It’s time to introduce Year 10s to hormones.
But before I run you through my tried and trusted lesson for this, I need to issue a Health and Safety warning – namely, that virtually none of the following detail is on the iGCSE specification. What? Teach something that’s not on the specification???? Outrageous! This is the kind of dangerous bolshevik thinking that gets teachers a bad name… Shocking stuff.
Bear with me. I hope you’ll see why and how it works….
I start with this picture….
What What are these two people trying to achieve?
OK, so that’s an easy one. They’re trying to get a tan.
By doing what?
By lying, scantily clad, in the sun.
So what’s this an example of? This interaction between sun and skin, what’s going on?
Straight off the back of their work on the Nervous System, they’re generally pretty quick to realise that we’re looking at a stimulus (UV rays) and a response (skin turns brown).
Can they suggest why is it unlikely to be a nervous response?
This can take a little longer, but the idea that skin goes brown slowly and gradually is obviously different to the rapid reflex actions they’ve been studying. Much comedy can be derived from imagining tanning as a reflex response. I’ll just go out in the sun – SPLAT – tan!
Right! Now move to this image.
A human body.
And this???? the yellow dot?
I love it when someone suggests it’s a brain. More chance for top class banter. Well, maybe your brain is that small, but generally brains fill skulls. Try again!
They usually don’t immediately know, so it’s then time for a quick game of Hangman, where I inevitably fail to break my losing run of 1,200 straight defeats, despite outrageous cheating, rule bending and general mayhem from yours truly.
Right – the pituitary gland! Let’s take a closer look…
And watch what it does…
The animation on my Powerpoint shows little blobs appearing in the pituitary and then moving out into the bloodstream.
The little blobs, I tell them, are a chemical called MSH, manufactured by the cells that make up the pituitary, which are secreted into the blood. And once it’s in the bloodstream, where’s it going?
Yes, everywhere!!! It’s all good Heart and Circulation revision from earlier in the year… With a little prompting they might even remember the part of the blood it’s dissolved in (blood plasma) and the name for these chemicals that travel in the blood (hormones).
Zoom back out to the body. Watch where this MSH molecule is going! And watch what happens when it gets there!
The animation shows it emerging from the pituitary, whizzing round the body, and arriving in the foot. And the foot then turning brown… In other words, it tans.
Huh? How does that work???
We need to look at what’s happening in the skin!
Here it is. A skin cell. And right behind it, another type of cell. With some recently arrived MSH in the top left corner.
What do they notice?
It’s pretty obvious. The cell behind the skin cell has little shapes on its membrane that, following their work on synapse mechanism, they can confidently call receptors. Which, they instantly see, the MSH can fit into.
It’s like I keep telling them – if you can do jigsaws, you can do Biology.
Let’s see what happens when the MSH fits into the receptor…
That is a molecule of the tanning chemical, stuff they’ve all heard of, melanin. And the cell that makes it is called a Melanocyte. Hence MSH – Melanocyte Stimulating Hormone.
The animation then shows the melanin migrating from the Melanocyte to the skin cell and accumulating around… where?
So why would it do that?
We discuss the importance of protecting a cell’s nucleus, and the DNA within, from the mutagenic effects of UV rays…
And what happens if you fill more receptors with hormone?
Exactly. More melanin production.
OK, so that’s the mechanism. How is it modified by the sun?
Back to the pituitary!
Look what happens when its stimulated by light from the sun!!!
Wow! LOTS more MSH…
…. which is duly taken all round the body in the blood….
…. and arrives at the skin.
Hmmmm. But skin only tans if it, too, is exposed to the sun. It can’t just be changes in the pituitary. So something must happen here too. What might that be?
They get it. The melanocyte responds by making more receptors!
And with so many more receptors filled with so much more MSH, what happens?
Bingo. Lots more melanin – in other words, a tan.
There is usually an avalanche of questions in this lesson. Partly to clarify things, but mainly to push for further answers. So you need to know your stuff – or just be very good a blagging. Either way, tt’s a great way of engaging students’ imagination and curiosity.
Tried and tested, this lesson works. It works really well. The combination of a clear narrative, simple but memorable animations, and a link to something they’re familiar with, is a winning combination. How can I be so confident? Well, 48 hours later, in the follow up lesson, they can recall every single detail – despite having not written a single thing down.
The full powerpoint, with notes and animations, is here…
Melanin production and hormonal control
They are also then ready to have a go at the follow up questions….
Hormonal Control of Tanning questions
Give it a go! Let me know what you think….