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    Hey!

    Can anyone explain how the tracheal system of an insect is used for gas exchange?

    I don't understand the point of the fluid at the ends of the tracheoles either. What's the point of it moving into muscle cells during exercise and back into tracheoles at rest?

    How does ventilation of this system work?

    I would really really appreciate any help!

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    (Original post by Aspiring Medic 7)
    Hey!

    Can anyone explain how the tracheal system of an insect is used for gas exchange?

    I don't understand the point of the fluid at the ends of the tracheoles either. What's the point of it moving into muscle cells during exercise and back into tracheoles at rest?

    How does ventilation of this system work?

    I would really really appreciate any help!

    Posted from TSR Mobile
    Insects:
    Insects do not have lungs; instead their respiration is entirely dependent on the diffusion of oxygen from the atmosphere directly into the tissues from the surroundings.
    The fact that they can do this is a direct result of their small size, were insects too large the diffusion pathway for the oxygen would be too large and the insect would be incapable of exchanging materials directly with its environment.
    There is evidence to suggest that in the past (e.g. the Carboniferous period ca. 300 million years ago) insects of a marge larger size were able to subsist, mostly thanks to the much higher percentage concentration of oxygen in those times.
    Exoskeletons:
    Insects have an exoskeleton made of chitin (C8H13O5)n. Chitin forms a polymer from N-Acetylglucosamine (C8H15NO6) via a series of condensation reactions. This is a hard, fibrous material covered by a rich lipid layer.
    This lipid layer makes the exoskeleton impermeable to water and gases as lipids have hydrophobic fatty acid tails, non-polar molecules, which do not interact with water. This prevents excessive water loss, but also gaseous exchange. This is not ideal but is a necessary compromise to allow for the maintenance of water inside the body.
    This inhibition of gaseous exchange across the exoskeleton means that a different method of introducing gases to the body and its tissues must be found. The method insects use is to essentially bring the external environment to the interior of the body and allow for what is a greatly reduced length of diffusion pathway, negating the necessity of a complex muscular respiratory system such as that, which is found in mammalian life forms.
    Tracheal System:
    Insects have holes in their exoskeletons, called spiracles. These spiracles then open up into a complex network of fine tubes, called tracheae, these are also lined with chitin rings to prevent the diffusion of the gases out of the tracheae as it is impermeable to gases. The tracheae then once again subdivide into an even smaller, more complex network of tubes, called tracheoles. These tracheoles are unlined and, as such gases may pass through them and into the insect’s tissues. Each tracheole also terminates in a tracheole cell. This, as aforementioned, reduces the length of diffusion pathway across which gaseous exchange must take place.

    Benefits of short diffusion pathway:
    A short diffusion pathway enables for a more rapid rate of diffusion, not only is this intuitive, but there is also a mathematical formula that describes the physical process. This is known as Fick’s Law.
    Here the equation defines the diffusion flux (rate of diffusion) in one spatial dimension, (with no effect of time) as a product of a partial derivative and a coefficient. (-D) This coefficient is the diffusivity. The diffusivity is a constant between molar flux which is itself found using surface integrals and vector calculus. The x coefficient is dependent on the length of the diffusion pathway.
    More rapid diffusion enables a more active insect, and a more efficient method of gaseous exchange, as oxygen from the air is required to be combined with glucose in the mitochondria to produce ATP, which is necessary for any form of muscular or digestive activity.

    Adaptations and Improvements:
    Some insects have developed improvements to the general formula of a tracheal system.
    For example most insects have evolved so that when they are at rest, water moves via osmosis, out of the cells and into the ends of the tracheoles. (A similar process occurs in human alveoli) This reduces the rate of diffusion as diffusion of molecules through a liquid is a slower process than it is in gas. This means that less respiration occurs when it is unnecessary, as the oxygen is slower to arrive at the mitochondria, and as a direct result the respiration rate is reduced to a minimum.
    Moreover when the insect is active their muscle cells produce lactic acid (due to anaerobic respiration). This lowers the water potential in the muscle cells, as some free water is attracted to the dissolved ions due to their partial charges form dipolar bonds, and is bound to the ions as a hydration shell. The reduction in water potential then causes a net movement of water, via osmosis into the muscle cells. The water, which was inhibiting diffusion is now removed and so diffusion rates increase. This means that actively respiring cells will automatically receive more oxygen.
    Some insects, particularly the larger ones such as locusts have valves which control the size of the aperture of the spiracles, enabling them to regulate the oxygen intake. In response to increasing CO2 concentrations the aperture will widen to allow the gas to escape.
    This control of aperture openings also minimises the water loss at time s of low activity, as water may escape via the spiracles, although it cannot pass through the rest of the exoskeleton.
    Finally some larger and more active insect species also have collapsible air sacs which are comparable to lungs, which can be inflated and deflated by the process of ventilation. (Or movements of the abdomen to pump air into the tracheal system) Normal tracheal tubes have a thin wire of cuticle called a taenidia, which prevents the tube collapsing. In the case of air sacs this reinforcing wire is absent, allowing them to be inflated, by internal pressure (i.e. when the air is present) and deflated when air is absent. The air sacs enable temporary storage of air while at times of need such as when the insect is particularly active.
    These adaptations are advantageous in that each provides an extra step that was improves upon the relatively simple tracheal system.

    Part of an essay I wrote. Hope this helps
 
 
 
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