Cardiovascular System

 

How the Cardiovascular System Works

The cardiovascular system is responsible for delivery of blood, which carries oxygen

and other nutrients, to the tissues of the body. The heart pumps the blood to

the body where it delivers nutrients and oxygen, picks up waste products, and then

returns to the heart.

The heart has four chambers. The upper chambers are the atria; the lower chambers

are the ventricles. In the middle, there is a septum, a wall that separates the

right side of the heart from the left side of the heart. Atrioventricular (AV) valves

control the blood flow between the upper and lower chambers of the heart. The tricuspid

valve is on the right side, while the mitral valve is on the left side between

the atria and the ventricle. The pulmonic valve controls the flow between the right

ventricle and the pulmonary artery, while the aortic valve controls the flow between

the left ventricle and the aorta.

Unoxygenated blood empties into the right atrium from the systemic circulation

via the inferior vena cava and superior vena cava. As the right atrium contracts, the

tricuspid valve opens, allowing the blood to flow into the right ventricle. With contraction

of the right ventricle, the pulmonic valve opens, allowing the unoxygenated

blood to enter the pulmonary artery to go to the lungs to pick up oxygen. Once

oxygenated, the blood returns to the heart via the pulmonary vein and enters the

left atrium. As the left atrium contracts, the mitral valve opens, allowing the blood

to flow into the left ventricle. As the left ventricle contracts, the aortic valve opens,

allowing the blood to flow into the aorta and systemic circulation. The blood will

return to the heart from the lower body via the inferior vena cava and from the

upper body via the super vena cava. The actions on the right side and left side of

the heart happen simultaneously. So when we listen to a normal heartbeat, the

sounds we hear are the sounds of the valves closing. The mitral and tricuspid valves

create the first heart sound (S1), while aortic and pulmonic valves create the second

heart sound (S2).

The electrical conduction system of the heart starts at the sino-atrial (SA) node,

which is located in the right atrium. It initiates the heart beat, ranging between 60

to 100 beats per minute, every day, for a lifetime. The electrical current travels

across both atria, then converges on the atrio-ventricular (AV) node, where the current

slows, allowing the atria to repolarize. The AV node is located in the superior

portion of the ventricular septum. In the bottom portion are located the right and left

Bundle of His, which is a group of special cardiac muscles that sends an electrical

impulse to the ventricle to begin cardiac contractions. These end in the Purkinje

fibers and spread out through the ventricles. The current passing through these

fibers causes ventricular contraction, forcing the blood from the right ventricle to

the lungs and from the left ventricle to the aorta, and thus, the systemic circulation.

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