Wilderness and Rescue Medicine 7th Edition Jeffrey Isaac, PA-C and David E. Johnson, MD

Chapter 4: The Circulatory System

One of the three critical body systems, the cir- culatory system is responsible for perfusing all body tissues with blood. This requires a complex arrangement of connected structures includ- ing a four-chambered heart, arteries, arterioles, capillaries, venules, and veins conducting a fluid consisting of millions of suspended and dissolved particles and chemicals. Failure of the circulatory system to perfuse body tissues adequately is called shock, and it is a serious critical system problem requiring immediate and aggressive life-saving treatment.

the blood, the blood vessels, and the heart. These components work together to distribute oxygen and nutrients and to remove waste. Blood, the primary transport medium of the circulatory system, is composed of fluid, cells, and dissolved gases. The fluid component of the blood consists of water, proteins, electrolytes, and the various chemical mediators of body func- tion called hormones. The cellular component includes red blood cells to carry oxygen, white blood cells to fight infection, and platelets to effect blood clotting. The average human body contains about 5 liters of blood; however, this volume is not contained in a closed system. The fluid component can migrate between the interior of body cells (intracellular space), the space between the cells (extracellular space), and the blood itself (vascular space). This ability to shift fluid explains how a patient can lose blood volume by losing water and electro- lytes from sweat glands. It also explains how blood volume can be restored by consuming water and electrolytes. The blood is distributed to all living cells in the body (except for the cornea of the eye) by traveling within a system of arteries, veins, and capillaries. There are two zones in the system; one circulating through the lungs (pulmonary circulation) and the other through the rest of the body (systemic

General Principles

Circulatory System

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Structure: • Blood • Vessels • Heart Function:

• Maintain perfusion pressure • Circulate oxygenated blood Problem: • Shock: inadequate perfusion pressure

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Structure and Function For field purposes, we can simplify the structure of the circulatory system to three basic components: