Anatomy of the Heart
The heart is a muscle located in the middle of the chest and behind the
breastbone (sternum) that is approximately the size of a fist. It is "powered"
by an "electrical system" that signals the heart muscle to beat rhythmically
approximately 72 times per minute.
If you were to slice it down the middle, you would find that it has three
layers, the endocardium (the smooth inside
lining of the heart); the myocardium (the
muscle layer of the heart); and the epicardium (the outside lining of the heart). The pericardium is the tough, fluid-filled sac that
surrounds the heart itself, this pseudo-fourth layer provides protection and
minimizes the friction created by the heart beat.
The Heart is divided into four chambers: The Right
Atrium (RA), the Right Ventricle (RV), the Left Atrium(LA) and the Left Ventricle (LV). The electraical signal
for each heartbeat begins in the Right Atrium in an area called the sinus node
(aka the heart's natural pacemaker). Each chamber has a one-way valve at its
exit that prevents blood from flowing backwards. When each chamber receives an
electrical pulse, it contracts, and the valve at its exit opens pumping blood
through it and when it is finished contracting the valve closes. As the lower
chambers fill with blood, the electrical signal travels along special conduction
tissues to the AV node, where it pauses for a few seconds, allowing the chambers
to finish filling.
There are four valves in the heart including the Tricuspid Valve, which is at the exit of the Right
Atrium, the Pulmonary Valve, which is at the
exit of the Right Ventricle, the Mitral Valve,
which is at the exit of the Left Atrium and the Aortic
Valve, which is at the exit of the Left Ventricle.
When the heart muscle contracts (or beats) it pumps blood out of
the lower chambers of the heart. The heart contracts in two stages. In the first
stage the Right and Left Atria contract at the same time, pumping blood to the
Right and Left Ventricles. Then the Ventricles contract together (called
systole) to propel blood out of the heart. After this second stage, the heart
muscle relaxes (called diastole) before the next heartbeat. During this time,
the muscle resets itself for contraction and blood fills the atria.
Functions of the Heart
The right side of the heart collects oxygen-poor blood
from the body and pumps it to the lungs where it picks up oxygen and releases
carbon dioxide while the left side collects oxygen rich blood from the lungs and
pumps it to the body so that the cells throughout your body have the oxygen they
need to function properly.
All blood enters the right side of the heart through two veins, the Superior Vena Cava(SVC), which collects blood from the
upper half of the body and the Inferior Vena
Cava (IVC), which collects blood from the lower half of the
When the heart is pumping, blood flows from the body to the Superior and Inferior
Vena Cava then to the Right Atrium through the Tricuspid Valve. It flows to the Right Ventricle through the Pulmonary Valve through the Pulmonary Artery to the Lungs.
There, the blood picks up oxygen and
drops off carbon dioxide in the lungs, and then flows from the lungs through the Pulmonary Veins to the Left Atriumthrough Mitral
Valve to the Left Ventriclethrough
the Aortic Valve to the Aorta through the two main coronary arteries -- the Left Coronary Artery (which divides into
two - the Left Anterior Descending Artery and
the Circumflex Artery) and the Right Coronary
Artery. From here blood flows the arterial system to the
The heart, just like any other organ, requires blood to supply it
with oxygen and other nutrients so that it can do its work. The heart does not
extract oxygen and other nutrients from the blood flowing inside it. The heart
gets its blood from coronary arteries, located on the outside surface of the
heart, that eventually carry blood within the heart muscle through a network of