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The Cardiovascular System

8 THE CARDIOVASCULAR SYSTEM

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Introduction

T he heart is the life-beating, always-thumping muscle in your chest. From inside the womb until

death, the thump goes on. The heart for the average human will contract about 3 billion times;
never resting, never stopping to take a break except for a fraction of a second between beats. If a person
lives to be 80 years old, his or her heart will continue to beat an average of 100,000 times a day. Many
believe that the heart is the first organ to become functional. Within weeks of conception the heart
starts its mission of supplying the body with nutrients even though the embryo is no bigger than a
capital letter on this page. The primary function of the heart is to pump blood through the arteries,
capillaries, and veins. There is an estimated 60,000 miles of vessels throughout an adult body. Blood
then transports oxygen, nutrients, disease causing viruses, bacteria, hormones and has other important
functions as well. The heart is the pump that keeps blood circulating properly. Americans today have
many options to take care of the heart and its counterparts. Due to expanding medical technology, it
makes it much easier to do so. This chapter is dedicated to the heart and its many parts.

The Heart

The heart is a hollow, muscular organ about the size of a fist. It is responsible for pumping blood
through the blood vessels by repeated, rhythmic contractions. The heart is composed of cardiac muscle,
an involuntary muscle tissue that is found only within this organ. The term "cardiac" (as in cardiology)
means "related to the heart” and comes from the Greek word kardia, for "heart." It has a four
chambered, double pump and is located in the thoracic cavity between the lungs.

The cardiac muscle is self-exciting, meaning it has its own conduction system. This is in contrast
with skeletal muscle, which requires either conscious or reflex nervous stimuli. The heart's rhythmic
contractions occur spontaneously, although the frequency or heart rate can be changed by nervous or
hormonal influence such as exercise or the perception of danger.

Myocardium

The myocardium is the muscular tissue of the heart. The myocardium is composed of specialized
cardiac muscle cells with an ability not possessed by muscle tissue elsewhere in the body. Cardiac
muscle, like other muscles, can contract, but it can also conduct electricity, like nerves. The blood to
the myocardium is supplied by the coronary arteries. If these arteries are occluded by atherosclerosis
and/or thrombosis, this can lead to angina pectoris or myocardial infarction due to ischemia (lack of
oxygen). Failure of the heart to contract properly (for various reasons) is termed heart failure, generally
leading to fluid retention, edema, pulmonary edema, renal insufficiency, hepatomegaly, a shortened life
expectancy and decreased quality of life

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