Heart pump project

by Fellowship Agency June 7, 2018

Get hearts pumping in your classroom, learn how the heart works, see how blood is pumped and understand the importance of valves.

Learning Outcomes

You will be able to:

Describe and model the workings of one of the chambers of the heart.
Describe and model how valves work in controlling the direction of blood flow.

You will need (per heart pump model):

1 x Shallow Gratnells F1 tray
1 x Glass or transparent plastic jar
1 x Balloon
Water sufficient to two-thirds fill the jar
5-10 x Drops of red food colouring
1 x Wooden skewer
2 x Bendy drinking straws
1 x Waterproof tape
1 x Scissors

What to do:

Take a look at our Heart Pump Project What’s In My Tray activity video on YouTube here.

Fill the glass jar with water to two-thirds full and add a couple of drops of red food colouring so that the liquid inside resembles blood.
Cut the neck off a balloon at the point at which it starts to widen.
Stretch the remaining part of the balloon across the top of the jar to form a seal, making sure it is stretched tightly, and secure in place with tape if needed.
The jar now resembles one of the four chambers of a human heart.
Pierce two small holes in the balloon about 2 cm apart using a wooden skewer.
Push a straw through each hole so the end goes under the level of the ‘blood’ in the jar. Bend the end of the straw so they point down.
The straws resemble the blood vessels that carry blood around the body.
Take the neck of the balloon and place it around the top of one of the straws. Secure tightly with tape so no air or liquid can escape. This represents a closed valve.
Gently pump down on the top of the balloon in between the two straws and watch as the ‘blood’ flows out of the top of one straw. This shows how the heart pumps blood around the body. The balloon on the end of one straw shows how a closed valve stops the blood that has been pumped from one chamber from going to the wrong place.

What is happening?

The jar and straw model creates a simple pump that can move liquid from the jar and through the straws when pressure is applied. The sealed straw represents a closed valve, liquid can not escape via this route, so it is forced out through the open straw. Increasing the air pressure in the jar by pressing down on the balloon (decreasing the volume of the chamber), forces the liquid up and out of the open straw.

The human heart pumps blood through the body in a similar way, except that the heart has four separate chambers instead of one and its valves open and close with every heartbeat. Unlike the simple model created here, there is no air in the chambers of the human heart or circulatory system, the entire volume of the heart and blood vessels is filled with blood. Valves are used to prevent blood that has been pumped from one chamber from flowing back into the chamber it came from. Valves direct the flow of blood in one direction. Blood is forced through the flexible values by pressure, which is created when the heart muscle contracts (in the model this is represented by pushing the balloon down). Once the blood has passed through the valve, the valve collapses back on itself, preventing the blood from flowing back again. Valves do not just control the flow of blood within the heart, they are also particularly important in the long veins that run from your arms and legs towards the centre of your body, gravity would allow the blood to flow the wrong way were it not for the presence of the valves.

The heart is a muscle, it pumps over 40 million times a year. Contraction of the heart muscle increases pressure in the heart’s chambers and forces blood held in the chambers out through the arteries. It is also possible to measure blood pressure, the pressure of the blood in the circulatory system, you may have seen this being done by a doctor.

Other things to try…

Try taking the closed balloon valve off the end of the straw and pump again, what happens? Why would this cause problems if it happened in a real heart? Research leaky heart valves, explore their consequences and how they are repaired.
Try securing the neck of the balloon to the end of the straw to make a flap, or functioning valve, that can open to allow liquid through but closes to prevent air coming back into the system. What is the effect on your model?
Try making a multiple chamber model heart by using additional jars, straws and balloons.
Measure your own heartbeat, either by taking your pulse manually, listening with a stethoscope or recording using a data logger with heart rate sensor. How many beats per minute (bpm) is your resting pulse? How is your resting pulse effected by exercise? How quickly does your pulse return to normal after exercise? Can you design and experiment with your classmates to investigate the effect of exercise on heart rate and plot your data on a graph?
What other factors can effect heart rate? Can you plan an experiment to investigate them?
At your resting pulse rate, how many times is your heart beating in a minute, an hour, a day and a year? Compare this to your classmates resting pulse rate by plotting the resting pule rates of everyone in your class on an appropriate graph.
Research how you could reduce your resting pulse rate. If you could reduce your resting pulse rate by one beat per minute, how many fewer times would your heart have to beat in a year?
Can you measure your own blood pressure using an electronic blood pressure monitor? What does each number of the reading mean? Compare blood pressure readings across your class and plot the data on a graph.

Health and Safety

As with all Gratnells What’s In My Tray activities, you should carry out your own risk assessment prior to undertaking any activities with children. In particular, young children can choke or suffocate on balloons, adult supervision is required and broken balloons should be disposed of immediately.