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Notify me of new posts by email. Skip to content Campbell Biology 12th Editio offers a reliable, accurate, current, and pedagogically innovative experience that guides students toward a true understanding of biology. Download here. Also, please note that we do not own the copyright to these books. We share this material with our valued users for educational purposes ONLY.
Therefore, we strongly advise our visitors to purchase original books from respected publishers. Physiology is the link between basic science and medicine. The great beauty of physiology is that it integrates the individual functions of all the different cells, tissues, and organs of the body into one functional whole, the human body. In fact, the human body is much more than the sum of its parts, and life is based on this total function, not just the function of individual parts of the body isolated from each other.
This brings us to an important question: How do the separate organs and systems coordinate to keep the entire body functioning properly? Fortunately, our bodies are endowed with a vast network of feedback controls that strike the necessary balances without which we could not live.
Physiologists call this high level of internal body control homeostasis. In disease states, functional balances are often seriously disturbed and homeostasis is impaired. And, when even a single disturbance reaches a limit, the whole body can no longer live. Respiration provides oxygen to the tissues and removes carbon dioxide.
This chapter is a discussion of pulmonary ventilation, and the subsequent five chapters cover other respiratory functions plus the physiology of special respiratory abnormalities. The lungs can be expanded and contracted in two ways: 1 by downward and upward movement of the diaphragm to lengthen or shorten the chest cavity, and 2 by elevation and depression of the ribs to increase and decrease the anteroposterior diameter of the chest cavity.
Figure shows these two methods. Normal quiet breathing is accomplished almost entirely by the first method, that is, by the movement of the diaphragm. During inspiration, contraction of the diaphragm pulls the lower surfaces of the lungs downward. Then, during expiration, the diaphragm simply relaxes, and the elastic recoil of the lungs, chest wall and abdominal structures compresses the lungs and expels the air.
During heavy breathing, however, the elastic forces are not powerful enough to cause the necessary rapid expiration, so the extra force is achieved mainly by contraction of the abdominal muscles, which pushes the abdominal contents upward against the bottom of the diaphragm, thereby compressing the lungs.
The second method for expanding the lungs is to raise the rib cage. This expands the lungs because, in the natural resting position, the ribs slant downward, as shown on the left side of Figure , thus allowing the sternum to fall backwards toward the vertebral column.
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