Human respiration


lungs, airways, oxygen exchange, pneumonia, bronchial asthma English: breathing

The human respiration has the task of absorbing oxygen for the energy production of the body cells and of releasing the used air in the form of carbon dioxide. Therefore, breathing (product of respiratory frequency/respiratory rate and depth of inhalation) is adjusted to the oxygen demand and the amount of carbon dioxide. Special cells in the carotid artery (Arteria carotis communis) and in the brain can measure the concentration of both gases in the blood and transmit corresponding information to the brain.

There, there is a cell group, the respiratory centre, which collects all available information. In addition to the results of chemical measurements in the blood, the signals taken into account include information about the expansion status of the lungs, signals from the respiratory muscles, but also messages from the autonomic nervous system (unconscious, independent (autonomous) nervous system regulating bodily functions). The respiratory centre thus quasi compares oxygen demand and supply and then gives corresponding commands to the respiratory muscles.

Respiration regulation is described as semi-autonomous. This means that it is automatically regulated by the respiratory centre. Therefore we do not have to think about how much we have to breathe.

Nevertheless, the breathing of a person can be deliberately influenced and, for example, hold the breath. With increasing time without breathing the oxygen content in the blood decreases and the carbon dioxide content increases. This stimulates breathing via the respiratory centre and creates the feeling of a lack of air. This topic might also be of interest to you: Diaphragmatic Breathing

  • Breathing,
  • Respiratory rate and
  • Depth of breath

Physiology of human respiration

The air that surrounds us and that we breathe in every day consists of almost 80% nitrogen, 20% oxygen and infinitesimal amounts of other gases. The air pressure depends on the sea level; at the water twice as high as at about 5000 m above sea level. It follows that although we absorb the same percentage of oxygen (namely 20% of the total amount), we inhale absolutely only half of the air due to the lower pressure.

This air now flows into our airways. Until the blood has reached the air bubbles, it is not ready for gas exchange. The volume effectively lost is called dead space volume.

It follows that an increased breathing frequency (shallower breathing, air reaches the air sacs to a lesser extent) triggers increased dead space ventilation; at the same time, the effectiveness (ratio of work of breathing to oxygen uptake) of breathing decreases. The air in the alveoli has a different composition. Here the proportion of carbon dioxide is increased because of the continuous supply by the blood.

Since the gases only have to travel a short distance because of the very thin cells, the pressures of the gases between blood and alveoli equalise. The blood that has passed through the alveoli finally has the same gas composition as the air in the alveoli. Since oxygen is much less soluble in water than carbon dioxide, the body needs a special oxygen transporter, the red blood cells (erythrocytes).

Since a certain amount of carbon dioxide remains in the alveoli, the blood leaving the lungs also contains a measurable amount. Most of the carbon dioxide is dissolved in the form of carbonic acid. The carbonic acid has an important task in controlling the blood pH (“blood acid”).