Alveolar ducts and sacs
Ductuli alveolares; sacculi alveolares
Also known as: alveolar sacs, alveolar duct
Elongated passages (generations ≈20–22) whose walls consist almost entirely of alveolar openings, ending in grape-like alveolar sacs (generation 23).
Overview
Alveolar ducts arise from respiratory bronchioles. Their "walls" are simply rows of alveolar openings, each ringed by a small knob of smooth muscle, elastic and collagen fibres. The ducts end in alveolar sacs — clusters of alveoli opening into a common space (atrium). Most of the lung's alveoli open into alveolar ducts and sacs.
The elastic fibres around the ducts form a continuous network that expands during inspiration and recoils during expiration, contributing to elastic recoil.
- Location
Distal parts of each pulmonary acinus.
Anatomy
- Histology
Walls formed by alveoli lined by type I and II pneumocytes; smooth muscle knobs at alveolar openings.
Function
- Deliver air to alveoli by diffusion.
- Provide most of the gas-exchange surface.
- Contribute elastic recoil.
Compiled from standard anatomy and physiology references — see the Respiratory System sources. For education only; not medical advice.