Alveolar duct

Alveolar ducts are tiny ducts that connect the respiratory bronchioles to alveolar sacs, each of which contains a collection of alveoli (small mucus-lined pouches made of flattened epithelial cells). They are tiny end ducts of the branching airways that fill the lungs. Each lung holds approximately 1.5 to 2 million of them. The tubules divide into two or three alveolar sacs at the distal end. They are formed from the confluence openings of several alveoli. Distal terminations of alveolar ducts are atria which then end in alveolar sacs.

Alveolar duct
An alveolus showing an alveolar duct
Details
System	Respiratory system
Function	Transmission of air from respiratory bronchioles to alveolar sacs
Identifiers
Latin	Ductus alveolaris
TH	H3.05.02.0.00022
FMA	7341
Anatomical terminology

In human anatomy, respiratory bronchioles exist proximal to the alveolar ducts. The epithelial lining consists of smooth muscle knobs covered by nonciliated, simple cuboidal cells. The smooth muscle constricts under parasympathetic innervation and relax under sympathetic innervation.