- 3 main stages of urine formation
- 1. Ultrafiltration
- 2. Reabsorption
- 3. Secretion
- How urine is eliminated
Urine is a substance produced by the body that helps to remove dirt, urea and other toxic substances from the blood. These substances are produced daily by the constant functioning of muscles and by the process of digesting food. If these residues were to accumulate in the blood, they could cause serious damage to various organs in the body.
This whole process of blood filtration, waste removal and urine formation takes place in the kidneys, which are two small, bean-shaped organs that are located in the lower back. Check out 11 symptoms that may indicate that your kidneys are not working properly.
Every day, the kidneys filter about 180 liters of blood and only produce 2 liters of urine, which is possible due to the various processes of elimination and reabsorption of substances, which prevent the elimination of excess water or important substances for the body.
Due to all this complex process done by the kidneys, the characteristics of the urine that is eliminated can help to discover some health problems. So, see what the main changes in urine may indicate.
3 main stages of urine formation
Before urine can leave the body, it has to go through some important stages, which include:
1. Ultrafiltration
Ultrafiltration is the first phase of the urine formation process that takes place in the nephron, the smallest unit of the kidney. Within each nephron, the small blood vessels in the kidney divide into even thinner vessels, which form a knot, known as the glomerulus. This node is closed within a small film that is known as a renal capsule, or Bowman's capsule.
As the vessels become smaller and smaller, the blood pressure in the glomerulus is very high and thus the blood is pushed hard against the vessel walls, being filtered. Only blood cells and some proteins, such as albumin, are large enough not to pass and therefore remain in the blood. Everything else passes into the kidney tubules and is known as the glomerular filtrate.
2. Reabsorption
This second phase begins in the proximal region of the renal tubules. There, a good part of the substances that were removed from the blood into the filtrate are again reabsorbed into the blood through active transport processes, pinocytosis or osmosis. Thus, the body ensures that important substances such as water, glucose and amino acids are not eliminated.
Still within this phase, the filtrate passes through the loop of Henle , which is a structure after the proximal tubule in which the main minerals, such as sodium and potassium, are again absorbed into the blood.
3. Secretion
In this final phase of the urine formation process, some substances that are still in the blood are actively removed to the filtrate. Some of these substances include remnants of medicines and ammonia, for example, which are not needed by the body and which need to be eliminated in order not to cause poisoning.
Since then, the filtrate is called urine and goes through the remaining kidney tubes, and through the ureters, until it reaches the bladder, where it is being stored. The bladder has the capacity to store up to 400 or 500 mL of urine, before it needs to be emptied.
How urine is eliminated
The bladder is formed by a thin, smooth muscle that contains small sensors. From the 150 mL of accumulated urine, the bladder muscles slowly dilate in order to store more urine. When this happens, the small sensors send signals to the brain that make the person feel like urinating.
When you go to the bathroom, the urinary sphincter relaxes and the bladder muscle contracts, pushing urine through the urethra and out of the body.
