What it shows
Veins have valves that let blood flow only towards the heart. A tube with a one-way valve and a squeezing hand shows how muscles help push blood back up the legs.
The science
Blood in the veins is under low pressure, so it needs help to climb up the legs against gravity. When leg muscles contract, they squeeze the veins, and the blood is pushed on. Valves inside the veins have flaps that open towards the heart and shut against backflow, so each squeeze moves blood only one way. Without working valves, blood pools in the legs, which is why long standing makes the feet swell.
Materials
Cost: under Rs 200. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- About 60 cm of soft clear plastic tube (aquarium air tube)
- A small aquarium one-way (non-return) valve
- Two small jars or cups
- Water with red food colour
- A piece of stiff card to hold the tube
- A plastic bottle, cut, to hold the water
- A towel
Safety
For this project: Keep the model away from electrical items and sit it on a tray or in a basin. An adult must help with cutting the tube.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Cut the tube into two pieces and join them with the one-way valve in between, with the flow arrow pointing the way you want water to go.
Put one end into the lower jar of coloured water and the other end into the upper jar, with the valve in the middle.
Fill the tube with water by sucking gently at the upper end or using a syringe, and avoid trapped air bubbles.
Squeeze the tube between the valve and the lower jar several times with your fingers, like a muscle squeeze, and watch the water move upward.
Release the squeeze and see the water not flowing back, because the valve closes.
Now reverse the valve, or remove it, and squeeze again to show water flowing back and forth with no net movement.
Count how many squeezes it takes to move 50 mL of water through the valve.
Draw a vein with a valve in open and closed positions, labelling the direction of blood and the muscle squeeze.
What you should see
With the valve, each squeeze pushes a little water upward and none comes back. Without the valve the water slides to and fro and does not climb.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What do the valves in veins do?
They stop blood flowing backwards.
2How do leg muscles help the blood?
They squeeze the veins and push the blood on towards the heart.
3Why are valves needed in veins but not much in arteries?
Veins carry blood at low pressure, while arteries carry it at high pressure from the heart.
4Why do feet swell after long standing?
Blood pools in the legs when the muscles do not squeeze the veins.
Take it further
Fit a second valve and a second squeeze point to make a two-stage pump and compare the volume moved per ten squeezes.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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