Part 1: BASIC FOUNDATIONS OF CARDIOLOGY Chapter 3:
The cardiovascular system functions to deliver oxygen, nutrients, and other essential molecules to the tissues and carry waste products (e.g., carbon dioxide, metabolic end products) to the organs responsible for their elimination (i.e., lungs, liver, kidney). To accomplish these functions, a system with two separate circulations in series has evolved. The pulmonary circulation is a low-resistance, high-capacitance vascular bed specialized for bidirectional gas exchange with the environment. The systemic circulation consists of multiple, relatively high resistance vascular beds specialized for the delivery of oxygen and nutrients to tissues and extraction of carbon dioxide and metabolic waste products. Blood is a solvent that dissolves and transports the substances required for and produced by metabolic processes. It travels sequentially through the two circulations and is pumped by two highly adapted pumps in series. The latter are combined in one organ, the heart, that is under coordinated local and neurohumoral control. Each side of the heart is composed of two chambers, a thin-walled atrium that accepts venous blood from its respective circulation and also has a booster pump function and a thicker-walled ventricle that pumps the blood to its respective circulation.
A key aspect of the cardiovascular system is that it must function under a wide variety of demands. Thus, during the stress of exercise, the amount of blood pumped, the cardiac output (CO), must increase fourfold or more.12 Extremes of temperature (e.g., during exercise) require that the cardiovascular system function to maximize heat loss or conservation. Beat-to-beat variations in loading of the heart related to normal functions such as respiration require exquisitely fine tuning of the stroke volume (SV) produced by each side of the heart. Moreover, the system has little or no room for error; even a slight, sustained mismatch of left- and right-sided SV would result in a catastrophe. This chapter reviews the cellular and organ-level cardiac and vascular mechanisms nature has devised to accomplish these tasks.
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This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.