Lungs and Respiratory Trees
The efficiency of a respiratory system which utilises a small number of discrete sites, such as lungs, for the exchange of respiratory gases depends primarily on two factors. Firstly an increase in the efficiency of the uptake of oxygen itself—that is to say an increase in the degree and extent of vascularisation —and secondly the development of an efficient circulatory system which can rapidly transfer oxygen from its site of uptake to the relevant tissue, and can also remove the carbon dioxide and other waste products of cellular respiration to prevent their concentrations from building up in the tissues.
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