AND A LEFT SIDE-- AND FOUR CHAMBERS,

THE TOP RECEIVING CHAMBERS OR ATRIA, AND THE LOWER CHAMBERS,

WHICH ARE THICK-WALLED PUMPING CHAMBERS,

CALLED VENTRICLES.

A RED BLOOD CELL WILL COME FROM EITHER THE SUPERIOR VENA CAVA

OR THE INFERIOR VENA CAVA AND ENTER INTO THE RIGHT ATRIUM.

THE BLOOD THEN FLOWS ACROSS THE TRICUSPID VALVE

TO THE RIGHT VENTRICLE.

THE RIGHT VENTRICLE THEN SQUEEZES AND EJECTS THAT BLOOD

CELL INTO A VESSEL CALLED THE "PULMONARY ARTERY."

THE PULMONARY ARTERY SPLITS INTO TWO VESSELS EACH GOING TO THE LUNGS.

AS THAT RED BLOOD CELL MAKES ITS WAY THROUGH THE LUNG,

IT RETURNS THROUGH THE PULMONARY VEINS TO THE LEFT ATRIUM.

THAT BLOOD IS NOW OXYGENATED.

IT'S PICKED UP OXYGEN THEN GOES ACROSS THE MITRAL VALVE

INTO THE LEFT VENTRICLE, WHICH DOES MOST OF THE WORK IN TERMS

OF DELIVERY OF BLOOD FLOW TO THE BODY.

THAT BLOOD CELL IS NOW EJECTED INTO THE AORTA TO SOME ORGAN

OR MUSCLE OR SKIN IN THE HUMAN BODY.