Inspiration Essay

Inspiration in a resting person involves contraction of the primary muscle, diaphragm and external intercostals muscles, enlarging the chest cavity. The flattening of the large, dome-shaped diaphragm results in inferior movement of the central tendon, a connective tissue that lies on top of the dome which causes the overall shape of the dome to slightly alter. Additionally, relaxation of the abdominal muscles allows the abdominal organs to shift out of the way of the diaphragm. Furthermore, the contraction of the external intercostals muscles elevates the ribs and pulls the sternum forward. This permits the costal cartilages to allow lateral rib movement and lateral expansion of the thoracic cavity, thus increasing the anterior-posterior dimensions on the thoracic cavity. The parietal layer of the pleura also moves with these structures as it is attached to the diaphragm within the chest wall. This results in decrease of interpleural pressure from -5cmH2O to about -9cmH2O. As a result, the visceral layer of the pleura, which is attached to the lungs, causes the lung to expand, increasing its volume. Increase in surface area of the lungs causes the intrapulmonary pressure to fall, generating partial vacuum which sucks air into the lungs by bulk flow. Air continues to travel into the lungs until the intrapulmonary pressure is same as atmospheric pressure.

Expiration in a resting person is a passive process that requires muscular relaxation. When the diaphragm and external intercostals muscles are at rest, the thoracic and the lung volume decreases passively. This compresses the air in the lungs, thus increasing its pressure above atmospheric level. Therefore, the air is driven out of the lungs due to the pressure differential unt...

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...ration. Furthermore, larger respiratory volumes also allow more oxygen to be diffused into the blood flow.

Secondly, aerobic fitness also helps increase the number and diameter of capillaries over a long period of time. As a result of this, more blood to flow in and out of the lungs allowing efficient delivery of oxygen and nutrients. Increase in the number of capillaries also increases the efficiency of gaseous exchange. The gradient between the blood and the tissues becomes larger as the exchange of oxygen and carbon dioxide progresses.

The amount of air that can be expired after maximal inspiration in one breath is known as the vital capacity. This increases when exercised regularly for a long period of time, developing a greater demand for oxygen. Therefore, this allows increase in capacity of the lungs to supply red blood cells with the amount of oxygen needed.