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Chapter 9

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York University
Kinesiology & Health Science
KINE 2011
Gillian Wu

Erythrocytes  The main function of erythrocytes is to transport oxygen in the blood.  They are flat disc-shaped cells indented in the middle; this shape helps them perform the major function in two ways: 1) The biconcave shape provides a larger surface area for the diffusion of oxygen and 2) the thinness of the shape allows oxygen to rapidly diffuse across the exterior of the cell.  Hemoglobin is the main component which allows red blood cells to transport oxygen and hemoglobin is only found in erythrocytes.  Hemoglobin molecule has two components: 1) The globin portion which is a protein made up of 4 highly folded polypeptide chains and 2) four iron containing non protein heme groups each of which is bound to one polypeptide chain.  Oxygen is poorly soluble in plasma therefore the majority of oxygen is bound to hemoglobin.  Hemoglobin is red because of the combination of iron and oxygen and when it is deoxygenated it is blue like venous blood.  Besides oxygen, hemoglobin can bind to:  Carbon Dioxide  H from carbonic acid, hemoglobin acts like a buffer to prevent this ion from causing big changes in pH of the blood  Carbon monoxide  Nitric Oxide  Erythrocytes contain no nucleus, organelles or ribosomes because during their development the majority of the space is taken up by hemoglobin.  Erythrocytes contain only two enzymes:  Glycolytic enzymes which are used to generate the energy required to fuel the active transport mechanisms used to maintain the proper ionic concentration levels. They don’t possess mitochondria so they rely on glycolysis for all their ATP.  Carbonic Anhydrase is critical for carbon dioxide transport. This enzyme converts carbon dioxide to the bicarbonate ion which is the major form of carbon dioxide that is transported  Erythrocytes have a short life span and the meet their final demise in the spleen  Erythrocytes cannot divide to give rise to more erythrocytes therefore they must continually replenished by the bone marrow  Erythropoiesis. Young children have red bone marrow that is capable of producing red blood cells however as you grow older you start to develop yellow bone marrow that has fat deposits on them, these bone marrows are incapable of erythropoiesis.  Red bloods also give rise to leukocytes and platelets. Erythropoietin  Low oxygen levels do not stimulate erythropoiesis by acting on the bone marrow instead it acts on kidneys which causes them to secrete erythropoietin into the blood and this hormone stimulates red blood cell production by the bone marrow. This increases the number of circulating red blood cells which in turn increases the oxygen carrying capacity of the blood. Once normal oxygen levels are delivery to the kidneys then erythropoietin production is turned down.  When demands for red blood cells is high the bone marrow might release some immature rbcs which are known as reticulocytes, this reticulocytes can develop into mature red blood cells later on. Anaemia  Refers to a below normal oxygen carrying capacity of the blood and it is characterized by a low hematocrit. It is usually caused by a decreased rate of erythropoiesis, excessive losses of erythrocytes or a deficiency in the hemoglobin content. There are six main causes of anaemia:  Nutrional  Pernicious-inability to absorb nutrients like B12  Aplastic  Renal  Haemorrhagic- caused by a loss of a lot of blood  Harmolytic- which is caused by the rupture of a lot of red blood cells.  Sickle cell Polycythaemia  The larger the bloods viscosity the larger the reduction of blood flow, so if the number of red blood increases a lot the viscosity is created by the drag between the blood red blood cell and the vessel wall.  Increasing hematocrit (red blood cell volume) helps by increases hemoglobin and oxygen carrying capacity but it is also bad because it reduces the hearts ability to circulate the blood because of the increased friction thereby decreasing the timely delivery of oxygen to tissues.  Polycythemia is characterized by too much circulating red blood cells and an elevated hematocrit. There are two types:  Primary- is caused by a tumor like condition of the bone marrow in which erythropoiesis proceeds at an uncontrolled rate, the excessive number of red blood cells increases the viscosity causing the blood flow to be sluggish and it might also increase the blood pressure.  Secondary- is an adaptive mechanism which is used to improve the bloods oxygen carrying capacity and it usually occurs in people living at high altitudes.  Relative polycythemia is when the number of red blood cells doesn’t increase it just that they take up
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