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A-Level Biology OCR A

Alveoli Air Surface Elastic Structure Makes Epithelial Fibres

Alveoli, tiny air sacs, are adapted for efficient gas exchange with a large surface area, thin walls, elastic fibers for recoil, abundant capillaries, good ventilation, and lung surfactant to prevent collapse.

Alveoli are tiny air sacs with a large surface area, thin walls (epithelial cells, collagen, elastin), elastic fibers for recoil, a good blood supply, good ventilation, and lung surfactant to prevent collapse, facilitating efficient gas exchange.

Front Describe the structure of alveoli & explain how its structure makes it adapted for its function
Back Alveoli:
  • Tiny air sacs - main gas exchange surface of body
  • Consist of flattened epithelial cells, collagen and elastic fibres (elastin)
  • Elastic fibres - allow alveoli to stretch when air is drawn in, when they return to their resting size they help squeeze air out - elastic recoil of lungs
  • Large surface area - high rate of diffusion
  • Thin layers - alveoli and capillaries surrounding are 1 epithelial cell thick
  • Good blood supply - surrounded by a lot of capillaries - constant flow of blood brings CO2 and carries O off maintaining steep conc gradient
  • Good ventilation - breathing moves air in/out maintaining steep gradient for both diffusions
  • Lung surfactant - thin solution layer the inner surface is covered with that makes it possible for alveoli to remain inflated

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