viernes, 18 de febrero de 2011

Formation of Urine

In the last post about the nephron function we studied how urine is produced, but in this new post we are going to explain very carefully all the process. I hope you'll be able to understand it.
The process of urine formation is as follows:
1. Blood flows into the kidney through the renal artery. The renal artery branches into capillaries inside the kidney. Capillaries and the nephrons lie very close to each other in the kidney.
2. In the nephron, the blood pressure within the capillaries causes water and solutes (small soluble molecules) such as salts, sugars, and urea to leave the capillaries and move into the Bowman’s capsule. (GLOMERULAR FILTRATION).
3. The water and solutes move along through the tubules of nephrons. At this point most of the water and solutes are returned to the capillaries that surround the nephron (TUBULAR REABSORPTION). Some chemicals are secreted in the las part of the tubules (TUBULAR SECRETION).
4. The fluid that remains in the nephron at this point is called urine.
5. The blood that leaves the kidney in the renal vein has much less waste than the blood that entered the kidney.
6. The urine is collected in the ureters and is moved to the urinary bladder where it is stored.
Nephrons filter 125 ml (about ¼ cup) of body fluid per minute. In a 24-hour period nephrons produce about 180 liters of filtrate, of which 178.5 liters are reabsorbed. The remaining 1.5 liters of fluid forms urine.
Urine enters the bladder through the ureters. Similar to a balloon, the walls of the bladder are stretchy. The stretchy walls allow the bladder to hold a large amount of urine. The bladder can hold about 400 to 620 ml of urine, but may also hold more if the urine cannot be released immediately. Urination is the process of releasing urine from the body. Urine leaves the body through the urethra.
Nerves in the bladder tell you when it is time to urinate. As the bladder first fills with urine, you may notice a feeling that you need to urinate. The urge to urinate becomes stronger as the bladder continues to fill up.
In this table it is possible to compare plasma and urine composition.

in urine

protein7 - 8.5

uric acid 0.002

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