hello and welcome to a level biology with ms estrich in this video we're going to be going through the circulatory system for a level biology if you are new here click subscribe so you don't miss out on any of the latest videos so the circulatory system you need to know for mammals in a level and in mammals they have a closed double circulatory system now what we mean by closed is all of the blood vessels are connected within a circuit so that means the blood always remains within those blood vessels as long as there's no damage to the blood vessels double circulatory system refers to the fact that the blood passes through the heart twice in each circuit and that's because there is one circuit that takes the blood from the heart to the lungs and then another circuit which takes the blood from the heart to the rest of the body now the reason that mammals have a double circulatory system is the need to control the pressure of the blood flow and that's because different parts of the body require blood at different pressures for the lungs blood is required at a lower pressure and this is so the blood flows through slower and therefore there is less damage or no damage to the capillaries which surrounds the alveoli in the lungs the second reason is if the blood is flowing at a lower pressure that also means it's moving more slowly so when the blood enters the capillaries and alveoli it's going slower and this means there's more time for oxygen to diffuse from the alveoli into the capillary and carbon dioxide to diffuse from the capillaries into the alveoli or in other words gas exchange now that's the lungs or pulmonary circuits for the circuit to the rest of the body the blood is required to be pumped at a higher pressure and the reason for this is to make sure that the blood is going at faster speed to make sure the blood will reach every single cell and that is so all of the result respiring cells in the body will receive oxygen so they can respire aerobically the next thing you need to know are the key blood vessels and for aqa you only need to know these blood vessels listed here now most of these i actually go into more detail in other videos so for example the coronary arteries and the blood vessels connected to the heart and the lungs you can find up here in my video on the heart and i'll link my video to do with kidneys and the nephron at the end so you can find out about these blood vessels as well so the coronary arteries these are the arteries which supply the heart the cardiac muscle with oxygenated blood so they can continually contract and relax and the heart can constantly beat the heart you need to know the four major blood vessels that enter and exit so we have the two veins the vena cava and the pulmonary vein and the two arteries the pulmonary artery and the aorta lungs there are the pulmonary artery and the pulmonary vein which we can see up here and any blood vessels connected to the lungs will have pulmonary in front of it so that refers to the lungs lastly is the kidneys and the blood vessels that connect to the kidneys will have renal in front of them so the blood vessel entering the kidneys is called the renal artery the blood vessel exiting the kidneys is the renal vein and that will then be delivering the blood back into the heart in addition to that you do need to know about the structure and function of the arteries arterials capillaries and veins but that is going to be in more detail in my video up here on blood vessels exclusively so that is it for today's video on the blood vessels and the circulatory system in particular i hope you find it helpful if you have please give it a thumbs up