Chapter 4

### The Cardiovascular System

#### Overview

The cardiovascular system consists of the heart, blood vessels, and blood. Its primary function is to transport materials to and from all parts of the body. The heart pressurizes blood and provides the driving force for its circulation through the blood vessels. Blood is propelled away from the heart in the arteries and returns to the heart in the veins. Substances transported throughout the cardiovascular system can be categorized as (1) materials entering the body from the external environment (e.g., O2 and nutrients); (2) materials moving between cells within the body (e.g., hormones and antibodies); and (3) waste products, from cells, requiring elimination (e.g., heat and CO2). The exchange of materials between blood and interstitial fluid occurs across capillaries in the microcirculation.

#### Anatomic Organization of the Cardiovascular System

The heart has four chambers. The two atria serve as reservoirs for blood returning to the heart. The two ventricles are pumps that propel blood through the circulation (Figure 4-1). A septum divides the heart into right and left sides. The right atrium is the reservoir serving the right ventricle, which pumps blood to the pulmonary circulation via the pulmonary artery. Blood returns from the lungs to the left atrium via the pulmonary veins. The left ventricle propels blood, via the aorta, to all other organs in the body through the systemic circulation.

###### Figure 4-1

Overview of the cardiovascular system. Systemic and pulmonary circulations are arranged in series. Organ blood supply in the systemic circulation is arranged in parallel. Blue indicates deoxygenated blood; red indicates oxygenated blood.

Circulation of blood is completed as the blood from the systemic circulation drains into the right atrium via the superior and inferior venae cavae. The term “right side” of the circulation refers to the pulmonary circulation, which is served by the right ventricle. The term “left side” of the circulation refers to the systemic circulation, which is served by the left ventricle. The right side of the heart propels deoxygenated blood to the lungs, and the left side of the heart propels oxygenated blood to the tissues.

Heart failure results from conditions that impair the ability of the heart to fill with, or to pump out, sufficient blood. Either side of the heart may be affected, or both sides may be affected in some patients. In right-sided heart failure, there is a buildup of pressure that begins with the failing right ventricle and then moves to the right atrium and back to the systemic veins. Clinical signs include jugular venous distention and peripheral edema. The most common cause of right-sided heart failure is preexisting left-sided heart failure. In left-sided heart failure, pressure begins to build in the left ventricle, then ...

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