Transcript 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
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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
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• 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
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