Tracheole (trā'kē-ōl') is a fine respiratory tube of the

trachea The trachea, also known as the windpipe, is a cartilaginous tube that connects the larynx to the bronchi of the lungs, allowing the passage of air, and so is present in almost all air- breathing animals with lungs. The trachea extends from t ...

of an

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

or a

spider Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species ...

, part of the

respiratory system The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies g ...

. Tracheoles are about 1 µm in diameter, and they convey oxygen to cells while providing a means for carbon dioxide to escape. Tracheoles branch from the larger tracheae (which can be several mm in diameter) much like capillaries branch from arteries, or twigs from branches of a tree. This increases the surface area for gas exchange in the insect. Areas of intense metabolic activity, such as the digestive tract and flight muscles, have very dense aggregations of tracheoles. Though usually closely associated with cells, tracheoles physically penetrate only the flight muscle cells which have the highest oxygen demands. Unlike the larger tracheae which are derived of

ectodermal The ectoderm is one of the three primary germ layers formed in early embryonic development. It is the outermost layer, and is superficial to the mesoderm (the middle layer) and endoderm (the innermost layer). It emerges and originates from the o ...

stem cells, tracheoles do not molt with the insect. Instead, they remain in place and fuse themselves to new tracheae at each molt by a cement they produce.Klowden, M. J. 2007. Physiological systems in insects. Elsevier/Academic Press. pp. 440–442.

References

Insect anatomy {{insect-anatomy-stub