the circulatory system is an example of an organ system and its role is to transport oxygen and nutrients to our body's tissues this organ system relies on three main things the blood which carries the all-important oxygen and nutrients the blood vessels which hold that blood and the heart which pumps the blood to keep it moving through the vessels in this video we'll take a closer look at the structure and the function of the heart then in two separate videos we'll take a look at the vessels and the blood as you can see from this image you can actually think of the circulatory system as a double circulatory system because there are two distinct loops one of them carries deoxygenated blood from the heart to the lungs where it gains oxygen and then flows back to the heart while this other one carries the oxygenated blood to the rest of the body where it gives up its oxygen to the tissues becoming deoxygenated and then flows back to the heart to start all over again taking a closer look at the heart though we can see that it consists of one two three four chambers with thick muscular walls surrounding them and then veins and arteries coming in and out now whenever you're looking at an image of the heart like we are here it's as if you're looking at another person from their front so their left side of the heart is actually on our right and their right side is on our left pretty much all of the diagrams of the heart that you come across are drawn in this way so just remember that the left side is on our right and the right side is on our left you also need to know that the top chambers are called atria with an individual one being called an atrium and the bottom chambers are ventricles between the chambers and the vessels we find valves which prevent the blood from flowing backwards ensuring that it always flows in the right direction let's take a look at the path the blood takes as it passes through the heart first blood flows into the heart via the vena cava and the pulmonary vein from these it flows into the right atrium and left atrium respectively blood from the pulmonary vein has just come from the lungs and so it's oxygenated whilst the blood in the vena cava is returning from the loop around the body and so it's deoxygenated then as the two atria contract together they push the blood into the ventricles and just an instant later the two ventricles contract and push the blood out into the pulmonary artery which travels to the lungs and the aorta which feeds the rest of the body at the same time the atria will refill with new blood and the whole cycle will repeat in fact this cycle repeats around 70 times a minute which is over 100 000 times each day to keep this beat steady we have a group of cells in the right atrium that act as a pacemaker and these pacemaker cells produce small electrical impulses which spread through the muscular walls of the heart causing them to contract in some rare cases though these pacemaker cells don't work properly to fix this doctors can implant an artificial pacemaker which is a small device that we place just under the skin above the heart and as a wire that can carry electrical current down to the heart telling it to contract regularly just like healthy functioning pacemaker cells would now to clear up any confusion we just wanted to point out that the term artery refers to any vessel that carries blood away from the heart while a vein is any vessel that carries blood to the heart often students get confused and think that the arteries have to carry oxygenated blood and veins have to carry deoxygenated blood although this is the case most of the time it's not always true for example the pulmonary artery here carries deoxygenated blood but it's still an artery because it carries blood away from the heart while the pulmonary vein carries oxygenated blood but it is a vein because it's carrying blood to the heart one last thing before we finish is that the heart also needs its own supply of oxygenated blood and it gets this small arteries that branch off the aorta called coronary arteries these vessels encircle the heart to make sure that the muscle tissue gets all of the oxygen and nutrients that it needs and that's everything you need to know about the heart if you found it useful then please do share it with your friends and we'll see you next time