What is respiration?
Respiration is the vital process by which oxygen is absorbed from the air (external respiration) and transported to all body cells, where it is used to generate energy (internal respiration). This produces water and carbon dioxide. The latter is released into the air to be exhaled in the lungs and thus removed from the body. But how does human respiration work in detail?
External respiration
External respiration (lung respiration) takes place in the lungs. It refers to the intake of oxygen from the air we breathe and the release of carbon dioxide into the air we breathe. The whole process is controlled by the respiratory center in the brain. In detail, external respiration takes place as follows:
Oxygen-rich breathing air flows into the windpipe via the mouth, nose and throat, where it is warmed, moistened and purified on its way. From the trachea, it continues into the bronchi and their smaller branches, the bronchioles. At the end of the bronchioles, the air we breathe enters the approximately 300 million air sacs (alveoli). These have very thin walls and are surrounded by a network of very fine blood vessels (capillaries). This is where gas exchange takes place:
Haemoglobin transports the bound oxygen with the bloodstream to all organs and cells that need it to generate energy.
Incidentally, the surface area of the alveoli, through which gas exchange takes place, covers a total area of 50 to 100 square meters. That is about fifty times more than the surface area of the body.
Internal respiration
Internal respiration is also known as tissue respiration or cellular respiration. It describes the biochemical process by which organic substances are changed (oxidized) with the help of oxygen in order to release the energy stored in the substances and make it usable in the form of ATP (adenosine triphosphate). ATP is the most important form of energy storage within cells.
In the course of internal respiration, carbon dioxide is produced as a waste product. It is transported from the blood into the lungs and exhaled there (as part of external respiration).
The respiratory muscles
The body needs the respiratory muscles to inhale and exhale air. During resting breathing, which is usually chest breathing, the diaphragm is the most important muscle for inhaling. The three rib-lifting muscles, which attach to the cervical vertebrae, also help. The intercostal muscles only serve to stabilize the chest wall during resting breathing.
Haemoglobin transports the bound oxygen with the bloodstream to all organs and cells that need it to generate energy.
Incidentally, the surface area of the alveoli, through which gas exchange takes place, covers a total area of 50 to 100 square meters. That is about fifty times more than the surface area of the body.
Internal respiration
Internal respiration is also known as tissue respiration or cellular respiration. It describes the biochemical process by which organic substances are changed (oxidized) with the help of oxygen in order to release the energy stored in the substances and make it usable in the form of ATP (adenosine triphosphate). ATP is the most important form of energy storage within cells.
In the course of internal respiration, carbon dioxide is produced as a waste product. It is transported from the blood into the lungs and exhaled there (as part of external respiration).
The respiratory muscles
The body needs the respiratory muscles to inhale and exhale air. During resting breathing, which is usually chest breathing, the diaphragm is the most important muscle for inhaling. The three rib-lifting muscles, which attach to the cervical vertebrae, also help. The intercostal muscles only serve to stabilize the chest wall during resting breathing.
If someone feels that they are not getting enough air, this is referred to as breathlessness or dyspnoea. Those affected often try to cover their oxygen requirements by breathing quickly and shallowly (hyperventilation) or by breathing more deeply.
There are many possible causes of dyspnoea. Sometimes it is caused by a lung disease such as asthma, COPD, pneumonia or pulmonary embolism. Heart diseases such as heart failure or a heart attack can also cause shortness of breath. In other cases, chest injuries (such as rib fractures), cystic fibrosis, allergic reactions or respiratory infections (such as diphtheria) are the cause. Finally, there is also psychogenic dyspnoea: Here, shortness of breath is triggered by stress, depression or anxiety disorders, for example.
If the oxygen content in the blood is reduced as a result of a disorder in the respiratory system, this is called hypoxia. It quickly becomes life-threatening when breathing stops completely (apnea): After about four minutes without oxygen, the brain cells begin to die, leading to brain damage and ultimately death.
