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Components Of Blood And Their Functions - Overview | Cells,Plasma,Circulation | Types | Wit Biology

                                      Components Of Blood


          We know that blood is divided into plasma and cells about 45% of the blood is going to be the cellular component the red cells and the white cells. The vast majority of that of course will be the red cells and we know that blood is also divided into the plasma. but on this talk we want to think mostly about the cells in the blood. So we have blood and we have cells in the blood. so what are the cells in the blood now there are two main types of cell in the blood.

          There are the Erythrocytes which are the red cells and they are the leukocytes which are the white cells.


Red Blood Cells (Erythrocytes)


         Now there's going to be about five million red blood cells per cubic millimeter of blood the vast majority of the cells in the blood are the erythrocytes the red cells and these cells live for about 120 days. After they've been released from the bone marrow from the red bone marrow where they're produced and they circulate in the blood grow round about a 120 days. so here we see a red cell and what we notice is the red cell is a biconcave disc. It's darker on the outside and it's lighter on the inside. 

          If we were to look at those in cross-section they look a bit like this they're thinner in the middle and they're about 7 micrometers in diameter. The red cells the erythrocytes and of course as the red cells pass through the loans they pick up oxygen.  

          The oxygen combines with the hemoglobin. which is the red pigment in the red cells forming oxyhemoglobin increasing the saturation of the blood the cells then circulate to the tissues the oxygen is liberated from the oxyhemoglobin restoring the hemoglobin to its reduced hemoglobin state sometimes, that's called deoxyhemoglobin and that will circulate back to the lungs to be reoxygenate and the red cells are very flexible cells. So for example in the brain and in the kidneys there are very small capillaries and there can actually squeeze down to get through after 120 days or so lifespan. 

          They're broken down by macrophages largely in the liver and spleen they're broken down the hemoglobin is recycled in the form of bilirubin to form bile. So it's not wasted it's used as as buying the protein components are reabsorbed. So the red cells are being produced all the time in the red bone marrow and of course in the circulation the red cells do not have a nucleus they are the only cells in the body that are living cells. 

          They are metabolizing cells. but they don't have any now when they were in the bone marrow when they were forming they did have a nucleus. But the mature cell doesn't and actually for the first couple of days when the red cells have just been released from the bone marrow. It's still possible if there correctly stained to see some nuclear fragments in those very very young red cells when they're only a day or two old and these very young red cells are called reticular sites. So that's the Aretha size.


White Blood Cells (Leukocytes)


           Next we think about the leukocytes the white blood cells now people started looking at these a long time ago under rather primitive light microscopes and that's when their names were generated. So blood samples were taken they were stained and the cells were examined underneath the light microscope so the way we classify these is based on this early observational data.

          So the leukocytes there are a class of leukocytes that is a class of white blood cell called the granular size and the granular sites are so called because they have visible staining granules in their cytoplasm so granule own sites the cells with granules and the most common one of these are the neutrophils then there's another type called eosinophils and there's a less common type called basophils.

          So you might have noticed already that all of the granule ascitic leukocytes so these are leukocytes but they are granular sites so they are granular CITIC leukocytes they all end in film neutrophils,  eosinophils, basophils.

Neutrophils

          Now as we've said the most common form are the neutrophils and the neutrophils have a lobed nucleus held together by thinner strands and on a blood slide you might observe three or four lobes in the nucleus and for this reason these are sometimes called polymorphonuclear cells or polymorphs. 

          Because poly means many morph is the shape they're polymorphonuclear cells and these have granules that are visible or the light microscope after the cell has been appropriately scaled they are granular sitting leukocytes and they are polymorphic they are poly nucular cells  Polymorphonuclear sites. 

          But we normally call them neutrophils particularly important for fighting bacterial infections. because they can phagocytose bacteria and indeed they can phagocytose dead tissue cells as well. So the neutrophils absolutely vital for protection against bacterial infection.

Eosinophils

          The eosinophils have a two lobe nucleus something like this two lobes held together by a thicker strand. So these are the eosinophils and these have larger tend to have larger granules and the eosinophils are particularly important for fighting parasitic infections. So infections with worms for example the eosinophils will combat that so we've got neutrophils, eosinophils and the third class of granular CITIC leukocyte.

Basophils

           We have are the basophils and the basophils again have a two lobed nucleus my kind of shape although very often it's very hard to see the nucleus in the basophils. Because of the large granules filling the cytoplasm now the amount of basophils in the blood is very low. But what the basophils will do is they will migrate into the tissues and in the tissues we call basophils   mast cells and these help to facilitate the inflammatory response.

           The next classification of leukocyte we want to think about are the a granular size the a granular size now a means without granules now it's not that these cells don't have granules it's just that people couldn't see them under the light microscope.

           Because indeed some of these cells do have granules in fact so when we think about the a granular sites there are monocytes.

Monocytes 

          Monocytes are fairly large leukocytes they are a granular citic leukocytes present in the blood and they have a fairly large kind of kidney shape like this and the monocytes in the blood are very important for combating chronic bacterial infections such as tuberculosis for example but the key thing about the monocytes is they don't stay in the blood the monocytes can migrate out of the blood vessels into the tissues and in the tissues the monocytes will become macrophages.

Macrophages

         Now macro means big phage means to eat these are the big eaters they will phagocytose bacteria they will phagocytose dead tissue cells and they will also release numerous cytokines chemical messengers released by the macrophages that coordinate processes such as inflammation and wound healing.

          So absolutely vital that there are these macrophages in the tissues and we also now know that monocytes can differentiate into dendritic cells.

          The dendritic cells are like they have kind of like octopuses really they are beating one things coming off the myelin tentacles coming off them and that means if any antigens come along to their or come along to the other side of it. Then these can detect them they are antigen detecting cells. So they might detect viruses they might detect bacteria and if they are detected they will migrate to the lymph nodes and present this antigen to the other immunological cells present in the lymph nodes. So they are antigen detecting and they are antigen presenting cells and they both differentiate from the sighs so the monocytes can become macrophages or dendritic cells once they are in the tissues now another cell fragment that we get in the blood are the thrombocytes now the thrombocytes are cell fragments in the bone marrow. There's a large cell called a mega carrier site and the megakaryocytes break up into hundreds of little fragments and these fragments are the thrombocytes.


Platelets (Thrombocytes)


          Thrombocytes are platelets. It's two words for the same thing thrombocytes and platelets means exactly the same thing and these are absolutely essential for the process of blood clotting. So if a blood vessel is clogged is cut first of all the platelets will the platelets or thrombocytes will come together to form a platelet plug to form an initial hemostasis and then they can initiate the full coagulation cascade to cause full blood clotting. So the thrombocytes absolutely essential in that process now.

          We're still on a granular sites after make a bit of space here go far away granular sites so the a granular sites monocytes,  thrombocytes the other main classification of the a granular sites are the lymphocytes. The lymphocytic leukocytes still white cells still a granular citic white cells but these are the lymphocytes as the name suggests these can be associated with lymphatic tissues but they're also present in the blood and we can identify two forms of lymphocyte there's the large and the small that's quite easy now the large ones are the NK s the large lymphocytes are n case do you know what NK s stand for it's a great name the NK s are the natural killer cells.  


           The natural killers lies lymphocytes will kill sellers of the body why would you want to kill cells of the bottom well if those cells of the body are infected with viral particles so viruses are obligate intracellular parasites the viruses don't breed they don't reproduce independently like bacteria do in the tissue spaces they have to be inside a cell they have to hijack the genetic apparatus of the cell in order to reproduce. So the NK cell will come along and it will just completely kill the virally infected cell and of course killing all the viruses that are in it at the same time and also NK lymphocytes can kill cancer cells sometimes. 

            So as long as the natural killer cell can recognize that the cancer is abnormal it can eradicate malignant tissue so the large lymphocytes are the NK s now the small lymphocytes all look much the same they've got a very large nucleus relatively small area for the cytoplasm around the outside and the small lymphocytes can be divided into B and t-lymphocytes.

            The B lymphocytes are so called because they mature in the bone the T lymphocytes are so called because they originally mature in the thymus gland in the thoracic cavity.

            There are different types of T cell so there are T helper cells there are T suppressor cells and there are T cytotoxic cells.

            The T helper cells what these do is they help the B cells so the T helper cells help the B cells to produce antibodies that is the immunoglobulins the specific immune proteins the T suppressor cells inhibit that process and decide when the infection is finished when it's time to stop producing large amounts of antibody and the T cytotoxic cells a bit like their big brothers and sisters the natural killer cells these can kill virally infected cells and also they can kill cancer cells which of course is great when that happens so the lymphocytes can be large or small. The small can be B or T. 


            The T can be help of suppressor or cytotoxic now it's the B cells that are actually helped by the T helper cells to produce the antibodies the immunoglobulins. So the B cells are producing the immunoglobulins the specific immune proteins that give a specific acquired immunity absolutely liable.

            So for example if someone has HIV infection human immunodeficiency virus infection the HIV virus primarily attacks the T helper cells reduces the population of T helper cells meaning the T helper cells no longer help the b-cells to produce the immunoglobulins meaning the patients become immuno compromised get infections and of course tragically that can include life-threatening infections. 

            But when there is an infection the B cells proliferate there's a process of program operation and you get millions or billions of these b-cells produced in order to produce huge amounts of immunoglobulins and these are called the plasma cells. So if someone had a viral infection for example you would expect the number of plasma cells to increase so that huge amounts of immunoglobulins too can be produced to get rid of the infection and then when the infections gone another type of B cell is called a memory cell a memory B cell and that remembers how to make that specific immunoglobulin against a specific antigen meaning that the immune response will be much quicker the next time so the agranulocytes are the monocytes, thrombocytes and lymphocytes the monocytes in the tissues can divide into macrophages and dendritic cells. 

             The lymphocytes can be large which are the natural killer cells or they can be small. The small can be subdivided into the B or the T. The T can be subdivided into the helpers suppressors and cytotoxic s-- and the b-lymphocytes can be subdivided into plasma cells and memory cells.

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