While talking with friends I was posed an interesting question in relation to oxygen and how she had read that it can be toxic. She isn’t wrong; oxygen is literally killing everyone over time but it is considered to be a part of the normal aging process. I decided to take this though as an opportunity to have an in-depth discussion about oxygen, why it is important and why its consumption, to a degree, is what is causing you to age.
Breathing is a vital step of existence in this sense of biology. Atmosphere is being inhaled and exhaled approximately 23,000 times a day. This atmosphere consists of approximately 78% nitrogen, 21% oxygen, 0.9% argon and an array of other gases and water vapor. The component that we are particular interested in, physiologically, is oxygen. Oxygen isn’t only just important for us physiologically but it is essential for plants to be able to photosynthesis, leading to respiration and an allotrope of oxygen (ozone) is vital for the minimization of harmful radiation from entering our atmosphere. We’re currently damaging this thanks to the overproduction of greenhouses such as methane and carbon dioxide but that’s an article for another day. You can read about it a little in one of my previous articles about the Great Barrier Reef.
The percentages of gases we inhaled was just mentioned but what about the percentages of what we exhale? Well the percentage of nitrogen stays the same because our body doesn’t need it, oxygen decreases from 21% to approximately 14% and carbon dioxide increases from 0.04% to around 4.8%. Now these levels can vary depending on physical activity whether that be post exercise or in a state of rest. What happens? Why is it that these percentages change? Let’s have a look at some biochemistry involved.
When we inhale, our diaphragm contracts and moves in a downwards fashion. This action decreases the pressure of the space within the lungs and air from the outside moves into the lungs to equalize this pressure difference. This forces our lungs to expand, filling them with oxygen rich air. Fun fact; you’re told to not rock on your chair while in school because if you fall back and hit your head, you can damage your medulla oblongata which controls your breathing. If this becomes damaged, your diaphragm can not contract and you won’t be able to breathe; it’s not just a student-teacher power struggle. Here there is a gas exchange which is the biological process of oxygen diffusing into our bloodstream and carbon dioxide diffusing out into your lungs to be exhaled. When you hold your breath, it is the buildup of carbon dioxide that makes you eventually gasp, not the lack of oxygen, because carbon dioxide is toxic.
The movement of oxygen and carbon dioxide is a passive process (doesn’t require energy) and it moves quite easily through the single cell layering of the alveoli thanks to a concentration gradient; high concentration moves to lower concentration. Once oxygen moves into your bloodstream, it binds to one of four iron atoms which are part of a heme group which put together makes haemoglobin which is the main unit of our red blood cells. The iron is what gives our blood that umami metallic taste as well as its red colouring. Oxygenated blood is then pumped around the body and once it has reached it’s target, the same process of passive diffusion occurs moving the oxygen from high to low concentration. This is where respiration occurs. Fun fact; deoxygenated blood or the blood in your veins isn’t actually blue. The very basic reason as to why they appear that way is because when light hits your skin, particularly areas with veins close to the surface, all other wavelengths of colour are absorbed to a particular degree except for blue. So they’re not blue because of a pigment or blood but because of something called structural colouration.
Respiration simply put is the process of combusting sugar with oxygen to produce carbon dioxide, water and energy. Put more complicatedly for people who were wondering, it is the combination of glycolysis, oxidative decarboxylation of pyruvate, the citric acid cycle and oxidative phosphorylation; essentially nightmare fuel for me back in university. During this process is when the happy-go-lucky oxygen turns into something more damaging; a reactive oxygen species.
Reactive oxygen species (ROS) are a group of chemicals that contain oxygen that are created from the normal metabolic reactions and are important for homeostasis and cell signalling e.g. peroxides. They can however become too high in concentration and this could be because of environmental stresses placed on the body (UV light, smoke or pollutants) or by the decreased effectiveness of antioxidants within the body. When this occurs, ROS can cause harmful effects in the form of damaging DNA, damaging cell walls, the breakdown of proteins and inhibiting enzyme activity. It is this damaging over time that is contributed to the ageing process. A majority of the time, this damage can be reverse by counter methods put in place by the body but sometimes, during periods of high stress, this damage can lead to apoptosis (programmed cell death) or even necrosis in intensely stressful situations.
Some of these ideas can definitely be quite daunting but you have to remember that this is a normal process that is constantly occurring. To ensure that your body doesn’t go through all of this to a harmful extent, try to de-stress from time to time. Exercise and meditation are excellent tools when trying to relax the body and mind, getting plenty of sleep and drinking plenty of water also allows for your body to heal and manage the daily stresses. Now take a breath; see, that wasn’t too bad.