Urine is a clear, yellowish liquid formed in the kidneys that carries metabolism waste to the outside of the body.
It consists of 95% water, in which urea, toxins and minerals such as chlorine, magnesium, potassium, sodium, calcium, among others (which form the remaining 5%), are dissolved. It may also contain common substances, often used by the body, but which may be in excess, so the body has to get rid of them.
Are nephrons always working?
Yes, your activity is continuous and permanent. More than 1000 liters of blood pass through the kidneys daily, which means they filter all the blood from our body several times a day (because in our body there are only 5 liters of blood). Within 24 hours, nephrons produce about 180 liters of urine, but on average each person only excretes about 1.5 liters a day.
So where do the remaining gallons of urine the kidneys produce go?
It is true that a much larger amount of urine forms than is actually expelled, that is, not everything that comes out of the bloodstream will stop outside the body. If the kidneys daily produce 180 liters of urine, but are only responsible for excretion of 1.5 liters, this means that 178.5 liters have a different destination.
When blood is filtered, many things that pass to the kidneys are lacking in the body. So there are mechanisms to prevent these products from getting lost. It is the mechanism called reabsorption, which allows much of the water that comes out of the blood (about 99%) to get into the urine. Don't forget that 70% of our body is water and so we can live, so it has to go on. If we excrete every gallon of urine that forms, imagine the amount of water we would not have to drink every day to avoid dehydration. It is a matter of conserving the body's water content. But apart from water, with other substances happens exactly the same. Certain salts play very important roles in the body's functioning and their release could endanger health. In addition, it would be a waste to expel substances that may still be useful. In this way the body controls the quantities of the substances leaving and remaining.
Do the kidneys always form the same amount of urine?
No, because the amount of urine produced depends on the type of diet and obviously the amount of water ingested. If you eat very salty foods such as chips, your blood salt level increases. This increase causes the salt reabsorption (which normally occurs to prevent salt loss) from decreasing and so the amount of salt in the urine will increase. If you notice a decrease in the amount of salt in your blood, the body responds with an increased resorptive capacity and more salt comes back into the bloodstream. And this happens to many other substances. When their amounts increase in the blood, the body has mechanisms to prevent them from staying in the body and thus increases their amount in the urine. On the other hand, if their quantities fall, the intensity of the resorption of the substances in question increases, so that larger quantities are kept in the body.