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Heart Structure and Blood Supply It seems odd that the tissues making up the heart must have their own separate blood supply. You might think that the torrent of blood rushing through the heart every minute would more than adequately meet the needs of the organ. The walls of the heart, however, consist of layers of specialized muscle. These walls are quite thick—the wall of the left ventricle is often over 1 inch thick. Since the lining of the heart is watertight, the blood cannot seep through the layers of muscle to provide the nourishment essential to these constantly working masses. Blood is carried through the muscle layers that form the heart wall by means of the two coronary arteries. These two small vessels branch off the aorta just after it leaves the heart and curl back across the surface of the chambers, sending twigs through the walls (Fig. 4-1). The coronary arteries are so named because of the supposed resemblance to a crown or “corona” of the little arteries as they...

Blood Flow Through the Heart Blood is pumped through the chambers of the heart and out through the great vessels by a simple squeezing action of the heart chambers. You have probably seen a bulb syringe with a glass nozzle like the one pictured in Figure 3-1. Suppose it is full of water. If you squeeze forcefully, expelling the water, you would be imitating the contraction of a heart chamber. This is called systole (sis-toe-lee). After the syringe had been emptied, imagine that you placed the nozzle in a container of water and let the bulb expand so that it filled. This is what a heart chamber does when it relaxes and fills with blood. The movement is called diastole (die-as-toe-lee). You can picture the process by holding your left hand over your right, fists clenched. If your left hand represents the atria, your right hand will represent the ventricles. Now clench your left fist (the atria) while opening your right fist (the ventricles). This is what happens during atrial systole whe...

Valve Structure and Function Like any pump, the heart has valves to keep the blood flowing in the right direction. Proper function of these small flaps of tissue spells the difference between good health and sickness, and often between life and death. Almost everyone is familiar with the word valve. Very few people, however, really know what a valve is or what it does. Imagine pumping water through a pipe with a farm pump. To keep the water from flowing back toward the pump between strokes, you could place a valve in the pipe leading out of the pump. The simplest kind of valve would consist of two semicircular flaps hinged to open only one way—forward with the flow of water. These flaps would close the pipe completely when they swung shut. When the water flowed forward from the pump, the flaps of the valve would swing open allowing the water to pass. Between strokes the valves would snap shut if any water attempted to flow back toward the pump (Fig. 2-1). Note: The heart is equipped ...

Before you begin to learn about heart disease, you must learn how the normal heart is constructed and how it functions. This is easier than you might think, because the heart is a surprisingly simple organ. An hour's easy reading will give you all the information you need to begin. The Chambers of the Heart and their Connections The heart is a hollow organ divided into four chambers, two on the top and two on the bottom (Fig. 1-1). Study this simple diagram until you know it as well as your own name: it's basic to everything else in the book. The top two chambers are thin-walled structures that act primarily as holding chambers for the blood. They are called atria. This is the plural of the Latin word atrium, meaning “anteroom” or “porch,” and, in fact, these chambers do act as entryways to the great chambers below. The ventricles are large, thick-walled chambers that do the real work of pumping the blood. (This name comes from the Latin ventriculum, meaning a “cavity...