Left

Materials stopwatch or clock with second hand r^lB

Determining Heart Rate

Materials stopwatch or clock with second hand

Procedure

1. Have your partner find the pulse in your wrist and count your heartbeats for 15 seconds while you are seated. Calculate your resting heart rate in beats per minute.

2. Have your partner count your heartbeats for 15 seconds while you are standing. Calculate your heart rate in beats per minute.

3. Have your partner count your heartbeats for 15 seconds after you jog or march in place for

1 minute. Calculate your heart rate in beats per minute.

Analysis What causes your pulse?

What causes the change in your heart rate in each situation?

figure 46-2

Trace the path of blood through the heart. Notice that illustrations of a heart are drawn as if the heart were in a person facing you. That is, the left side of the heart is shown on the right as you face the heart, and the right side of the heart is on the left as you face the heart.

Valves are flaps of tissue that open in only one direction. The atrioventricular (AY-tree-oh-ven-TRIH-kyuh-luhr) valve (AV valve) on the right side of the heart is called the tricuspid valve. The mitral valve, also called the bicuspid valve, is on the left. As the ventricles pump, blood pressure closes the AV valves to prevent blood from flowing backward into the atria. From the ventricles, blood is pumped out of the heart into large vessels. A semilunar (SEM-ee-LOON-uhr) valve (SL valve) separates the ventricles from these large vessels on each side of the heart. The SL valve on the right side is known as the pulmonary valve, and the SL valve on the left side is known as the aortic valve. The SL valves prevent blood from flowing back into the ventricles when the heart relaxes.

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