Steps towards health. Water-salt exchange

The kidneys, adrenal hormones and the central nervous system play a leading role in maintaining and regulating the water-salt balance.

The kidneys regulate the excretion or retention of water and electrolytes. This process depends on the concentration of salts in the body, which is maintained at the required level. Basically, this regulation is associated with sodium ions.


The kidneys are part of the urinary system, which also includes the ureters, bladder, and urethra.The urine filtered by the kidneys descends through the ureters into the bladder, where it can stay for some time, and then, as a certain volume is reached, it is expelled out through the urethra. This is the main way out of the "waste fluid" from the body.

Normally, urine does not contain the elements necessary for the body: proteins, amino acids, glucose.The kidneys are located in the retroperitoneal space on both sides of the spine, approximately around the 12th thoracic and 2nd lumbar vertebrae. As a rule, the right kidney is slightly lower than the left, as this depends on the adjacent liver.

The capsule of the kidneys is protected and securely fixed by the fatty tissue surrounding them. The presence of adipose tissue is vital! In its absence (with a pronounced weight deficit, body mass index less than 19 - see the article "Obesity Epidemic"), fixation is disturbed and mobility and prolapse of the kidneys become possible.

The kidneys are bean-shaped, dense structure 10–12 cm long and 5–6 cm wide, each weighing 120–200 g. With such small sizes, the kidneys perform a large number of vital functions:

  • removal of excess fluid;
  • excretion with urine of end products, in particular, products of nitrogen metabolism toxic to the body;
  • regulation of total blood volume and, consequently, blood pressure
  • regulation of the ionic composition and osmotic concentration of blood plasma;
  • acid-base state of the blood, in violation of which, multiple changes in functions in other organs are formed;
  • regulation of the formation of blood cells (erythropoiesis) and blood clotting;
  • regulation of calcium, protein, lipid and carbohydrate metabolism;
  • production of biologically active substances.

What structures provide all these functions?

The main structural and functional unit of the kidney is the nephron. There are up to 1.3 million of them in each kidney. And if for any reason the nephrons stop working, all kidney functions are disrupted. A nephron is a network of vascular capillaries through which blood flows. An arterial vessel enters each nephron, breaks up into many small vessels, forming a glomerulus (glomerulus), which reunite into one outgoing vessel.

In this system, primary urine is first formed from the blood, which, passing further along the complex canal apparatus of the nephron, is transformed in its composition into the final version of the “waste fluid”. The kidneys are able to do their job even with only 30% of their functional capacity (people can live normally with one kidney).

There is no other organ that is so heavily dependent on the blood supply. When it is violated, the kidney ceases to fully perform its functions. With the same mass of the kidneys and heart, 25% of the minute volume of blood falls on the blood supply to the kidney, while other organs - up to 7-8%.

Urine formation

Urine is formed from blood. What causes the liquid part of the blood to pass through the walls of the vessels into the capsule of the kidneys? Fluid filtration is provided by the difference in blood pressure in the vessel entering and exiting the nephron (due to the different diameters of the vessels).

Capillaries are the smallest and thinnest vessels. Usually the pressure in them is insignificant - about 15 mm Hg, but in the capillaries of the kidneys it reaches values ​​of 70 mm Hg, more characteristic of the middle artery.

As a result of such a difference in pressure, filtration occurs, which occurs spontaneously, without control from hormones and the central nervous system. Abundant blood supply and adequate blood pressure are important factors, changes in which in diseases (for example, kidney disease, hypertension) can lead to impaired urine formation and water and electrolyte balance in general.

What is filtered from the blood into the urine?

First, primary urine is formed in the kidneys (about 200 liters per day at a filtration rate of 125 ml / min), which, in fact, is blood plasma. Plasma differs from whole blood in the absence of formed elements (erythrocytes, leukocytes, platelets).

Normally, primary urine still contains low molecular weight components and glucose necessary for the body. But already at this stage, blood cells and proteins should not enter the urine.

What happens next?

At the second stage of urine formation, the amino acids necessary for the body, glucose and other substances remaining in the primary urine are returned back to the blood. There is also reabsorption (reabsorption) of salt (and here only sodium is meant) and water. And out of 200 liters, 60 liters remain - a third of the filtered volume.

Further, as a result of a cascade of sodium and water reabsorption processes, the volume of fluid in the kidneys gradually decreases and, accordingly, the concentration of urine increases.

Normal kidney function helps to retain water in the body.

How does this happen? Why is water returned to the bloodstream, and not brought out, and diuresis in humans is not 20–30 liters per day, but only 1.5–2 liters?

After the urine has come a long way, it enters the final section of the nephron, in which the reabsorption of sodium from the renal tubule into the blood is already under the control of the hormone of the adrenal cortex aldosterone.

We already know that sodium is an osmotically active substance. The salt passes back into the bloodstream and the water follows the sodium as a solvent. As a result, urine has the highest concentration at the exit.

How does kidney function depend on blood pressure?

The kidneys are the first organ to respond to changes in blood pressure.

With a drop in blood pressure, blood flow in the kidneys decreases, which leads to their hypoxia (oxygen starvation). In response, the kidneys secrete renin into the bloodstream (translated from the Latin "ren" means "kidney"), which starts a complex chain of reactions in the body, leading to vasoconstriction and an increase in overall blood pressure. As a result, blood flow to the kidneys increases and their functions are restored. So normally (when a person is healthy, attentive to himself, and all his physiological mechanisms of regulation are preserved), the compensatory renin-angiotensin-aldosterone mechanism of regulation of blood pressure and blood volume in the body works.

Why do these mechanisms fail?

At first, we do not feel a decrease in blood pressure. Feeling some weakness or just for the sake of pleasure, we “keep up” with a cup of coffee or tea in the morning and throughout the day. The effect of caffeine on blood vessels, the lack of a normal drinking regimen, and taking medications lead to a failure of the well-established system, which is already causing arterial hypertension.

For what? And why is it said that the liver is “to blame” for the increase in pressure?

This is because the liver produces angiotensinogen, an inactive form of angiotensin. It constantly circulates in the blood and does no harm to us. But when renin is released into the blood, a chain of angiotensinogen conversion (under the action of a substance produced by lung cells - angiotensin-converting enzyme - ACE) is launched into the active substance angiotensin, which already has a powerful vasoconstrictor effect. This is one of the mechanisms for increasing blood pressure. Blood pressure lowering drugs often contain an ACE blocking agent that prevents the production of active angiotensin.

In addition to the vasoconstrictor and hypertensive action, angiotensin also activates the release of the adrenal hormone aldosterone into the blood, which increases sodium reabsorption. Following this, the return of water to the blood increases, which leads to an increase in its volume. And any increase in the volume of circulating blood again contributes to an increase in blood pressure. 

It turns out a vicious circle!

Why did I describe this in such detail? To understand how everything is complex and interconnected, how one pulls the “tail” of the other ... Any violations always have causes, and their consequences become the causes of the following changes, leading to diseases that, at first glance, can be very far from the root causes. 

Now we know how the work of the kidneys, the volume of circulating fluid and blood pressure are related.

There is another hormone produced in the central nervous system (in the hypothalamus), which is involved in the regulation of the normal level of fluid in the body - vasopressin. Its other name is antidiuretic hormone, that is, it reduces fluid secretion. It retains sodium, and therefore water.

This is important to prevent dehydration (as a result of polyuria) and maintain the amount of fluid the body needs.

Inadequate secretion of antidiuretic hormone leads to a disease such as diabetes insipidus, one of the clinical signs of which is polyuria - increased urination. Diuresis can increase up to 20 liters per day, respectively, such patients constantly drink fluid to make up for its loss.

So, normally a person has the following indicators: the volume of urine is 1.5–2 liters with a high osmotic concentration, there are no glucose, proteins, blood cells, microorganisms. If any of the above is determined in the urine, then now it is not difficult to understand at what stage of urination the violation occurred.

What do diuretics (diuretics) do?

They enhance the process of urination by inhibiting the reabsorption (reabsorption) of sodium. Sodium pulls water along with it, which leads to an increase in urine output. Usually diuretics are prescribed for hypertension, edema, kidney disease. And, as a rule, it is recommended to limit the amount of liquid and salt (up to a salt-free diet). Is it correct?

On the scale of the body, this is a violation of water-salt metabolism.

"Spot acting" medicines can be used to reduce pressure or swelling in the here and now. These are emergency actions. How can you take them for years, and sometimes decades, constantly increasing the number of other medicines designed to neutralize the side effects of diuretics?

Children's features

In early childhood, the kidneys are insensitive to antidiuretic hormone.

Babies should be given water to drink. Not juices, not “soothing” sweet teas, but just water, since it is the lack of water in the tissues that can cause anxiety.

If children do not get enough water (not milk, since milk is food), then this can lead to tissue dehydration, intoxication, fever, stool and sleep disturbance.

Remember, newborns and infants do not develop a sense of thirst!

If you violate the feeding regimen and give children (according to their habits) highly salty foods, this can cause swelling in the tissues, since increased osmolarity contributes to fluid retention in the body. Therefore, it is necessary to treat the feeding regimen of children and the water regime with great care and caution.

Why am I talking about this in too much detail? Definitely not for you to understand complex mechanisms, which even many doctors do not remember. But in order for you to understand how many organs and systems are involved in a seemingly “simple” decrease or increase in blood pressure, a decrease in urine output, the formation of edema, etc. So that you do not calm down on the medicines chosen for you “until the end of your life”, which “stabilize” pressure, urine output, etc., but set out to improve the functioning of your organs through lifestyle control. (The lack of control of which has already led or will certainly lead to illness). To avoid taking medications as much as possible, which are always toxic and alien to the human body, and lead to secondary changes in other organs.

I urge you not to calm down on “slightly increased” indicators in the analyzes, “small doses” of medications taken, and not to rely on “maybe it will somehow resolve itself”.

Be aware of your condition. Map out the path you will take to become healthy.

What is needed for this?

Establish food and water intake.

A person cannot even think if he wants to eat or drink heavily. Our ability to think also depends on the physical and chemical parameters of our body.

JUST DRINK WATER! This will prevent tissue dehydration, blood clotting and increased blood pressure.

Tea, coffee, fruit drink, compote, milk, soup - this is not water. These are either drinks that have their own effect on the body, or food that consumes water in the process of assimilation.

Pay attention to the consumption of natural salt. It is needed, but its quantity matters. Salt-free diets also lead to disorders. We need a balance, a “golden mean”.

Move! Energy practices such as qigong, taiji, breathing and yoga practices can help. And it is good if we do not interfere with the healing actions of these practices with the wrong diet.

Keep a sleep and wake schedule! Give the body the opportunity to recover and cleanse itself during sleep from 22.00 to 04.00.

Do not eat after 19.00.

Be calm, balanced, kind to everyone. To calm the mind, do meditation regularly. Reading prayers is also meditation.

If you already have health problems, or you don’t know where to start the examination, seek help from alternative medicine specialists involved in restoring the functions of the whole organism. This will make it possible to reduce or completely refuse to take chemical medications and go to a healthy full life without them.

Be healthy!


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