How do my kidneys work? What is a nephron?
Each kidney contains approximately one million similar functional units called nephrons. Each nephron consists of a glomerulus, this is a tuft of small blood vessels (glomerular capillaries) surrounded by a capsule (Bowman’s capsule), from which a tubule arises. The nephrons are situated in the cortex of the kidneys.1
Blood flow through the kidneys is immense in order to remove all the wastes that accumulate in the blood and thereby fulfill one of the renal functions. Approximately 1.2 litres of blood passes through the kidneys every minute which means that the kidneys process a total of approximately 1,700 litres of blood per day. The blood reaches the kidney via the renal arteries, which divide into many smaller blood vessels. Finally, the blood passes through the glomerular capillaries.1
The glomerular capillaries act as a filter and are thereby an important part of the renal filtering system.Because of the pressure exerted by the blood as it flows through the capillaries, substances such as water, salts, sugar, and wastes are pressed out of the blood vessels into the space of the Bowman’s capsule. This mixture is called primary urine. The primary urine passes through the tubule. The tubule is surrounded by a network of blood vessels. As it passes through the tubule, most of the components of the primary urine are reabsorbed, depending on the needs of the body. Of the approximate 150 - 180 litres of primary urine filtered through the glomerular capillaries during the course of a day, only about 1 to 2 liters of urine are actually excreted.1
The urine that remains in the tubule is collected in the collecting tubule and transported to the calices of the kidney. From there, the urine reaches the renal pelvis and is transported through the ureter into the bladder, the place of urine storage. The urethra transports the urine out of the body.1
- Tortora G, Derrickson B: Principles of Anatomy and Physiology, 11th Edition. Wiley 2006.