Tracheoles - Respiration
The tracheal system consists of an air filled system of tubes - the tracheal tubes that branch repeatedly until they become fine as capillaries, and are called tracheoles. The tracheolar endings arc in close proximity to the cells of the body and sometimes they indent into the plasma membrane giving the impression that they actually enter the cells. Trachea varies in diameter from 1-2 mm and the diameter of tracheoles is between 0.6-0.8 mm. In the larger tracheae, thickenings known as taenidia in the cuticular lining prevent the tubes from collapsing. The walls of the tracheae become progressively thinner as they branch so that the tracheolar endings are only 5, μn in diameter. Figure shows the arrangement of tracheal system in some insects.
Figure: Some modifications of the tracheal system in insects. (a) The basic pattern, (b) mechanically ventilated air sacs, (c) terminal spiracles in aquatic insects.