Overview of the bronchioles and alveoli.
This is a representation of the
; the length of the different types of bronchioles is not drawn to scale.
, which give rise to many branches as they move distally within the lung (Fig. 11-1). Bronchioles
have no cartilage and continue to divide into smaller bronchioles.
are the ±
nal parts of the conducting airway.
They extend into alveolar sacs to give rise to
, which connect to the alveolar ducts. Respiratory bronchioles
are small in diameter, are lined by cuboidal cells, and contain increased numbers of alveoli. Respiratory bronchioles mark the transi-
tion from the conducting portion to the respiratory portion in which gas exchange occurs. An
is a hallway that con-
nects the respiratory bronchiole to an alveolar sac. Alveolar ducts are lined by squamous alveolar epithelium and knobs of cuboidal
epithelium lying on the smooth muscle cells. An
is the blind end of an alveolar duct and includes a common opening for
two or more alveoli. Alveoli have very thin walls lined by alveolar epithelium that contains
The basement membrane of the type I pneumocytes and endothelial cells of the capillaries are fused together to form the
(Fig 11-12). Type I pneumocytes are squamous cells that line the alveoli (Fig. 11-13). Type II pneumocytes are
that are important for reducing the surface tension of the alveoli (Fig. 11-14).
, lying free on the alveolar wall, are shown here and can also be found in the septa of the alveoli (Fig. 11-15). Dust
cells move around on the alveolar surface like vacuum cleaners to clear dust particles and other debris on the surface of the alveoli
and also help remove excess surfactant.
vein (to the left atrium)
Type I pneumocyte
(from the right ventricle)