Lub Dub: Why Does the Heartbeat of Mammals Make a Sound?
Why does the heartbeat of mammals make a sound?
- Construction paper
- Large thread spool
- Cellophane tape
- Cut and glue a circle of construction paper over each end of the thread spool. Allow the glue to dry for several hours.
- Use a pencil to punch a hole in the paper circles to line up with the hole in the spool.
- Cut a smaller paper circle about 1 inch (2.5 cm) in diameter.
- Center this small paper circle over the other paper circle on one end of the spool, and secure it on one side with a piece of tape about ¼ inch (6 mm) wide. This makes a flap over the hole.
- With your mouth, blow through the hole in the spool end without the flap. This pushes up the paper flap on the other end.
- Suck air back through the hole with enough force to cause the paper flap to hit against the top of the spool.
- Repeat the blowing and sucking of air through the hole in the spool.
- Listen to the sound made as the paper flap moves up and down.
A swishing sound is heard when the air pushes the flap up, and a thumping sound results each time the flap hits the surface of the spool.
In all mammals, the heart is a double pump. Each side of the heart has an upper and lower chamber. The top parts are called atriums and the lower parts are called ventricles. A one-way flap called a valve connects the upper and lower chambers. When the heart muscle relaxes, blood flows through the open valves from the atriums into the ventricles. When the heart contracts, the flap is closed with a thump. The valve prevents the blood from moving back into the atrium, and it is forced out of the heart through another opening. The opening and closing of the paper flap on the thread spool produces a sound like that made by heart valves. The sound from the valves can be heard through the tissues of the body and is often described as a lub-dub sound.
Would a hole in the flap affect the sound? Repeat the experiment first with a small hole in the paper flap. Repeat several times with increasingly larger holes in the flap.
- How can blood flow in only one direction in blood vessels? Veins and arteries both have valves. Build a model using a box and two flaps of stiff paper to demonstrate the movement of blood through the one-way valves in blood vessels. A marble can be used to represent blood. Tilt the container forward so that the marble hits the flap and opens it. Tilt the container backward, and the marble hits against the flap, closing it. Your model, along with diagrams of vessels, can be used as part of a project display.
- How much blood moves with each heartbeat? This can vary with the size of the heart. In humans, the average is about ¼ cup (60 ml) per beat, or about 5 quarts (5 liters) per minute. Demonstrate the work done by the heart by using a ¼-cup (60 ml) measuring cup to transfer 5 quarts (5 liters) of water from one container to another. Remember that the job must be done in one minute. Dip the measuring cup into the water, and pour the water into the other container. Photographs of this experiment are the best way to display the procedure. Count each transfer to determine the number of times the heart would have to beat in one minute in order to pump 5 quarts (5 liters) of blood.
Check It Out!
- Animals have hearts with two or more chambers that pump blood through their circulatory system. Discover more about the hearts of different animals. How do the hearts of fish, amphibians, mammals, and birds differ? What is the specific difference between the hearts of birds and mammals? Use diagrams of animal hearts as part of your project display.
- Insect blood is usually greenish in color. Some insects have pulsating sacs in their knee joints that push the blood throughout the body. Find out more about the circulatory system of insects.
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