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THE BOXER UNIVERSITY AT BU
by
"Professor"Theresa Garton
Heart Anatomy & Function
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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.
Quiz
Questions: (Give yourself 20 points for
each correct answer.)
- Name the valve that allows blood to flow
from the left ventricle to the aorta, and then through the body.
- Where does the electrical stimulation that
initiates a normal heart beat start?
- Name the chambers of the heart that serve to
build blood pressure to ensure blood is pumped in adequate volume to the appropriate
places?
- Name the 3 heart problems boxers are prone
to.
- The right side of the heart pumps blood
where?
100 points = A+; 80 points = B; 60
points = C; 40 or less = Hit the books again! :-)
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