Draw a block diagram to represent the mechanism or breathing in human
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Answer:
Air moves in and out of the lungs in response to differences in pressure. When the air pressure within the alveolar spaces falls below atmospheric pressure, air enters the lungs (inspiration), provided the larynx is open; when the air pressure within the alveoli exceeds atmospheric pressure, air is blown from the lungs (expiration). The flow of air is rapid or slow in proportion to the magnitude of the pressure difference. Because atmospheric pressure remains relatively constant, flow is determined by how much above or below atmospheric pressure the pressure within the lungs rises or falls.
The diaphragm contracts and relaxes, forcing air in and out of the lungs.
The diaphragm contracts and relaxes, forcing air in and out of the lungs.
Encyclopædia Britannica, Inc.
Alveolar pressure fluctuations are caused by expansion and contraction of the lungs resulting from tensing and relaxing of the muscles of the chest and abdomen. Each small increment of expansion transiently increases the space enclosing lung air. There is, therefore, less air per unit of volume in the lungs and pressure falls. A difference in air pressure between atmosphere and lungs is created, and air flows in until equilibrium with atmospheric pressure is restored at a higher lung volume. When the muscles of inspiration relax, the volume of chest and lungs decreases, lung air becomes transiently compressed, its pressure rises above atmospheric pressure, and flow into the atmosphere results until pressure equilibrium is reached at the original lung volume. This, then, is the sequence of events during each normal respiratory cycle: lung volume change leading to pressure difference, resulting in flow of air into or out of the lung and establishment of a new lung volume.
Overview of the mechanics of respiration.
Overview of the mechanics of respiration.
Encyclopædia Britannica, Inc.
The lung–chest system
The forces that normally cause changes in volume of the chest and lungs stem not only from muscle contraction but from the elastic properties of both the lung and the chest. A lung is similar to a balloon in that it resists stretch, tending to collapse almost totally unless held inflated by a pressure difference between its inside and outside. This tendency of the lung to collapse or pull away from the chest can be measured by carefully placing a blunt needle between the outside of the lung and the inside of the chest wall, thereby allowing the lung to separate from the chest at this particular spot. The pressure measured in the small pleural space so created is substantially below atmospheric pressure at a time when the pressure within the lung itself equals atmospheric pressure. This negative (below-atmospheric) pressure is a measure, therefore, of the force required to keep the lung distended. The force increases (pleural pressure becomes more negative) as the lung is stretched and its volume increases during inspiration. The force also increases in proportion to the rapidity with which air is drawn into the lung and decreases in proportion to the force with which air is expelled from the lungs. In summary, the pleural pressure reflects primarily two forces: (1) the force required to keep the lung inflated against its elastic recoil and (2) the force required to cause airflow in and out of the lung. Because the pleural pressure is below atmospheric pressure, air is sucked into the chest and the lung collapses (pneumothorax) when the chest wall is perforated, as by a wound or by a surgical incision.
The force required to maintain inflation of the lung and to cause airflow is provided by the chest and diaphragm (the muscular partition between chest and abdomen), which are in turn stretched inward by the pull of the lungs. The lung–chest system thus acts as two opposed coiled springs, the length of each of which is affected by the other. Were it not for the outward traction of the chest on the lungs, these would collapse; and were it not for the inward traction of the lungs on the chest and diaphragm, the chest would expand to a larger size and the diaphragm would fall from its dome-shaped position within the chest.
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