Cardiac Cycle Review

Answers

1. The cardiac cycle begins with stimulation of the atria to contract. As the atria relax, the ventricles will contract, forcing the blood upward, closing the "cuspid" valves, and out the pulmonary artery and aorta. When the ventricles relax, blood flows slightly backward, closing the semilunar valves.

2. Lub and Dub. Lub is the closing of the semilunar valves and the Dub is the closing of the "cuspid" valves

3. When a valve is defective blood can flow backwards due to the pressure changes in the heart. This creates a 'gurgling' sound known as a murmur.

4. The pacemaker is a special group of cardiac cells which are self-stimulating, creating impulses that will stimulate the rest of the heart to contract. Because the cells 'fire' at a specific rate, it sets the hearts base pace.

5. By sending out a stimulus which spreads throughout the hearts tissue, the pacemaker causes the atria to contract as a regular unit.

6. Functional Syncytium. They allow the atria and ventricles to contract as individual units instead of as a single muscle.

7. Contraction = Systole. Relaxation = Diastole

8. For example, 120/80. 120 is the systolic pressure, pressure created as the heart is contraction, and 80 is the diastolic pressure, the pressure on the blood when the heart is relaxed.

9. Staggering is necessary for the heart to be most efficient. If the atria and ventricles contract at the same time their pressures will counteract each other, reducing blood flow.

10. Staggering occurs because the atria and ventricles are separate muscular units, and it takes time for the impulse to reach the ventricles because of a delay at the AV node.

11. The AV node collects the impulse that has spread through and stimulated the atria and then sends it down to the apex of the heart. This allows for the staggering of contraction phases.

12. The Bundle of His receives the impulse from the AV node and transfers it to the apex through the interventricular septum. The Purkinje fibers then spread the impulse throughout the tissue of the ventricle.

13. The Cardiac center is a region of the brain (in the Medulla Oblongata) which alters the rate at which the heart beats by sending a "speed-up" (sympathetic nerves) or "slow down" (parasympathetic nerves) message to the SA node

14. Parasympathetic nerves from the Medulla release acetylcholine at the SA node, reducing its rate of firing.

15. Sympathetic nerves from the Medulla secrete norepinephrine which stimulates the SA node to fire more rapidly.

16. If blood pressure is too high, then messages are sent to the heart to slow heart rate, reducing cardiac output, thus reducing BP. If blood pressure is too low, then the message is to speed-up heart rate, increasing cardiac output and thus increasing BP.