TASK 1 – (ASSESSMENT CRITERIA 1.1)
Describe the major components and explain the main physical properties of the blood.
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TASK 2 – (ASSESSMENT CRITERIA 1.2, 2.1 and 2.2)
Describe the formation of blood cells.
The formation, or haematopoiesis of both red and white blood cells occurs in the hematopoietic tissue contained in the red bone marrow which is found in the epiphyses (Rounded ends) of long bones and is also found in flat bones such as the pelvis, ribs and vertebrae. During pregnancy, the foetus forms blood in the liver. As age takes effect, blood is produced less in the long bones and more in the flat bones. Cell differentiation occurs and different cells are produced dependent on the body’s requirement. Erythropoiesis the formation of Red blood cells and begins with the creation of Proerythroblasts from hematopoietic stem cells. These cells originally have a nucleus. During a period of 3 to 5 days, ribosome’s and Haemoglobin synthesise and the nucleus is ejected and the production of the reticulocyte (Immature Erythrocyte) cell is complete. These reticulocytes are larger than normal Erythrocytes. After a day or two in the blood stream, the reticulocyte becomes a mature fully formed Erythrocyte. The lifespan of a red blood cell is approximately 120 days.
Leucocytes develop into differentiated cells that perform functions within the body’s defence mechanism. They are fewer in number than Erythrocytes, (approximately 1:7000). Leucocytes are split into two groups, Granulocytes, (Neutrophils, Eosinophil’s and Basophils), so called due to the granular appearance of the cytoplasm and are formed from Myoblasts. The second group is Agranulocytes (Lymphocytes (T and B), and monocytes). Monocytes, Neutrophil’s and Eosinophil’s are phagocytic. They engulf bacteria and destroy this from within the cell. Basophils produce antihistamines, heparin and serotonin. The heparin prevents the unnecessary clotting of blood and the Serotonin helps to make the capillaries porous to allow Phagacytes to exit the blood and enter infectious areas where bacteria are located. The lifespan of white blood cells (Leucocytes) is dependent on the bodies needs due to their unique role in defending the body.