2.4 Human Breathing and Respiration
is used to absorb oxygen (°2), which the organism needs to generate energy, and to release carbon dioxide (CO₂), which is the end product of the "combustion" of food.
The processes of energy generation using oxygen (°2) and the release of carbon dioxide (CO₂) in the cell are referred to as internal respiration .
The gas exchange in the lungs is called external respiration.
The lungs are preceded by the upper airways .
This includes:
Noses, mouth, pharynx, larynx, trachea, main bronchi for the two lungs .
The outside air is humidified, heated and cleaned in the upper airways. The main bronchi branch into lobar bronchi, which, after further branching into smaller and smaller bronchial branches, finally end in the alveoli . The pulmonary sacs (alveoli) arranged in a grape-like manner are surrounded by a network of the finest blood vessels (hair vessels or capillaries).
The thickness of the layer between the blood in the capillaries and the air in the alveoli is so thin here (less than 1/1,000 mm) that °2 can pass into the blood and CO. into the interior of the alveoli.
The inhaled air contains around 21% °2 and 0.04% CO₂, and the exhaled air contains approx. 17% °2 and 4% CO₂. The body absorbs around 4% °2 of the outside air and releases 4% CO₂. These values change under load.
The two lungs are protected by the ribs and are located in the chest, they are separated from the abdomen by the diaphragm. Air is inhaled by tensing the intercostal muscles. This leads to a lifting of the ribs and thus to an expansion of the thorax in depth and width diameter. The simultaneous flattening of the diaphragm causes a further enlargement of the thorax downwards.
This enlargement of the thoracic cavity creates a negative pressure in the thorax, which is compensated for by the air flowing in via the airways supplying it. The inhaled air fills the afferent airways and the alveoli; gas exchange can take place.
Exhalation occurs under resting conditions by passive lowering of the ribs when the inspiratory muscles relax and by contraction of the elastic elements in the lung tissue. With increased exhalation, special exhalation muscles are also activated.
