Pulmonary acinus
The ending of a tiny airway in the lung, where the alveoli (air sacs) are located.</P> In anatomy, an acinus is a round cluster of cells, usually epithelial cells, that looks somewhat like a knobby berry.</P> The word 'acinus' means 'berry' in Latin.
(The plural is 'acini'.) There are also acini, round clusters of epithelial cells, in the salivary glands and in the pancreas.