Bodily Defenses Image Map

Kidney Function

We learned earlier that kidneys detoxify by secreting toxins or filtering toxins out of the blood into urine.  But how do we know this?

The best way to learn what kidneys do is to examine the product of their function- urine. Examining the urine is also a good way to know if anything is wrong with kidney function. Medical technicians in hospitals and clinics routinely examine urine ("urinalysis") looking for any abnormalities. Any abnormalities could signal kidney disease. Examples of diseases that can be detected by urinalysis include diabetes, kidney stones, and chronic infections of the urinary tract.

Kidneys stones, after they have been concentrated and removed from urine. Such stones in the urine can block urine formation and cause severe pain.

Urine is analyzed in three ways:

  1. Unmagnified ("macroscopic"): check for amount, color, clarity
  2. Chemical analysis with a "dip stick": check for acidity, density, amount of protein, glucose, ketones, nitrites, and white blood cells. Special tests can be done for other substances, such as illegal drugs.
  3. Magnified (microscopic): check for crystals, squamous (flat) cells, bacteria, and other large objects.

Macroscopic Abnormalities:

  • Not enough urine might mean that the kidneys are not filtering blood well.
  • Too much urine might mean that the kidneys are not reabsorbing the water that is filtered out of blood - a common sign of diabetes mellitus.
  • Urine should be yellow. If it is pale or clear it may mean dilution, either because too much water is being lost or it could be that you just drank a lot of liquid.

Chemical Abnormalities:

  • Urine should be near neutral (pH=7), neither acidic nor basic.
  • Presence of the substances listed above may indicate that the kidney is not cleaning the blood adequately or that the body contains more of the substance than even normal kidneys can handle.

Microscopic Abnormalities:

  • Red blood cells should not be in urine, unless the urine is collected from females during menstruation.
  • White blood cells should not be in urine. They could indicate infection of the kidneys, bladder, or other parts of the urinary tract.
  • Too many crystals and stones could indicate a risk for blockage of the urinary tract. This prevents urine from being discharged, puts pressure on the kidney tubules, and stops urine formation.

Kidney Failure

Kidneys can become physically damaged by precipitates such as stones or by excess pressure (high blood pressure, obstructions in the bladder or the tube (urethra) that leads outside the body). The damage can progress to renal insufficiency and end-stage kidney disease, which require renal dialysis or a kidney transplant.

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