Tuesday 13 September 2011

On Kidneys

Funny things, kidneys. The kidneys are totally off the Edexcel A-Level syllabus, which is a shame as ultrafiltration, selective reabsorption and the inevitable coverage of the goddamned ornithine cycle are good for the soul (when I was younger I automatically assumed any teacher who used the term "good for the soul" was a sadistic bastard. Now I use the term, and I am a sadistic bastard). But they're still on the (also Edexcel) BTEC syllabus for Unit 12: Physiology of Human Regulation and Reproduction.

So I'm teaching the kidney to a class of mainly male Year 2 students. And it's killing me, because I'm so desperate to mention something about "taking the piss", but if I do I'll have to put 20p into my swear box (them's the rules - students 10p if they swear, I have to pay double). I did teach them what micturition was, and suggested they used it when conversing with their tutor.

We've just started looking at selective reabsorption, and they're struggling a bit with the idea that the kidney rather inefficiently chucks everything out into the renal capsule, then takes back what is needed (yes, I am anthropomorphising my kidney - BTEC is not renowned for its academic rigour). On the spur of the moment, I came up with an analogy, and I thought I'd throw it out here in case it's useful to anyone else teaching the same unit.
Imagine you have a nice big bag of M&Ms. And you really don't like the red ones. The sensible thing to do would be to pick out and throw away the red ones, leaving the ones you do want in the bag for you to eat. But instead, the kidney takes the bag and tips the contents out on the floor, before picking up the yellow, green, purple and brown ones and putting them back in the bag.
The students got it after that. Flying Spaghetti Monster only knows how they'll cope with dealing with osmotic pressure, let alone the action of antidiuretic hormone.

In other winning news, one of the students had heard of a disease that meant if you put a beaker of your urine on a windowsill it would turn purple. I couldn't for the life of me remember what it was, but Paul reminded me it's porphyria. The lads were well chuffed when they heard about purple pee, but not so much when they realised they had to expose it to UV light and that the condition was extremely painful. They're going to stick with eating asparagus and beetroot though, so I've told the canteen to watch out for a sudden interest in such vegetables.


  1. I bet you could make that an exercise as well. Bring bags of smarties (Or M&Ms, but I'm in the US and I miss Smarties) and have them try out those methods. The tipping everything out and picking out the nice ones are probably more likely to guarantee no red is included, but it'd be worth a try.

  2. That's a really good idea. I wonder if I have a chance to do it as an activity after their dissection tomorrow...

    I loathe Smarties personally, but I do remember that the orange ones always tasted of orange and were therefore disgusting. So they could pick out all the orange ones for me!


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