The major function of the cardiovascular system is to deliver, via the blood, oxygen and nutrients to all tissues of the body and to remove from them carbon dioxide and other waste products of cellular metabolism. In this regard, the cardiovascular system is the link between external respiration (gas exchange between the atmosphere and lungs) and cellular respiration (use of oxygen for energy production by the mitochondria). Other vital functions include, transport of heat to maintain body temperature, delivery of white blood cells to sites where they defend against foreign material, and transport of hormones from the site of release to their target organs. Thus, the cardiovascular system is a key contributor to constancy of the body’s internal milieu or homeostasis.
These tasks are accomplished by two interconnected yet distinct components of the cardiovascular system: the pulmonary circulation and the systemic circulation (Fig. 5-1). Each component is made up of (1) a pump (right ventricle for the pulmonary circulation, left ventricle for the systemic circulation) that provides energy to propel the blood, (2) a system of arteries and arterioles that distributes blood throughout the region each pump supplies, (3) a network of capillaries through which gases and nutrients are exchanged with the tissues supplied, and (4) a system of venules and veins that returns the distributed blood to the pump. The two components differ in the amount of the total blood volume each contains at any one point in time, the pressure of operation, thickness of vessel walls, and resistance to blood flow (Table 5-1).
Schematic representation of the functional divisions of the circulatory system. Note that the pulmonary and systemic circulations are connected in series so that the blood flows through the chambers of the right heart and the lungs, then to the chambers of the left heart, and the rest of the body. RA, right atrium; RV, right ventricle; LA, left atrium; LV, left ventricle; PA, pulmonary artery; PV, portal vein. (Modified with permission from West JB, ed. Best and Taylor’s Physiological Basis of Medical Practice. 12th ed. Baltimore, MD: Lippincott Williams & Wilkins; 1991.)
Table 5-1Comparison of the Systemic and Pulmonary Circulations ||Download (.pdf) Table 5-1 Comparison of the Systemic and Pulmonary Circulations
| ||Systemic Circulation ||Pulmonary Circulation |
|Distribution of total blood volume (%) ||80–95 ||5–20 |
|Pump (ventricular) pressure (mm Hg) ||120/0 ||25/0 |
|Distributing artery pressure (mm Hg) ||120/80 ||25/10 |
|Vessel wall thickness ||Thick ||Thin |
|Resistance to blood flow ||High ||Low |
Blood and Its Constituents
Blood is composed of solid components—the red and white blood cells and platelets, which are suspended in a liquid component, the plasma.1 Plasma is an aqueous solution of gases, salts, carbohydrates, proteins, and lipids. In normal circumstances, the proportion of cells ...