Respiration is the process by which the respiratory system facilitates the exchange of gases, primarily oxygen and carbon dioxide, between the body and the environment.
The mechanism of respiration can be divided into four main processes: ventilation, external respiration, internal respiration, and cellular respiration.
1. Ventilation:
a. Inhalation:
Mechanism: The diaphragm contracts and moves downward, while the external intercostal muscles lift the ribcage, expanding the thoracic cavity.
Effect: This increases thoracic volume, creating negative pressure that pulls air into the lungs via the respiratory tract, reaching the alveoli.
b. Exhalation:
Mechanism: The diaphragm and external intercostal muscles relax, decreasing the thoracic cavity's volume.
Effect: This creates positive pressure, pushing air out of the lungs.
2. External respiration:
Location: Alveoli and pulmonary capillaries.
Mechanism: Oxygen diffuses from the air in the alveoli into the blood, binding to hemoglobin in red blood cells.
Simultaneously: Carbon dioxide diffuses from the blood into the alveoli to be exhaled.
3. Internal respiration:
Location: Systemic capillaries and body tissues.
Mechanism: Oxygen-rich blood from the lungs is pumped through systemic circulation.
Oxygen diffuses from the blood into tissues, while carbon dioxide produced by cells diffuses into the blood.
The carbon dioxide-rich blood returns to the lungs via the right side of the heart.
4. Cellular respiration:
Location: Mitochondria in cells.
Mechanism: Cells use oxygen to produce ATP (energy) through glycolysis, the citric acid cycle, and the electron transport chain.
By-product: Carbon dioxide is produced and transported back to the lungs for elimination..