CS - the heart

• the circulatory system is made up of the heart, blood vessels and blood
• humans have a double circulatory system - two circuits joined together. in the first one, the right ventricle pumps deoxygenated blood to the lungs to take in oxygen. the blood then return to the heart. in the second one, the left ventricle pumps deoxygenated blood around all the other organs of the body. the blood gives up it's oxygen at the body cells and the deoxygentated blood returns to the heart to be pumped out of the lungs again
• 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 heart has valves to make sure that blood flows in the right direction - they prevent it flowing backwards
• the four chambers of the heart are the right atrium, left atrium, left ventricle and right ventricle
• 1. blood flows into the two atria from the vena carva and the pulmonary vein
  2. the atria contract, pushing 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 over
• the heart 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
• 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 smaller electric impulse which spreads to the surrounded muscle cells, causing them to contract
• an artificial pacemaker is often used to control heartbeat if the natural pacemaker cells don't work properly. it's a little device that's implanted under the skin and has a wire going to the heart. it produces an electric current to keep the heart beating regularly