CHAPTER 7 – THE CIRCULATORY SYSTEM


How the heart pumps blood A complete cycle of blood through the body undergoes the following stages: 1. Deoxygenated blood enters the right atrium through the vena cava. 2. Blood is pumped from the right atrium through a valve and into the right ventricle.


3. The right ventricle contracts and forces blood up and out through a different valve. The blood leaves the heart through the pulmonary artery.


4. The pulmonary artery delivers blood to the lungs. At the lungs, carbon dioxide is lost from the blood and oxygen is taken into the blood.


5. The pulmonary vein brings oxygenated blood back to the left atrium.


CONCENTRATE! The pulmonary artery is the only artery that carries deoxygenated blood. The pulmonary vein is the only vein that carries oxygenated blood.


6. Blood is pumped from the left atrium through a valve and into the left ventricle.


7. The left ventricle contracts and forces blood up and out through a different valve. The blood leaves the heart through the aorta and is delivered to all cells and organs in the body by other arteries.


8. Exchange of molecules in the blood occurs at the capillaries. All of the small capillaries join together to form a larger blood vessel called a vein. The largest veins are the venae cavae that return to the right atrium. This completes one entire cycle.


Capillaries surrounding the lungs


Pulmonary artery


Pulmonary vein


Vena cava Right atrium


Valve


Right ventricle Septum


Aorta Left atrium Left ventricle


) Fig. 7.8 Blood flow through the heart


? TEST TUBE


7. Starting and finishing at the right atrium, draw a flow chart to represent the route taken by blood as it leaves the heart, travels around the body and then returns to the heart.


8. What two important gases are exchanged between the blood in capillaries and the air in our lungs? 9. Name: a. the major artery in the body b. the major vein in the body


Elements of Science 61


Capillaries surrounding body tissues


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