You are most certainly familiar with this: every day you have an insane amount of things to do, to make your life work exactly how you want it to. Your body feels the same way! To ensure that all tasks are being completed reliably, there are specialists for this in your body, your organs. You probably know most of them, but do you know what they are secretly doing for you?
With some of them it is quite clear: your heart pumps your blood through the body and your lungs are responsible for breathing. With others, it gets a bit more complicated. What does your liver do? Or your kidneys?
Basically, you can imagine this just like a big company: as long as all the specialists do their jobs reliably, the boss doesn't need to know exactly what they are doing all day. It's only when something stops working that he/she has to take a closer look and understand which tasks need some help.
In your body, you are the boss!
Why do we have kidneys and what do they do?
The kidney is so important that you actually have two of them. They are located at about the same height as your lower ribs, at the very back, to the right and left of your spine. Try finding your lower ribs to get an idea where the kidneys are!
Each of them weighs as much as an apple, so together they weigh about 300g. Because they are so important, they are protected by a layer of fat and a strong skin. This is called the renal fascia.
What are the key parts of a kidney?
Blood is pumped into the outer part of the kidney through the renal artery, which is normally red. This is called the kidney cortex.
Inside the kidney cortex are the renal corpuscles (glomeruli -- this will be explained in more detail in a moment), which are balls of tiny little veins. The wall of these veins have many tiny holes in it, much like a sieve. And that's exactly what's happening here: your blood is being sieved. You can think of it much like straining pasta in the kitchen. Your red and white blood cells and blood protein stay in the strainer, while sugars, urea, electrolytes, and water drain out. Behind the veins are the urinary tracts (tubules) that catch the sieved components.
Each renal corpuscle has its own urinary tract. They work so closely together that they are also called a functional unit of the kidney (=nephron). Only together can they function properly. In fact, you have about 1 million of these units in your kidneys.
Your kidneys produce your body's urine
The fluid collected in the urinary tract is called primary urine. Every minute, 125ml of primary urine are produced in your kidneys this way, which is almost 180 litres a day. Of course, you can't excrete that much. That's why your kidneys filters most of it back, retaining a few important substances, such as electrolytes. This way, it concentrates the primary urine. The result of this is the actual urine (secondary urine). It is collected in the renal pelvis and flows from there through tubes (=ureters) to your bladder.
Additional functions of the kidney
But that's not all. Your kidneys not only clean your blood, they also play an important role in regulating the fluid balance in your body. They also produce hormones. These are important for your bone strength, blood pressure regulation, and help you make blood.
Erythropoietin (short, "EPO") is an example of such a hormone produced in the kidneys. It enriches your blood with red blood cells, enabling oxygen transport. EPO is also one of the substances that top athletes, especially cyclists, are often caught for doping. By taking additional EPO, their blood becomes able to transport more oxygen. This leads to increased performance, especially in endurance sports.
As you can see, your kidneys are real workhorses. They work tirelessly and around the clock.
Each person has two kidneys, which are located at the level of the lower ribs
The kidneys cleanse your blood and act as a sieve, filtering excess fluid, salts and other substances into your urine
The magic of this filtering process happens in the so-called glomeruli, where excess substances are pressed out of the blood into the urinary tract