the heart 2.2.2

• the heart is a pumping organ that keeps the blood flowing around the body
• the walls of the heart are mostly made of muscle tissue
• the atria are the top chambers of your heart where the blood enters, the atria contract together and force blood down the ventricles
• the ventricles contract and force blood out of the heart
• the valves close to make sure the blood flows in the right direction
• the pulmonary artery (right side) takes deoxygenated blood to the lungs
• the aorta (left side) takes oxygenated blood around the body
• 1. blood flows into the two atria from the vena cava and the pulmonary vein
  2. the atria contract, pushing the blood into the ventricles
  3. the ventricles contract, forcing the blood into the pulmonary artery and the aorta and out of the heart
  4. the blood then flows to the organs through arteries and returns through veins
  5. the atria fill again and the whole cycle starts again
• the right ventricle pumps blood to the lungs where gas exchange takes place 
• the left ventricle pumps blood around the rest of the body
• your resting heart rate is controlled by a group of cells in the right atrium wall that act as a pacemaker, these cells produce a small electric impulse which spreads to the surrounding muscles causing them to contract
• the heart also needs its own supply of oxygenated blood, arteries called coronary arteries branch off the aorta and surround the heart, making sure that it gets all the oxygenated blood it needs
• the valves opening and closing causes the noise of the heartbeat
• if the pacemaker stops working, the person will not get enough oxygen and so functions around the body will begin to fail
• an artificial pacemaker is often used to control heartbeat if the natural pacemaker cells dont work properly. its a little device thats implanted under the skin and has a wire going to the heart, it produces an electric current to keep the heart beating regularly
• the muscle wall of the left ventricle is thicker than the right ventricle because the left side has to pump blood further to the whole body so it needs more muscle