Download Left primary bronchus

Functional anatomy of pulmonary
system, pulmonary circulation and
mechanics of breathing
Presenter: Dr. Satyajit Majhi
Moderator: Dr. J.P. Sharma
University College of Medical Sciences & GTB Hospital,
Delhi
www.anaesthesia.co.in
Email: [email protected]
5 Functions of the
Respiratory System
1. Provides extensive gas exchange surface area
between air and circulating blood
2. Moves air to and from exchange surfaces of lungs
3. Protects respiratory surfaces from outside
environment
4. Produces sounds
5. Participates in olfactory sense
The Nose
• Air enters the respiratory system:
– through nostrils or external nares
– into nasal vestibule
• Nasal hairs:
– are in nasal vestibule
– are the first particle filtration system
The Nasal Cavity
• The nasal septum:
– divides nasal cavity into left and right
• Superior portion of nasal cavity is the olfactory
region:
– provides sense of smell
• Mucous secretions from par nasal sinus and
goblet cells:
– clean and moisten the nasal cavity
• Lined by ciliated mucosal layer
Epistaxis
• Most common site Little’s area
• Situated anterior inferior part of nasal septum.
• Anastomosis of 4 arteries, anterior ethmoidal, septal
branch of superior labial, septal branch of
sphenopalatine and greater palatine.
• Woodruff area, anastomosis of sphenopalatine
artery and posterior pharyngeal artery causes
posterior epistaxis
Air Flow
Meatuses
• Constricted passageways that produce air
turbulence:
– warm and humidify incoming air
– trap particles
• During exhalation these structures:
– Reclaim heat and moisture
– Minimize heat and moisture loss
The Palates
• Hard palate:
– forms floor of nasal cavity
– separates nasal and oral cavities
• Soft palate:
– extends posterior to hard palate
– divides superior nasopharynx from lower pharynx
Nasal Cavity
The Pharynx and Divisions
• A chamber shared by digestive and respiratory
systems
• Extends from internal nares to entrances to larynx
and esophagus
• Nasopharynx
• Oropharynx
• Laryngopharynx
The Nasopharynx
• Superior portion of the pharynx
• Contains pharyngeal tonsils and openings to left and
right auditory tube
• Pseudo-stratified columnar epithelium
The Oropharynx
• Middle portion of the pharynx
• Communicates with oral cavity
• Stratified squamous epithelium
The Laryngopharynx
• Inferior portion of the pharynx
• Extends from hyoid bone to entrance to larynx and
esophagus
Air flow from the pharynx, enters the larynx:
a cartilaginous structure that surrounds the
glottis
Cartilages of the Larynx
• 3 large, unpaired cartilages form the larynx:
– the thyroid cartilage
– the cricoid cartilage
– the epiglottis
ANATOMY OF LARYNX
ANATOMY OF LARYNX
The Thyroid Cartilage
•
•
•
•
Also called the Adam’s apple
Is a hyaline cartilage
Forms anterior and lateral walls of larynx
Ligaments attach to hyoid bone, epiglottis, and
laryngeal cartilages
The Cricoid Cartilage
•
•
•
•
Is a hyaline cartilage
Form posterior portion of larynx
Ligaments attach to first tracheal cartilage
Articulates with arytenoid cartilages
The Epiglottis
• Composed of elastic cartilage
• Ligaments attach to thyroid cartilage and hyoid bone
Cartilage Functions
• Thyroid and cricoid cartilages support and protect:
– the glottis
– the entrance to trachea
• During swallowing:
– the larynx is elevated
– the epiglottis folds back over glottis
• Prevents entry of food and liquids into respiratory
tract
3 pairs of Small Hyaline Cartilages of the
Larynx
arytenoid cartilages, corniculate (Santorini)
cartilages and Cuneiform (Wrisberg) cartilages
Cartilage Functions
• Corniculate and arytenoid cartilages function
in:
– opening and closing of glottis
– production of sound
The Glottis
Ligaments of the Larynx
• Vestibular ligaments and vocal ligaments:
– extend between thyroid cartilage and arytenoid cartilages
– are covered by folds of laryngeal epithelium that project into
glottis
1) The
Vestibular Ligaments
• Lie within vestibular folds:
– which protect delicate vocal folds
Speech
• Speech – intermittent release of expired air while
opening and closing the glottis
• Pitch – determined by the length and tension of the
vocal cords
• Loudness – depends upon the force at which the air
rushes across the vocal cords
• The pharynx resonates, amplifies, and enhances
sound quality
• Sound is “shaped” into language by action of the
pharynx, tongue, soft palate, and lips
The Laryngeal Musculature
• Laryngeal muscle can be
– Extrinsic muscles that
• Elevates or depresses the hyoid bone
– Intrinsic muscles that:
• control vocal folds
• open and close glottis
• Coughing reflex: food or liquids went “down the
wrong pipe”
Nerve supply of Larynx
• Mucous membrane above vocal fold – internal
laryngeal branch of superior laryngeal branch of
vagus nerve
• Below that its supplied by – recurrent laryngeal
nerve (RLN)
• All intrinsic muscle, except cricothyroid – RLN,
cricothyroid by external laryngeal branch of SLN
Laryngeal paralysis
RLN
UNILATERAL
BILATERAL
Cords remain in median or para-median
position
Cords remain in median or para-median
position
Asymptomatic
Dyspnoea and stridor, voice good
SLN
UNILATERAL
BILATERAL
Ipsilateral cricothyroid muscle and anaesthesia
of larynx above the vocal cord
Both cricothyroid muscle paralysis and
anaesthesia of upper larynx
Asymptomatic
Aspiration of food and weak voice
UNILATERAL
COMBINED
BILATERAL
Cord remains in cadaveric position, 3.5 mm
from midline and unilateral paralysis of all
muscle except interarytenoid
All laryngeal muscle paralysed, both vocal cord
lie in cadaveric position and total anaesthesia
of larynx
Hoarsness of voice, aspiration and ineffective
cough
Aphonia, aspiration, inability to cough,
bronchopneumonia
Sphincter Functions of the Larynx
• The larynx is closed during coughing, sneezing, and
Valsalva’s maneuver
• Valsalva’s maneuver
– Air is temporarily held in the lower respiratory tract by
closing the glottis
– Causes intra-abdominal pressure to rise when abdominal
muscles contract
– Helps to empty the rectum
– Acts as a splint to stabilize the trunk when lifting heavy
loads
Organization of the
Respiratory System
• The respiratory system is divided into the upper
respiratory system, above the larynx, and the lower
respiratory system, from the larynx down
The Respiratory Tract
• Consists of a conducting portion:
– from nasal cavity to terminal bronchioles
• Transitional portion
–the respiratory bronchioles and alveolar ducts
• Respiratory portion:
– the alveoli and alveolar sac
Alveoli
• Are air-filled pockets within the lungs
– where all gas exchange takes place
The Trachea
• Extends from the cricoid cartilage into mediastinum
– Formed of rings of cartilages, incomplete posteriorly
– Lined by ciliated columnar epithelium
– It bifurcates into right and left main bronchi at the level of
T5
The Tracheal Cartilages
• 15–20 tracheal cartilages:
– strengthen and protect airway
– discontinuous where trachea contacts esophagus
• Ends of each tracheal cartilage are connected by:
– an elastic ligament and trachealis muscle
The Primary Bronchi
• Right and left primary bronchi:
– separated by an internal ridge (the carina)
•
•
•
•
The Right Primary Bronchus
Is larger in diameter and shorter (2.5 cm) than the
left
Descends at a steeper angle (25⁰) –
The Left Primary Bronchus
Is narrower and longer (5cm)
Descends at broader angle (55⁰)
• Bronchi subdivide into secondary bronchi, each
supplying a lobe of the lungs
• Air passages undergo 23 orders of branching in the
lungs
• Tissue walls of bronchi mimic that of the trachea
• As conducting tubes become smaller, structural
changes occur
– Cartilage support structures change
– Epithelium types change
– Amount of smooth muscle increases
Secondary Bronchi
• Branch to form tertiary bronchi, also called the
segmental bronchi
• Each segmental bronchus:
– Supplies air to a single bronchopulmonary segment
– The right lung has 10
– The left lung has 8 or 9
Division of primary bronchus
Right primary bronchus:
a)
Upper lobe:
b)
Middle lobe:
c)
Lower lobe :

Apical bronchus
Posterior
bronchus
Anterior bronchus


Lateral bronchus
Medial bronchus


Apical bronchus
Medial basal
bronchus
Anterior basal
bronchus
Posterior basal
bronchus
Lateral basal
bronchus





Left primary bronchus
a)
Upper lobe:
b)
Lingula:
c)
Lower lobe:





Apical bronchus
Posterior
bronchus
Anterior bronchus
Superior bronchus
Inferior bronchus




Apical bronchus
Anterior basal
bronchus
Posterior basal
bronchus
Lateral basal
bronchus
Bronchial Structure
• The walls of primary, secondary, and tertiary bronchi:
– contain progressively less cartilage and more smooth
muscle
– increasing muscular effects on airway constriction and
resistance
The Bronchioles
• Each tertiary bronchus branches into multiple
bronchioles
• 1 tertiary bronchus forms about 6500
terminal bronchioles
• Bronchioles branch into terminal bronchioles
Bronchiole Structure
• Bronchioles:
– have no cartilage
– are dominated by smooth muscle
Autonomic Control
• Regulates smooth muscle:
– controls diameter of bronchioles
– controls airflow and resistance in lungs
Bronchodilation
• Dilatation of bronchial airways
• Caused by sympathetic ANS activation
• Reduces resistance
Bronchoconstriction
• Constricts bronchi
• Caused by:
– parasympathetic ANS activation
– histamine release (allergic reactions)
Pulmonary Lobules
• Are the smallest compartments of the lung
• Are divided by the smallest trabecular partitions
(interlobular septa)
• Each terminal bronchiole delivers air to a single
pulmonary lobule
• Each pulmonary lobule is supplied by pulmonary
arteries and veins
Exchange Surfaces
• Within the lobule:
– each terminal bronchiole branches to form several
respiratory bronchioles, where gas exchange takes place
Alveolar Organization
• Respiratory bronchioles are connected to
alveoli along alveolar ducts
• Alveolar ducts end at alveolar sacs:
– common chamber connected to many
individual alveoli
An Alveolus
• Has an extensive network of capillaries
• Is surrounded by elastic fibers
Alveolar Epithelium
• Consists of simple squamous epithelium
• Consists of thin, delicate Type I cells
• Patrolled by alveolar macrophages, also called dust
cells
• Contains septal cells (Type II cells) that produce
Surfactant- an oily secretion which
– Contains phospholipids and proteins
– Coats alveolar surfaces and reduces surface tension
Respiratory Membrane - The thin membrane of
alveoli where gas exchange takes place
3 Parts of the Respiratory Membrane
• Squamous epithelial lining of alveolus
• Endothelial cells lining an adjacent capillary
• Fused basal laminae between alveolar and
endothelial cells
Diffusion- Across respiratory membrane is very rapid:
–
–
because distance is small
gases (O2 and CO2) are lipid soluble
Blood Supply to
Respiratory Surfaces
• Each lobule receives an arteriole and a venule
1. respiratory exchange surfaces receive blood:
•
from arteries of pulmonary circuit
2. a capillary network surrounds each alveolus:
•
as part of the respiratory membrane
3. blood from alveolar capillaries:
•
passes through pulmonary venules and veins
•
returns to left atrium
Gross Anatomy of the Lungs
• Left and right lungs:
– are in left and right pleural cavities
• The base:
– inferior portion of each lung rests on superior
surface of diaphragm
The Root of the Lung
• Site of attachment of bronchus, nerves, and vessels
in hilus:
– anchored to the mediastinum
Lung Shape
• Right lung:
– is wider
– is displaced upward by liver
• Left lung:
– is longer
– is displaced leftward by the heart forming the cardiac
notch
Pleural Cavities and
Pleural Membranes
• 2 pleural cavities:
– are separated by the mediastinum
• Each pleural cavity:
– holds a lung
– is lined with a serous membrane (the pleura)
• Pleura consist of 2 layers:
– parietal pleura
– visceral pleura
• Pleural fluid:
– lubricates space between 2 layers
Blood supply to lungs
• Lungs are perfused by two circulations: pulmonary
and bronchial
• Pulmonary arteries – supply systemic venous blood
to be oxygenated
– Branch profusely, along with bronchi
– Ultimately feed into the pulmonary capillary network
surrounding the alveoli
• Pulmonary veins – carry oxygenated blood from
respiratory zones to the heart
Blood supply to lungs
• Bronchial arteries – provide systemic blood to the
lung tissue
– Arise from aorta and enter the lungs at the hilus
– Supply all lung tissue except the alveoli
• Bronchial veins anastomose with pulmonary veins
• Pulmonary veins carry most venous blood back to
the heart
Pulmonary Circulation
• Thin walled vessels at all levels.
• Pulmonary arteries have far less smooth muscle in
the wall than systemic arteries.
• Consequences of this anatomy- the vessels are:
– Distensible.
– Compressible.
– Low intravascular pressure.
Influences on Pulmonary Vascular
Resistance
• Vessel diameter influenced by extra vascular forces:
–
–
–
–
–
Gravity
Body position
Lung volume
Alveolar pressures/intrapleural pressures
Intravascular pressures
Control of pulmonary vascular resistance
Passive influence on PVR
Influence
Effect on PVR
mechanisim
↑ Lung Volume
(above FRC)
Increase
Lengthening and
Compression
↓ Lung Volume
(below FRC)
Increase
Compression of Extra
alveolar Vessels
↑ Flow, ↑Pressure
Decrease
Recruitment and Distension
Gravity
Decrease in Dependent
Regions
Recruitment and Distension
↑ Interstitial Pressure
Increase
Compression
Positive Pressure
Ventilation
Increase
Compression and
Derecruitment
Gravity, Alveolar Pressure and Blood Flow
• Pressure in the pulmonary arterioles depends on both mean
pulmonary artery pressure and the vertical position of the
vessel in the chest, relative to the heart.
• Driving pressure (gradient) for perfusion is different in the 3
lung zones:
– Flow in zone 1 may be absent because there is inadequate
pressure to overcome alveolar pressure.
– Flow in zone 3 is continuous and driven by the pressure in
the pulmonary arteriole – pulmonary venous pressure.
– Flow in zone 2 may be pulsatile and driven by the pressure
in the pulmonary arteriole – alveolar pressure (collapsing
the capillaries).
Control of Pulmonary Vascular Resistance
• Active Influences on PVR:
Increase
Decrease
Sympathetic innervation
Parasympathetic innervation
α- adernergic agonist
Acetylcholine
Thromboxane/PGE2
β- adrenergic agents
Endothelin
PGE1
Angiotensin
Prostacycline
Histamine
Nitiric oxide
Alveolar hypoxemia
Bradykinin
Hypoxic Pulmonary Vasoconstriction
• Alveolar hypoxia causes active vasoconstriction at level of precapillary arteriole.
• Mechanism is not completely understood:
– Response occurs locally and does not require innervation.
– Mediators have not been identified.
– Graded response between pO2 levels of 100 down to 20
mmHg.
• Functions to reduce the mismatching of ventilation and
perfusion.
• Not a strong response due to limited muscle in pulmonary
vasculature.
• General hypoxemia (high altitude or hypoventilation) can
cause extensive pulmonary artery vasoconstriction.
Regulation of breathing
• Medullary rhythmicity center
– Nerves extend to intercostals and diaphragm
– Signals are sent automatically
– Expiratory center is activated during forced breathing
• Pneumotaxic area
– Controls degree of lung inflation; inhibits inspiration
• Apneustic area
– Promotes inspiration
Chemoreceptors
• Breathing can be controlled voluntarily, up to a point
• Too much CO2 and H+ will stimulate inspiratory area,
phrenic and intercostal nerves
• Central chemoreceptors: medulla oblongata
monitors CSF
Peripheral chemoreceptors
• Aortic bodies (vagus nerve)
• Carotid bodies (glossopharyngeal nerve)
• Respond to fluctuations in blood O₂, CO2 and H⁺
levels
• Rapid respond
• Pulmonary stretch receptors prevent over inflation of
lungs (promote expiration)
Pulmonary ventilation
• Inhalation:
– always active
• Exhalation:
– active or passive
3 Muscle Groups of Inhalation
1.
2.
3.
Diaphragm:
–
–
–
contraction draws air into lungs
Increases transverse diameter of thorax
75% of normal air movement
–
–
assist inhalation
25% of normal air movement
–
–
–
–
sternocleidomastoid
serratus anterior
pectoralis minor
scalene muscles
External intercostals muscles:
Accessory muscles assist in elevating ribs:
Muscles of Active Exhalation
1. Internal intercostal and transversus thoracis
muscles:
–
depress the ribs and decreases thoracic volume
2. Abdominal muscles:
–
–
–
compress the abdomen
force diaphragm upward
Forcefully contracts while coughing and sneezing
Inspiration
Expiration
Ventilation
• Depends on
• Lung volume
• Alveolar ventilation
• Anatomic and physiological dead
space
• Regional difference in ventilation
Lung volume
• Total lung volume is divided into a series of volumes
and capacities useful in diagnosis in pulmonary
function tests
• Measure rates and volumes of air movements
4 Pulmonary Volumes
1. Resting tidal volume:
–
in a normal respiratory cycle
2. Expiratory reserve volume (ERV):
–
after a normal exhalation
3. Residual volume:
–
–
after maximal exhalation
minimal volume (in a collapsed lung)
4. Inspiratory reserve volume (IRV):
–
after a normal inspiration
4 Calculated
Respiratory Capacities
1.
Inspiratory capacity:
tidal volume + inspiratory reserve volume
2. Functional residual capacity (FRC):
expiratory reserve volume + residual volume
3. Vital capacity:
expiratory reserve volume + tidal volume +
inspiratory reserve volume
4. Total lung capacity:
vital capacity + residual volume
 Closing capacity: Minimum volume at which smaller
airways begin to close and causes air trapping.
Respiratory Volumes and capacities
Alveolar Ventilation
• Amount of air reaching alveoli each minute
• Calculated as:
AV= RR X (TV – DV) = 12 X (500-150) = 4200 ml/min
• Alveoli contain less O2, more CO2 than atmospheric
air:
– because air mixes with exhaled air
Alveolar Ventilation Rate
• Determined by respiratory rate and tidal volume:
– for a given respiratory rate:
• increasing tidal volume increases alveolar ventilation rate
– for a given tidal volume:
• increasing respiratory rate increases alveolar ventilation
Dead space
• Anatomical
» Volume of conducting airway
» Its about 150ml
• Physiological
» Volume of gas that does not eliminate CO₂
» Volume is same as above
» It is increased in many lung disease
Mechanics of breathing
Depends on
Pressure volume curve
Compliance
Elastic properties of chest wall
Surface tension
Resistance
Pressure volume curve
• The pressure volume curve varies between apex and
base of the lung. At the base the volume change is
greater for a given change in pressure.
• Hence alveolar ventilation declines with height from base
to apex.
• This is because at the base the lungs are slightly
compressed by the diaphragm so upon inspiration have
greater scope to expand.
• Thus a small change in intrapleural pressure brings about
a relatively large change in volume
Elastance
Physical tendency to return to original state after deformation
Lung volume at any given pressure is slightly more during deflation
than it is during inflation, it is called Hysteresis (due to surface
tension)
Compliance
•
•
•
•
An indicator of expandability
∆V/∆P (200 ml/ cm H₂O)
Low compliance requires greater force
High compliance requires less force
Factors Governing Compliance
1.
2.
3.
Connective-tissue structure of the lungs
Level of surfactant production
Mobility of the thoracic cage
Factors That Diminish Lung Compliance
• Fibrosis or scar tissue in lung
• Decrease surfactant
• Restricted movement of chest wall
• Deformity of thorax
• Ossification of costal cartilages
• Paralysis of intercostal muscles
• Blockage of smaller air way
Elastic properties of chest wall
• Lung has a tendency to collapse inward and chest
wall springs out ward
• FRC is the equilibrium volume where both force
balance each other
• Chest wall tends to expand at volumes up to about
75% of total vital capacity
Surface tension
• Surfactant reduces surface tension forces by forming
a monomolecular layer between aqueous fluid lining
alveoli and air, preventing a water-air interface
• Produced by type II alveolar epithelial cells
• Complex mix-phospholipids, proteins, ions
– dipalmitoyl lecithin, surfactant apoproteins, Ca++ ions
Stabilization of Alveolar size
• Role of surfactant
– Law of Laplace P=2T/r
• Without surfactant smaller alveolar have
increased collapse & would tend to empty into
larger alveoli
– Big would get bigger and small would get smaller
• Surfactant automatically offsets this physical
tendency
– As the alveolar size ⇓ surfactant is concentrated
which ⇓ surface tension forces, off-setting the ⇓ in
radius
Resistance
• Airway resistance
Or
• Tissue resistance
Airway resistance
• Friction is the major nonelastic source of resistance
to airflow
• The relationship between flow (F), pressure (P), and
resistance (R) is:
∆P
F=R
• The amount of gas flowing into and out of the alveoli
is directly proportional to ∆P, the pressure gradient
between the atmosphere and the alveoli
• Gas flow is inversely proportional to resistance with
the greatest resistance being in the medium-sized
bronchi
• As airway resistance rises, breathing movements
become more strenuous
• Severely constricted or obstructed bronchioles:
– Can prevent life-sustaining ventilation
– Can occur during acute asthma attacks which stops
ventilation
• Epinephrine release via the sympathetic nervous
system dilates bronchioles and reduces air resistance
Tissue resistance
• Due to tissue displacement during ventilation (lungs,
thorax, diaphragm)
• It is the 20% of total resistance
• Mainly from lung tissue resistance and chest wall
resistance
• Air flow resistance is around 1 cm H₂O/L/sec
• Increases up to 5 folds in obstructive lung disease
• ↑ by obesity, fibrosis, ascites
Work of breathing
• Done by respiratory muscles to over come elastic and
frictional forces opposing inflation.
W= F X S ( force X distance)
= ∆P X ∆V
= area under P-V curve
• Normal breathing
– active inhalation
– passive exhalation (work of exhalation recovered from
potential energy stored in expanded lungs & thorax during
inspiration)
Area 1 = work done against elastic forces ( compliance) = 2/3
Area 2 = work done against frictional forces ( resistance work) =1/3
Area 1+2 = total work done = 2/3 + 1/3 = 1
↑TV → ↑ elastic component of work
↑ RR ( flow) → ↑ frictional work
• People with diseased lungs assume a ventilatory
pattern optimum for minimum work of breathing.
• COPD/Obstructive disease-Slow breathing with
pursed lips(↓ frictional work)
• Fibrosis/Restrictive disease-Rapid shallow
breathing(↓elastic work)
References
• Miller’s Anesthesia- Ronald D. Miller 7th edition
• Respiratory physiology- John B. West, 8th edition
• A Practice of Anesthesia- Wylie and Chuchill
Davidson, 5th edition
www.anaesthesia.co.in