A professor gave the following analogy of kidney function to his freshman biology class: "Imagine your desk is a disorganized mess, containing things worth keeping and things you should throw out. Instead of picking through each item one by one and considering if it is to keep or toss, you sweep your arm across your desktop in one smooth motion, knocking the entire contents of the desk into your

Question

large trash can. Then you pull the items you want to keep out of the trash can and place them back on your desk." In what ways is this analogy accurate? In what ways is it inaccurate? Some students in his class argue that the kidneys are inefficient and poorly designed. How should the professor respond? What modern medical device may he cite in his response?

What will be an ideal response?

Answer 1

His analogy is accurate in that the glomerulus does dump contents into the nephron that the body needs and will
take back. His analogy is inaccurate in that the entire contents of the plasma are not dumped, rather about 1/5 of
the volume enters the nephron. While one could easily imagine a more efficient way to remove waste from the
blood, the kidneys can only use the tools they have, namely various membrane transport processes and the
physical laws governing movement of water and solutes. Kidney dialysis machines rely on diffusion through
semipermeable membranes, mimicking part of normal kidney function.