Download 41. Trachea, bronchi, bronchial tree

Trachea
– Extends from larynx to superior border of T5
• Divides into right and left primary bronchi
– 4 layers
•
•
•
•
Mucosa
Submucosa
Hyaline cartilage
Adventitia
– 16-20 C-shaped rings of hyaline cartilage
• Open part faces esophagus
 The trachea is a mobile cartilaginous and
membranous tube
 It begins in the neck as a continuation of
the larynx at the lower border of the
cricoid cartilage at the level of the sixth
cervical vertebra
 It descends in the midline of the neck
Location of Trachea
 In the thorax the trachea ends below at
the carina by dividing into right and left
principal (main) bronchi
 During expiration the bifurcation rises by
about one vertebral level
 During deep inspiration may be lowered
as far as the sixth thoracic vertebra
 In adults the trachea is about 4½ in.
(11.25 cm) long and 1 in. (2.5 cm) in
diameter
 The fibroelastic tube is kept patent by the
presence of U-shaped rings of hyaline
cartilage embedded in its wall
 The posterior free ends of the cartilage
 Anteriorly: The sternum, the thymus, the
left brachiocephalic vein, the origins of
the brachiocephalic and left common
carotid arteries, and the arch of the aorta
 Posteriorly: The esophagus and the left
recurrent laryngeal nerve
 Right side: The azygos vein, the right
vagus nerve, and the pleura
 Left side: The arch of the aorta, the left
common carotid and left subclavian
arteries, the left vagus and left phrenic
nerves, and the pleura
 The upper two thirds are supplied by the
inferior thyroid arteries
 The lower third is supplied by the
bronchial arteries
 The lymph drains into the pretracheal and
paratracheal lymph nodes and the deep
cervical nodes
 The sensory nerve supply is from the
vagi and the recurrent laryngeal nerves
 Sympathetic nerves supply the trachealis
muscle
Bronchi
– Right and left primary bronchus goes to right lung
– Carina – internal ridge
• Most sensitive area for triggering cough reflex
– Divide to form bronchial tree
• Secondary lobar bronchi (one for each lobe), tertiary
(segmental) bronchi, bronchioles, terminal bronchioles
– Structural changes with branching
• Mucous membrane changes
• Incomplete rings become plates and then disappear
• As cartilage decreases, smooth muscle increases
– Sympathetic ANS – relaxation/ dilation
– Parasympathetic ANS – contraction/ constriction
 The trachea bifurcates behind the arch of
the aorta into the right and left principal
(primary, or main) bronchi
 The bronchi divide into several million
terminal bronchioles that terminate in one
or more respiratory bronchioles
17
Wider,
shorter, and
more vertical
than the left
Right
Primary
Bronchus
trachea
Left
primary
bronchus
Both primary bronchi have the same anatomic structure
as the trachea.
 Each respiratory bronchiole divides into 2
to 11 alveolar ducts that enter the
alveolar sacs
 The alveoli arise from the walls of the
sacs as diverticula
• The primary bronchi divide to form
SECONDARY BRONCHI (lobar bronchi).
• There is one secondary bronchus for each lobe
of the lungs.
• There are 2 lobes on the left lung.
• There are 3 lobes on the right lung.
• These also have the same anatomy as the
trachea.
• The secondary bronchi branch to form
TERTIARY BRONCHI.
• They continue to branch.
• As they get smaller, they lose their cartilage.
• When they lose their cartilage, they are called
BRONCHIOLES which are microscopic.
Histology of the
Bronchus
• The bronchioles terminate in the ALVEOLI
through an ALVEOLAR DUCT.
• The walls of the alveoli are one-cell thick
and is covered in capillaries.
• The alveoli are the functional unit of the
lungs.
Bronchiole and Alveolar Duct
• There are air sacs, where gas exchange occurs.
• Walls of the alveoli are highly vascularized.
• The alveoli are the terminal branches of the
BRONCHIAL TREE. This arrangement allows
for a drastic increase in surface area.
Bronchial tree
• A highly branched system of air-conducting passages
that originate from the left and right primary bronchi.
• Progressively branch into narrower tubes as they
diverge throughout the lungs before terminating in
terminal bronchioles.
• Incomplete rings of hyaline cartilage support
the walls of the primary bronchi to ensure that they
remain open.
• Right primary bronchus is shorter, wider, and more
vertically oriented than the left primary bronchus.
• Foreign particles are more likely to lodge in the right
primary bronchus.
Bronchial tree
• The primary bronchi enter the hilus of each lung
together with the pulmonary vessels, lymphatic vessels,
and nerves.
• Each primary bronchus branches into several secondary
bronchi (or lobar bronchi).
• The left lung has two secondary bronchi.The right lung
has three secondary bronchi.
• They further divide into tertiary bronchi.
• Each tertiary bronchus is called a segmental bronchus
because it supplies a part of the lung called a
bronchopulmonary segment.
Bronchial Tree
• Secondary bronchi tertiary bronchi bronchioles
terminal bronchioles
• with successive branching amount of cartilage decreases and
amount of smooth muscle increases, this allows for variation
in airway diameter
• during exertion and when sympathetic division active 
bronchodilation
• mediators of allergic reactions like histamine 
bronchoconstriction
• epithelium gradually changes from ciliated pseudostratified
columnar epithelium to simple cuboidal epithelium in
terminal bronchioles
Respiratory Zone of Lower Respiratory
Tract
Conduction vs. Respiratory
zones
• Most of the tubing in the lungs makes up
conduction zone
– Consists of nasal cavity to terminal
bronchioles
• The respiratory zone is where gas is
exchanged
– Consists of alveoli, alveolar sacs, alveolar
ducts and respiratory bronchioles
Respiratory Bronchioles,
Alveolar Ducts, and Alveoli
• Lungs contain small saccular outpocketings called
alveoli.
• They have a thin wall specialized to promote diffusion
of gases between the alveolus and the blood in the
pulmonary capillaries.
• Gas exchange can take place in the respiratory
bronchioles and alveolar ducts as well as in the
alveoli, each lung contains approximately 300 to 400
million alveoli.
• The spongy nature of the lung is due to the packing of
millions of alveoli together.
Bronchial
“tree” and
associated
Pulmonary
arteries
33
• This “air-blood barrier” (the respiratory
membrane) is where gas exchange occurs
– Oxygen diffuses from air in alveolus (singular
of alveoli) to blood in capillary
– Carbon dioxide diffuses from the blood in
the capillary into the air in
the alveolus
34