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Q: A toxin blocks the ability of the nephron tubule reabsorption but does not affect filtration. What are the possible short-term effects of this toxin?

Randall’s response: A doctor and nurse are in surgery.

Nurse: Doctor, the patient is losing consciousness! We need a decision!

Doctor: Hang on! I want to get an Internet cartoonist to weigh in.

My response: Wait a minute, I am a doctor! Ha!

However, I am not a medical doctor, which means that this blog post is not intended to diagnose, treat, cure, or prevent any disease.

Now, I only have a vague idea what those medical terms mean beyond that they have to do with the kidneys, so I had to look them up, but once I did, it became quite simple.

Filtration is the process by which (relatively) large waste particles like dead cells and proteins are removed from the blood by the kidneys. However, this process brings a lot of fluid along with it. Nephron tubule reabsorption is the process by which this excess fluid is reabsorbed into the bloodstream. If it is blocked, the kidneys will continue to draw excessive fluid from the bloodstream without putting it back.

Therefore, a toxin that blocks reabsorption, but not filtration is likely to have the short-term effects of excessive urination, followed by extreme thirst, electrolyte imbalance, and dehydration, a condition that in its chronic form is known as diabetes insipidus (not to be confused with the usual meaning of diabetes).

Interestingly, the most common toxin that causes this particular problem is an overdose of lithium.