Wednesday, 5 May 2010

DESCRIBE THE STRUCTURE OF A RED BLOOD CELL AND EXPLAIN HOW THIS RELATES TO FUNCTION






RBCs (Red blood cells) are manufactured in the red bone marrow of bones. In adults, RBCs are only manufactured in specific bones; thoracic, vertebrae, cranial, and the ends of femurs and humerous bones. In infants, every bone in their body has the ability to manufacture RBC.
RBCs are the most common blood cells in our body. Typically blood contains 25 trillion RBCs, which are continuously being replaced at a rate of approximately 3 million per second.
The lifespan of a RBC is short- 120 days. This means that they will be working at their optimum capacity over this time but after this time they are worn out and need replacing. When they need replacing, phagocyte cells will digest them. The bone marrow will release matured RBCs into the blood stream, to replace the ones that have reached the end of their life span. So there is no noticeable loss in our bodies.
RBCs are only released into the blood when they are mature. Whilst maturing a macrophage cell is attached to them. This macrophage cell is of particular importance. When a RBC is mature, its nucleus is squeezed out. The macrophage cell ingests this nucleus. This is an extremely important defence mechanism of the body. If a RBC still had a nucleus whilst working in the body, and antigen specifically a virus would be able to take over the RBC for its only purpose i.e. cause infection. The virus would be able to replicate and spread. Having no nucleus means that a virus cannot invade and disrupt the RBC’s vital role in the body.
RBCs are called so due to them being red in colour. The reason that they are red in colour is that they contain haemoglobin. Haemoglobin contains iron pigments, which gives its red colour. When RBCs are matured 90% is haemoglobin.
Haemoglobin is of vital importance. Haemoglobin easily combines with oxygen, and for every molecule of haemoglobin, 4 molecules of oxygen can attach to it.


Haemoglobin + 4 oxygen = oxyhaemoglobin

This is a large quantity of oxygen for one single molecule to hold. This therefore makes haemoglobin a highly efficient substance to use, to carry oxygen. When haemoglobin becomes saturated with oxygen this is called ‘oxyhaemoglobin’. Oxyhaemoglobin is therefore the source of oxygen in the body. It is able to be the source of oxygen in the body simply because the reaction to combine oxygen with haemoglobin is reversible. Oxygen can be released easily from the haemoglobin, out of the RBC and diffused to where it is needed such as the muscles during exercise. Oxygen is of vital importance, it is needed by every cell in the body for cellular respiration. Without oxygen, all our body systems would eventually shut down and we would die.
(When oxyhaemoglobin is present in a RBC the red colour of the RBC becomes more intense)
RBC is not only important for transporting oxygen due to the ability of its haemoglobin; it also helps transport carbon dioxide and delivers it to the lungs to expel from the body by exhalation. Carbon dioxide is poisonous; it needs to be taken as efficiently as possible to be excreted via exhalation.
To transport carbon dioxide safely and efficiently this is done by dissolving carbon dioxide to form the solution carbonic acid. To convert carbon dioxide to carbonic acid would naturally take a long time. Therefore RBCs contain an enzyme called carbonic anhydrase that acts as a catalyst, so this conversion is quick to occur. Due to the presence of this specific enzyme the majority of carbon dioxide will be carried in the RBC. Occasionally plasma (also found in blood) will also carry carbon dioxide. This is not an ideal situation due to the fact that if too much is carried in the plasma this leads to high amounts of lactic acid being formed.
So RBCs need to be present in our blood in high quantities to deliver oxygen to all our cells in our bodies for respiration and to take away waste carbon dioxide to be excreted. This is why infants can manufacture RBCs in every bone in their bodies. They need a huge amount of mature efficient RBCs to deliver the oxygen to the body systems for the rapid period of growth that all infants under go. To be able to achieve this, RBCs must be able to move efficiently through our blood vessels in our bodies. These blood vessels widen and narrow, and twist and turn. RBCs specialised shape enables this to happen


RBCs are round discs which are bi-concave. This allows them to be flexible, and twist and turn through all the blood vessels easily. Bianco C (2010) “An RBC can change shape to an amazing extent, without breaking, as it squeezes single file through capillaries”. So whether transporting oxygen or carbon dioxide this can be done efficiently.
RBCs are also important to maintain health. We need iron in our bodies. Iron in the haemoglobin is responsible for the vast uptake of oxygen one haemoglobin molecule can do. If we had limited numbers of RBCs are levels of iron in our body would be low. We would not have enough oxygen in our bodies and not enough oxygen means our bodies would not be able to produce energy through respiration. One physiological effect of this on our bodies would be feeling tired all the time. This would be medically described as being ‘anaemic’ and could require iron tablets

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