Gas Exchange

From the air sacs, the tracheae branch and ramify to the appendages and the organs. Tracheae then end in tracheoles that terminate blindly within cells. Proximally tracheoles are about a micrometer in diameter, but they taper to diameters of a tenth of a micrometer. Physiological cascades draw oxygen from this fluid into the mitochondria during oxidative metabolism. It is uncertain if the tips of tracheoles ever become truly intracellular.

Distributions of tracheoles to end-organs reflects their demands for oxygen, as tracheoles are most numerous in muscles, glands and neural tissues where oxygen consumption is highest. Some carbon dioxide produced by the metabolizing cells cannot be funneled into the air conduits. This carbon dioxide, instead, discharges into the hemolymph, and after circulating may diffuse through soft areas of cuticle or be converted into bicarbonate and excreted through the Malpighian tubules into the midgut (Ref: Respiration).

Might we someday construct air sac-like reservoirs in devices that could accommodate shifting fluids within rigid interiors? Sacs might also insulate hot spots in devices much as they help insulate thoracic motors by confining heat flows, permitting a warm thorax and a cooler abdomen to co-exist at different temperatures. More about heat exchange in Chapter 9.

Chapter six

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