primary urine daily. This corresponds to roughly 120 ml/min. Approximately 99% of primary urine is reabsorbed through the tubule epithelium so that only 1.8 liters have to be excreted every day.

3 Composition

The components of primary urine correspond to the composition of protein-free blood plasma. Macromolecules (e.g. proteins) cannot pass the glomerular filter which forms the blood-urine barrier.

Besides water, primary urine is mainly comprised of sodium and chloride ions as well as bicarbonate (hydrogen carbonate). Other components are:

see also: Kidney, Nephron, Filtration

This page was last edited on 29 April 2017, at 13:54.

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