Introduction to the Heart

Learning Objectives

  1. Describe the pathway of blood as it completes a round trip through the pulmonary and systemic circuits beginning and ending in the right atrium.
  2. Compare the pulmonary and systemic circuits in terms of length, pressure, volume, resistance, arterial gas content, and venous gas content.
  3. Explain how pressure differences between the atria and ventricles are responsible for atrioventricular valve opening and closing.
  4. Explain how pressure differences between the ventricles and the aortic and pulmonary trunks are responsible for valve opening and closing.
  5. Identify and describe the heart’s intrinsic cardiac conduction system including the locations and roles of all five major parts of the system.
  6. Describe the effect of medullary cardiac centers on the activity of the heart.
  7. Describe each of the four phases of the cardiac cycle. In your discussion describe what is happening to ventricular volume and pressure, whether the atria are in systole or diastole, whether the ventricles are in systole or diastole, whether the atrioventricular valves are open or closed, whether the semilunar valves are open or closed. Also include in your discussion a comparison of the pressures in the left atrium, left ventricle, and aorta.
  8. Define end diastolic volume, end systolic volume, stroke volume, heart rate, and cardiac output. Include their mathematical relationships in your discussion.
  9. Describe how changes in preload, contractility, and afterload can affect stroke volume.
  10. Describe the effect of the following on heart rate: cardioacceleratory activity, norepinephrine, cardioinhibitory activity, acetylcholine, and epinephrine.
This photo shows a human heart.

Figure 1. This artist’s conception of the human heart suggests a powerful engine—not inappropriate for a muscular pump that keeps the body continually supplied with blood. (credit: Patrick J. Lynch)

In this chapter, you will explore the remarkable pump that propels the blood through the cardiovascular system. There is no single better word to describe the function of the heart other than “pump,” since its contraction develops the pressure that ejects blood into the major vessels: the aorta and pulmonary trunk. From these vessels, the blood is distributed to the remainder of the body. Although the connotation of the term “pump” suggests a mechanical device made of steel and plastic, the heart is a living, sophisticated muscle. As you read this chapter, try to keep these twin concepts in mind: pump and muscle.

Although the term “heart” is an English word, cardiac (heart-related) terminology can be traced back to the Latin term, “kardia.” Cardiology is the study of the heart, and cardiologists are the physicians who deal primarily with the heart.