How do kidneys work?

Depending on your weight, you have 4-6 litres of blood circulating in your body. This blood is transported to your kidneys via the renal arteries. Every day, approximately 1,500 litres of blood pass through your kidneys and are treated, thanks to roughly one million nephrons.

The nephrons consist of small filters called glomeruli that filter out a mixture of water, salts and waste materials from the blood. Protein and blood cells remain in the blood. The filtered fluid (primary urine) is transported in small tubules. There, we have a particular type of cells (tubular cells) that capture water and salts, such as sodium, calcium, phosphate and magnesium, and bring them back into the blood. What remains is excreted as final urine.

The amount of salts are absorbed through the tubular cells depends on the blood pressure and the concentration of certain hormones that affect these cells. Conversely, our kidneys also affect our blood pressure (for example, when the blood pressure decreases, more water and sodium is fed back into our blood). Thus, the kidneys regulates the balance of water and salts in our bodies.

Our kidneys also produce the hormone erythropoietin, which stimulates the production of red blood cells.