14 Chapter 14: Cardiovascular System
Figure 14.1 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)
The human body needs blood to deliver nutrients to and remove wastes from our trillions of cells. The heart pumps blood throughout the body in a network of blood vessels. Together, these three components—blood, heart, and vessels—makes up the cardiovascular system.
Learning Objectives
After studying this chapter, you should be able to:
- Identify the basic structures and function of the heart, including
- a. the chambers and valves
- b. the basic sequence of events in a heartbeat
- Understand the difference between the systemic circuit and pulmonary circuit of the cardiovascular system.
- Understand the structure and function of vessels and blood by
- a. Distinguishing among the basic structures and functions of veins, arteries and capillaries
- b. Listing and describing the main components of blood
14.1 The Heart: Heart Anatomy
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 anatomical structure is a living, sophisticated muscle. As you read about the heart, try to keep these twin concepts in mind: pump and muscle.
The vital importance of the heart is obvious. If one assumes an average rate of contraction of 75 contractions per minute, a human heart would contract approximately 108,000 times in one day, more than 39 million times in one year, and nearly 3 billion times during a 75-year lifespan. Each of the major pumping chambers of the heart ejects approximately 70 mL blood per contraction in a resting adult. This would be equal to 5.25 liters of fluid per minute and approximately 14,000 liters per day. Over one year, that would equal 10,000,000 liters or 2.6 million gallons of blood sent through roughly 60,000 miles of vessels. In order to understand how that happens, it is necessary to understand the anatomy and physiology of the heart.
Location of the Heart
The human heart is located within the thoracic cavity and is separated from the other structures by a tough membrane known as the pericardium, or pericardial sac.
The position of the heart in the torso between the vertebrae and sternum (see Figure 14.2 for the position of the heart within the thorax) allows for individuals to apply an emergency technique known as cardiopulmonary resuscitation (CPR) if the heart of a patient should stop. By applying pressure with the flat portion of one hand on the sternum in the area between the line at T4 and T9 (Figure 14.3), it is possible to manually compress the blood within the heart en