Terminal bronchioles
Bronchioli terminales
The smallest purely conducting airways (generation ≈16, ≈0.5 mm), each supplying one pulmonary acinus — the end of the anatomical dead space.
Overview
Terminal bronchioles are lined by simple cuboidal epithelium of ciliated cells and numerous club cells, with a thin layer of smooth muscle and no alveoli in their walls. All the tissue distal to one terminal bronchiole — respiratory bronchioles, alveolar ducts, alveolar sacs and alveoli — forms a pulmonary acinus, the functional unit of gas exchange; the lungs contain ≈30,000 acini.
By this generation the combined cross-sectional area of the airways has increased from ≈2.5 cm² at the trachea to well over 100 cm², so the forward velocity of inspired air falls sharply and diffusion becomes the main mechanism of gas movement beyond this point.
- Location
Within the lobules, at the transition between conducting and respiratory zones.
Anatomy
- Histology
Simple cuboidal ciliated epithelium with abundant club cells; thin smooth muscle; no cartilage, goblet cells or glands.
Function
- Last conducting airway; delivers air into the acinus.
- Marks the boundary of the anatomical dead space.
Clinical significance
Emphysema classification
Emphysema is defined by destruction of airspaces distal to the terminal bronchiole; the pattern within the acinus (centriacinar vs panacinar) points to the cause (smoking vs α1-antitrypsin deficiency).
Compiled from standard anatomy and physiology references — see the Respiratory System sources. For education only; not medical advice.