If you were a fish, you’d have to work a lot harder at getting oxygen to your blood cells. The air around us contains 13 times more oxygen than water does. Fish and amphibians are able to use that oxygen by absorbing it through their gills but they have to use 10% of their oxygen intake for the activity required to do it. We, lucky humans, and other mammals, only use 1-2 % of our oxygen intake for respiration. But the bottom line is that every living thing needs oxygen. It is the ingredient needed to make our cells function.
It is so vital to humans that doctors are always alert to signs that we’re not getting enough. If our hemoglobin, the oxygen-carrying component in the blood, is low, alarm bells go off that something is wrong. If we’re sick and a doctor draws a blood sample directly from an artery to determine how much oxygen and CO2 are in the blood, he will be looking for sufficient oxygen numbers that indicate the blood is able to do its job.
Our bodies are miraculous mechanisms that survive by using the elements around them. Our bodies eat food which gives cells raw materials to make, repair, and replace cells as needed. But in order to use the materials, the cells need oxygen to cause the chemical reaction that makes energy. But, let’s go back to the beginning the drawing in of air and see what happens.
We inspire breathe in through the use of diaphragm muscles that expand our lungs and draw air in. The air passes over alveoli, special cells in the lungs which are able to absorb oxygen. An extraordinarily thin membrane between alveoli and capillaries in the lungs allows the oxygen to transfer into the blood where it is picked up by hemoglobin. Bright red hemoglobin contains Iron which makes it an excellent transport for oxygen and CO2. The oxygen-rich blood then cycles back to the heart where it is sent on its way via the aorta, arteries, veins, and tiny capillaries to every cell in the body. Every cell in the body (except those in the cornea) needs oxygen to activate the chemical process that makes energy.
In the cells, a protein called cytochrome C oxidase makes two molecules of water out of every molecule of oxygen that arrives. The process of making the water releases energy and it is this energy that fuels our body. If not enough oxygen is delivered, cells slowly die. Muscles weaken without fuel and people feel weak. But, in the well-functioning human body, the process goes smoothly and the oxygen-depleted red blood cells (hemoglobin) now carry CO2 and other waste gases of energy making, back to the heart via veins where the oxygenation process begins anew.
The chemical process that takes place in the cells is actually quite complicated. Glycol sis, the breaking down of glucose, a six-carbon sugar, is anaerobic meaning it doesn’t require oxygen. Each chemical reaction (there are many) produces some hydrogen ions that are used to make energy packets, ATP, (adenosine triphosphate). ATP is the energy messenger that goes to cells. But nothing is going anywhere without the transfer of oxygen via a series of electron bearing molecules moving across membranes. When the cells are fully loaded with oxygen, they are ready to nourish the body.
If there is not enough oxygen present, the only other source of ATP is through glycol sis, the byproduct of which is lactic acid leading to muscle fatigue. As humans, we sense when we are not getting enough oxygen. High elevations, respiratory illnesses, or low hemoglobin counts can all contribute to not getting enough oxygen into our bodies. Instinctively, we breathe more deeply, slow down, or in the case of high elevation climbers, use supplemental oxygen.
The oxygen transport system in our bodies is so complex it takes pages of chemical equations and drawings to explain what happens. To understand it in even the simplest of terms should lead all of us to a feeling of awe of the life-giving act of breathing in and out.