1ahmedhassan


 * The Heart **

The heart pumps blood around the body. The wall of the heart contains muscle fibres. The diagram below shows the structure of the heart. Blood returns to the heart from the body in **[|veins].** It enters the **right atrium**, which contracts forcing the blood into the **right ventricle**. When this contracts it forces blood out of the heart through the pulmonary artery to the lungs, where carbon dioxide is removed and oxygen is absorbed. Blood from the lungs enters the **left atrium** of the heart and is forced into the **left ventricle**. This chamber has a very thick muscular wall to push blood out of the heart into the main artery, the **aorta,** and around the body. There are **valves** in the heart to make sure that blood flows in the correct direction.  The heart is said to be a double pump, because the right side of the heart pumps blood to the lungs, and the left side pumps it around the body. This is called a [|**double circulation**.] 



media type="file" key="الجهاز الدوري الدموي ... CVS.flv"