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Potassium is a group one element which very rarely occurs in nature in its elemental form due to its extreme reactivity. The word potassium comes from the word potash which is a compound used in the making of glass. The symbol for potassium is K which comes from the Latin word ‘kalium’ (Knapp, 1996). Potassium’s structure consists of a central nucleus surrounded by four outer shells, the first shell contains two electrons, and the next two shells contain eight electrons each with the last shell containing just one electron giving the structure a total of 19 protons, 19 electrons and 20 neutrons (Knapp, 1996). The fact that the last shell has only one electron is the reason why the element is so reactive and is classed as a group one element. Potassium has a tendency to give away its electron in its outer shell in order to become stable as it is more efficient to give it away than taking on seven more electrons to fill its outer shell. This usually takes place in an ionic bonding scenario. Potassium is the seventh most common element on earth and makes up nearly three percent of the earths crust (Knapp, 1996). Of all the potassium contained in the human body, 97 percent is intracellular (Marieb, 2004). Excess potassium in the body, known as Hyperkalemia, may be caused by severe dehydration or by kidney failure. This condition may cause adverse effects in the body such as: muscular weakness, cardiac abnormalities, and possible cardiac failure (Marieb, 2004). An interesting note that relates to this is that a solution of potassium chloride is used in lethal injections for state executions in America, which causes the heart to stop beating (Death Penalty Information Center, 2007). A lack of potassium in the body, known as Hypokalemia, may be caused by severe diarrhoea and severe vomiting. This condition can cause muscular weakness, paralysis, nausea, vomiting, and possible cardiac failure (Marieb, 2004). The recommended daily intake of potassium for healthy adults is around four to six grams (Ministry of Health, 2003). A major role that potassium plays in the body is in the sodium-potassium pump. Without this pump we would be unable to control our muscles and use our nerves. Basically it is a process of keeping more potassium inside the cell than outside, and more sodium on the outside than on the inside. The membrane of the cell is almost completely impermeable to sodium but allows potassium ions to leak out (Marieb, 2004). Looking at one cycle of the pump, you can see that every cycle expels three sodium ions and takes in three potassium ions with the aid of ATP. As a result of the three positive sodium ions being expelled and only two potassium ions being brought back in, plus the leakage of potassium, the inside of the cell becomes negatively charged compared to the outside and the cell is said to be ‘polarized’. If this process of actively transporting the ions did not occur the ions would eventually equalize through diffusion down their concentration gradient and no voltage potential could exist (Marieb, 2004). This process is shown in the diagram in Figure 10.25. All excitable cells in the body need this voltage potential across the membranes. To see the need for this polarity of the cells, we can look at the how action potentials are sent to muscles. When a stimulus is created, tiny ion gates in the excitable cells will open and let sodium ions into the cell which depolarizes the cell. This depolarization creates a tiny current which then triggers the next cell creating a domino affect along the excitable cells until it reaches its target. This process happens in just a few milliseconds and just after a cell has depolarized, the sodium-potassium pump restores the cell back to its polarized resting state (Marieb, 2004). References: Chemistry 420 - Principles of Biochemistry: The Sodium-Potassium Pump. [Art]. Retrieved August 19, 2007, from University of Notre Dame: http://www.nd.edu/~aseriann/nak.html Death Penalty Information Center, 2007. Lethal Injections: Some Cases Stayed, Other Executions Proceed. Retrieved August 19, 2007, from http://www.deathpenaltyinfo.org/article.php?did=1686&scid=64 Knapp, B. (1996). Elements: Sodium and Potassium. Oxon, England: Atlantic Europe Publishing. Marieb, E. N. (2004). Human anatomy & physiology (6th ed.). San Francisco: Pearson Benjamin Cummings. Ministry of Health. (2003). Food and nutrition guidelines for healthy adults: A background paper. Wellington, N.Z.: Ministry of Health. Goss, F., Robertson, R., Riechman, S., Zoeller, R., Dabayebeh, I., Moyna, N., Boer, N., Peoples, J., & Metz, K. (2001). Effect of Potassium Phosphate Supplementation on Perceptual and Physiological Responses to Maximal Graded Exercise. Journal of Sport Nutrition and Exercise Metabolism, 11, 53 – 62. Retrieved August 13, 2007, from EBSCOhost database. Clothing Alterations Hamilton NZ
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