tracheoles

Tracheoles are the finest branches of the insect tracheal system and provide the direct route for oxygen delivery to body tissues. They originate from larger tracheae or tracheal trunks and spread throughout the body, reaching close to individual cells and often surrounding them to minimize diffusion distances.

Structurally, tracheoles are extremely narrow tubes with thin walls. Their lumens may be air-filled, though some species have a small amount of tracheal fluid present at rest to keep the network moist. The ends of tracheoles come into close contact with cells, forming a dense network that maximizes the surface area available for gas exchange.

Function and gas exchange occur mainly by diffusion. Oxygen moves from the air within the tracheoles into surrounding cells, while carbon dioxide diffuses in the opposite direction. The large surface area and very short diffusion path enable efficient oxygen delivery even in small insects. Air enters the system through spiracles, travels via tracheae and tracheoles, and can be ventilated actively in some species through body movements or wing movements during flight.

Relation to other structures: tracheoles are the site of gas exchange and differ from the larger, reinforced tracheae that transport air from the outside. The insect’s respiratory efficiency arises from the extensive tracheolar network that directly serves tissues, reducing the need for oxygen transport by circulating fluids.