Trachea systems

1
Trachea systems

• Insects

2
The life of an Insect

• Most insects are small terrestrial animals (live
  on land).
• They have a large surface area to volume ratio.
• Their exoskeletons are hard and waxy to minimise
  water loss.
• One advantage terrestrial animals have over
  aquatic animals is that oxygen is more abundant
  in air than in water

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Gas exchange system - Trachea

• Insects exchange oxygen and carbon dioxide
  between their tissues and the air by a system of
  air-filled tubes called trachea.
• Trachea open to the outside through small holes
  called spiracles.
• 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, called tracheoles, they may
  be less than 1 µm in diameter, and are filled
  with liquid.
• Every cell in the insect's body is adjacent, or
  very close to, the end of a tracheole.

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• This photomicrograph show how the walls of the
  tracheal tubes are stiffened with bands of
  chitin. Even so, there is a limit to the pressure
  they can withstand without collapsing. This may
  be one reason why insects are relatively small.
  The increased weight of the tissues of an animal
  the size of a rabbit, for example, would crush
  tracheal tubes filled only with air.
• Trachea

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• As water vapor and carbon dioxide diffuse out of
  the animal this could pose a problem in dry
  environments. Drosophila avoids the risk of
  dehydration 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.

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• Tracheae and spiracle of an insect. At top center
  is a spiracle (brown), from which numerous
  branching tubes the tracheae can be seen
  running to many parts of the insects body. The
  spiracles are usually located on the sides of the
  body segments, the number varying in different
  kinds of insects. (See previous figure for a
  drawing of terminal branches, or tracheoles.

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• Spiracles of two insects. (A) Scanning electron
  micrograph of a fully open ant spiracle. The
  pointed projections are sensory hairs that
  monitor external conditions and can trigger
  spiracle closing when necessary. (B) A nearly
  closed grasshopper spiracle the black areas are
  the valves. Note the resemblance to the stoma of
  a leaf.

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Aquatic insects

• http//www.cals.ncsu.edu/course/ent425/tutorial/aq
  uatic.html

Biozone p 194