Every minute nearly one and a half quarts of blood passes through our kidneys. That’s 500 quarts of fluid a day going into the kidneys and yet all but a single quart is recycled. An efficiency of 499/500 is unheard of in the machines built by man. The method by which this efficiency is achieved is truly remarkable.
When blood comes into the kidney it flows into a tight bundle of capillaries called glomeruli. Rising pressure forces water, salts and other molecules into a cuplike structure surrounding the glomeruli called Bowman’s capsule. Larger molecules such as protein and blood stay in the blood stream.
In the Bowman’s capsule the useful molecules of glucose, amino acids and other materials are returned to the blood stream along with over 90% of the water. The unusable substances continue through the tubes called nephrons to collecting ducts which transport it to the center of the kidney called the renal pelvis. More than 40 miles of tubes are involved in this incredible filtering system which is four inches long and weighs five ounces.
The kidneys don’t just filter our blood. They secrete the enzyme renin which adjusts blood pressure so the filtering ratio in the nephrons is constant, no matter how much water we drink. If the kidney runs short of oxygen, another enzyme will speed up the formation of red blood cells to increase the transporting of oxygen. If one kidney fails, the other will enlarge to pick up its load. We have three times as many nephrons as we need and 10% of what we have would support life.
A perfect kidney machine to replace the Original Equipment Manufacturer’s model has not been developed in spite of years of research and the work of our brightest medical and engineering minds. Here is a design which is more than dandy – it’s magnificent.
Science Digest, Nov. 1983, p. 93
Wikipedia, “kidney”, “glomerulus”, “Bowman’s capsule”
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