GAS EXCHANGE IN INSECTS Flashcards
What are spiracles?
Openings along the side of the thorax & abdomen, site of entry and exit for respiratory gases, opened or closed by sphincters.
What are tracheae?
Largest tubes of the insect respiratory system, carry air directly into the body for gas exchange. Run into and along the body of the insect.
What are tracheoles?
Minute tubes site of gaseous exchange in insects.
What are the tracheae supported by?
Spirals of chitin, they hold the tracheae open if they are squashed or deformed - like rings of cartilage in the mammalian trachea.
How does chitin affect tracheae?
It makes it relatively impermeable to gases, little gas exchange takes place in these vessels.
Describe the structure of tracheoles.
Each tracheole is a single elongated cell, have no chitin. Freely permeable to gas. They spread through the tissue of insects and even penetrate into individual cells.
Why are the spiracle sphincters kept closed as much as possible?
They are the major site of water loss from the surface of the insect.
How does air move across the insect?
Moves along the tracheae and tracheoles by diffusion alone, this is sufficient to reach all tissues. Tiny tracheoles gives a large surface area.
How does the water content of tracheoles affect there function?
They may contain water towards the end of their length, limiting the penetration of gases for diffusion. However, when the insect is active, lactic acids builds up in the muscle tissue. This affects the osmotic concentration of the cells and so water moves out of the tracheoles into the cells by osmosis. The additional surface area exposes is used for gaseous exchange.
How does a carbon dioxide build up affect the opening/closing of the spiracles?
Spiracles control the rate of gas exchange, it is coordinated by respiratory centres in the nervous system, which are stimulated by carbon dioxide levels & by lactic acid that builds up. Both of these factors cause the opening of the spiracles to allow more/less oxygen to enter.
What is mechanical ventilation?
Air is actively pumped into the tracheal system. Spiracles open, insect makes muscular pumping movements of thorax, abdomen or both. Changes volume and therefore pressure inside body, drawing air/out of tracheae and tracheoles
How is the volume of air moved through the respiratory system increased?
By collapsible tracheae or air sacs that act as air reservoirs: ventilating movement of thorax/abdomen inflate/deflate them. In some insects they can be ventilated by general body movements.
