Oxygen (O2) is essential for humans. Oxygen uptake from the air we breathe takes place in the lungs. From there, the oxygen-rich blood is transported to the cells. These need the oxygen as part of internal cellular respiration for energy production.
What is oxygen uptake?
Oxygen (O2) is essential for humans. Oxygen uptake from the air we breathe occurs in the lungs. With each inhalation, the air we breathe enters the lungs through the nose, mouth and throat, trachea and bronchi. The lungs contain the so-called alveoli, the air sacs in the lungs. The alveoli are arranged like grapes. The human lung is estimated to consist of 300 million alveoli. This is where gas exchange takes place and thus oxygen uptake. Around each alveolus are capillaries, small blood vessels. The basis of the exchange of substances in the lungs is diffusion. Diffusion is a physical process that leads to a balanced mixing of two different substances. Oxygen-poor blood, which comes from the entire body and was pumped into the lungs by the right heart, flows through the vessels surrounding the alveoli. After inhalation, there is a lot of oxygen in the alveoli. Thus, oxygen moves from the place of high concentration, which is the alveoli, to the place of lower concentration, which is the blood in the capillaries. In connection with gases, diffusion is also referred to as partial pressures. Every gas exerts a partial pressure. The partial pressure describes the proportion that a gas has of the total pressure in a gas mixture. Different partial pressures now act in the lungs. In the pulmonary alveoli, there is a high partial pressure of oxygen, while the partial pressure of O2 in the capillaries is rather low. Thus, oxygen passes into the pulmonary capillaries. This exchange establishes an equilibrium between the partial pressure of O2 in the alveoli and the partial pressure of O2 in the surrounding vessels. For carbon dioxide (CO2), there is a partial pressure difference in the opposite direction. Thus, CO2 diffuses from the pulmonary capillaries into the alveoli and is then exhaled. In the blood, the oxygen binds to the hemoglobin of the red blood cells. From the lungs, the oxygen-rich blood then travels to the left heart and is distributed throughout the body. The partial pressure also plays a role in the oxygen uptake of the individual cells. There is a lower partial pressure of O2 in the cells of the body than in the small blood vessels that supply the cells. Just as in the lungs, oxygen now diffuses from the oxygen-rich blood into the oxygen-depleted cells.
Function and purpose
Humans cannot exist without oxygen, so oxygen transport and uptake are essential to life. Oxygen itself does not contain energy, but it creates the conditions for energy production in the body’s cells. This process is also known as aerobic respiration or cellular respiration. It takes place in the mitochondria of the cell. Mitochondria are cell organelles. Due to their function, they are also called the power plants of the cell. To produce energy, the mitochondria need oxygen and glucose, i.e. sugar. Through various metabolic processes within the mitochondrial matrix, energy is obtained from the sugar and oxygen in the form of adenosine triphosphate (ATP). Cellular respiration proceeds in four steps: glycolysis, oxidative decarboxylation, citrate cycle and respiratory chain. Except for glycolysis, all processes require oxygen for smooth operation. ATP is a universal and, above all, immediate energy carrier. In each cell of the body, an estimated 10 million ATP molecules are consumed per second. By-products of cellular respiration are water and carbon dioxide. About 32 ATP molecules can be obtained from one molecule of glucose under the influence of oxygen. Energy in the form of ATP can also be obtained under anaerobic conditions. However, lactate is formed there as a waste product. This can lead to signs of fatigue, especially in muscle tissue. In addition, the balance of 2 molecules of ATP per glucose molecule is rather poor.
Diseases and ailments
In chronic lung disease, oxygen uptake in the lungs is severely limited. The consequence of chronic obstructive pulmonary disease (COPD) is often emphysema. Chronic obstruction of the airways causes air to remain in the alveoli when the patient exhales.This ultimately leads to overinflation of the alveoli. The partition walls between the individual alveoli are destroyed and a large air space is formed within the lungs. Gas exchange can no longer take place here and oxygen uptake is accordingly prevented. Patients with emphysema suffer from shortness of breath and cyanosis, i.e. a blue discoloration of the skin and mucous membranes. If the functional lung tissue undergoes connective tissue remodeling, this is referred to as pulmonary fibrosis. This can be caused by autoimmune diseases or asbestos exposure, for example. Connective tissue forms between the alveoli and the pulmonary capillaries. This impedes oxygen uptake. Symptoms of pulmonary fibrosis include shortness of breath, low exercise tolerance and constant coughing. Severe lung diseases such as advanced fibrosis or advanced emphysema may require oxygen therapy to compensate for the oxygen deficit. However, even with healthy lungs, normal inhalation and a normal oxygen content in the air we breathe, oxygen deficiency can occur. The cause here is a lack of absorption capacity of the red blood cells due to anemia. Although the oxygen reaches the blood from the alveoli, it cannot bind to the red blood cells. The same applies to carbon monoxide poisoning. The gas binds to hemoglobin, blocking the space that oxygen molecules would occupy. Carbon monoxide poisoning can be fatal in a very short time.
