[MUSIC] In the last video we covered the aspects of cellular respiration and the entire process used to deliver oxygen to your cells. A follow up question is now what cells need oxygen? Nearly every cell needs a constant supply of oxygen to function. If that supply of oxygen stops the whole process of life stops. But some cells have more intense demands than others. To best investigate this question, we'll need to look at what happens when the process breaks down. Think back to our description of our case study, Glacier and Coxwell, first experienced tunnel vision, confusion and inability to move their fingers. These symptoms are all indicating that certain organs are starting to shut down as oxygen supplies become depleted. The first ones, the shutdown are then the ones with the highest need for oxygen and therefore most easily affected by hypoxia or too little oxygen. Throughout this course paid close attention to the greek prefix hypo because it indicates that the body is suffering from too little of some resource or activity. In this case oxygen. Looking at the symptoms we can see in which tissues oxygen is the most quickly depleted. The pathophysiology, or how the body is breaking down is revealed by the symptom. From the tunnel vision, we can infer that vision is a very expensive process. Your eyes are always relaying information about the outside world, and this process needs a constant supply of energy in the form of ATP. Your eyes send this information to the brain through electrical impulses. Among many other tasks, your brain also organizes thoughts without a constant supply of oxygen. The energetically expensive process of consciousness becomes compromised and confusion sets in. Finally, the loss of dexterity and the fingers reveals that the muscles of the body are also oxygen sponges. Your muscles need to be ready to explode with movement, which requires ATP. Without a supply of oxygen, movement becomes increasingly difficult. To this last point, hypoxic symptoms are progressive and will quickly worsen over time, the eyes, brain and muscles will try to function and continue to deplete the already limited oxygen supplies further worsening the symptoms. Tunnel vision may become a total loss of vision, confusion becomes a total loss of consciousness and muscle weakness may lead to loss of function in large muscles needed for standing upright. Prolonged oxygen starvation, completely wiped at stores and lead to permanent organ failure as these cells begin to die off. An organ where all these concepts, meet is the heart, an electrical signal generator and muscle that will beat on average 2.5 billion times in a lifetime. This marvelous organ enables the whole process of circulating blood to deliver oxygen and itself needs lots of oxygen. Any loss of oxygenation can lead to myocardial infarction more commonly referred to as a heart attack, where heart cells permanently die off. Because of its role sustaining the rest of the body, loss of the heart almost certainly leads to death. Someone watching Glacier and Coxwell, would it know how they are feeling, but would only be able to look for external signs. If Glacier is feeling confused, he would be visibly panicked, you would have disorganized sentences and likely have trouble concentrating on a conversation. Perhaps the biggest tell tale sign of not enough oxygen as blue lips and fingertips called cyanosis. The body will attempt to compensate by changing breathing rates, circulation rates and blood pressure. So now we have our first issue hypoxia, but it doesn't answer why Glacier and Coxwell suffered from it in the first place, returning to the chain of events that work to bring oxygen from outside our bodies into ourselves. If any link in that chain breaks, we can see the signs and symptoms of hypoxia. There are four primary types of hypoxia that we will consider, starting at the smallest level. If the ultimate recipients, the mitochondria are not functioning or not accepting oxygen, we call this histotoxic hypoxia. This is possible with cyanide poisoning, but that wouldn't be a particularly relevant discussion for a course on space medicine. So let's say that Glacier and Coxwell's mitochondria and cells are eager to accept oxygen. The next link in the chain we might look at is that the blood itself is not flowing in what is called stagnant hypoxia, possibly caused by a blockage of arteries or heart failure. But these causes spontaneously occurring. And two men is highly unlikely. Third if the blood is circulating, but the red blood cells inside aren't accepting oxygen, or there is a loss of blood itself, this is called anemic hypoxia. Again, poisoning is unlikely, and neither man was reported as bleeding. The process of elimination leads us to the aptly named hypoxic hypoxia, which is a problem with getting air into the lungs in the first place. To finally begin answering our questions instead of asking more. The last detail to remember is that our two travelers set a new record for elevation, reaching over the height of mount Everest. Altitude hypoxia then is a special type of hypoxic hypoxia, but we'll need to know a little bit more about pressure before we fully understand the picture.
