Respiratory System of Insects Flashcards
What are the two main components of the respiratory system of an insect?
- 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?
- Continuous O2 uptake and CO2 storage to create suction
- CO2 is expelled in cylindrical bursts and stored in the hemolympth as bicarbonate in between creating negative pressure -> air gets sucked into trachea
- 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?
- 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
- 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)
- Suspend internal organs
- Create air pressure needed for ecdysis
- Thermoregulation - create insulating layer of trachea around flight muscles
- Create pathways for the development of the nervous system
- Reduce weight of the insect - hollow structures
- Sound perception - tympanum is modified spiracle
- 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
What is hemolymph?
The blood of an insect
How does the circulatory system work in insects?
The hemocoel (body cavity) is filled with hemolymph (blood) that bathes the organs
What are the circulatory organs?
The heart and the aorta (dorsal blood vessel) - number of chambers varies amongst insects
What does each chamber of the heart have?
Ostia
What are ostia? what do they do?
They are inlet valves that draw hemolymph into the heart
What are the three cavities of an insect? What do they contain?
- Pericardial - heart
- Perivisceral - ligaments
- Perineural - ventral nerve cord
What is the dorsal diaphragm?
a horizontal membrane in the abdomen that separates the hemocoel into two regions
What is the area above the membrane of the diaphragm called?
Pericardial sinus
What does the pericardial sinus do?
Allows hemolymph to enter the heart
How does blood flow throughout the body?
Blood is pumped anteriorly through the aorta to the head where it flows posteriorly into the abdomen
What do insects have at the base of the wings and antennae?
local pulsating organs
What dot he airsacs near the coxae facilitate?
blood flow into the legs
What color is hemolymph?
colorless
What are the several cell types of the hemolymph called?
hemocytes
What are the most abundant hemocytes?
phasmatocytes
What do phasmatocytes do?
- phagocytic on bacteria and other foreign microorganisms
- some encapsulate parasitoid eggs
What are the functions of the hemolymph? (7)
- Transport nutrients, wastes and hormones
- Water storage
- Lubrication of internal organs
- Heat exchange - wing acts as solar colectors
- Hydraulics - molting, wing expansion, active ventilation, leg/antennal movement
- Protection from microorganisms, parasites
- Defense - reflec bleeding
