The Argument
In the
argument section of his book, Shenk suggests that Kenyans who out-perform their
Caucasian athletes in the Olympics come from the “Kalenjin tribe in the Great
Rift Vally region of western Kenya, where they have a centuries-old tradition
of long-distance running”(p.103). This tradition of cattle raiding was directly
linked to economic and social success; “ ‘the better a young man was at raiding
[cattle]- in large part a function of his speed and endurance- the more cattle
he accumulated’”… “ ‘and since cattle were what a prospective husband needed to
pay for a bride…it’s not hard to imagine that such a reproductive advantage
might cause a significant shift in a group’s genetic makeup over the course of
a few centuries’”(p.103). Compare the tidal volume, vital capacity, and
residual volume of the lungs of a Kenyan athlete to the lungs of an average
American. Would an athlete in training experience a Right Bohr shift or a Left
Bohr shift, and what causes this shift? Relate back to Chapter 42 on the
Respiratory System as well as the biological theme of homeostasis.
Tracy Lai (tracymlai@hotmail.com)
The tidal volume of a Kenyan athlete, even during rest, would be greater than that of an average American, because athletes naturally need more oxygen than their sedentary counterparts. A study by the Uppsala University department of nutrition found that endurance athletes have higher basal metabolic rates than their non-exercising counterparts, even when controlled for body composition and muscle mass (http://www.ncbi.nlm.nih.gov/pubmed/8775359). During moderate exercise, however, the tidal volume of a sedentary American would increase more than the tidal volume of an elite athlete because the exercise would be more demanding for the unfit American than an endurance runner. However, the relative respiratory strain of exercise would vary depending on which region of America or the Great Rift Valley the average Joe and Kenyan athlete came from; inhabitants of the Rockies, Appalachians, Catskills, etc. or mountainous edges of the Great Rift Valley would have an advantage because high altitudes increase the production of erythropoietin by the kidneys. The hormone, according to Campbell, “stimulates erythrocyte production,” which means there are more red blood cells in the blood to transport oxygen to body cells (914). Each response to oxygen deprivation- increased breathing rate or erythrocyte production- is the body’s way of maintaining homeostasis; when more carbon dioxide is produced through cellular respiration than oxygen is inhaled, the blood pH drops below homeostatic levels.
ReplyDeleteThe vital capacity of runners would also be higher than that of non-athletes. The University of Lagos published a study showing that “TV [tidal volume] and FVC [forced vital capacity]. . . were significantly higher in male athletes than in male non-athletes” (http://www.ajol.info/index.php/ajbr/article/viewFile/53962/42504..). The greater vital capacity in athletes could be a result of a stronger diaphragm and rib muscles, as well as “other muscles of the neck, back, and chest” that, according to Campbell, are often recruited to increase lung capacity during exercise (920). However, residual volume would not be a significant difference between athletes and non-athletes; although residual volume tends to increase with age, a study by the Journal of Applied Physiology found that exercise does not have a significant effect of residual volume among men of the same age (http://jap.physiology.org/content/65/1/101.abstract).
An athlete in training would experience a right Bohr shift during training. Exercise would increase the cellular respiration rate of muscle cells, both decreasing the amount of oxygen in the blood and increasing the levels of carbon dioxide. As carbon dioxide reacts with water to form carbonic acid, the blood pH drops. In order to maintain homeostasis in blood acidity, the hemoglobin molecules would release oxygen more readily to counteract the increase in carbon dioxide in the blood, and to provide the body cells with oxygen. Campbell describes the Bohr shift as “Low pH decreas[ing] the affinity of hemoglobin for O₂” (924). Since hemoglobin exhibits cooperativity between its four oxygen-carrying subunits, the increased affinity of one subunit of hemoglobin to release oxygen results in all four subunits releasing oxygen into the blood.
Mackenzie Levy (GinnyFan@comcast.net)
Kenyan runners are not regular athletes at all because they have rare characteristics. Shenk states, “smaller physiques, narrow shoulders, lean legs, much less muscle mass, and higher proportion of ‘slow-twitch’ muscles, rendering them ideal endurance athletes” (Shenk 299), but he fails to talk about the lungs of the great aerobic athletes. The Kalenjin tribe resides in high altitude environments, so the air is very thin and less dense than usual. Members of the Kalenjin tribe are acclimated to the high altitude air because that is where they reside and train. This is an advantage because according to livestrong.com, “Increased lung capacity due to an acclimation to high altitudes a running culture among Kenyan tribes, physiology and genetics all likely play a significant role in the success of Kenyan marathon runners” (http://www.livestrong.com/article/361725-famous-male-marathon-runners-in-kenya/). Since the Kalenjin live at a high altitude, the hormone erythropoietin is secreted and produced from the kidney to stimulate the production of red blood cells. This hormone essential tells the bone marrow by Paracrine signaling to start making red blood cells so that there can be more hemoglobin. Hemoglobin is what the oxygen molecules bind to, so if there is more hemoglobin, then there will be more oxygen being distributed throughout the body cells for cellular respiration. The hormone is told to stop being produced when the pH is very low because there is a great amount of carbon dioxide molecules. This is related to homeostasis, which is one of the six biology themes. The medulla senses a high acidity in the blood because there is a lot of carbon dioxide from cellular respiration. So, the medulla will tell the kidney to stop the production of EPO because there will be less oxygen and less oxygen means less cellular respiration and less carbon dioxide molecules and high blood pH. The blood pH and the release of EPO at high altitudes can be graphed as a sinusoidal curve because the pH and EPO levels may go above or below the respective homeostatic set points.
ReplyDeleteThe tidal volume is defined as, “the volume of air a mammal inhales and exhales with each breath” (Campbell G-36). The tidal volume of a Kenyan runner is higher than that of an average person because the Kenyan runner’s lung is so efficient that he or she is able to inhale and exhale for a long time. The same is with vital capacity as well. Vital capacity is defined as, “The maximum volume of air that a mammal can inhale and exhale with each breath” (Campbell G-38). A Kenyan runner will have a higher vital capacity than an average person because the muscles that surround the lungs that are constantly worked by the aerobic athletes are stronger than an average person’s muscles, so the muscles can contract and stretch further than an average person’s muscles could (http://www.livestrong.com/article/401044-does-lung-capacity-increase-with-running/). As a Kenyan is running or exercising, he or she would experience a right Bohr shift because he or she is working his or her muscles hard. He or she is working his or her body cells, so in return, the body cells need oxygen so that cellular respiration can take place and 38 ATPs can be produced. So, the right Bohr shift calls for the decrease in affinity between hemoglobin and oxygen, so that oxygen can be distributed to all body cells instead of staying on hemoglobin. Also, more cellular respiration means more carbon dioxide molecules, so the pH decreases. The carbon dioxide reacts with water and forms carbonic acid that prompts hemoglobin to release its oxygen. So, since oxygen is needed all around the body, the hemoglobin must release the oxygen early than usual, so that is why it is called a right Bohr shift.
Krish Desai (kjdesai5@mac.com)