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What are the two main components of the respiratory system of an insect?

1. Spiracles
2. Trachea


What are spiracles?

External openings, hypothetically one per segment


Where do spiracles usually occur?

On the Mesothorax, Metathorax, and abdominal segments (1-8)


What are trachea?

Series of air-filled tubes unique to insects that are entirely separate from the circulatory system.
- Excessively branched


What are trachea lined with?

lined with cuticle


What are tracheal trunks?

Logitudinal tubes connected to the main tubes from the spiracles


What are Taenidia?

Spiral circular thickening running through trachea


What is the function of the taenidia?

prevents tubes from collapsing under reduced pressure


What are tracheoles?

smallest diameter tubes that cover most of the insects body, even extending between muscle fibres


When are tracheoles fluid filled?

At rest


When are tracheoles air filled? why?

during activity for maximum gas diffusion


What are two types of ventilation in insects?

Passive and active


What insects might use passive ventilation?

Smaller insects


What is passive ventilation?

The simple diffusion of O2 and CO2 controlled by spiracles


What happens during passive ventilation?

1. Continuous O2 uptake and CO2 storage to create suction
2. CO2 is expelled in cylindrical bursts and stored in the hemolympth as bicarbonate in between creating negative pressure -> air gets sucked into trachea
3. When CO2 conc. in trachea is greater than 6.5%, the spiracles relax and CO2 is released


Which insects might use active ventilation? why?

Large insects - they need to physically move air in and out of their tracheal system


How is active ventilation performed?

1. Close forward spiracles and force air out of rear ones via blood pressure or muscle contraction in order to create negative pressure up front when rear spiracles closed
2. Close rear spiracles in order to suck air into front spiracles


What is the purpose of the tracheal air sac in flying insects?

Can increase tidal flow, reduce density of the insect and can provide room for egg development


During flight, how do locusts create separate ventilation in the pterothorax?

via movement of the nota/pleura during wing beats


What is a holopneustic arrangement of spiracles?

All spiracles are functional


What is a Metapneustic arrangement of spiracles?give an example

only abdominal segment 9 is functional - mosquito larvae


What is a Propneustic arrangement of spiracles?give an example

only prothoracic spiracles and functional - mosquito pupae


What is a Apneustic arrangement of spiracles? give an example

no functional spiracles, tracheal gills may be present - mayfly, damselfly naiads


How do giant water bugs breathe?

through a pair of siphons at the posterior end of the abdomen


How do diving beetles breathe?

Trap an air bubble between the elytra and the abdominal terga; spiracles have migrated to the dorsal surface of the abdomen and use bubble for air


How do Waterboatmen breathe?

Hair on the abdomen hold a thin, continuous air bubble in place, giving the abdomen a silvery appearance


how do Atracheate insects breathe? give examples

All gas exchange takes place through the integument - collembola (springtails) and hymenopterous larvae


What are some additional functions of the tracheal system? (7)

1. Suspend internal organs
2. Create air pressure needed for ecdysis
3. Thermoregulation - create insulating layer of trachea around flight muscles
4. Create pathways for the development of the nervous system
5. Reduce weight of the insect - hollow structures
6. Sound perception - tympanum is modified spiracle
7. defense


What kind of a circulatory system do insects have?

An open system (blood is not enclosed in vessels)


What is the hemocoel?

The body cavity of an insect