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The Heart and the Circulatory System
Some brief activities to begin exploration of the circulatory system...
I. Using a stethoscope to identify the heart sounds.
1. Obtain a stethoscope and wipe the ear pieces with an alcohol swab. Place the ear pieces in the ears.
2. Place the bell of the stethoscope on your subject's chest, and listen for the heart sounds.
3. Identify the first sound, which signals ventricular contraction or systole. How long is the interval between the first sound and the second sound, which signals ventricular relaxation or diastole?
4. Time the interval between the second sound and the next first sound. After five of these intervals, estimate the average time the heart is at rest in a minute, and the average time the heart is in contraction in a single minute.
II. Identification of Venous Valves
1. Role up your sleeve so you can see the veins on the palmar side of the forearm.
2. Place your forefinger on one of the veins evident, then push the thumb along the vein toward the shoulder. Leave the finger in place, and observe if the blood flows back into the vein. Now remove the finger, and observe what happens.
3. Place the finger on one of the veins (preferably the same vein) and push the thumb along the vein toward the hand. Leave the finger in place, and observe if the blood flows back into the vein. Now remove the finger, and observe what happens.
4. Based on these observations, predict where the valves are in the vein. You may choose to repeat this on of the veins on the top of the hand.
III. Observation of the Heart of Daphnia
1. Obtain a vial of Daphnia. Measure and record the temperature of the water in the vial.
2. Draw the Daphnia into a small pipette or dropper, and close the end with petroleum jelly.
3. Place the dropper under the stereoscope and focus on the reddish pulsating object in the thorax of the Daphnia. This is the heart. Increase the magnification as high as possible, and observe the flow of blood. Record the number of heartbeats in a minute.
4. Place the dropper in a beaker of ice water for a few minutes, then remove and place back under the microscope. Do not forget to record the temperature of the water. Again focus on the heart and count the number of beats in a minute. Record this number.
5. Leave the dropper in place under the scope and observe if the heart rate changes as the temperature increase in the dropper. Observe for eight minutes, recording the rate every two minutes.
6. Place the dropper in a beaker of warm water, preferable warmer than room temperature but not boiling. Record the temperature, then repeat the observation of the heart rate under the microscope.
7. Based on your observations, what can you infer about the effect of temperature on heart rate?
IV. Microscopic Observation of Blood Flow
1. Obtain a frog from your instructor.
2. Wrap the specimen in a wet cloth.
3. Place the hind foot on the stage of microscope and spread the toes.
4. Illuminate the stage with transmitted light.
5. Focus on the webbing between the toes. You will be able to see the capillaries.
6. Observe the flow of blood through the arteries, veins, and capillaries in your field of view.
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