[MUSIC] If traveling to high altitude has such large and often debilitating effects on humans. How do people permanently live in high mountains? After all over 140 Million people live in altitudes above 2500 meters. The answer is that they have genetic adaptations or physiological traits, that enhance their ability to cope with low oxygen environments. As a result native highlanders thrive in high altitude environments, and often do not exhibit the adverse symptoms characteristic of Acute Mountain Sickness. These genetic adaptations are the result of evolution over thousands of years. Unlike de-climatization that involves reversible physiological changes, adaptations result in permanent characteristics that are inherent to an individual. [SOUND] Some of the adaptations of people whose ancestors have permanently lived at high altitudes include, increased lung volume, the ability to carry more oxygen on each red blood cell, increased blood vessel diameter and faster and deeper breathing. Interestingly high landers from different regions in the world, have developed different traits that have allowed them to successfully live at altitude. A common characteristic of native highlanders around the world is an increased lung volume that's easily recognized by their barrel-chested appearance. An enlarged lung capacity increases their tidal volume. Remember that this increases the total amount of air that they can inhale with each breath. In addition, the efficiency of oxygen exchange is increased, because the lower proportion of inhaled air enters dead space. Increased lung volumes are also associated with an increase in the surface area of alveoli. Which increases the raid of oxygen diffusion into the blood, beyond larger lungs, there's other ways that high-altitude populations have adapted to these high places. These adaptations vary by region due to long term genetic selection. In South America, Andean highlanders have developed an ability to carry more oxygen due to an increased number of red blood cells. And increased concentration of haemoglobin. This adaptation increases the delivery of oxygen to their tissues and allows them to breathe at the same rate as lowlanders. However, this is not a permanent adaptation. After spending several weeks at low altitudes, their haemoglobin levels drop. So this is an example of reversible acclimatization, which occurs in response to living at altitude. On the other hand, Tibetan highlanders have red blood cell and haemoglobin concentrations similar to that of lowlanders. This means that they've not developed an ability to carry more oxygen like the Andean people have. Instead, they breathe faster and more deeply and have an increased blood vessel diameter. The increased breathing rate of Tibetan highlanders is permanent and does not go away if they travel to lower altitudes. Their increased blood vessel diameter also allows for greater circulation of red blood cells, and consequently, enhanced oxygen transport. Ethiopian highlanders are also able to live at high altitudes and low oxygen levels without any apparent complications. However they did not seem to possess the adaptations that had been identified in Andean or Tibetan highlanders. One recent study suggests that a gene called Endothelin receptor type-B is associated with high altitude adaptation. And this improves cardiac tolerance to hypoxia in Ethiopian Highlanders. For now though, scientists are still uncertain what traits enable them to successfully inhabit these challenging mountain environments. Although native Highlanders have adaptations that enable them to live at high altitudes without risk of Acute Mountain Sickness. They may be as susceptible to Chronic Mountain Sickness, Chronic Mountain Sickness or CMS only affects people who have lived at high altitudes for many years. CMS is believed to be caused by increased production of red blood cells, which makes the blood viscous and sticky. As a result, the heart has to work harder to pump blood through the body. Many symptoms of CMS mirror those of AMS. However, increased strain on the circulatory system also places individuals at greater risk of heart attack and stroke. Because CMS is largely due to an excessive production of red blood cells it's largely diagnosed in Andean populations but not Tibetan. Like AMS the symptoms of CMS are generally improved if individuals descend to lower altitudes. In, some settings blood letting, a process where blood is withdrawn from the patient to maintain balance is still performed as an acute treatment to temporarily decrease the number of red blood cells. There are several well established field stations used to study how humans respond to altitude. These dedicated research centers allow researchers to conduct studies on climate, the environment, geology and human physiology. In many cases, these research centers are global endeavors and allow scientists from all over the world to conduct their investigations. Examples of these field stations include the Pyramid International Laboratory Observatory, a high altitude scientific research center located at 5050 meters in the Khumbu Valley in Nepal. The Jungfraujoch High Altitude Research Station is located at 3,450 meters in the Swiss Alps. The Barcroft Station is located at 3,800 meters in the White Mountains in California. And the Mount Chacaltaya Laboratory is located at 5,270 meters in the Bolivian Andes. In Canada some incredible pioneering high altitude physiological studies were conducted in the 1960s and 70s, on the 5,280 meter summit plateau of Mount Logan in Kluane National park in Yukon. The high altitude physiology study on Mount Logan was a challenging logistical program. Involving numerous researchers flying in small planes to the summit plateau of Mount Logan. This research was led by Dr. Charles Houston who spent his life studying the consequence of oxygen deprivation. He was the first person to identify High Altitude Pulmonary Edema and studies on Mount Logan identified High Altitude Retinal Hemorrhages, an unusual pathology of the retina which was first observed in 1968. Altitude presents serious physiological challenges for humans. Exploring, visiting, and living in these regions can push the boundaries of our physiology, yet our bodies are robust and have many ways to adapt to the challenge. Over generations traits emphasizing successful strategies for living at altitude have evolved independently in various mountain populations. Understanding how low landers and high landers respond thrive or become ill in mountain environments is an important area of science. With this information we can better prepare travelers as they enjoy these environments and treat those who become sick with AMS or HAPE or HACE. The stress of high altitude is also very similar to other non altitude related health conditions. Making these places ideal environments to study various types of medical problems. As we continue, throughout this course, we'll see that humans are not the only living things affected by lower partial pressures of atmospheric gases at high elevation. All life, including plants, and animals, require adaptations to survive, and thrive in high mountain environments. Are you out of breath? Let's break here. It's now time to return to your mountain world and try to locate some of the places we visited this time. Laura and Matt have a great tech tip on trip preparedness, and don't forget your end of lesson quiz. Good luck. Join me next time as we move from air to that other important element, water.