AzurePhoenix Posted March 28, 2005 Posted March 28, 2005 On the cellular level, which is generally thought to be more efficient, the respiratory capillaries of birds, or mammalian alveoli? And if it's possible, in regards to volume, which is lighter, the avian or the mammalian lung (on average)?
Mokele Posted March 28, 2005 Posted March 28, 2005 AFAIK, there's no difference at the cellular level. Because of the nature of the air-sacs and avian lung, compared to the complex alveolar structure of mammals, I'd guess the bird lung is lighter per unit volume. The main difference in efficiency is the flow of air through the system. In mammals (and other creatures with tidal airflow in the lungs), there's a lot of "dead air" in the lungs, and the blood can only have the same O2 concentration as the air. In birds, because there is no "dead air" in the gas-exchange surfaces, and the flow is unidirectional (with the blood flowing the opposite way), the system is a counter-current exchanger. As a result. The concentration of O2 in the blood can actually be *higher* than in the air, and the exhaled CO2 per breath is higher too. Mokele
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