 The next cells are the leukocytes, also we call them white blood cells. These blood cells are actually transparent. If we stain them, then we can look at them. We can make a slide of blood cell. If we want to, we can take a drop of blood cell on a slide and make a smear and stain them to observe under the microscope. The leukocytes of the white blood cells are categorized into two main categories, A granulocytes, the granulocytes. A granulocytes are then further categorized into two, the monocytes and the lymphocytes. That is, they are called A granulocytes because they don't have any granular bodies inside their cytoglass. Granulocytes are the cells as a granulo in size. Granulocranules have granules inside the cells, the cells which have granules inside. When we stain them, we can see certain granules present inside them which are stained. These are three, vasophils, eocenophils and neutrophils. These are some cells which are also responsible for different types of allergies, which are also involved sometimes in phagocytosis, that is, eating large particles and destroying them. Then comes the third category, the platelets. Platelets are the cells, also called the thrombocytes. Platelets are actually fragments of a single cell, a large cell called megagaruocyte is present inside the bone marrow. It is fragmented into about 1,000 cells at a time when activated. We call them platelets. So platelets are the cell-like bodies. The function of platelets is very important in the blood. They causes clotting of the blood. Whenever blood needs clotting, they actually come in action. Now we look at diagrams or pictures of various cells, blood cells and talk about their functions. First of all, have a look on the picture, not diagram but a picture, red blood cells, the erythrocytes. They look red under the microscope because they have an hemoglobin group with an iron inside. In mammals, red blood cells don't have a nucleus at maturity. Initially, they do have a nucleus, but when they get mature, they lose their nucleus. And because they lose their nucleus, we know that nucleus is present in the center. They look like a biconcave cell. As you can see in this picture, they are concave on both surfaces due to removal of the nucleus from inside, destroying of the nucleus from inside. There most of the cytoplasm is actually filled with the hemoglobin because their major function is to carry the oxygen to all the tissues and remove carbon dioxide from various tissues. These cells are not very long lived. They live for about 120 days, that is about 4 months and then they die and they are replaced. Red blood cells have to be replaced at times. They always keep replacing, so it means that keep destroying the old RBCs and making new RBCs. When they are destroyed, they have iron group inside, so they have to be destroyed carefully. Liver is the organ which carefully destroy them and do not allow them to produce any toxicity inside the tissues. Now we look at the white blood cells. Have a look on the diagram. This diagram is to show you that how different types of cells are present and moving or flowing inside an artery. You can see in the red circle an artery with its lumen from which various cells are coming out. The red ones, biconcave ones are the RBCs. The small irregular particles are the platelets and quite large and with the purple nucleus are the white blood cells. So blood is actually the combination of these cells with plasma. Now we look at them one by one. We have already talked about the RBC, the red blood cell. Now we talk about the white blood cells. On the top, the two first ones from left are monocytes and lymphocytes. These are agranulocytes. As you can see that in their cytoplasm, no granular content is observed. Monocytes are very large, about twice the size of the red blood cell. You can compare the sizes because there is an erythrocyte, the RBC in the lower layer, in the lower side of the diagram. Monocytes are large particles. Their function is phagocytosis to kill the larger particles which may be bacteria or some other invaders. Sometimes they enter inside the tissues, that is seeps out of the blood and go inside the tissues. At there, they are called macrophages. They change their shape, they modify their shape and they can kill the invading bacteria or other infectious particles. For example, if there is an injury to a tissue and bacteria invaded and blood vessels is broken, then they go out in the tissues and they are converted to the macrophages. The larger, more irregular cells and they eat up the bacteria and the infectious particles by amoebic movement, that is extending towards the direction of the infectious particle or bacterium and engulf it by surrounding it with their cytoplasm in the membrane. The second ones are lymphocytes. You can see that their nucleus is so large that it almost covers the whole of the cytoplasm. Lymphocytes makes the circulating antibodies. These are extremely important because when an invader organism like bacteria or virus comes inside the body, then these cells are converted to active antibodies and they identify the antigens, that is, some specific proteins present on the surface of that organism, bacterium, for example, and they attack on them and kill them. And more importantly, these antibodies are a long-term memory of the blood because these antibodies then remain inside the cell. If next time that infectious agent comes, they quickly go and kill them. This is called sort of unnatural immunity. For example, against various viral diseases like chickenpox, once we get this disease, next time we do not get it because our body have made the circulating antibodies against that bacterium, against its surface antigens and identifies them and then quickly kill them before they create a disease, before we can say they produce the disease symptoms. Even the granulocytes, the neutrophils, these are also phagocytes. They also engulf large particles which are invaders and they kill them. They usually work inside the blood. Then comes the eocenophils. Eocenophils, as you can see, they have bilob nucleus. You have seen previously that neutrophils have a trilob nucleus in this diagram, but neutrophils sometimes may have four lobes of their nucleus or may have five lobes. So their lobes of the nuclei are three to five. Actually based upon the lobes of nuclei, we identify different white blood cells because their identification is important. Then anyway, eocenophils which have bilob nucleus, these are specific cells which produces, which actually deals with or we can say kill or attack the parasitic worms. There are different types of parasites which enters in our body. These are the cells which identify those and produce some toxins to kill them. The last one are the bisophils. Bisophils are specific cells which help actually in inflammation reaction, which causes the inflammation reaction. This produces, when some body part is injured, for example, they release a content called histamine which activates the macrophages and kill the, which kill the invading bacteria or viruses or infectious agents. They also release haparin, haparin is a chemical which stop blood from clotting. So for some time, they allows blood to enter in that part so that the white blood cells can enter in that area and they can kill the invader bacteria or viruses or other organisms. Now this is very important that in some diseases and in some other conditions, these cells have to be counted. Sometimes if you have an allergic reaction or you have a parasitic worm infection, you are suspected to have a parasitic worm infection. And your doctor call you to go to a laboratory and get your leukocyte count. Actually, leukocyte count is count of all these five blood cells, monocytes, lymphocytes, neutrophils, eocenophils, bisophils. And their percentage tells the doctor that which problem could exist. If bisophils are high, maybe there is an inflammatory reaction. Eocenophils are high, there is a suspicion of, you are suspected to have maybe a parasitic infection and so on. You can see platelets on the right, small fragments of a cell. Platelets, very, very important. You may have heard of these a lot many times during the Dengue if you were outbreak. These are the cells which help, these are the cell like bodies we can say, which help blood in clotting. If these are less in number, then there is a chance of leaking of blood from different parts of the body. As you may have heard that the Dengue if you were patients may have a very sharp decrease in number of their platelets, which may result in the loss of blood from under the skin, from the nose and under the tongue. So if a Dengue if you were patient experience spots on the surface of their skin, dabbe it on the skin, then it means that their platelets are very low and their blood is coming out of their circulatory system, their vessels, but this is a very dangerous sign. If this happens then at the same time you should contact the hospital immediately. So platelets are very important, now look at their quantities, red blood cells we talked about, they are per mm cube, per millimeter cube, they are about 5 to 6 million RBCs. As we said as we previously talked about that men have quite more RBCs and women have quite less RBCs, but RBCs may be different in people living in different area, for example those people who are living at higher altitudes, because we know that there is a deficiency of oxygen in those areas, they have more RBCs in comparison to us. You can see that their blood is very dry in their cheeks, the reason for that is that there are more RBCs in them, this is also a reason, there are other reasons as well. Why they have more RBCs? Because the air is less saturated with oxygen and when they have more RBCs they can extract more oxygen from less air in comparison to the people who are living in planes at a normal pressure, then the leukocytes in total they are about 5000 to 10000 cells per mm cube all of these, though they have different concentrations and the neutrophils are present more about 62% of the white blood cells are the neutrophils, basophils are about less than 1%, eocenophils are about 1 to 2%, lymphocytes are quite more about 8 to 10% to make a total of say 100% and the platelets importantly because you should know these numbers, platelets are about 250,000 to 400,000 per mm cube, this is the normal number of platelets and these are responsible for as we talked about the blood clotting, so these are different types of blood cells which are present in the blood.