Class 11 Biology - Body Fluids and Circulation

Activities

Activity 15.1: Measuring Pulse Rate and Heart Sounds

Aim/Objective: To observe the relationship between heart activity and pulse rate.

Materials Required:

• A stopwatch
• Stethoscope (optional)
• Notebook

Procedure:

1. Place your index and middle fingers on the inner side of your wrist (radial artery).
2. Count the number of pulses felt in one minute while at rest.
3. If a stethoscope is available, place it on the left side of the chest to listen to the 'lub-dub' sounds.
4. Perform mild exercise (e.g., 20 jumping jacks) and measure the pulse rate again.

Observation:

• The pulse rate increases significantly after physical activity. The heart sounds become faster and more distinct.

Explanation:

• Each pulse corresponds to a ventricular systole (contraction) that pumps blood into the arteries. The 'lub' sound is the closure of the tricuspid and bicuspid valves, and 'dub' is the closure of semilunar valves. Exercise increases the body's oxygen demand, prompting the sino-atrial node (pacemaker) to increase the heart rate to maintain adequate cardiac output.

Conclusion:

• Pulse rate is a direct indicator of heart rate and responds dynamically to the body's energy needs.