Gas Exchange in Insects
Insects have a unique respiratory system adapted for efficient gas exchange in terrestrial environments. The key components are:
Spiracles: These openings along the thorax and abdomen control gas entry and exit. They can open and close, similar to plant stomata.
Vocabulary: Spiracles are small openings on an insect's exoskeleton that allow air to enter and exit the respiratory system.
Tracheae: Large tubes that carry air into the insect's body. They have spiral reinforcements of chitin but contribute little to actual gas exchange.
Tracheoles: Smaller tubes branching from the tracheae, analogous to capillaries in vertebrates. These thin-walled structures are where most gas exchange occurs.
Highlight: The tracheal system allows for direct gas exchange with tissues, eliminating the need for blood to transport oxygen.
Ventilation Mechanism: Insects use muscular contractions to move air through their respiratory system:
- Wing movements decrease thoracic volume, creating pressure.
- This pressure differential drives air movement through the system.
- Sphincter cells controlling spiracles are stimulated by CO₂ and lactic acid buildup.
Example: When an insect flies, the wing muscles' movement helps pump air through the tracheal system, enhancing gas exchange during periods of high metabolic demand.
Mammalian Respiratory System
Mammals rely on efficient lungs for gas exchange, as their body surface is inadequate for this purpose. Key features include:
Nasal Cavity: The primary air entry point, offering several advantages over mouth breathing:
- Larger surface area
- Good blood supply
- Mucus and hairs for filtering air
Definition: The nasal cavity is the air-filled space above and behind the nose, serving as the first line of defense in the respiratory system.
Breathing Mechanism:
Inhalation:
- Intercostal muscles contract
- Ribcage moves up and out
- Diaphragm flattens and moves down
- Thoracic volume increases, drawing air in
Exhalation:
- Intercostal muscles relax
- Ribcage moves down
- Diaphragm moves up and domes
- Thoracic volume decreases, pushing air out
Alveoli: Microscopic air sacs where gas exchange occurs, featuring:
- Thin walls for short diffusion distance
- Large surface area to volume ratio
- Rich blood supply maintaining concentration gradients
- Moist, permeable surfaces
Vocabulary: Surfactant is a phospholipid coating that prevents alveoli from collapsing and makes breathing easier.
Protective Mechanisms:
- Cilia and mucus in airways trap and remove particles and pathogens
- Macrophages in alveoli engulf bacteria
