Frog Heart - Tharp Questions

Tharp Questions Cardiac Function Normal Heart Beat 2. How does the duration of the ventricular refractory period compare with that fir skeletal muscle? For a neuron? Similar to skeleton muscle because both has absolute refractory where systole cannot occur. Of what value is the length of the refractory period to pumping action of the heart? Has to be low because heart is constantly pumping; long refractory period results in decreases blood circulation. What causes the compensatory pause following an extra systole? In order for the ventricle to go back to the rhythm set by the pacemaker on the atria. 3. Explain the response obtained and its importance in the functioning if the heart as a pump. No tetany because this would lead to d-fib 4. Under what conditions would Starling’s law be of importance in the intact animal? Enlarged heart muscles in animals with blocked circulatory system causes the enlarged heart to pump slower A person suffering from heart failure often has an enlarged heart. How is this hypertrophy related to Starling’s Law? An increases workload stretches the muscle tissues. 5. Cold ringer’s solution slows the heart down to prevent heat loss. The blood will be shunt to the core of the body, the higher the temperature, the blood will be pushed to the peripheral regions of the body to cool down. 6. Explain the Mechanisms whereby acetylcholine and epinephrine alter the heart rate. a. Acetylcholine- Decreased rate of depolarization and the maximum diastolic potential. It also increased the threshold. b. Epinephrine- Increased the rate of depolarization and decreased the threshold. 7. How did the ligature produce heart block in the preparation? a. First degree-the arterial pump had to increase to make up for the lack of pressure from being cut off from the ventricle. b. Second degree- not observed because people were not dexterous enough c. Third degree- completely blocked off the circulation to the ventricle, and saw a pronounced arterial curve and no ventricular curve because it the ligature was blocked off. How might a heart block be produced in pathological cases? Heart worm may actually cause real blockage of the heart.

Explain how the excitation generated by the cardiac pacemaker spreads to the ventricular muscle fibers. The excitation generated travels from the sinus venosus down the internodal pathway pass the AV node and continues toward the ventricular muscle.