Changes

**'''Alveolar Ducts''': These have alveoli which open on all of it's sides, they have no 'walls' as such. Openings to individual alveoli are guarded by smooth muscle.

**'''Alveolar Ducts''': These have alveoli which open on all of it's sides, they have no 'walls' as such. Openings to individual alveoli are guarded by smooth muscle.

**'''Alveolar Sacs''': These are rotunda-like areas on the end of the alveolar ducts, usually there are clusters of these at the end of each duct.

**'''Alveolar Sacs''': These are rotunda-like areas on the end of the alveolar ducts, usually there are clusters of these at the end of each duct.

**'''Alveoli''': These are minute, polygonal chambers, whose diameter changes with the processes of inspiration and expiration, and varies by species. The wall of the alveoli is extremely thin, consisting of 2 irregular layers of epithelial sheets, 'sandwiching' a network of capillaries. Thus the ''Blood-Gas Barrier'' is just a single basal lamina - ideal for gaseous exchange.

**'''Alveoli''': These are minute, polygonal chambers, whose diameter changes with the processes of inspiration and expiration, and varies by species. The wall of the alveoli is extremely thin, consisting of 2 irregular layers of epithelial sheets, 'sandwiching' a network of capillaries. Thus the ''Blood-Gas Barrier'' is just a single basal lamina - ideal for gaseous exchange. The alveolar interstitium is formed from connective tissue fibres and cells, which include collagen fibrils and elastin fibres.

The alveolar interstitium is formed from connective tissue fibres and cells, which include collagen fibrils and elastin fibres.

==Function==

==Function==