An Overview of Heart Anatomy and Function

The primary role of the heart is to pump deoxygenated blood from the body to the lungs, where it picks up oxygen and drops off carbon dioxide, and then to return the newly oxygenated blood to the body.

The human heart is comprised of four chambers, the right atrium, right ventricle, left atrium and left ventricle.  The heart can be described as having two sides – the right side and the left side, each functioning as a separate pump.  The right side of the heart propels blood into the pulmonary circulation while the left side of the heart sends it into systemic circulation.

The heart receives deoxygenated blood from the upper body via the superior vena cava and from the lower body via the inferior vena cava.  These two veins join together to return the deoxygenated blood to the right atrium.  The right atrium is separated from the right ventricle by an atrioventricular valve, also known as the tricuspid valve, which ensures that blood only flows in one direction.  The blood from the right ventricle is then sent into the lungs where it picks up oxygen.

Upon returning to the left atrium, fully oxygenated, the blood flows past the left atrioventricular valve, which also goes by the names mitral valve or bicuspid valve, and into the left ventricle.  Finally, the blood from the left ventricle is returned to the systemic circulation via the aorta, the largest artery of the body.
 
The pressures associated with the filling and emptying of the heart’s ventricles are referred to as diastole and systole.  Diastole is the pressure measured in the arterial system when the ventricles are relaxed and filling with blood.  Systole is the pressure associated with ventricular contraction, when the blood is being pushed into the systemic and pulmonary circulations.  The 120 is the systole and the 80 is the diastole in a 120/80 blood pressure.

The heart can vary the speed of its contractions based on feedback it receives from the body and brain.  When the body requires more oxygen, such as during exercise, when frightened, or any other time the sympathetic nervous system is activated, the heart increases its rate of contraction.  When the heart receives the message that the body needs more oxygen it begins beating faster and increases the heart rate.  Conversely, when the parasympathetic nervous system is activated, such as during times of rest, the heart rate slows down.

The heart has an internal electrical system which causes the heart to contract and relax over 100,000 times a day depending on the person and activity level.  This electrical system begins at the sinoatrial node (SA node), located in the right heart, and quickly causes the contraction of both atria (left and right).  The action potential which is generated, travels to a second node called the AV, or atrioventricular node.  When the AV node is activated it causes a series of steps to occur resulting in the contraction of the ventricles.  There is a slight delay between the contraction of the atria and the contraction of the ventricles.  This allows the filling of the ventricles before they contract to propel the blood into the pulmonary and systemic circulations.  The entire process of atrial and ventricular contraction is approximately two-tenths of a second from start to end.

When an individual listens to the heart through a stethoscope or through the chest wall, they will hear two beats.  These are referred to as S1 and S2 and correspond to the closing of the valves between the atria and ventricles and also the valves which are found at the opening to the pulmonary artery and aorta.

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