 What would life be without blood? Well that's a silly question because we wouldn't be here. Nor would any mammals or actually any vertebrates in fact. It is fundamental to our survival and so we need to know all about it. You should already know that blood consists of red blood cells, white blood cells, platelets and plasma. But if you have forgotten, watch our What Is Blood video first. In this video we're going to look at white blood cells in particular. These are our warriors, the army inside our body that protects us from infectious diseases and foreign invaders. They may only make up 1% of our blood but my gosh they are important. Our body has a first line of defense which we saw in the video on body defense against pathogens. But when this fails our white blood cells kick into action. White blood cells are the cells of our immune system. There are two types of white blood cells, phagocytes and lymphocytes. Phagocytes have a multi-loop nucleus within the cytoplasm. They are made on your bone marrow and they actively seek out to engulf bacteria. They will even squeeze out of the blood through the capillary walls to reach infected tissue. Nothing stops these cells when they are on a charge. They will often die loaded with bacteria that they have engulfed and killed. In boils and cuts this is seen as yellow pus. There are different types of phagocytes with neutrophils being the most common. Lymphocytes have a huge nucleus and just a little cytoplasm. They are formed in lymph nodes and are found all around the body such as in your armpits and neck. The invading pathogens contain a chemical on their surface called anthogens. The lymphocytes detect this and produce antibodies in response to it. The antibodies stick to the surface of the pathogen and kill it either by making it easier for the phagocytes to ingest them or making the pathogen burst or by making the pathogens clump together which turns them into a sticky mess and makes it easier for phagocytes to find them. Each antibody is very specific. It will only attack one type of bacteria. Other lymphocytes produce antitoxins which combine with the invaders toxins and make them harmless. Sometimes the body cannot produce antibodies naturally or fast enough and so we can have vaccinations to help us out. We will look at vaccinations in another video. They may only be 1% of our blood but our white blood cells can really peg a punch. You just need to remember that phagocytes engulf pathogens and lymphocytes produce antibodies and antitoxins.