General

Nephrons

A nephron contains a tiny ball of capillaries called a glomerulus, which is connected to a long, thin tubule. In the glomerulus, the blood comes into contact with the filter of the kidney.

The high pressure of the blood in the capillaries causes fluid containing dissolved substances (including drugs) to be released from the blood through the filter (1). The resulting liquid is called primary urine. The kidneys produce about 180 litres of primary urine per day.

More than 99 per cent of the primary urine is returned to the blood. This takes place via capillaries that surround the nephron tubule. The liquid, minus the waste products, is reabsorbed by the blood (2). What remains in the tubule is a small amount of water containing the waste matter. This is the final urine. The tubule conducts the urine to the renal pelvis, from where it flows on to the bladder (3).