Explain how the kidney is adapted for efficient reabsorption.

The fluid that filters through the glomerulus and Bowman’s capsule (glomerular filtrate) is very similar to blood plasma without the proteins, and at this point not at all like urine. If this filtrate flowed straight to your bladder and then out your body, you would lose more than 10-times the entire volume of your extracellular body fluids (plasma and interstitial fluid) every day. Fortunately, tubular reabsorption mechanisms in the nephrons of your kidneys return the water and solutes that you need back into your extracellular fluid and circulatory system. In addition to reabsorbing the substances that you need, your nephrons are able to secrete unwanted substances from your bloodstream into the filtrate. Together these processes complete the transformation of the glomerular filtrate into urine.

Tubular reabsorption is the process that moves solutes and water out of the filtrate and back into your bloodstream. This process is known as reabsorption, because this is the second time they have been absorbed; the first time being when they were absorbed into the bloodstream from the digestive tract after a meal.

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