We examined the relationship between respiratory airflow and spiracle activity .. was made through the major tracheal tube attached to the spiracle in order to. Spiracles open into large tracheal tubes. These, in turn, lead to ever-finer branches. The branches penetrate to every part of the body. At their extreme ends. An insect's respiratory system is the biological system with which it introduces respiratory gases Insects have spiracles on their exoskeletons to allow air to enter the trachea. In insects, the tracheal tubes primarily deliver oxygen directly into the insects' tissues. The spiracles can be opened and closed in an efficient manner.
To prevent its collapse under pressure, a thin, reinforcing "wire" of cuticle the taenidia winds spirally through the membranous wall. This design similar in structure to a heater hose on an automobile or an exhaust duct on a clothes dryer gives tracheal tubes the ability to flex and stretch without developing kinks that might restrict air flow. The absence of taenidia in certain parts of the tracheal system allows the formation of collapsible air sacs, balloon-like structures that may store a reserve of air.
What Are the Functions of the Spiracles? | Sciencing
In dry terrestrial environments, this temporary air supply allows an insect to conserve water by closing its spiracles during periods of high evaporative stress.
Aquatic insects consume the stored air while under water or use it to regulate buoyancy. During a molt, air sacs fill and enlarge as the insect breaks free of the old exoskeleton and expands a new one. Between molts, the air sacs provide room for new growth—shrinking in volume as they are compressed by expansion of internal organs.Honey Bee Tracheal Dissection
Small insects rely almost exclusively on passive diffusion and physical activity for the movement of gasses within the tracheal system. However, larger insects may require active ventilation of the tracheal system especially when active or under heat stress. They accomplish this by opening some spiracles and closing others while using abdominal muscles to alternately expand and contract body volume.
Although these pulsating movements flush air from one end of the body to the other through the longitudinal tracheal trunks, diffusion is still important for distributing oxygen to individual cells through the network of smaller tracheal tubes.
In fact, the rate of gas diffusion is regarded as one of the main limiting factors along with weight of the exoskeleton that prevents real insects from growing as large as the ones we see in horror movies. Theoretical models[ edit ] Insects were once believed to exchange gases with the environment continuously by the simple diffusion of gases into the tracheal system.
More recently, large variation in insect ventilatory patterns have been documented, suggesting that insect respiration is highly variable. Some small insects do demonstrate continuous respiration and may lack muscular control of the spiracles. Drosophila avoids the risk by controlling the size of the opening of its spiracles to match the need of its flight muscles for oxygen.
When oxygen demand is less, it partially closes its spiracles thus conserving body water. Large, active insects like grasshoppers, forcibly ventilate their tracheae. Contraction of muscles in the abdomen compresses the internal organs and forces air out of the tracheae. As the muscles relax, the abdomen springs back to its normal volume and air is drawn in.
Large air sacs attached to portions of the main tracheal tubes increase the effectiveness of this bellowslike action. The experiment illustrated first performed by the insect physiologist Gottfried Fraenkel shows that there is a one-way flow of air through the grasshopper.
The liquid seals in the tubing move to the right as air enters the spiracles in the thorax and is discharged through the spiracles in the abdomen. The rubber diaphragm seals the thorax from the abdomen. The one-way flow of air increases the efficiency of gas exchange as CO2-enriched air can be expelled without mingling with the incoming flow of fresh air.
Gas Exchange in Aquatic Insects Even aquatic insects use a tracheal system for gas exchange. Some, like mosquito larvae "wigglers"get their air by poking a breathing tube — connected to their tracheal system — through the water surface.
Some insects that can submerge for long periods carry a bubble of air with them from which they breathe.
Still others have spiracles mounted on the tips of spines. With these they pierce the leaves of underwater plants and obtain oxygen from the bubbles formed by photosynthesis within the leaves. Even in aquatic insects that have gills, after oxygen diffuses from the water into the gills, it then diffuses through a gas-filled tracheal system for transport through the body.