Urine formation: stages of the process, the role of the kidneys

The Human body provides an average of 2500 milliliters of water. About 150 milliliters appears in the process of metabolism. For uniform distribution of water in the body of its incoming and outgoing number should correspond to each other.

A Major role in the withdrawal of water play buds. Diuresis (urination) during the day equal to an average of 1500 milliliters. The remaining water is excreted by the lungs (about 500 ml), skin (about 400 milliliters) and a small amount goes a stool.

The Mechanism of formation of urine is a vital process that is implemented by the kidneys, it consists of three stages: filtration, reabsorption and secretion.

In the urine contains water, certain electrolytes and products of metabolism in cells. The formation of urine in the kidney is the nephron.

The Nephron is the morphological and functional unit of the kidney, the underlying mechanism of urine formation and excretion. Its structure has a doughnut, a system of tubules, the Bowman capsule.

In this paper, we consider the formation of urine.

Supply the kidneys with blood

Every Minute through the kidneys is approximately 1.2 liters of blood, which equals 25% of the blood entering the aorta. In human kidneys in mass amount to 0.43% of body weight. From this we can conclude that blood supply to the kidney is high (as a comparison, in terms of 100 g of tissue blood flow to the kidneys is 430 milliliters per minute, the coronary system of the heart – 660, brain – 53). What is primary and secondary urine? More on that later.

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An Important feature of the renal blood supply is that the flow of blood in them remains unchanged when changing blood pressure more than 2 times. Since renal arteries extend from the aorta peritoneum, there is always a high level of pressure.

Primary urine and its formation (glomerular filtration rate)

The First step of urine formation in the kidneys originates from the process of filtration of blood plasma, which occurs in kidney glomeruli. The liquid part of blood follows through the capillary walls into the recess of the capsule of the renal body.

Filtering is possible thanks to a number of features that are associated with the anatomy:

• Flattened endothelial cells; the edges are especially thin and have pores through which can not pass the protein molecule because of their large size;
• The inner wall of the container Shumlyansky-Bowman preplanetary is formed by epithelial cells, which are also not allowed to take large molecules.

Where the secondary urine is formed? More on that below.

What contributes to this?

The Main force, which provides the ability to filter the kidney, become:

• High blood pressure in the renal artery;
• Not bringing the same diameter of the renal arterioles of the body and the outflow.

Pressure in the capillaries is about 60-70 millimeters of mercury, and in the capillaries of other tissues it is equal to 15 millimeters of mercury. The filtered plasma easily fills the capsule of the nephron, as it is low pressure about 30 mm Hg. Primary and secondary urine – a unique phenomenon.

From the capillaries in the recess of the capsule filtered water and substances dissolved in plasma except for large molecular compounds. Salt related to the inorganic as well as organic compounds (uric acid, urea, amino acids, glucose), without resistance enter the cavity of the capsule. High molecular weight proteins normally do not go into its recess and is retained in the blood. The liquid which is filtered in the recess of the capsule is called primary urine. The kidneys of a person during the day form a 150-180 liters of primary urine.

Secondary urine and education

The Second stage of urine formation is called recurrent absorption (reabsorption) that takes place in the convoluted channels and loop of Henle. The process is passive on the principle of impulse and diffusion, and active, through the cell walls of the nephron. The purpose of this action is to return to blood and vital substances in the right amount, and output the final elements of exchange, foreign and toxic substances.

But where the secondary urine is formed?

The Third stage is the secretion. In addition to reverse suction, the channels of the nephron is an active process of secretion, that is, the allocation of blood substances which is performed by the cells of the walls of the nephron. During the secretion in urine from blood is creatinine, and therapeutic substances.

During the flowing process of reverse suction and the allocation of the secondary urine is formed, which is quite different from the primary urine in its composition. In the secondary high urine concentration of uric acid, urea, magnesium, chloride ions, potassium, sodium, sulfate, phosphate, creatinine. About 95 percent of the secondary urine is water, the dry residue remaining substances only five percent. A day is about one and a half liters secondary urine. Most of the load experienced kidney and bladder.

Regulation of urine formation

The kidneys samoreguliruetsja, as they are extremely importantbody. Kidneys contain plenty of fibers of the sympathetic nervous system and parasympathetic (endings of the vagus nerve). During stimulation of sympathetic nerves decreases the number coming to the kidneys and blood pressure in the glomeruli is going down, and the result is a slowing of urine formation. It becomes scarce in pain irritations due to sudden vascular contraction.

When the vagus nerve is irritated, it leads to increased urine formation. Also at the absolute intersection of all the nerves that come to the kidney, it continues normal operation, which indicates a high ability of self-regulation. This is evident in the formulation of active substances, erythropoietin, renin, prostaglandins. These elements control the blood flow to the kidneys, as well as the processes associated with filtration and absorption.

What hormones regulate it?

A Number of hormones regulates the functioning of the kidneys:

• Vasopressin, which generates a part of the brain the hypothalamus, increases the return absorption of water in the channels of the nephrons;
• Aldosterone which is a hormone of the adrenal cortex, is responsible for the increased absorption of Na⁺ and K⁺;
• Thyroxine which is a hormone of the thyroid gland, increases urine formation;
• The adrenaline produced by the adrenal gland and causes a decrease in the formation of urine.