The smaller they are, the more complex and sophisticated work they perform. This could be the description of the kidneys, effective and specialized filters ridding the body of waste and toxic substances and returning minerals, vitamins, amino acids, glucose, hormones and other vital substances to the bloodstream. (1) "Most people know that the main function of the kidneys is to remove waste products and excess fluid from the body through urine," confirm experts at the National Kidney Foundation.
"However, that is far from all. We must not forget their regulatory and endocrine functions." (2) Among other things, the kidneys play a key role in regulating salt, potassium and acid content in the body. The endocrine function of the kidneys consists in the production of hormones that affect the function of other organs. "For example, erythropoietin, a hormone produced by the kidneys, stimulates the production of red blood cells. Other hormones created by the kidneys help regulate blood pressure or manage calcium metabolism," state nephrologists from the National Kidney Foundation. (2)
We will now look at what the functions of the kidneys are in more detail.
Basic function of the kidneys: Regulation of water and minerals in the body and removal of waste and toxic substances
1st function: Regulation of water intake and output
The proper functioning of the body depends on the optimal amount of contained water. One of the important functions of the kidneys is to remove excess water from the body, or to retain it when the body needs it (for example, when it is fighting an illness). The following table shows what the balance between water intake and output looks like. (3)
2nd function: Illustrative water balance
A constant water content in the body is the result of a balanced water balance. If we record the amount of water entering and leaving the body under standard conditions, i.e. in a normal daily regime without significant changes in the ambient temperature, physical activity and types of fluids consumed, we will obtain the following data:
| Intake (ml) | Output (ml) |
| 800 - 1 500 ml (drinking) | 800 - 1 500 ml (urination) |
| 500 - 700 ml (fluids in food) | 150 - 500 ml (sweating) |
| 200 - 300 ml (metabolism) | 250 - 400 ml (respiration)
100 - 150 ml (emptying school) |
| Total 1 500 - 2 500 ml | Total 1 300 - 2 500 ml |
3rd function: Balancing the level of minerals in the blood
The amount of minerals in the body must be subject to regulation in order to maintain their optimal level. Only in this way can the body function properly. "We receive sodium (in the form of salt) and potassium in food. The body cannot do without these minerals, but their correct level must be maintained, because an excess would not be good for health," explain experts from Michael Garron Hospital. (3) The proper function of the kidneys is such that the extra supply of sodium and potassium regularly leaves the body in the urine. The kidneys, of course, help regulate the level of other minerals, such as calcium and phosphorus. We take in a lot of minerals in food, in which case there is a risk of a simpler "overdose", which can also look like this:
- Sodium – excessive intake of sodium retains water in the body, which causes high blood pressure,
- Potassium – accumulation of potassium causes irregular heartbeat,
- Calcium and phosphorus – these electrolytes are closely related. (4)
4th function: Removal of waste and toxic substances from the body
Healthy kidneys filter about half a cup of blood every minute, removing waste products and excess water from the body through urine. (5) Urine removes waste products such as urea and creatinine from the body. “Urea and other waste products are created when the body breaks down proteins (for example, from meat food). Creatinine is a waste product of muscle activity," explain nephrologists from the Kidney Foundation. (6)
Did you know that: Decreased kidney function is recognized by the fact that the level of urea and creatinine in the blood increases? Blood creatinine level is an essential screening measure of kidney function. It is detected during an examination of the kidneys and urinary tract.
5. Advanced kidney functions: Reabsorption of glucose and transport of organic substances by the kidneys
Advanced kidney functions depend on the activity of the so-called sodium-potassium pump, which ensures the transport of organic substances, typically amino acids, urea, glucose, lactate, phosphates, proteins and uric acid (7), through the blood. The essential role of the kidneys is the so-called renal reabsorption of glucose, which means the return transport of filtered glucose into the blood, which prevents its elimination from the body through urine. Glucose is carefully guarded by the kidneys because it is an important organic substance involved in a number of body processes.
Simply put, it is the return of glucose back into the bloodstream. If glucose is not reabsorbed by the kidneys, it appears in the urine, a condition known as glycosuria, which is associated with diabetes (diabetes mellitus). Recent studies have shown that the kidneys are responsible for up to 20% of all glucose production, a process called gluconeogenesis. Under normal circumstances, up to 180 grams of glucose per day are filtered by the kidney glomeruli, and practically all of it is then reabsorbed back into the bloodstream. (8)
6. Endocrine function of the kidneys: Production of the three most essential hormones: erythropoietin, vitamin D and renin
Another important function that the kidneys perform is the endocrine process or the process of producing hormones essential for the optimal functioning of the body. Among other things, the kidneys are involved in the creation of three important hormones: vitamin D, erythropoietin and renin. (9) We will now look at them in more detail.
Vitamin D
The final activation of vitamin D to the hormone calcitriol takes place in the kidneys (10). Most of the vitamin D contained in the blood is initially inactive and its activation depends on the activity of the kidneys and other tissues. Active vitamin D stimulates calcium intake from food, maintains healthy bones and helps regulate the immune system's response to infection. (9) It also participates in the synthesis of collagen. (10)
Erythropoietin
The greater part of erythropoietin (90%) is synthesized in the kidneys, the rest in the liver. (10) Erythropoietin is a hormone that is formed when the oxygen level in the blood is low. It works in the bone marrow, where it stimulates the formation of red blood cells (in a process called erythropoiesis) and maintains the optimal level of oxygen in the tissues. (9)
Renin
Renin is a hormone involved in the regulation of water and minerals in the body. The impetus for its creation is low blood pressure. It follows that it is a hormone that participates in the regulation of blood pressure and the body's management of minerals and water. (10)
How do I know if I have reduced kidney function? The solution is to undergo an examination, because the disease is often only detected by a test
Reduced kidney function is not characterized by any obvious symptoms and is often only detected by a kidney function test. We recommend taking it every year. An examination of the kidneys and urinary tract, will show you how the filtering organ is doing with efficiency and health. Only healthy kidneys mean a healthy and fulfilling life.
Tip: The work of the kidneys is often connected with the work of the liver https://sk.unilabs.online/en/liver-profile (for example, with the mentioned renin) and the thyroid gland (for example, the relationship between reduced kidney function and hypothyroidism), so do not forget to undergo a liver examination and thyroid gland. Preferably every year so you don't neglect anything.
Kidneys are not only for removing waste substances from the body, the scope of their activity is much richer. They purify the blood, regulate the level of water and mineral substances in the body, participate in the creation of hormones and, last but not least, affect the work of other organs, most notably the liver and thyroid gland. Keep in mind the range of kidney function and don't forget to take care of them.
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