anatomy and mechanics of respiratory system

1. Anatomy and Mechanics
of Respiratory System
Presenter- Dr. Dharmraj Singh

2. Anatomy of respiratory system
• The respiratory system consists of all the tissue and organs designed
to bring air to the gas exchange surface where O2 is absorbed and CO2
is released.
• The respiratory system can be divided into:
• Upper respiratory system that includes the nose, nasal cavity,
paranasal sinuses and pharynx
• Lower respiratory system that includes the larynx, trachea, bronchi
and lungs.

3. Contd…
• The respiratory system is essentially designed to support the
respiratory tract that consists of the passageways through which the
air travels to reach the gas exchange surface.
• The respiratory tract can be divided into-
• Conducting portion from the nasal cavity to the terminal bronchioles
through which no gas exchange occurs
• Respiratory portion that includes the respiratory bronchioles and
alveoli where gas exchange occurs

4. Functions
1. Provide a gas exchange surface
2. Move air to and from exchange surface
3. Protect respiratory surfaces from environment
4. Defend against invasion by pathogens
5. Production of sound
6. Involvement in regulation of blood volume and pressure, and control
of body pH

5. Contd…
• Breathing (Pulmonary Ventilation)
Inhalation (inspiration) draws gases into the lungs.
Exhalation (expiration) forces gases out of the lungs.
• Gas Conditioning
• As gases pass through the nasal cavity and paransal sinuses, inhaled
air becomes turbulent. The gases in the air are
• warmed to body temperature
• humidified
• cleaned of particulate matter

6. Contd…
• Produces Sounds
• The larynx, nasal cavity, paranasal sinuses, teeth, lips, and tongue work to
produce sound. Sound allows speech, singing, and nonverbal
communication
• Provides Olfactory Sensations
• When airborne molecules are inhaled and dissolve in the mucus in the nose,
the molecules can bind to receptors in the olfactory epithelium.
• Protects the Body
• Hairs, twisted pathways, goblet cells, mucous glands, lysozyme in the
mucus all help defend the body against infection by airborne pathogens.

7. Pathway of Air
• nose ---> pharynx ---> larynx ---> trachea ---> primary bronchi --->
secondary bronchi ---> tertiary bronchi ---> bronchioles ---> terminal
bronchioles ---> respiratory bronchioles ---> alveolar duct ---> alveoli

8. Respiratory Epithelium
• Most of the mucous membrane lining the conducting portion of the
respiratory tract is lined by pseudostratified, ciliated, columnar
epithelium (PCCE), which is also know as respiratory epithelium.
• PCCE serves the protective function of the respiratory system.
• Goblet cells, and mucous glands found in the lamina propria,
produce mucus that traps particles on the surface.
• The cilia move sheets of mucus with trapped debris and pathogens out
of the tract and toward the esophagus.

11. Upper Respiratory System
Nasal Cavity
• The nasal cavity is the chamber between external and internal nares.
• Coiled, shelf-like extensions of bones called conchae (turbinates) extend
from the lateral walls of the nasal cavity toward the nasal septum.
• Narrow passageways between the conchae are called meatuses.
• The air that passes through the meatuses is filtered, warmed and
humidified.
Pharynx
• The pharynx is the passageway connecting the nasal cavity, oral cavity,
esophagus and larynx.
• It is shared by the digestive and respiratory tracts.

14. Characteristics of neonates and infants that
differentiate them from adult patients
Anatomic
• Relatively larger head and tongue
• Narrower nasal passages
• Anterior and cephalad larynx
• Relatively longer epiglottis
• Shorter trachea and neck
• More prominent adenoids and tonsils
• Weaker intercostal and diaphragmatic muscles
Greater resistance to airflow
Physiological
• Increased respiratory rate
• Reduced lung compliance
• Increased chest wall compliance
• Reduced functional residual capacity
Pharmacological
• More rapid rise in FA/FI and more rapid
induction and recovery from inhaled
anesthetics
• Increased minimum alveolar concentration
• Immature neuromuscular junction
FA/FI, fractional alveolar concentration/fractional inspired concentration.

15. Sagittal section of the adult (A) and infant (B) airway.
A B

16. Contd…
• The cricoid cartilage is the narrowest point of the airway in children
younger than 5 years of age, in adults the narrowest point is the glottis
(vocal cords).
• rate of oxygen consumption of neonates and infants, 6 to 8 mL/kg/
min versus 3 to 4 mL/kg/min in adults.
• anterior and cephalad larynx (the glottis is at a vertebral level of C4
versus C6 in adults
• neonates and young infants obligate nasal breathers until about 5
months of age.

17. Lower Respiratory System
Larynx
• Air enters the lower respiratory system through an opening called the
glottis.
• The larynx is a cylindrical structure that surrounds, protects and controls
the glottis.
• Vocal folds flank the glottis and contain elastic tissue that vibrate to
produce sound.
Trachea
• The trachea is a tough, flexible tube that is supported by 15 to 20 C-shaped
tracheal cartilages which are attached by annular ligaments.
• The trachea is lined by typical respiratory epithelium (PCCE).

19. Trachea
• conduit for ventilation, average length of 10 to 13 cm
• for clearance of tracheal and bronchial secretions
• begins at the lower border of the cricoid cartilage and extends to the
carina
• C-shaped cartilaginous rings (anterior and lateral walls) are connected
posteriorly by the membranous wall of the trachea
• cricoid cartilage is the narrowest part (average diameter of 17 mm in
men and 13 mm in women).

20. Contd…
• tracheal lumen narrows slightly as it progresses toward the carina,
• bifurcates into the right and left mainstem bronchi at the level of the
sternal angle
• right mainstem bronchus lies in a more linear arrangement with the
trachea,
• whereas the left mainstem bronchus lies in a more angular orientation
with the trachea
• The right mainstem bronchus continues as the bronchus intermedius
after the take-off of the right upper lobe bronchus.

21. Contd…
• distance from the tracheal carina to the take- off of the right upper lobe
bronchus is an average of 2.0 cm in men and approximately 1.5 cm in
women
• left mainstem bronchus is longer than the right mainstem bronchus and
measures an average of 5.0 cm in men and 4.5 cm in women.
• left mainstem bronchus divides into the left upper lobe bronchus and
the left lower lobe bronchus.

23. Contd…
Primary Bronchus
• The trachea divides into right and left primary bronchi which are
similar to the trachea in design.
• The primary bronchi enter each lung at an indentation called the hilus.
Superficial Anatomy of Lungs
• The right and left lungs are situated in the pleural cavities and are
shaped like blunt cones with a blunt superior apex within the base of
the neck and a concave base on the surface of the diaphragm.

24. Contd…
• The primary bronchi first divide into the secondary or lobar bronchi
that supply the lobes of each lung.
• Inside the lobes of the lungs, the lobar bronchi divide into tertiary or
segmental bronchi that provide the bronchopulmonary segments
within each lung.
• Each bronchopulmonary segment has its own blood supply and
drainage in addition to its own segmental bronchi.
• Each lung has 10 bronchopulmonary segments.

25. Contd…
• The bronchioles continue to divide and give rise to smaller bronchioles
until the bronchiole is supplying air to a pulmonary lobule.
• At this point the bronchiole is called a terminal bronchiole and this
marks the end of the conducting system of the respiratory tract.
• The terminal bronchioles still have smooth muscle in their walls that
control the flow of air into the lobule.
• Contraction of the smooth muscle is called bronchoconstriction
which causes the opening to narrow.
• Relaxation is called bronchodilation which causes the opening to
widen.

26. Respiratory Divisions
• Conducting Zone
• Made up of rigid passageways that serve to warm, moisten, and filter
the inhaled air: nose, nasal cavity, pharynx, larynx, trachea, primary
bronchi, tertiary bronchi, bronchioles, terminal bronchioles.
• Air passages undergo 23 orders of branching in the lungs which
significantly increases cross sectional area for flow.

28. • Respiratory Zone
• Site of gas exchange
Consists of respiratory bronchioles, alveolar ducts, alveolar sacs, and
about 300 million alveoli Accounts for most of the lungs’ volume
Provide tremendous surface area for gas exchange.

31. Lobes of lungs
• Each lung is divided into distinct lobes.
• The right lung has three lobes, a superior, middle and inferior lobe.
• The left lung has only two lobes, a superior and inferior lobe.

32. Internal Structure of the Lungs
Bronchi
• After the primary bronchi enter the lungs they immediately branch into
smaller and smaller passageways giving rise to what is called the
bronchial tree.
• The bronchi within the lungs are now referred to as intrapulmonary
bronchi.

34. Bronchioles
• As the tertiary bronchi branch within a segment and become smaller,
the cartilaginous plates that supported the wall disappear and the outer
wall is dominated by smooth muscle.
• These passageways are now called bronchioles (“little bronchi”).

36. • Within the lobule the terminal bronchiole divides into bronchioles
whose walls become thinner and develop thin pouches called alveoli.
• These bronchioles are now called respiratory bronchioles and the
alveoli are line by simple squamous epithelium across which gas
exchange occurs.
• The respiratory bronchioles are the beginning of the respiratory
portion of the respiratory tract.

37. • Alveolar Ducts and Alveoli
• The respiratory bronchioles divide into multiple linear passageways
lined by alveoli that end in sacs surrounded by alveoli.
• The linear passageways are alveolar ducts and the sacs are alveolar
sacs.
• The alveolar walls are associated with capillaries and elastic fibers
that enable the alveolar ducts and sacs to maintain their relative
positions after expansion.

38. Alveolus and Respiratory Membrane

39. • The alveolar epithelium is primarily simple squamous epithelium. The
alveolar epithelium consists of:
1. Squamous epithelial cells also called Type I cells or respiratory
epitheliocytes
2. Large cells called septal cells, surfactant cells, Type II cells or large
alveolar cells. This cell (of many names!) produces an oily secretion
called surfactant
• Surfactant consists of a mixture of phospholipids that reduce the surface
tension of the fluid in alveoli
3. Alveolar macrophages that phagocytize any particulate matter or
pathogens that managed to get through the defenses of the respiratory
tract.

40. • The respiratory membrane consists of:
1. alveolar epithelium;
2. capillary endothelium;
3. fused basal laminae of the alveolar and endothelial cells
• The respiratory membrane is thin and permits rapid exchange of the
lipid soluble respiratory gases.

42. MECHANICS OF BREATHING
• 2 PROCESSES-
• Inspiration-Inflow of atmospheric air into lungs.
• Expiration-Outflow of air from lungs into atmosphere.

43. Muscle of respiration
MUSCLE OF INSPIRATION MUSCLE OF EXPIRATION
Muscle of normal tidal inspiration-
Diaphragm
External intercostal
Accessory Muscle of inspiration-
Sternocleidomastoid
Scalene
Serratus Anterior
Pectoralis major and minor
Laryngeal muscle
Internal intercostal
Abdominal muscles include-
Abdominal Rectii
Transversus Abdominis
Internal oblique

45. Boyle’s Law
Boyle's Law states that the relationship
between the pressure and volume of gases is
inversely proportional for a gas held at a
constant temperature
P1V1 = P2V2
P = pressure of a gas in mm Hg
V = volume of a gas in cubic millimetres
That is-
as pressure decreases, volume increases
as volume decreases, pressure increases

46. Important Pressures
• Atmospheric Pressure –Pressure exerted
by the air surrounding the body i.e 0 cm
H2O pressure
• Intrapulmonary Pressure /intra-alveolar
pressure–pressure exerted by the air within
the lungs
• Intrapleural Pressure /intrathoracic
pressure-pressure within the pleural cavity
exerted by pleural fluid.
• Transpulmonary Pressure/recoil
pressure

47. Thoracic Volume Changes
• At rest the diaphragm is
relaxed
• As the diaphragm contracts,
thoracic volume increases
• As the diaphragm relaxes,
thoracic volume decreases

48. Pressure Relationships in the Thoracic
Cavity
• Respiratory pressure is always described relative to atmospheric
pressure
• Atmospheric pressure (ATM) - pressure exerted by all of the gases in
the air we breathe (760 mm Hg at sea level)
• Negative respiratory pressure is less than ATM
• Positive respiratory pressure is greater than ATM

49. Intrapulmonary pressure
• pressure within the alveoli ~760mmHg (when even with ATM )
• intrapulmonary pressure always eventually equalizes itself with
atmospheric pressure
Intrapleural pressure
• pressure within the pleural cavity which adheres lungs to thoracic
cavity ~ 756mmHg
• intrapleural pressure is always less than intrapulmonary pressure and
atmospheric pressure Intrapulmonary pressure and intrapleural
pressure fluctuate with the phases of breathing

50. • 2 forces hold the thoracic wall and lungs in close apposition –
stretching the lungs to fill the large thoracic cavity
• Intrapleural fluid cohesiveness – polarity of water attracts wet
surfaces
Transmural pressure gradient – atmospheric pressure (760mmHg) is
greater than intrapleural pressure (756mmHg) so lungs expand

53. Bucket handle & Pump handle movement

54. Inspiration
• The diaphragm and external intercostal muscles (inspiratory muscles)
contract and the rib cage rises, stretching the lungs and increasing
intrapulmonary volume.
• Intrapulmonary pressure drops below atmospheric pressure (1 mm Hg)
drawing air flow into the lungs, down its pressure gradient, until
intrapleural pressure = atmospheric pressure

56. • Expiration
• Inspiratory muscles relax and the rib cage descends due to gravity,
elasticity.
• Thoracic cavity volume decreases, elastic lungs recoil passively and
intrapulmonary volume decreases.
• Intrapulmonary pressure rises above atmospheric pressure (+1 mm
Hg), gases flow out of the lungs down the pressure gradient until
intrapulmonary pressure is 0

58. Respiratory Cycle
Single cycle of inhalation and exhalation
Amount of air moved in one cycle = tidal volume

59. Physical Factors Influencing Ventilation
• Friction
• Is the major nonelastic source of resistance to airflow
The relationship between flow (F), pressure (P), and resistance (R) is
• Flow = ΔP /R
• Compliance
• Is the ability to stretch, the ease with which lungs can be expanded due to change
in transpulmonary pressure Is determined by 2 main factors:
• Distensibility of the lung tissue and surrounding thoracic cage
• Surface tension of the alveoli
• High compliance - stretches easily
Low compliance - Requires more force
Restrictive lung diseases - fibrotic lung diseases and inadequate surfactant
production

60. • Elastic Recoil
• Is how readily the lungs rebound after being stretched
Elasticity of connective tissue causes lungs to assume smallest possible size
Surface tension of alveolar fluid draws alveoli to their smallest possible siz
• Elastance
• Is returning to its resting volume when stretching force is released
• Surface Tension
• Is the attraction of liquid molecules to one another at a liquid-gas interface,
the thin fluid layer between alveolar cells and the air
This liquid coating the alveolar surface is always acting to reduce the
alveoli to the smallest possible size
Surfactant, a detergent-like complex secreted by Type II alveolar cells,
reduces surface tension and helps keep the alveoli from collapsing

62. Compliance
• Elastic recoil is usually measured in terms of compliance (C)
• change in volume divided by the change in distending pressure
• C measurements can be obtained for either the chest, the lung, or both
together
• In the supine position, chest wall compliance (Cw) is reduced because
of the weight of the abdominal contents against the diaphragm.
• Measurements are usually obtained under static conditions, (ie, at
equilibrium).
• Dynamic lung compliance [Cdyn], which is measured during rhythmic
breathing, is also dependent on airway resistance.)

63. • Lung compliance (CL) is defined as:
• CL = Change in lung volume/ Change in transpulmonary pressure
• CL is normally 150 to 200 mL/cm H2O.
• A variety of factors, including lung volume, pulmonary blood volume,
extravascular lung water, and pathological processes (eg, inflammation
and fibrosis) affect CL,
• CW = Change in chest volume/ Change in transthoracic pressure
• where transthoracic pressure equals atmospheric pressure minus
intrapleural pressure.
• Normal chest wall compliance is 200 mL/cm H O.

64. • Total compliance (lung and chest wall together) is 100 mL/cm H2O
and is expressed by the following equation:
• 1/C total= 1/CW+1/CL

65. Airway Resistance
• Gas flow is inversely proportional to resistance with the greatest
resistance being in the medium-sized bronchi,
Severely constricted or obstructed bronchioles: COPD
• Diseases of the Lungs
• Emphysema--destruction of alveoli reduces surface area for gas
exchange
Fibrotic lung disease--thickened alveolar membrane slows gas
exchange, loss of lung compliance Pulmonary edema--fluid in
interstitial space increases diffusion distance
Asthma--increased airway restriction decreases airway ventilation

67. Intrapulmonary and intrapleural pressure during
spontaneous & controlled ventilation
spontaneous ventilation controlled ventilation

68. Lung Capacities and Volumes
• Tidal volume (TV) – air that moves into and out of the lungs with each breath
(approximately 500 ml)
• Inspiratory reserve volume (IRV) – air that can be inspired forcibly beyond the
tidal volume (2100–3200 ml)
• Expiratory reserve volume (ERV) – air that can be evacuated from the lungs
after a tidal expiration (1000–1200 ml)
• Residual volume (RV) – air left in the lungs after strenuous expiration (1200 ml)
• Inspiratory capacity (IC) – total amount of air that can be inspired after a tidal
expiration (IRV + TV)
• Functional residual capacity (FRC) – amount of air remaining in the lungs after
a tidal expiration (RV + ERV)
• Vital capacity (VC) – the total amount of exchangeable air (TV + IRV + ERV)
• Total lung capacity (TLC) – sum of all lung volumes (approximately 6000 ml in
males)

69. Lung volumes and capacities
Measurement Definition
Average Adult
Values (mL)
Tidal volume (Vt) Each normal breath 500
Inspiratory reserve volume
(IRV)
Maximal additional volume that can be
inspired above Vt
3000
Expiratory reserve volume
(ERV)
Maximal volume that can be expired
below Vt
1100
Residual volume (RV)
Volume remaining after maximal
exhalation
1200
Total lung capacity (TLC) RV + ERV + Vt + IRV 5800
Functional residual capacity
(FRC)
RV + ERV 2300

71. Dead Space
• Anatomical dead space – volume of the conducting respiratory
passages (150 ml)
Alveolar dead space – alveoli that cease to act in gas exchange due to
collapse or obstruction Total dead space – sum of alveolar and
anatomical dead spaces

72. CONTROL OF BREATHING
• Spontaneous ventilation is the result of rhythmic neural activity in
respiratory centers within the brainstem.
• This activity regulates respiratory muscles to maintain normal tensions
of O2 and CO2 in the body.
• The basic neuronal activity is modified by inputs from other areas in
the brain, volitional and autonomic, as well as various central and
peripheral receptors (sensors).

74. Central Respiratory Centers
• The basic breathing rhythm originates in the medulla.
• Two medullary groups of neurons are generally recognized: a dorsal
respiratory group, which is primarily active during inspiration, and a
ventral respiratory group, which is active during inspiration and
expiration.
• Two pontine areas influence the dorsal (inspiratory) medullary center.
• A lower pontine (apneustic) center is excitatory, whereas an upper
pontine (pneumotaxic) center is inhibitory.
• The pontine centers appear to fine-tune respiratory rate and rhythm.

76. Central Sensors
• The most important of these sensors are chemoreceptors that respond
to changes in H+ concentration.
• Central chemoreceptors are thought to lie on the anterolateral surface
of the medulla and respond primarily to changes in CSF [H+].
• This mechanism is effective in regulating PaCO2, because the blood–
brain barrier is permeable to dissolved CO2, but not to HCO3
-

77. Peripheral Sensors
• Peripheral chemoreceptors include the carotid bodies (at the
bifurcation of the common carotid arteries) and the aortic bodies
(surrounding the aortic arch).
• The carotid bodies are the principal peripheral chemoreceptors in
humans and are sensitive to changes in Pao2, Paco2, pH, and arterial
perfusion pressure.
• They interact with central respiratory centers via the glossopharyngeal
nerves, producing reflex increases in alveolar ventilation in response
to reductions in Pao2, arterial perfusion, or elevations in [H+] and
Paco2.

79. Lung receptors
• Impulses from these receptors are carried centrally by the vagus nerve.
• Stretch receptors are distributed in the smooth muscle of airways.
• They are responsible for inhibition of inspiration when the lung is
inflated to excessive volumes (Hering–Breuer inflation reflex) and
shortening of exhalation when the lung is deflated (deflation reflex).
• Stretch receptors normally play a minor role in humans.
• In fact, bilateral vagal nerve blocks have a minimal effect on the
normal respiratory pattern.

80. Other receptors
• Various muscle and joint receptors on pulmonary muscles and the
chest wall.
• Input from these sources is probably important during exercise and in
pathological conditions associated with decreased lung or chest
compliance

81. Effect of Anesthesia on the control of
breathing
• The most important effect of most general anesthetics on breathing is a
tendency to promote hypoventilation.
• The mechanism is probably dual: central depression of the chemoreceptor
and depression of external intercostal muscle activity.
• The magnitude of the hypoventilation is generally proportional to anesthetic
depth.
• With increasing depth of anesthesia apneic threshold increases.
• The peripheral response to hypoxemia is even more sensitive to anesthetics
than the central CO2 response and is nearly abolished by even subanesthetic
doses of most inhalation agents (including nitrous oxide) and many
intravenous agents.

82. Thank you