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Sickled red blood cells and homeostasis - essay

FredParisFrance 61 / 7  
Jul 8, 2008   #1

Could you please read my essay and give me some feedback?

The prompt is:

Select a topic (anatomy or physiology) that interests you from this week's reading material and write a "lecture" (300 to 500 words) to your classmates; describing the topic to them as if your were the instructor teaching the class.

Thank you in advance


Sickle cell disease is an epitome of the mutual influences of the six levels of organizations of the human body on homeostasis. Indeed, sickle cell disease is a group of inherited red blood cells disorders harming the transportation of oxygen transferred from inhaled air, thanks to the respiratory system, to body cells through the cardiovascular system (Jurmain, Kilgore, & Trevathan, 2006). This pathology has been characterized by the proliferation of red blood cells presenting a sickle shape, i.e. a shape similar to the letter "C", whose detrimental effect has been to block the flow of blood in small blood vessels leading to the various tissues of organs (Jurmain, Kilgore, & Trevathan, 2006).

From the cell level point of view, sickle cell disease has stem from a genetic mutation modifying the sequence of amino acids taking part in the production of an altered form of a protein known as haemoglobin S (HbS) at the root of the "C" shape of red blood cells (Jurmain, Kilgore, & Trevathan, 2006). This condition has exclusively originated from genetic inheritance, i.e. transmitted from parents to offspring on the form of a recessive allele (Jurmain, Kilgore, & Trevathan, 2006). Subsequently, genitors carrying this gene have contributed to giving birth to individuals whose genotype may be HbA / HbS (i.e. affected by a condition called sickle-cell trait) or even HbS / HbS (i.e. suffering from sickle cell anaemia) (Jurmain, Kilgore, & Trevathan, 2006).

What is astonishing, at the very most, is that this harmful trait has propagated from West Africa to many areas in the world due to a zoonotic disease. As a matter of fact, specific environmental factors have played a prominent part in the process of natural selection, and its corollary adaptation, since at least about one thousand year (Currat et al., 2002). This dissemination, on the one hand, has sprung from the meeting of a pathogen agent and a vector, respectively the single-celled organism known as malaria and mosquitoes. On the other hand, this diffusion has arisen from the fact that malaria can only reproduce if it benefits from a sufficient amount of oxygen in the blood of its human host once introduced in the cardiovascular system. Subsequently, in areas such as Senegal where malaria has been endemic (Currat et al., 2002), individuals with sickle cell trait, that is to say heterozygotes whose genotype is HbA / HbS, have had a higher reproductive success than those with normal haemoglobin or those with sickle cell disease. Actually, they "enjoy" this trait that is at the root of the deprivation of oxygen experienced by malaria whereas homozygotes, whose genotype is HbA / HbA, produce normal haemoglobin and are likely to die because of malaria. As far as homozygotes whose genotype is HbS / HbS are concerned, they have sickle cell anaemia and will certainly expire because of it.

Finally, surprisingly as it may be, homeostasis can be achieved in certain areas and during periods whereas conditions seem to be the worst for ensuring human life on earth. This is a reminder that homeostasis is preserved in a certain ecosystem and that any change in this environment or any relocation in anther one can be far more noxious than it can appear at first sight for both autochthons and colonizers. This is all the more true that hitherto, though treatments have been developed, no panacea has been available (National Heart Lung and Blood Institute [NHLBI], 2007).


Currat, M., Trabuchet, G., Rees, D., Perrin, P., Harding, R. M., Clegg, J. B., et al. (2002). Molecular Analysis of the -Globin Gene Cluster in the Niokholo Mandenka Population Reveals a Recent Origin of the Senegal Mutation. American Journal of Human Genetics, 70(1), 207-223.

Jurmain, R., Kilgore, L., & Trevathan, W. (2006). Essentials of physical anthropology (6th ed.). Belmont, CA: Thomson Higher Education.

National Heart Lung and Blood Institute (2007). How Is Sickle Cell Anemia Treated?

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