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ANATOMY OF
TRACHEOBRONCHIAL TREE
AND
PULMONARY VENTILATION
Presented by
Dr. Sunil Kumar Arora
1
Organs of the Respiratory System
A. The organs of the respiratory tract
can be divided into two groups:
1.Upper Airways
2.Lower airways
2
Upper Airways
• Nose
• Paranasal sinuses
• Pharynx
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Lower Airway
Begins with true vocal cords and extends to
alveoli
•
•
•
•
•
Larynx
Trachea
Main stem bronchi
Segmental bronchi
Subsegmental bronchi
• Bronchioles
• Terminal bronchioles
• Respiratory
bronchioles
• Alveolar ducts
• Alveolar sacs
• alveoli
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Organization and Functions of
the Respiratory System
• Conducting portion transports air.
- includes the nose, nasal cavity, pharynx,
larynx, trachea, and progressively smaller
airways, from the primary bronchi to the
terminal bronchioles
• Respiratory portion carries out gas exchange.
- composed of small airways called respiratory
bronchioles and alveolar ducts as well as air sacs
called alveoli
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Tracheobronchial Tree
• A highly branched system of air-conducting passages
that originate from the trachea and progressively
branch into narrower tubes as they diverge
throughout the lungs before terminating in terminal
bronchioles.
•Series branching airways commonly referred to as
“generations” or of “orders”
The first generation or order is zero (0), the trachea itself
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Trachea
• A flexible tube of 10-12 cm length and 1.5-2.5 cm width also called
windpipe. Extends to second rib anteriorly and T4-T5 posteriorly.
• Extends through the mediastinum and lies anterior to the esophagus
and inferior to the larynx.
• Anterior and lateral walls of the trachea supported by 15 to 20 Cshaped tracheal cartilages.
• Cartilage rings reinforce and provide rigidity to the tracheal wall to
ensure that the trachea remains open at all times
• Posterior part of tube lined by trachealis muscle.
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Tracheal lining
• Pseudostratified columnar epithelium with
cilia; goblet cells, serous cells, and
specialized submucosal bronchial glands
• 200+ cilia per cell, 5-7 microns long
• Beat cephalid (head) toward oropharynx
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Primary bronchus
• At the level of the sternal angle, the trachea
bifurcates into two smaller tubes, called the
right and left primary bronchi.
• Each primary bronchus projects laterally toward
each lung.
• The most inferior tracheal cartilage separates
the primary bronchi at their origin and forms an
internal ridge called the carina.
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Main Stem Bronchi
• Right bronchus
–
–
–
–
Wider
More vertical
5 cm shorter
Supported by C
shaped cartilages
– 20-30 degree angle
– First generation
• Left bronchus
–
–
–
–
Narrower
More angular
Longer
Supported by C
shaped cartilages
– 40-60 degree angle
– First generation
•Foreign particles are more likely to lodge in the right
primary bronchus.
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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.
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Lobar Bronchi
• R main stem divides
into:
– Upper lobar bronchus
– Middle lobar bronchus
– Lower lobar bronchus
• L main stem divides
into:
– Upper lobar bronchus
– Lower lobar bronchus
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Segmental Bronchi
3rd generation
• R lobar divides into
– Segmental bronchi
– 10 segments on right
• L lobar divides into
– Segmental bronchi
– 8 segments on left
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Subsegmental Bronchi
•
•
•
•
4th to 9th generations
Progressively smaller airways
1-4 mm diameter
At 1 mm diameter connective tissue
sheath disappears
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Noncartilagenous Airways
Bronchioles
– 10-th to 15th
generation
– Cartilage is absent
– Lamina propria is
directly connected with
lung parenchyma
– Surrounded by spiral
muscle fibers
– Epithelial cells are
cuboidal
– Less goblet cells and
cilia
– With no cartilage,
airway remains open
due to pressure
gradients
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Terminal Bronchioles
• 16th to 19th generation
• Average diameter is 0.5 mm
• Cilia and mucous glands begin to
disappear totally
• End of the conducting airway
• Canals of Lambert-interconnect this
generation,provide collateral ventilation
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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.
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Segmental anatomy
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Gas exchange zone
• Respiratory bronchioles
• Acinus
• Alveolar Ducts, sacs, alveoli
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Functional Units of Gas
Exchange
• Three generations of respiratory
bronchioles
• Three generations of alveolar ducts
• 15-20 clusters--sacs
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Acinus or Lobule
• Each acinus (unit) is approximately 3.5
mm in diameter
• Each contains about 2000 aveloli
• There are approximately 130,000 primary
lobules in the lung
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Anatomic Arrangement of
Alveoli
• 85-95% of alveoli covered by small
pulmonary capillaires
• The cross-sectional area or surface area is
approximately 70m2
•
Total of about 300 million alveoli in
2 lungs
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Cells in Alveolus
Type I cells : 95% of Alveoler surface,
Major site of gas exchange
Type II cells : or Septal cells secrete
surfactant,About 5% of Alveoler surface.
Alveolar macrophages-Plays role in defence
mechenism.
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Surfactant
Is a substance produce by type II alveolar epithelial cells
(~ 5% of the surface area of the alveoli) which reduce the
surface tension of the fluid in the inner surface of the
alveoli
it is a mixture of phospholipids, proteins, and ions, the
most important component is phospholipid dipalmitoyl
phosphatidylcholine which is responsible for reducing the
surface tension.
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Respiratory Zone of Lower Respiratory
Tract
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Respiratory Membrane
Diffusion of gases occurs through Respiratory mambrane.
•
•
•
•
•
squamous cells of alveoli .
basement membrane of alveoli.
basement membrane of capillaries
simple squamous cells of capillaries
about .5 μ in thickness
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Anatomy of the Respiratory
Membrane
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Epithelial basement
membrane
Interstitial
space
Capillary basement
membrane
Capillary endothelium
Alveolar epithelium
Red
blood
cell
Fluid and
surfactant
layer
Alveolus
Diffusion
Diffusion
Capillary
O2
CO2
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Intersitium/interstial space
• Surround, supports, and shapes the
alveoli and capillaries
• Composed of a gel like substance and
collagen fibers
• Contains tight space and loose space
areas
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Factors that affect the rate of gas
diffusion through the respiratory
membrane
1.The thickness of the respiratory
membrane.The thickness of the respiratory
membrane is inversely proportional to the rate of
diffusion through the membrane.
2.Surface area of the membrane.
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3. The diffusion rate of the specific gas.
Diffusion coefficient for the transfer of
each gas through the respiratory
membrane depends on its solubility in the
membrane and inversely on the square
root of its molecular weight. CO2 diffuses
20 times as rapidly as O2.
4. The pressure difference between the two
sides of the membrane (between the alveoli
and in the blood).
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Pores of Kohn
• Small holes in the walls of adjoining alveoli
(alveaolar septa)
• Between 3 to 13 µ in diameter
• Formation of pores may be due to:
– Desquamation due to disease
– Normal degeneration due to aging
– Movement of macrophages leaving holes
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Blood supply of Lungs
• Bronchial circulation – bronchial arteries supply
oxygenated blood to lungs, bronchial veins carry
away deoxygenated blood from lung tissue.
• Pulmonary circulation
• Response of two systems to hypoxia –
pulmonary vessels undergo vasoconstriction,
bronchial vessels like all other systemic vessels
undergo vasodilation
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Bronchial Blood Supply
• Bronchial arteries
– Arise from thoracic aorta(Anatomic variation is
there),usually there are 1 artery for Rt lung and 2
arteries for Lt Lung.
– Bronchial arteries run along with the branching
bronchi and supply lung tissue except the alveoli.
– Much of the blood supplied by Bronchial arteries is
Returned via Pulmonary veins rather than
bronchial veins.
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Bronchial arteries
• Also nourish
– Mediastinal lymph nodes
– Pulmonary nerves
– Some muscular pulmonary arteries and veins
– Portions of the esophagus
– Visceral pleura
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Bronchial venous system
• Approx.1/3 blood returns to right heart
– Azygous vien
– Hemiazygous vein
– Intercostal veins
– This blood comes form the first two or three
generations of bronchi
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Bronchial venous return
• 2/3 of blood flowing to terminal bronchioles
drains into pulmonary circulation via
“bronchopulmonary anastomoses”
• Then flows to left atrium via pulmonary
veins
• Contributes to “venous admixture” or
“anatomic shunt” (1-2% of C.O.)
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Pulmonary Vascular System
• The second source of blood to the lungs
• Primary purpose is to deliver blood to
lungs for gas exchange
• Also delivers nutrients to cells distal to
terminal bronchioles
• Composed of arteries, arterioles,
capllaries, venules, and veins
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• Pulmonary Trunk arises from the infundibulum of
Rt ventricle and divide into Rt and Lt
branches.Which carry deoxygenated blood.
• Pulmonary arteries branch profusely along with
the bronchi leading to capillary network
sorrunding the alveoli.
• 4 Pulmonary veins(2 from each Lung) form post
alveoli to carry oxygenated blood to the Lt
Atrium
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Pulmonary Capillaries
• Walls are less than 0.1µ thick
• Total external thickness is about 10µ
• Selective permeability to water,
electrolytes, sugars
• Produce and destroy biologically active
substances
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Nerve Supply
• Lung and Pleura are innervated by Anterior and
posterior pulmonary plexuses
• They are mixed plexuses containing
vagal(Parasympethatic) and sympathetic fibers.
• Vagus Nerve(Parasympathetic)—
Bronchoconstriction,vasodilatation and
Secretomotor
• Sympathetic Fibres—
Bronchodilator,vasocostrictor and inhibitor to the
glands of bronchial tree.
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Lymphatic System
• Lymphatic vessels
remove fluids and
protein molecules that
leak out of the
pulmonary capillaries
• Transfer fluids back
into the circulatory
system
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Lymphatic Drainage of Lungs
• There are 2 sets of Lymphatics,both of which
drain into the Bronchopulmonary nodes.
• Superficial vessels drain the peripheral lung
tissue lying beneth the pulmonary pleura
• Deep lymphatics drain the bronchial tree,the
pulmonary vessels and connective tissue septa
and then run towards the hilum.
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• Lymphatic vessels of upper lobe end up in
superior tracheobronchial node and from
lower lobe enters the inferior
tracheobronchial nodes.
• The tracheobronchial and
bronchopulmonary nodes end in the
bronchomediastinal lymph trunk
• This trunk reaches the thoracic duct on the
left and Rt lymphatic duct on the Rt side.
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Respiratory events
• Pulmonary ventilation = exchange of gases
between lungs and atmosphere
• External respiration = exchange of gases
between alveoli and pulmonary capillaries
• Internal respiration = exchange of gases
between systemic capillaries and tissue cells
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Breathing
• Breathing (pulmonary ventilation). consists
of two cyclic phases:
• inhalation, also called inspiration - draws gases
into the lungs.
• exhalation, also called expiration - forces gases
out of the lungs.
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Muscles of Inspiration
• During inspiration, the
dome shaped diaphragm
flattens as it contracts
Together:
– This increases the height of
the thoracic cavity
• The external intercostal
muscles contract to raise
the ribs
– This increases the
circumference of the
thoracic cavity
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Inspiration continued
• Intercostals keep the thorax stiff so sides don’t
collapse in with change of diaphragm
• During deep or forced inspiration, additional
muscles are recruited:
–
–
–
–
–
Scalenes
Sternocleidomastoid
Pectoralis minor
Quadratus lumborum on 12th rib
Erector spinae
(some of these “accessory muscles” of ventilation are
visible to an observer; it usually tells you that there is
respiratory distress – working hard to breathe)
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Expiration
• Quiet expiration in healthy people is
chiefly passive
– Inspiratory muscles relax
– Rib cage drops under force of gravity
– Relaxing diaphragm moves superiorly
(up)
– Elastic fibers in lung recoil
– Volumes of thorax and lungs decrease
simultaneously, increasing the pressure
– Air is forced out
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Expiration continued
• Forced expiration is active
– Contraction of abdominal wall muscles
• Oblique and transversus predominantly
– Increases intra-abdominal pressure forcing the
diaphragm superiorly
– Depressing the rib cage, decreases thoracic
volume
• Some help from internal intercostals and latissimus
dorsi
(try this on yourself to feel the different muscles acting)
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Expiration
Inspiration
Increased vertical
diameter
Increased A-P
diameter
External
intercostals
contracted
Elevated
rib cage
Internal
intercostals
relaxed
Diaphragmatic
contraction
Abdominals
contracted
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Muscles Of Breathing
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Boyle’s Law
• The pressure of a gas decreases if the volume of
the container increases, and vice versa.
• When the volume of the thoracic cavity increases even
slightly during inhalation, the intrapulmonary pressure
decreases slightly, and air flows into the lungs through
the conducting airways. Air flows into the lungs from a
region of higher pressure (the atmosphere)into a region
of lower pressure (the intrapulmonary region).
• When the volume of the thoracic cavity decreases during
exhalation, the intrapulmonary pressure increases and
forces air out of the lungs into the atmosphere.
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Alveolar pressure
Alveolar pressure: – is the pressure inside the lung
alveoli
During inspiration:  –1cm of H2O (this slight
negative pressure is enough to move about 0.5 liter
of air into the lungs in the first 2 second of
inspiration)
During expiration: it rises to about +1cm of H2O (this
forces 0.5 liter of inspired air out of the lungs during
the 2 to 3 seconds of expiration
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Compliance of the lungs
Definition:
the extent to which the lungs expand for
each unit increase in transpulmonary
pressure (difference between intraalveolar pressure and intra-pleural
pressure) ~ 200ml/cm of H2O (each time,
the transpulmonary pressure increase by
1cm of H2O, the lungs expand 200ml)
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Mechanism
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Respiratory Values
• A normal adult averages 12 breathes per
minute = respiratory rate(RR)
• Respiratory volumes – determined by using a
spirometer
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LUNG VOLUMES
• TIDAL VOLUME (TV): Volume inspired or expired with
each normalﾊbreath. = 500 ml
• INSPIRATORY RESERVE VOLUME (IRV): Maximum
volume that can be inspired over the inspiration of a
tidal volume/normal breath. Used during
exercise/exertion.=3100 ml
• EXPIRATRY RESERVE VOLUME (ERV): Maximal volume
that can be expired after the expiration of a tidal
volume/normal breath. = 1200 ml
• RESIDUAL VOLUME (RV): Volume that remains in the
lungs after a maximal expiration.ﾊ CANNOT be
measured by spirometry.= 1200 ml
• RESPIRATORY MINUTE VOLUME : Amount of air inspired
per minute. e.g. 500ml x 12 = 6 Ltr.
• Dead Space : Portion of each Tidal volume that does not
take part in gas exchange (150ml).
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LUNG CAPACITIES
• INSPIRATORY CAPACITY ( IC): Volume of maximal
inspiration:IRV + TV = 3600 ml
• FUNCTIONAL RESIDUAL CAPACITY (FRC): Volume of gas
remaining in lung after normal expiration, cannot be
measured by spirometry because it includes residual
volume:ERV + RV = 2400 ml
• VITAL CAPACITY (VC): Volume of maximal inspiration and
expiration:IRV + TV + ERV = IC + ERV = 4800 ml
• TOTAL LUNG CAPACITY (TLC): The volume of the lung
after maximal inspiration.ﾊ The sum of all four lung
volumes, cannot be measured by spirometry because it
includes residual volume:IRV+ TV + ERV + RV = IC +
FRC = 6000 ml
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Partial pressures of respiratory gases as they
enter and leave the lungs (at sea level)
N2
O2
CO2
H2O
Atmospheric Air*
(mmHg)
597.0 (78.62%) 159.0 (20.84%)
0.3 (0.04%)
3.7 (0.50%)
Humidified Air
(mmHg)
563.4 (74.09%) 149.3 (19.67%)
0.3 (0.04%)
47.0 (6.20%)
Alveolar Air
(mmHg)
569.0 (74.9%)
104.0 (13.6%)
40.0 (5.3%)
47.0 (6.2%)
Expired Air
(mmHg)
566.0 (74.5%)
120.0 (15.7%)
27.0 (3.6%)
47.0 (6.2%)
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The rate at which alveolar air is
renewed by atmospheric air:
The amount of air remaining in the lungs at
the end of normal expiration ~ 2300ml (FRC).
Only 350ml of air is brought into the alveoli
with each breath. Therefore, the amount of
alveolar air is replaced by new atmospheric
air with each breath is only 1/7th of the total.
This slow replacement of alveolar air is
important in preventing sudden changes in
gaseous concentrations in the blood.
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Ventilation-perfusion ratio (V/Q)
It is the ratio of alveolar ventilation to pulmonary
blood flow per minute. The alveolar ventilation at
rest (4.2L/min) and is calculated as:
Alveolar ventilation = respiratory rate x (tidal volume –
dead space air).
The pulmonary blood flow is equal to right ventricular
output per minute (5L/min).
This value is an average value across the lung.
At the apex, V/Q ratio = 3.
At the base, V/Q ratio = 0.6.
So the apex is more ventilated than perfused, and the
base is more perfused than ventilated.
During exercise, the V/Q ratio becomes more
homogenous among different parts of the lung.
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