<P> The gas exchanger in mammals is internalized to form lungs , as it is in most of the larger land animals . Gas exchange occurs in microscopic dead - end air - filled sacs called alveoli , where a very thin membrane ( called the blood - air barrier ) separates the blood in the alveolar capillaries ( in the walls of the alveoli ) from the alveolar air in the sacs . </P>
<P> The gas exchanger in mammals is internalized to form lungs , as it is in most of the larger land animals . Gas exchange occurs in microscopic dead - end air - filled sacs called alveoli , where a very thin membrane ( called the blood - air barrier ) separates the blood in the alveolar capillaries ( in the walls of the alveoli ) from the alveolar air in the sacs . </P>
where are gases exchanged in the respiratory system
where are gases exchanged in the respiratory system
microscopic dead - end air - filled sacs called alveoli
microscopic dead - end air - filled sacs called alveoli