Bodily Defenses Image Map
                                              

KIDNEY (Continued)                       
Blood Flow to Kidney

 

To be effective in cleaning blood, the kidneys must have a rich flow of blood. About 23% of the blood pumped by the heart over the course of a minute goes to the kidneys. So, within a few minutes, all of the blood in the body gets swept through the filtering system of the kidney.

Example Effects of the Kidney Function

Substance

Average percentage of filtered substance re-absorbed

Average percentage of filtered substance excreted

Water

99

1

Sodium

99.5

0.5

Glucose

100

0

Urea (waste product)

50

50

Phenol (waste product)

0

100

Drugs and the Kidney

Toxic compounds, drugs, or their breakdown products, are cleared from the blood by the kidneys. Can you think of some practical results of this? Do you see why the kidneys can help protect us from toxic chemicals? Do you see why drugs act for only a certain length of time? How long it takes to clear the blood of toxins or drugs varies with the chemical, but most substances are cleared within a matter of hours.  Many medications have to be taken every few hours in order to maintain a fairly constant level in the blood because the kidneys are constantly eliminating the drug. You have heard about testing the urine of drug users or athletes. The drugs people take will show up in the urine.

What If the Kidneys Go Bad?

Obviously, loss of kidney function will lead to death. Inability to reabsorb water would lead to severe dehydration. Inability to secrete potassium can actually cause death because build up of potassium would stop the heart. Fortunately, two kidneys provide excess capacity. Only one kidney is actually essential. However, the loss of both kidneys is fatal. The only cure if both kidneys failed would be to get a transplant or to have the blood cleaned by machine (a process called kidney dialysis).

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