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This photo (courtesy of the Anatomical Institute, Bern) shows a rubber cast of human lungs.


The Human Respiratory System

The Pathway

  • Air enters the nostrils
  • passes through the nasopharynx,
  • the oral

Control of Breathing

The rate at which cellular respiration takes place (and hence oxygen is consumed) varies with the general state of activity of the body. Vigorous exercise may increase by 20 to 25 times the demands of the tissues for oxygen. This increased demand is met by increasing the rate and depth of breathing.

It would be reasonable to assume that lack of sufficient oxygen triggers this response. It is quite easy to show, however, that oxygen deprivation plays only a very minor

Tracheal Breathing

Insects, and some other invertebrates, exchange oxygen and carbon dioxide between their tissues and the air by a system of air-filled tubes called tracheae.

Tracheae open to the outside through small holes called spiracles. In the grasshopper, the first and third segments of the thorax have a spiracle on each side. Another 8 pairs of spiracles are arranged in a line on either side of the abdomen.

The spiracles are guarded by

  • valves controlled by muscles that enables