They typically have an enlarged lumen (cavity), hence the name: they have a shape similar to alveoli, the very small air sacs in the lungs.

Some sources draw a clear distinction between acinar and alveolar glands, based upon the size of the lumen.

[1] A further complication in the case of the alveolar glands may occur in the form of still smaller saccular diverticuli growing out from the main sacculi.

"[3] Branched alveolar glands are classified as follows:

This anatomy article is a stub.