How does the kidney filter blood?

On a hot day you feel thirsty and gulp down glass after glass of water… Then comes the urge to pee, which originates from two bean-shaped organs that act as sensors for the body's purification. They balance the body's fluids, detect waste in the blood, and know when to deliver vitamins, minerals, and hormones that sustain life. These two organs are the kidneys.

The process of kidney blood filtration

The main role of the kidneys is to remove waste products and turn them into urine. The body's 8 liters of blood pass through the kidneys about 20-25 times a day, meaning that these two kidneys filter about 180 liters in 24 hours. The composition of substances in the blood is always changing as you digest food and drink, so the kidneys are constantly working.

Blood enters the kidneys through arteries, which then branch out until they become tiny blood vessels that weave into specialized parts of the kidneys called nephrons. Each kidney has 1 million nephrons that form a highly precise network of filters and sensors that meticulously monitor all the blood in the body as it passes through. To filter blood, each nephron uses two powerful components: a teardrop-shaped structure called a glomerulus and a long, straw-like tube called a renal tubule.

Balanced nutrition

The glomerulus acts as a filter that allows only certain substances, such as vitamins and minerals, to pass into the tubule. It is then the job of this circuit to determine which of these substances are needed and leave enough for the body to continue circulating in the blood.

Waste disposal

But blood carries not only nutrients but also waste products. Once again, the nephrons are needed to process them. The renal tubules detect compounds the body does not need, such as urea, a waste product of protein breakdown, and expel them from the kidneys as urine. The urethra carries the waste products to the bladder, where they are excreted from the body.

Water balance

There is also water in urine. If the kidneys detect that there is too much water in the blood, they will carry the excess water to the bladder to be excreted. On the other hand, if there is too little water in the blood, the kidneys will release some of it back into the blood, which means there will be less water in the urine. That is why urine is dark yellow when the body is dehydrated.

The kidneys also activate vitamin D, secrete a hormone called Renin that increases blood pressure, and another hormone called Erythropoietin that increases red blood cell production. Without the kidneys, the amount of fluid in the body would get out of control. The waste would build up and overload the body, and we would die. Therefore, each kidney is responsible for keeping the system running smoothly to sustain life. And fortunately, we have two kidneys.