Arteries, Veins and Capillaries:
What Harvey couldn’t see!
This could be the activity William Harvey wished he’d done at school! As someone who dropped biology at the age of 13 (just after we’d studied leaves and long before anything really interesting cropped up) I’ve always struggled with even the simplest anatomical knowledge. I suspect that many students also struggle with what Harvey discovered – and what he didn’t – so this activity, a simple physical representation, is intended to help the anatomically challenged – like me.
Setting Up
1. You need something red to represent blood e.g. a tin of tomatoes.
2. You also need to be able to distinguish between students who play arteries and those who play veins – but this is most simply done by one being arteries being played by girls and veins by boys.
The Activity
1. You need standing up
a) a strong student to play the heart (good at push ups)
b) two students to play the lungs
c) a handful of students to be veins
d) an equal handful to be arteries
e) two to be capillaries linking arteries to veins– but they have to be sitting down (to represent being invisible to Harvey)
2. Arrange your students in the manner of a diagram explaining the circulation of the blood (e.g. in White Medicine book p.88) but with capillaries sitting and rest standing or capillaries sitting on floor and rest on chairs. Make sure your arteries face away from the heart and the veins towards the heart.
3. Bring in your tin of tomatoes as the blood and give it to the heart.
Now do a commentary over the movement of the ‘blood’ round the body:
a) The heart pumps the blood to the lungs
b) The lungs returns the ‘blood’ to the heart – who hands it onto the first artery – and then the blood passes along the line of arteries until
c) it reaches the capillaries who hand it onto the veins – but Harvey couldn’t see the capillaries so he didn’t know what was happening so all he knew was that
d) the blood passed onto the veins and so back to the heart – and the whole cycle started again.
Throughout all this make sure the ‘heart’ keeps pumping his/her arms up and down because if the heart stops pumping then the blood flow stops.
Debriefing
1. What did Harvey understand and what couldn’t he see?
2. Why couldn’t he see the capillaries? (development of microscopes)
3. What idea did this replace? (Galen’s theory that blood was constantly being made in the liver to replace blood burned up in the body – a bit like petrol burns up in a car.)
4. Ask one or two students to do your commentary over a repeat of the activity, then annotate an outline diagram to explain what Harvey discovered – and what he couldn’t see.