Mechanisms of Breathing

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Mechanisms of Breathing...

Mechanism of Breathing:

Ventilation is the term used for the movement to and from the alveoli. The two aspects of ventilation are inhalation and exhalation which are brought about by the nervous system and the respiratory muscles. The respiratory centers are located in the brain stem. The respiratory muscles are the diaphragm and the internal and external intercostal muscles. The diaphragm is a done shaped muscle below the lungs. When it contracts, the diaphragm flattens and moves downward. The intercostal muscles are found between the ribs. The external intercostal muscles pull the ribs upward and outward and the internal intercostal muscles pull the ribs downward and inward. Ventilation is the result of the respiratory muscles producing changes in the pressure within the alveoli and bronchial tree.

There are three important pressure in respect to breathing:

atmospheric pressure- the pressure of the air around us. At sea level the atmospheric pressure is 760 mmHg, at higher altitudes the pressure is lower.

intrapleural pressure- the pressure within the potential pleural space between the parietal and visceral pleura. This space is a potential rather than a real space. Intrapleural pressure is always slightly below atmospheric pressure. This is called negative pressure because the elastic lungs are always tending to collapse and pull the visceral pleura away from the parietal pleura. The serous fluid, however, prevents separation of the pleural membranes.

intrapulmonic pressure- the pressure within the bronchial tree and alveoli. This pressure fluctuates below and above atmospheric pressure during each cycle of breathing.

INHALATION

Inhalation is also called inspiration, is a precise sequence of events.

The nervous system sends an impulse to the diaphragm and external intercostal muscles.

The diaphragm flattens, which increases top-to-bottom length of the thorax. Contraction elevates the ribs and increases the size of the thorax from the front to the back and from side to side.

This increase in the size of the chest cavity reduces pressure within it, and what follows is an active process where air moves into the lungs.

EXPIRATION

Quiet expiration is ordinarily a passive process. During expiration the thorax returns to its resting size and shape. Elastic recoil of lung tissues aids in expiration. However, expiratory muscles used in forceful expiration are the internal intercostals and abdominal muscles. Reduction of the size of the thoracic cavity builds pressure and air leaves the lungs.

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