our blood consists of four main things red blood cells white blood cells platelets and Plasma in this video we'll take a look at each of them in turn and then how we can replace blood for those people who don't have enough red blood cells are probably the most wellknown of these and they make up almost half of our blood by volume the role of red blood cells which you might sometimes see written as RBC is to carry oxygen from the lungs to our body's tissues so that our cells can use it in solar respiration to do this they contain a red pigment called hemoglobin which combin oxygen to become oxyhemoglobin and then once those red blood cells have traveled around the body to the tissues the oxyhemoglobin can split back into hemoglobin and oxygen again so that the oxygen is free to diffuse into our tissues Now red blood cells have two adaptations that you need to know about one is that they don't have a nucleus which means that there's more space for hemoglobin and oxygen the second is that they're shaped like a biconcave disc which gives them a large surface area for absorbing oxygen white blood cells meanwhile make up less than 1% of our blood but they're an essential part of our immune system which defends us against infection there are lots of different types of white blood cells and they can do a whole range of useful things for us but three examples of how they Defenders against pathogens include phagocytosis which is basically where a white blood cell will engulf or consume a microorganism producing antibodies which can bind onto pathogens and help destroy them and producing antitoxins which neutralize any toxins that the pathogens produce and one last thing to say about white blood cells is that unlike red blood cells they actually do have a nucleus in contrast platelets aren't actually cells they're just small fragments of cells and so these definitely don't have a nucleus what they do is float about in our blood waiting until we get a cut at which point they rush to the wound and act like a glue hatching up the hole and we call this process clotting as you can imagine the main reason that we need platelets is to stop blood from pouring out of us whenever we get a cut however another important reason is to stop microorganisms from getting in as they could cause us an infection finally we have plasma which makes up just over half of the blood's volume it's a pale straw colored liquid and it's what makes the blood watery so that it can flow it also carries just about everything including the red blood cells white blood cells and platelets that we've already seen in addition it carries nutrients like glucose and amino acids waste products like carbon dioxide and Ura as well as hormones proteins and the antibodies and antitoxins that were produced by the white blood cells now most adults have about 5 lers of blood flowing through their circulator system at any one time however if this drops too much for example due to a knife wound or surgical complications then there might not be enough blood left over to deliver the required oxygen to their tissues in these cases doctors can give the patient new blood and there are two types to know about artificial blood is a blood substitute that basically consists of salt water the main benefit is that it adds volume to our circulatory system which keeps our vessels full and allows the heart to keep on pumping the downside though is that it doesn't contain any red blood cells so it doesn't actually allow us to transport any more oxygen which means that we can only really replace onethird of our blood with it a better option is a blood transfusion in which a person is given real blood that's been donated by Blood donors this comes with this own red blood cells which is the key to surviving blood loss if you haven't heard yet you can find all of our videos on our website Cognito org you'll also find questions flashcards exam style questions and pass papers and we track all of your progress so that you always know what to study next so sign up for free by clicking here or browse our playlist here on YouTube