With the urine excretion the kidneys detoxify the body. At the same time they thus contribute to the regulation of the water and electrolyte balance. Urination takes place in three steps. First, the so-called primary urine is filtered through the work of the kidney. This is done by the kidney bodies. Primary urine is an almost protein-free, unfocused ultrafiltrate that is produced by the circulation of the kidneys. A total of 180 to 200 liters of primary urine are produced daily by the two kidneys. This comes from the 1500 to 1800 liters of blood that flow through the kidneys daily. Around 300 times a day, the entire blood flow of a person through the kidneys.
The composition of the primary urine is comparable to that of blood plasma. The difference lies essentially in the fact that larger blood components are trapped by the vessels before they can be processed by the kidneys.
The primary urine passes through the renal tubules, where it is resorbed and secreted. Protein, electrolytes, glucose and water are absorbed, resulting in secondary urine. From him about 19 liters are formed per day. Thereafter, these amounts of fluid are further concentrated and eventually pass through the renal pelvis and ureters into the bladder, from which they are excreted as urine. Every day these are 1.5 to two liters. Thus, the urine volume is reached.
The diuresis can fluctuate and in this context react to external factors. Under cold weather, diuresis increases in intensity. A similar effect is reduced air pressure from a height of 3000 meters. Numerous active ingredients in the diet also influence the urinary excretion. Caffeine increases diuretic activity. The same applies to alcohol. Both substances suppress the production of the hormone ADH (antidiuretic hormone), which in the kidneys promotes the return of water from the urine. However, when drinking coffee for long periods of time, the urinary excretion stabilizes again at a lower level.
Medicine makes use of the principle of diuresis by stimulating increased urinary excretion with special preparations in order to reduce the burden on the circulatory system. An increased volume of urine indirectly reduces the amount of blood and thus the burden on the heart. This effect helps especially patients with kidney and circulatory diseases.
Diuretic drugs are also used in poisoning. Water-soluble toxins are flushed out of the body in this way. Thus, the control of urine volume is one of the preferred treatment methods, especially in intensive care.
Diabetes patients, in turn, often have a much too high urinary output, which is why here, too, is usually intervened by medication. Increased urinary output of the kidneys due to increased pressure in the urinary tract is called osmotic diuresis. These processes are based on the retention of osmotically active substances in the tubules (tubes) of the kidneys. They are not returned to the blood after filtration.
In order to keep the concentration of the relevant substances at the required level, passively more water flows into the urine (polyuria) to be excreted. At the same time it is inspired by the drinking behavior. The osmotic diuresis can be artificially induced by administration of appropriate medicines to treat emergencies such as glaucoma, cerebral edema or acute renal failure.
The urine, thanks to its pH value, allows well-founded conclusions about human nutrition. For this measurement, the urine volume is used as a basis for reliable results. In normal diet, the pH of the urine varies between 4.6 and 7.5. He is thus in the acidic area. A protein-stressed food intake shifts the pH even more into the acidic environment. A high vegetable consumption in turn leads rather to the shift into the basic area.
The so-called urinary status in the early stage can refer to diseases of the kidneys (kidney stones, kidney tumor) and inflammation of the urinary tract. Also metabolic diseases such as diabetes mellitus and liver weakness are displayed in this way. If, for example, proteins, nitrite, ketones and blood components can be found in the urine, this indicates various possible diseases.
Nephrology is a branch of internal medicine, as well as urology, which is primarily responsible for surgical matters. It is a very diverse range of tasks, because in addition to the elimination of final products of metabolism, the kidneys also ensure the balancing of the physical water balance, the long-term regulation of blood pressure and the control of the acid-base balance.
The pH of the blood, which significantly influences the kidney activity, may, for example, only fluctuate within a relatively narrow range, as otherwise life-threatening conditions may occur. Again, the measured and logged urine volume provides important information. It also provides information on the synthesis of glucose in the kidneys, their hormone production and the concomitant breakdown of hormones such as peptides.