Mammals have a ____ circulation, which means that the right hand side of the heart pumps ____ blood to the lungs in the pulmonary artery to pick up oxygen and release ____. The oxygenated blood then returns to the ____hand side of the heart in the pulmonary vein. From there the blood is pumped to the body in the ____, eventually returning to the ____hand side of the heart in the ____ to start the cycle again. Since the right side pumps to the ____which are situated close to the heart, the walls are much ____ than the left side which has to pump blood out of the heart to the ____. The heart has 4 ____; 2 on the right hand side and 2 on the left. The top chamber on each side is called the ____; the bottom is called the ____. The ____ receive blood as it enters the heart and pumps it into the ventricles. The ventricles pump blood out of the ____ . Due to this, the ____ of the atria are much thinner than the walls of the ventricles. Inside the heart and at the base of the vessels that leave the heart are ____. These valves only open one way, which ensures that there is no ____ of blood. The valves are held open or closed by ____, which are attached at the other end to the papillary muscles in the ventricle walls. The valves open to let blood through and then snap shut. This sound of the valves closing is the ____sound of the heartbeat. The muscle of the heart is called ____ muscle and is made of tightly connecting cells. This close contact allows rapid ion transport from cell to cell. This then allows smooth, efficient waves of depolarisation produce contractions (and repolarisation to bring about relaxation), which pass through the heart. The tissue is said to be ____, i.e. it does not need electrical impulses from a nerve to make it contract. If the cardiac muscle is supplied with oxygen and nutrients (a task carried out by the coronary ____ which you can see running over the ____ of the heart) it will continue to contract at a steady pace.

CAX KS5 passage of blood through the heart, basic

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