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Alveoli: Gas Exchange

Flash cards every weekday:   / igcsebioflashcards   The alveoli ("many alveoli", "one alveolus") are the sites of gas exchange in the lungs. They are tiny air sacks sometimes described as being cauliflower-shaped. Oxygen diffuses across the lining of the alveoli and blood capillaries into and into red blood cells. Carbon dioxide diffuses from the blood to the alveoli. A concentration gradient is maintained by breathing as well as blood flow. The main adaptation of the gas exchange surface are: 1. Large surface area 2. Thin wall 3. Moist lining 4. Good blood supply 5. Good ventilation