Thursday, March 1, 2012

Respiration in Insects

Insects and most other land arthropods transport oxygen and carbon dioxide by means of tiny hollow tubes called tracheae, which open to the air by spiracles. The amount of air flowing into the tracheae is regulated in many insects by spiracular valves. Tracheae branch and rebranch, becoming smaller and smaller, finally ending in tracheoles; in many cases the tracheoles end within the cells that they supply. Diffusion accounts for most of the gas exchange. However, diffusion is a slow process and especially in large insects it must be supplemented, particularly during flight, by pumping movements of the abdoment or ventilation. Insects have remained small for several reasons; one is the inability of the tracheal system, which depends largely on diffusion, to supply oxygen to active cells, which are more than a few millimeters away from the external air.