Unit 5 Day 5 – The Cardiovascular System
Standard: 5.3
Name: __________________________________________________
Date: _______________________________ Period: ___________
Heart Contraction, Blood Flow & The Cardiac Cycle
“The heart has its reasons of which reason knows nothing.” - Blaise Pascal
1. The heart has been attributed to a
variety of human emotions, namely
love. But what is the main
physiological function of the heart?
2. The human heart is roughly the size
of a fist and composed of cardiac
muscle tissue. Below is a diagram of
the heart, with major anatomical
structures labeled. Draw arrows to
depict typical blood flow through
the heart.
Now, label the structures of the heart that
conduct electrical signals and allow
contraction to occur. Include:
 SA Node
 AV Node
 Bundle of His
 Left & Right Bundle Branches
 Purkinje fibers
3. What structure is often called the “pacemaker” of the heart? WHY?
4. What about the membrane potential of the heart at the SA Node allows for its autorhythmicity? Explain how.
5. Why is it important that there is a delay at the AV node?
6. During atrial contraction, the ventricles are relaxed and filling with blood. What would happen if there was a
malfunction in the heart and the ventricles contracted too soon? What part of the heart is malfunctioning?
Contraction of the heart is a highly specialized and specific process. If these mechanisms do not occur precisely in the
right order, your body will not receive the oxygen-and-nutrient-rich blood that it needs to stay alive.
7. What is the name of the vein that brings blood from the body back to the heart?
Blood at this point is (circle one) deoxygenated/oxygenated.
8. At what point during electrical stimulation of the heart does atrial contraction occur? Ventricular contraction?
9. Where does the blood travel to after atrial contraction of the right side? Through what valve?
10. Where does the blood travel to after ventricular contraction of the right side? Through what blood vessel?
11. What gas is released from the blood at the lungs? What gas is added to the blood at the lungs?
12. What happens to heart rate after exercise? WHY?
13. After traveling to the lungs, to what chamber of the heart does the blood return to? Through what blood vessel?
14. Where does the blood travel to after atrial contraction of the left side? Through what valve?
15. Ventricular contraction is caused by depolarization of the SA-Node  __________________  ________________________
 __________________________________________  ______________________________________
16. This wave of depolarization is the result of many action potentials occurring, which tell the sarcomeres of the
cardiac muscle tissue to shorten, leading to contraction of the heart. What is significant about the anatomy of
cardiac muscle tissue that allows for this rapid transmission of ions across the cell membrane?
17. What is different about cardiac action potentials and how is this physiologically significant for the heart?
18. After contraction of this ventricle of the heart, where does blood flow? Through what blood vessel?
Blood at this point is (circle one) deoxygenated/oxygenated.
19. Does only one side of the heart contract during the cardiac cycle or do both left and right ventricles contract at
the same time? WHY? (Hint: think about the electrical nerve structures)
20. Do the atria and ventricles contract during the cardiac cycle at the same time, or is atrial and ventricular
contraction staggered in time? WHY is this important and HOW do you know? (Hint: think about blood flow
and the electrical nerve structures)