The Flow of Blood in the Human Circulatory System

Blood re-enters heart from body Oxygen-poor blood Enters right atrium Upper body – Superior (Upper) Vena Cava Lower Body – Inferior (Lower) Vena Cava RA

Right atrium contracts Tricuspid Valve opens Oxygen-poor blood Blood enters Right Ventricle RA RV

Right Ventricle Contracts Pulmonary valve opens Oxygen-poor blood Blood enters Pulmonary Artery RV

Blood enters capillaries in lungs Pulmonary artery takes oxygen-poor blood to lungs Gas exchange occurs – Carbon dioxide leaves blood, oxygen enters blood Oxygen-rich blood returns to heart via Pulmonary Vein

Blood Enters Left Atrium Oxygen-rich blood returns to heart Pulmonary veins empty blood into left atrium RV LA

Left Atrium Contracts Bicuspid valve opens Oxygen-rich blood Blood exits left atrium, enters left ventricle RV LA LV

Left Ventricle Contracts Aortic valve opens Oxygen-rich blood Blood enters Aorta, which branches into the Ascending (Upper) Aorta and Descending (Lower) Aorta RV LA LV

Blood travels to all areas of the body Oxygen-rich blood Aorta branches into network of arteries and capillaries that supply each cell in the body with oxygen and nutrients

Oxygen-rich blood enters body capillaries Oxygen is dropped off at body cells and carbon dioxide is absorbed Nutrients are dropped off and wastes are absorbed Blood becomes oxygen-poor

Capillaries return blood to veins Oxygen-poor blood returns to veins Veins have series of valves to keep blood from flowing backwards Veins are often sandwiched between muscles that contract and squeeze the veins to keep blood moving

Blood re-enters heart from body Oxygen-poor blood Enters right atrium Upper body – Superior (Upper) Vena Cava Lower Body – Inferior (Lower) Vena Cava RA