[Music] hi and welcome back to three sites lesson Scholl UK by the end of this video you should be able to describe the structure of the heart you should then be able to describe how the heart comes blood around the body now in order to understand how the heart works we're going to start by looking at circulation in fish fish have a single circulatory system deoxygenated blood is pumped from the heart to the gills where it collects oxygen and becomes oxygenated the oxygenated blood now passes straight from the gills to the organs where the oxygen diffuses out of the blood and into the body cells the blood now returns to the heart the problem with a single circulatory system such as this one is that the blood loses a lot of pressure as it passes through the gills before reaching the organs this means that the blood travels to the organs relatively slowly so it cannot deliver a great deal of oxygen now unlike fish humans have a double circulatory system here deoxygenated blood is pumped from the heart to the lungs where it collects oxygen this oxygenated blood then returns to the heart the heart now pumps the oxygenated blood to the organs where the blood transfers its oxygen to the body cells the blood now returns back to the heart the benefit of the double circulatory system is up because the blood passes through the heart twice it can travel rapidly to the body cells delivering the oxygen that the cells need this shows a simplified picture of the human heart the heart is an organ consisting mainly of muscle tissue the job of the heart is to pump blood around the body and you need to learn the details of the structure of the heart the first key fact is that the heart has got four chambers at the top we have the left atrium and the right atrium at the bottom of the heart we have the left ventricle and the right ventricle you can see that the atria are separated from the ventricles by valves we'll take a closer look at these later now you'll notice that the heart appears to be back to front that's because diagrams of the heart always show it as if you're looking at a person there are four main blood vessels entering and leaving the heart and again you were expected to know these the vena cava brings in the oxygenated blood from the body the blood now passes from the heart to the lungs in the pulmonary artery in the lungs the blood collects oxygen oxygenated blood passes from the lungs to the heart in the pulmonary vein and then the blood is pumped from the heart to the body in the aorta let's look now at the pattern of blood flow through the heart first blood enters the left atrium and the right atrium the atria now contract and the Bloods forced into the ventricles the ventricles now contract and force blood out of the heart the valves in the heart stop the blood from flowing backwards into the atria when the ventricles contract you'll notice that the left side of the heart has a thicker muscular wall on the right side this is because the left ventricle pumps blood around the entire body so it needs to provide a greater force the right ventricle only comes blood to the lungs now a really important type of blood vessel are the coronary arteries and you can see these here these arteries branch out of the aorta and they spread out into the heart muscle the purpose of the coronary arteries is to avoid oxygen to the muscle cells of the heart the oxygens used in respiration to provide the energy for contraction we'd be looking at the coronary arteries in more detail in a later video now the natural resting heart rate is controlled by a group of cells found in the right atrium scientists call this the pacemaker sometimes the pacemaker stops working correctly in this case doctors can implant an artificial pacemaker an artificial pacemaker is a small electrical device and it corrects irregularities in the heart rate remember you'll find plenty of questions on the structure of the heart in my vision workbook and you can get up by clicking on the link above okay so hopefully now you should be able to describe the structure of the heart you should then be able to describe the heart pumps blood around the body [Music]