810
UNIT 4
Maintenance of the Body
22
Te air passageways in the lungs branch and branch again,
about 23 times overall, in a pattern ofen called the
bronchial
tree
(Figure 22.7)
. At the tips oF the bronchial tree, conduct-
ing zone structures give way to respiratory zone structures
(Figure 22.8)
.
Conducting Zone Structures
Te trachea divides to Form the
right
and
lef main (primary)
bronchi
(brong
9
ki) approximately at the level oF ±
7
in an erect
(standing) person. Each bronchus runs obliquely in the medi-
astinum beFore plunging into the medial depression (hilum) oF
the lung on its own side (²igure 22.7). Te right main bronchus
is wider, shorter, and more vertical than the lef. Consequently, it
is more common For an inhaled Foreign object to get stuck there.
Once inside the lungs, each main bronchus subdivides into
lobar (secondary) bronchi
—three on the right and two on the
lef—each supplying one lung lobe. Te lobar bronchi branch
into third-order
segmental (tertiary) bronchi
, which divide
repeatedly into smaller and smaller bronchi (Fourth-order, fifh-
order, etc.). Passages smaller than 1 mm in diameter are called
bronchioles
(“little bronchi”), and the tiniest oF these, the
ter-
minal bronchioles
, are less than 0.5 mm in diameter.
(a) Cross section of the trachea
and esophagus
(b) Photomicrograph of the tracheal
wall (320
m
)
Hyaline cartilage
Lamina propria
(connective tissue)
Submucosa
Mucosa
Seromucous gland
in submucosa
(c) Scanning electron micrograph of cilia in the trachea (2500
m
)
Posterior
Lumen of
trachea
Anterior
Esophagus
Trachealis
muscle
Pseudostratified
ciliated columnar
epithelium
Adventitia
Goblet cell
Figure 22.6
Tissue composition of the tracheal wall.
In the scanning electron micrograph
in (c), the cilia appear as yellow, grasslike projections. Mucus-secreting goblet cells (orange) with
short microvilli are interspersed between the ciliated cells.
previous page 844 Human Anatomy and Physiology (9th ed ) 2012 read online next page 846 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off