|Heart Anatomy & Function by Theresa Garton, MD - published in The Boxer Underground|
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I. Introduction: The Heart is an organ that serves a biomechanical function in the body. It is basically a two-stage pump, that serves to pressurize blood, and then send it through the body to nourish the other tissues.
II. Anatomy: The heart consists of two sides, the left and the right. Each side has an atrium, or a chamber into which the blood first flows, and a ventricle. The ventricle is the main pumping chamber. The right side of the heart pumps blood into the lungs, where it is exposed to oxygen. The left side of the heart receives blood from the lungs, and then pumps it through the rest of the body proper. Each side has two valves, one between the atrium and the ventricle for that side, and one between the ventricle and either the lungs or the body. The valve between the right atrium and the right ventricle is called the tricuspid valve, the valve between the right ventricle and the pulmonary artery that carries blood to the lungs is called the pulmonic valve. The valve between the left atrium and the left ventricle is called the mitral valve, the valve between the left ventricle and the aorta, a huge artery that carries blood to the body proper, is called the aortic valve. There are also coronary arteries that carry blood to the heart muscle itself.
III. Function: The heart is "wired" with an electrical system that dictates when and how the heart muscle does its pumping. There is a structure, called the sinus node, in the right atrium, that initiates the electrical impulse. The signal, or depolarization, travels from the sinus node, and stimulates both atria, right and left. This wave of depolarization causes both atria to contract. This wave of stimulation and contraction eventually reaches another structure, called the A-V node (Atrial-Ventricular node). Once the wave reaches this structure, there is a brief pause, which allows time for the blood to fill each ventricle. Then the wave progresses down special fibers called the Purkinje fibers, and stimulates the ventricles, causing them to contract. Each of these events is recorded on the electro-cardiogram, or EKG (or ECG).
IV. Disease, as it applies to boxers: Boxers have an inherited tendency to develop a thickening below the aortic valve, that can eventually interfere with the passage of blood out of the left ventricle, and into the body. This condition is called "Subaortic Stenosis." It can lead to abnormal blood pressure, and an inadequate amount of blood circulating through the body. It also causes extra work for the heart, and can lead to heart failure. Boxers also have an inherited tendency toward problems with the electical system of the heart, which has been somewhat misnamed as "Boxer Cardiomyopathy." We are not clear exactly what the problem is, but it leads to large numbers of electrically abnormal beats. In other words, the beats start in the wrong place, and cause the heart to contract in an abnormal fashion. This can also lead to a precipitous drop in the amount of blood circulating through the body, and hence, fainting spells. If the beats occur in large numbers together, the heart may lapse into chaotic muscle contraction, that may cause either collapsing spells, or sudden death as the heart is unable to return to any sort of normal function. Boxers may also have a condition called "Dilatative Cardiomyopathy," in which the heart muscle does not function properly, leading to a build up of blood in the chambers as the heart is unable to push it all out. In the past, some investigators have believed that Boxer Cardiomyopathy may progress eventually to Dilatative Cardiomyopathy, but that is seeming less and less to be the case for the majority of dogs with Boxer Cardiomyopathy.
Questions: (Give yourself 20 points for each correct answer.)
100 points = A+; 80 points = B; 60 points = C; 40 or less = Hit the books again! :-)