Summary
The kidney is the organ of the urinary system where urine is produced. Urine is transported to the bladder by the ureters. It is finally eliminated from the organism through the urethra.Urine contains blood waste (urea, creatine, certain medications, etc).
It is at the level of the nephron of the kidney where the waste passes from blood to urine.
Click on
to view a section of a kidney and a nephron.Learning goals
- Discover the organs of the urinary system.
- Understand the structure and the role of the kidney.
- Explain the function of the nephron and the production of urine.
Learn more
Thanks to the formation of urine, the organism can eliminate waste found in blood: these are the substances resulting from metabolism (urea, urique acid, creatine...), medicinal or toxic substances. The formation of urine in the kidney allows for the regulation of the quantity of water and mineral salts (sodium ions, potassium...) from an organisms diet.Urine is comprised of 95% water, the 5% remaining are waste products.
Kidneys produce about 1.5 liters of urine per day.
Nephrons are the functional units of the kidney, where urine is produced. There are more than a million per kidney, situated on the cortex of the medulla. They are heavily integrated with blood vessels.
- at the Bowman's capsule, the blood arrives from the arterioles that form the glomerulus. It is here that filtration occurs. Most of the small molecules present in the blood pass through the Bowman's capsule and into the renal tubules (the larger molecules such as proteins, blood cells and platelets remain in the blood). This filtrate is called primitive urine. It contains mainly water, glucose, mineral salts, amino acids, vitamins and waste (urea, uric acid, creatine...).
- Along the renal tubules, the reabsortion of a large part of the previously filtered substances occurs. They return to the bloodstream. This is particularly the case with glucose molecules, amino acids and vitamins. Variable quantities of water and mineral salts are also reabsorbed.
- Along the renal tubules secretion also occurs. This means that molecules that are not filtered by the glomerulus, pass through capillaries toward the tubules. Urine is enriched with substances such as waste (urea, uric acid, creatine, ammonia..), certain medications, mineral salts... Urine is now called definitive urine. It is transported by the collector tubules to the calyx, which flow into the renal pelvis. Urine is then transported by the ureter to the bladder.
Sign up here with your email
ConversionConversion EmoticonEmoticon