The heart

• double circulatory system


  blood passes through the heart twice and has two seperate circuits, one for oxygenated blood and one for deoxygenated blood
• The heart is a pumping organ that keeps blood flowing around the body
• Valves make sure blood flows in the right direction
• De-oxygenated blood comes into the right atrium through the vena cava. The atrium contracts pushing the blood into the right ventricle. The ventricle contracts forcing the blood into the pulmonary artery and out of the heart and to the lungs where gas exchange takes place
• The blood flows to the organs through arteries and return through veins
• Oxygenated blood enters the left atrium through the pulmonary vein. The atrium contracts pushing the blood into the left ventricle. The ventricle contracts forcing the blood into the aorta to the rest of the body.
• Pacemaker

  resting heart is controlled by a group of cells in the right atrium wall that act as pacemaker

  • these cells produce a small electric impulse which spreads to the surrounding 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. Produces an electric current to keep the heart beating regularly