Circulation

Oxygenated blood is pumped by the left ventricle to all parts of the body, with the exception of the lungs. The body tissue uses much of the oxygen for its own needs. The blood, which is now carrying less oxygen, returns to the heart. Blood from the head, neck and arms now returns to the right atrium (RA) via the SVC or superior vena cava; blood from the lower portion of the body returns to the RA via the IVC or inferior vena cava.

The RA contracts once filling is completed. This builds up pressure within that chamber and pushes the tricuspid valve open. Blood now rushes from the RA to the right ventricle (RV). When the RV is filled, the walls begin to contract and raises pressure within the RV. The increased pressure shuts the tricuspid valve and pumps blood into the pulmonary artery through the pulmonic valve (PV) which is pushed open by the increased pressure.

The pulmonic valve is made up of three cusps or flexible cup like structures. When the pressure in the right ventricle is low (as is the case during the filling phase of the chamber) the three cusps are full of blood and their sides touch each other to close the opening. This prevents blood from leaking into the pulmonary artery while the RV is filling. When the RV contracts to empty, the pressure within the chamber rises above that of the pulmonary artery. This forces the three cusps of the PV to open and blood rushes through the pulmonary arteries to the lungs. Here, the red blood cells pick up fresh oxygen.

The oxygenated blood from the lungs now returns to the left atrium (LA) via four tubes that are known as pulmonary veins. They empty into the back portion of the LA, which contracts after it is completely filled. This opens the mitral valve and forces blood into the left ventricle (LV). When the LV is completely filled, it starts to empty its contents by contacting its walls. This increases pressure within the chamber, shuts the mitral valve, and opens the aortic valve (AV). The sequence is similar to that described for the RA, RV and pulmonic valve.

Blood now rushes through the large artery know as the aorta. The aorta is the main "highway" blood vessel that supplies blood to the head, neck, arms, legs, kidneys, etc. Blood is brought to each of these organs and limbs via branches that originate from the aorta. The cells within each part of the body pick up oxygen and nutrients from the blood. The oxygen-poor blood then returns to the RA, via the superior and inferior vena cava, and the cycle repeats.