Every organ in the human body has vital functions. The kidneys play fundamental roles in maintaining human health.

One of the most important functions of the kidneys is producing urine. This function is performed by nephrons, the morphological unit in our kidneys. A nephron is simply made up of the glomerulus, where urine is filtered from blood, and tiny tubes where the filtered fluid passes through and is finally turned into urine (these tubes are proximal tubule, loops of henle, distal tubule, and collector channels).

There are approximately one million nephrons in the two kidneys of an adult. Each nephron is designed to produce urine by itself. Kidneys cannot renew nephrons. The number of nephrons, therefore, decreases gradually because of kidney damage, disease, or aging. After the age of 40, the number of nephrons generally decreases ten percent every ten years, and as a result, an 80-year-old has 40% fewer nephrons than 40 years ago. This loss is not life-threatening because adaptive changes in the remaining nephrons enable them to dispose of water, electrolytes, and metabolic waste in proper amounts.

The functions of the kidneys can be stated as follows:

• Discharging metabolic waste from the body, i.e cleaning our blood. The most significant of types of waste are urea, creatine, and uric acid. The kidneys are the path to eliminating medicine and hormones from the body. Many antibiotics and hormones, or their metabolic end-products, are discharged through the kidneys.
• Maintaining the body’s water-electrolyte balance. The kidneys are charged with balancing the amounts or concentrations of water and substances conducting electricity, such as dissolved sodium, calcium, chlorine, and potassium. If there is too much water or salt, it is discharged through urine. If the amount of water or salt has decreased, then the kidneys keep them in the body by preventing their discharge through urine and hence maintain the balance.
• Establishing an acid-base balance. It is vital to balance the acid or base level of the blood and other bodily fluids. The pH of blood is maintained at 7.4. If is too low, there is an excess of acid. A great excess of acid (acidosis) can cause sudden death. If it too high – called alkalosis – it leads to many disorders.
• Regulating the osmolarity of bodily fluids. The solid substances in blood (Na, K, glucose, amino acids, protein, etc.) must have a certain density. We can talk about the collective, rather than individual, density of the solid substances. One mole of solid particle in a liter of water (6,02 x 10²³) produces an osmotic pressure of 1 osmole. All bodily fluids (intracellular fluids, extracellular fluids, and blood) have an osmolarity of 300 milliosmoles. The discharge of solid particles and water are performed by the kidneys according to this delicate balance.
• Regulating blood pressure. The kidneys perform critical functions in balancing blood pressure by increasing the amount of urine when blood pressure increases or by decreasing the amount of urine when blood pressure decreases. The amount of urine is normal during normal blood pressure. If blood pressure decreases by half, the amount of urine becomes zero. If blood pressure doubles, the amount of pressure increases eightfold.
• Secreting hormones. The kidneys act like an endocrine gland in the secretion of several hormones. One of the most important of these hormones is erythropoietin, used in the production of blood cells in bone marrow. The kidneys also play a significant role in the production of vitamin D, which has recently been considered to be a hormone rather than a vitamin. Renin is also secreted from the kidneys when blood pressure drops.
• Glyconeogenesis: This function is primarily performed by the liver. Yet we know that this process is carried out by kidneys as well. Glyconeogenesis is the production of sugar (glucose) from the glycerol of non-sugar substances and all amino acids.

What should we pay attention to if we want to protect our kidneys?

• Proteins. They are probably the most valuable nutrients. Meat, milk, and eggs are rich in proteins, but grains like wheat and legumes contain proteins, too. Amino acids obtained from proteins are used as building blocks of the body. In this regard, proteins are essential for nutrition. When they are taken in excess amounts, however, proteins are converted into other substances (sugar and fats) or spent for energy production. Meanwhile, ammonia and then urea are produced in the liver. The urea produced in the liver is discharged by the kidneys through urine. Excess urea is considered a burden for the kidneys, so it is a risk for our kidneys to consume too much protein (particularly red meat). If there is a case or probability of renal failure, protein intake should be reduced.
• Salt. Kidneys can easily get rid of water, yet it takes some effort to discharge salt. Kidneys especially suffer when they are left without water. If kidneys cannot discharge enough salt, blood pressure rises. Therefore, if a person has a risk of heart or kidney failure or have high blood pressure, you should cut down on salt. It is crucial for anyone overweight to stop consuming salt. Foods without salt (such as minced meat and potatoes) decrease the appetite and stop a person from eating too much. Besides, meals without salt partly reduce the absorption of food in the intestines. A low-salt diet is good not only for the heart and blood pressure but also for kidneys. Yet people whose kidneys work perfectly, especially children and teenagers, run no risk when they consume salty food. It is also known that excess salt contributes to the formation of kidney stones.
• Water. It is vital for kidneys. Water helps kidneys clean the blood. It is not possible without water to cleanse blood of salt, other waste materials, and drugs. You should therefore be careful about drinking sufficient water. The daily requirement varies from person to person. Drinking 4-8 glasses, or 1.5–2 liters, of water will usually meet the body’s daily requirement. Drinks such as tea and coffee cannot be substituted for water because they increase water discharge. The minimum amount of water required for cleaning an adult body in a desert environment is half a liter. Though rare, it can also be a burden or problem for the kidneys if a person drinks too much Solid substances such as sodium, potassium, and calcium can be lost in excess as a result of overdrinking water, just like dirt is washed away by a flood.
• Acidic foods and drinks. One of the most important functions of the kidneys is to get rid of the acids produced through metabolic activities in the body and to balance the pH of blood. It is harder to discharge acids than bases. Acidic foods and drinks should therefore be consumed moderately. Pickles, sour foods, sodas, and other fizzy drinks should not be eaten in excess. It should also be remembered that acidic foods and drinks can cause kidney stones.
• Smoking. One of the primary harms of the nicotine in cigarette smoke is the fact that it causes blood vessels to contract. Smoking is the main reason for vessel stiffness. Nicotine causes kidney vessels to contract, hence a decrease in blood circulation in the kidneys. When blood circulation in the kidneys decreases, blood is no longer cleaned and blood pressure rises.
• Alcohol. Alcoholic beverages raise acid levels in the blood and causes acidosis, which damages all the organs and primarily the liver. Alcohol has the same effect as smoking on kidney vessels and causes them to contract. Not only does excessive acid damage kidneys but it also facilitates kidney stones.
• Drugs. Of the body’s organs, the kidneys are the most sensitive to drugs. Using antibiotics in high doses may lead to kidney damage and acute kidney failure. It is a common mistake in public to use antibiotics without consulting with a doctor. Using painkillers for every pain also causes chronic damage in our kidneys. It is normal for a person to have certain pains in daily life. They should consult with a doctor to identify the cause of the pain and should refrain from using painkillers unless absolutely necessary.
• Vitamins. A lack of vitamin B₆ is known to cause kidney stones. Thankfully, vitamins are among the innumerable blessings bestowed upon humanity. Vitamin B₆is abundant in sunflowers, pistachios, chickpeas, fish, and starchy vegetables.