report 代写 The Cardiovascular System Description Biology Essay

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BLOOD AND THE CARDIOVASCULAR SYSTEM

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.

的形成,或造血的红细胞和白细胞发生中的红骨髓是造血组织(骨骺发现圆形端)长骨也发现如骨盆扁平骨、肋骨和椎骨。妊娠期间,胎儿的肝脏形成血液。随着年龄的影响,血液在骨骼中的产生较少,而在骨骼更为扁平。细胞分化发生和不同的细胞产生依赖于身体的要求。红细胞红细胞的形成始于从造血干细胞产生红细胞。这些细胞最初有一个核。一期3至5天期间,核糖体和Haemoglobin synthesise和核喷射和网织红细胞生产(未成熟红细胞)细胞是完整的。这些网织红细胞比正常红细胞。一天或者两天血液中后,网织红细胞成为一个成熟的完全形成红细胞。红细胞的寿命约为120天。

白细胞发展成分化的细胞进行功能在人体的防御机制。他们的数量非常少,比Erythrocytes(约兔)。白细胞分为两组,Granulocytes,(中性粒细胞、嗜酸性粒细胞和嗜碱性粒细胞),所以称由于细胞质的颗粒形貌和形成的成肌细胞。第二组是Agranulocytes(淋巴细胞(T、B),和单核细胞)。单核细胞、中性粒细胞和嗜酸性粒细胞的吞噬。他们吞噬细菌和破坏这种细胞内。嗜碱性粒细胞产生抗组胺、肝素和5-羟色胺。肝素可以防止不必要的凝血与5-羟色胺能使毛细血管多孔允许phagacytes退出和进入血液传染病菌的地方位于。白血细胞(白细胞)的寿命取决于身体的需求由于其在维护身体的独特作用。

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