Recent comments in /f/askscience

lascivious_boasts t1_j9pxpbj wrote

Reply to How can Doctors tell if one of your kidneys isn't working? by FineLetMeSayIt

The short answer is that you are correct. Routine tests, including the rate of urine production, the ability of the body to clear waste products (creatinine, eGFR, urea) may all be normal in the case of only a single kidney working.

It's not very rare to find someone with one kid ey by accident when doing a scan. These are caused by congenital issues that led to a solitary kidney or an issue in early childhood that damaged one kidney and not the other.

Occasionally there will be mild derangement of some of those values that lead to the suspicion that a single kidney is not working and the other is working much better.

In this case there are some tests that can be used. As one of the main reasons for kidneys to fail is blockages in the arteries that feed blood into them, an arteriogram can show if one kidney is getting blood while the other isn't. This can be done with an intravascular catheter, but is more commonly done with CT and arterial phase contrast. If one kidney is getting lots of blood, and something is blocking the artery to the other (renal artery stenosis) then it's a fair bet that the one not getting blood isn't working well.

Equally, structural differences can show if there is a blockage in the outflow of one kidney and not the other (unilateral hydronephrosis, where the kidney retains urine due to the pressure needed to push it through a narrow ureter).

Finally, the test that really shows this is a differential renal function test. This can be done in a variety of ways. One includes injecting a dye and seeing how much comes out of each kidney by CT scanning and looking at how much dye is in each kidney. Another involves the differential clearance of a radioactive marker.

As to why we have two of some organs and one of others: it's just evolution in action. These body shapes and functions arose and persisted because animals with these survived and thrived when others didn't.

182

UmdieEcke2 t1_j9ptqpg wrote

Reply to comment by aTacoParty in How do our brains know where in the body a nerve impulse came from? by kzorlk0

Does that mean there is a single neuron strand for each tiny area we can feel something with? so basicall a full nerve strand, from every square-milimeter of skin or internals all the way up into the brain? Or is it more like a couple of strands, which form different patterns depending on where exactly the sensory information comes from?

2