One of the most abundant elements on Earth is oxygen. About one-fifth by volume of this chemical element is present in the air, and it is colorless, tasteless and odorless. It is equally abundant in water and in the earth’s crust. Most living things and living cells require oxygen for respiration.
What is oxygen?
In the periodic table, oxygen is indicated by the symbol “O” and has the atomic number “8.” It mostly occurs in compounds and as diatomic and triatomic molecules. The latter is also referred to as “ozone.” Rocks and minerals are often oxygenated, such as quartz, marble or limestone. Free and single oxygen atoms, on the other hand, are only possible in stable form under extreme conditions. This is the case in the vacuum of space. Oxygen can be separated from the air by distillation and then acquires a bluish color when liquefied. Such conditions are used, for example, in the refining of metals, the extraction of chemicals, or as a medical application to sustain life. Oxygen is always gaseous under normal conditions and, in combination with other elements, is involved in many combustion processes. It was discovered and researched in 1772 by the chemist and pharmacist Carl Wilhelm Scheéle. The latter isolated oxygen as a gas, a process that had similarities with the pasteurization process, and in this way also discovered other elements, besides nitrogen, for example. However, since he did not publish his work on this until several years later, he was preceded in the meantime by the chemist Josep Priestley, who, independently of him, made the same discovery, including what effect oxygen had on combustion processes, although the actual process itself had not yet been deciphered. Previously, fire was considered more metaphysically, as a basic substance of the four elements that made up being. Besides fire, these were earth, air and water. Then in the 17th century, heat was associated with fire, and through discovery in the 18th century, the substance became the element. But only by the private scholar Antoine Laurent de Lavoisier it was then possible to interpret combustion and respiration correctly. He conducted experiments with pure oxygen and determined the composition of air.
Function, effect and tasks
In the atmosphere oxygen always occurs in gaseous form and dissolved from waters. The element is thereby very reactive and is produced mainly by plants by means of photosynthesis, consumed again by respiration and other combustion processes. Blue-green algae or cyanobacteria also have a share in these processes, which began more than three billion years ago to store sunlight and use it for the synthesis of organic compounds. Oxygen was and is therefore a very effective waste product. Humans, plants and bacteria need oxygen to live and to generate energy in this form. Processing takes place in the mitochondria, where the oxygen is then turned back into water in the respiratory chain. Enzymes, in turn, break down substances in the organism through oxygenation.
Formation, occurrence, properties, and optimal values
However, the good reactivity of oxygen and its compounds can also lead to more dangerous destruction of cell structures. Although humans need oxygen to breathe, too much oxygen is toxic and can even cause lung damage in increased amounts over a long period of time. The human organism functions with an oxygen concentration of about 21 percent in the air. Red blood cells transport the oxygen from the lungs to the organs. If this is too high, there is swelling of the alveoli and necrosis of the wall cells in the lungs, damage to the pneumocytes and deposition of protein masses on the inner wall. The result is greatly reduced gas exchange during respiration and in the bloodstream. Similarly, a gas mixture with increased oxygen can damage the central nervous system and cause central nervous symptoms. This is referred to as the Paul Bert effect, which can manifest itself in ringing in the ears, dizzy spells, nausea, vomiting, and also drastic conditions such as personality changes and mental confusion. This is a frequent accompaniment, especially in diving, so that oxygen content and maximum diving depth must be taken into account.
Diseases and disorders
Most organisms have protective enzymes such as peroxidase and catalase to detoxify oxygen. Oxygen depletion in the body produces free radicals that damage mitochondrial DNA, which can be counteracted by antioxidants. Such are ingested with food and include vitamins C, A and E, minerals and trace elements. An imbalance between reducing and oxidizing substances in the cells leads to a disruption of the body’s detoxification function and damages the cell. This is called oxidative stress, which in turn leads to aging processes. Oxygen deficiency often occurs in heart and lung diseases. This in turn has damaging effects on the arteries and the tissue of all vital organs. In such cases, additional oxygen must be administered and artificial respiration must be induced. Likewise, oxygen serves the wound healing process itself. After operations, infections of the wounds can occur, whereby the oxygen tension of the tissue and the defense cells in the blood play a role, which fight the bacteria in the body with free radicals. Therefore, oxygen is usually given even after anesthesia to reduce the risk of infection. Diseases associated with chronic oxygen deficiency require long-term oxygen therapy. Causes may include narrowing of the airways, pulmonary emboli, damage to lung tissue, or severe heart defects.
