Chapter 22, Respiratory System (Anatomy)
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Transcript Chapter 22, Respiratory System (Anatomy)
The Respiratory System
Anatomy
Chapter 22, Respiratory System
22
1
Respiratory System
Consists of the respiratory and conducting zones
Respiratory zone
Site of gas exchange
Consists of bronchioles, alveolar ducts, and alveoli
Chapter 22, Respiratory System
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Respiratory System
Conducting zone
Provides rigid conduits for air to reach the sites of
gas exchange
Includes all other respiratory structures (e.g., nose,
nasal cavity, pharynx, trachea)
Respiratory muscles – diaphragm and other muscles
that promote ventilation
Chapter 22, Respiratory System
3
Respiratory System
Chapter 22, Respiratory System
4
Figure 22.1
Major Functions of the Respiratory System
To supply the body with oxygen and dispose of
carbon dioxide
Respiration – four distinct processes must happen
Pulmonary ventilation – moving air into and out of
the lungs
External respiration – gas exchange between the
lungs and the blood
Chapter 22, Respiratory System
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Major Functions of the Respiratory System
Transport – transport of oxygen and carbon dioxide
between the lungs and tissues
Internal respiration – gas exchange between
systemic blood vessels and tissues
Chapter 22, Respiratory System
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Function of the Nose
The only externally visible part of the respiratory
system that functions by:
Providing an airway for respiration
Moistening (humidifying) and warming the
entering air
Filtering inspired air and cleaning it of foreign
matter
Serving as a resonating chamber for speech
Housing the olfactory receptors
Chapter 22, Respiratory System
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Structure of the Nose
The nose is divided into two regions
The external nose, including the root, bridge,
dorsum nasi, and apex
The internal nasal cavity
Philtrum – a shallow vertical groove inferior to the
apex
The external nares (nostrils) are bounded laterally
by the alae
Chapter 22, Respiratory System
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Structure of the Nose
Chapter 22, Respiratory System
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Figure 22.2a
Structure of the Nose
Chapter 22, Respiratory System
Figure
22.2b
10
Nasal Cavity
Lies in and posterior to the external nose
Is divided by a midline nasal septum
Opens posteriorly into the nasal pharynx via internal
nares
The ethmoid and sphenoid bones form the roof
The floor is formed by the hard and soft palates
Chapter 22, Respiratory System
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Nasal Cavity
Vestibule – nasal cavity superior to the nares
Vibrissae – hairs that filter coarse particles from
inspired air
Olfactory mucosa
Lines the superior nasal cavity
Contains smell receptors
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Nasal Cavity
Respiratory mucosa
Lines the balance of the nasal cavity
Glands secrete mucus containing lysozyme and
defensins to help destroy bacteria
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Nasal Cavity
Chapter 22, Respiratory System
Figure
22.3b
14
Nasal Cavity
Inspired air is:
Humidified by the high water content in the nasal
cavity
Warmed by rich plexuses of capillaries
Ciliated mucosal cells remove contaminated mucus
Chapter 22, Respiratory System
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Nasal Cavity
Superior, medial, and inferior conchae:
Protrude medially from the lateral walls
Increase mucosal area
Enhance air turbulence and help filter air
Sensitive mucosa triggers sneezing when stimulated
by irritating particles
Chapter 22, Respiratory System
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Functions of the Nasal Mucosa and Conchae
During inhalation the conchae and nasal mucosa:
Filter, heat, and moisten air
During exhalation these structures:
Reclaim heat and moisture
Minimize heat and moisture loss
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Paranasal Sinuses
Sinuses in bones that surround the nasal cavity
Sinuses lighten the skull and help to warm and
moisten the air
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Pharynx
Funnel-shaped tube of skeletal muscle that connects
to the:
Nasal cavity and mouth superiorly
Larynx and esophagus inferiorly
Extends from the base of the skull to the level of the
sixth cervical vertebra
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Pharynx
It is divided into three regions
Nasopharynx
Oropharynx
Laryngopharynx
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Nasopharynx
Lies posterior to the nasal cavity, inferior to the
sphenoid, and superior to the level of the soft palate
Strictly an air passageway
Lined with pseudostratified columnar epithelium
Closes during swallowing to prevent food from
entering the nasal cavity
The pharyngeal tonsil lies high on the posterior wall
Pharyngotympanic (auditory) tubes open into the
lateral walls
Chapter 22, Respiratory System
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Oropharynx
Extends inferiorly from the level of the soft palate to
the epiglottis
Opens to the oral cavity via an archway called the
fauces
Serves as a common passageway for food and air
The epithelial lining is protective stratified
squamous epithelium
Palatine tonsils lie in the lateral walls of the fauces
Lingual tonsil covers the base of the tongue
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Laryngopharynx
Serves as a common passageway for food and air
Lies posterior to the upright epiglottis
Extends to the larynx, where the respiratory and
digestive pathways diverge
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Larynx (Voice Box)
Attaches to the hyoid bone and opens into the
laryngopharynx superiorly
Continuous with the trachea posteriorly
The three functions of the larynx are:
To provide a patent airway
To act as a switching mechanism to route air and
food into the proper channels
To function in voice production
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Framework of the Larynx
Cartilages (hyaline) of the larynx
Shield-shaped anterosuperior thyroid cartilage with
a midline laryngeal prominence (Adam’s apple)
Signet ring–shaped anteroinferior cricoid cartilage
Three pairs of small arytenoid, cuneiform, and
corniculate cartilages
Epiglottis – elastic cartilage that covers the
laryngeal inlet during swallowing
Chapter 22, Respiratory System
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Framework of the Larynx
Chapter 22, Respiratory System
Figure2622.4a, b
Vocal Ligaments
Attach the arytenoid cartilages to the thyroid
cartilage
Composed of elastic fibers that form mucosal folds
called true vocal cords
The medial opening between them is the glottis
They vibrate to produce sound as air rushes up from
the lungs
Chapter 22, Respiratory System
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Vocal Ligaments
False vocal cords
Mucosal folds superior to the true vocal cords
Have no part in sound production
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Vocal Production
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
Chapter 22, Respiratory System
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Movements of Vocal Cords
Chapter 22, Respiratory System
Figure
22.5
30
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
Chapter 22, Respiratory System
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Trachea
Flexible and mobile tube extending from the larynx
into the mediastinum
Composed of three layers
Mucosa – made up of goblet cells and ciliated
epithelium
Submucosa – connective tissue deep to the mucosa
Adventitia – outermost layer made of C-shaped
rings of hyaline cartilage
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Trachea
Chapter 22, Respiratory System
Figure
22.6a
33
Conducting Zone: Bronchi
The carina of the last tracheal cartilage marks the
end of the trachea and the beginning of the right and
left bronchi
Air reaching the bronchi is:
Warm and cleansed of impurities
Saturated with water vapor
Bronchi subdivide into secondary bronchi, each
supplying a lobe of the lungs
Air passages undergo 23 orders of branching in the
lungs
Chapter 22, Respiratory System
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Conducting Zone: Bronchial Tree
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
Chapter 22, Respiratory System
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Conducting Zone: Bronchial Tree
Bronchioles
Consist of cuboidal epithelium
Have a complete layer of circular smooth muscle
Lack cartilage support and mucus-producing cells
Chapter 22, Respiratory System
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Respiratory Zone
Defined by the presence of alveoli; begins as
terminal bronchioles feed into respiratory
bronchioles
Respiratory bronchioles lead to alveolar ducts, then
to terminal clusters of alveolar sacs composed of
alveoli
Approximately 300 million alveoli:
Account for most of the lungs’ volume
Provide tremendous surface area for gas exchange
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Respiratory Zone
Chapter 22, Respiratory System
Figure
22.8a
38
Respiratory Zone
Chapter 22, Respiratory System
Figure
22.8b
39
Respiratory Membrane
This air-blood barrier is composed of:
Alveolar and capillary walls
Their fused basal laminas
Alveolar walls:
Are a single layer of type I epithelial cells
Permit gas exchange by simple diffusion
Secrete angiotensin converting enzyme (ACE)
Type II cells secrete surfactant
Chapter 22, Respiratory System
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Alveoli
Surrounded by fine elastic fibers
Contain open pores that:
Connect adjacent alveoli
Allow air pressure throughout the lung to be
equalized
House macrophages that keep alveolar surfaces
sterile
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Chapter 22, Respiratory System
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Respiratory Membrane
Chapter 22, Respiratory System
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Figure 22.9b
Respiratory Membrane
Chapter 22, Respiratory System
Figure4322.9.c, d
Gross Anatomy of the Lungs
Lungs occupy all of the thoracic cavity except the
mediastinum
Root – site of vascular and bronchial attachments
Costal surface – anterior, lateral, and posterior
surfaces in contact with the ribs
Apex – narrow superior tip
Base – inferior surface that rests on the diaphragm
Hilus – indentation that contains pulmonary and
systemic blood vessels
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Lungs
Cardiac notch (impression) – cavity that
accommodates the heart
Left lung – separated into upper and lower lobes by
the oblique fissure
Right lung – separated into three lobes by the
oblique and horizontal fissures
There are 10 bronchopulmonary segments in each
lung
Chapter 22, Respiratory System
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Gross Anatomy of Lungs
Base, apex (cupula), costal surface, cardiac notch
Oblique & horizontal fissure in right lung results in 3 lobes
Oblique fissure only in left lung produces 2 lobes
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Mediastinal Surface of Lungs
Blood vessels & airways enter lungs at hilus
Forms root of lungs
Covered with pleura (parietal becomes visceral)
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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
Chapter 22, Respiratory System
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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
Chapter 22, Respiratory System
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Pleurae
Thin, double-layered serosa
Parietal pleura
Covers the thoracic wall and superior face of the
diaphragm
Continues around heart and between lungs
Chapter 22, Respiratory System
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Pleurae
Visceral, or pulmonary, pleura
Covers the external lung surface
Divides the thoracic cavity into three chambers
The central mediastinum
Two lateral compartments, each containing a
lung
Chapter 22, Respiratory System
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Breathing
Breathing, or pulmonary ventilation, consists of two
phases
Inspiration – air flows into the lungs
Expiration – gases exit the lungs
Chapter 22, Respiratory System
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Pressure Relationships in the Thoracic Cavity
Respiratory pressure is always described relative to
atmospheric pressure
Atmospheric pressure (Patm)
Pressure exerted by the air surrounding the body
Negative respiratory pressure is less than Patm
Positive respiratory pressure is greater than Patm
Chapter 22, Respiratory System
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Pressure Relationships in the Thoracic Cavity
Intrapulmonary pressure (Ppul) – pressure within the
alveoli
Intrapleural pressure (Pip) – pressure within the
pleural cavity
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Pressure Relationships
Intrapulmonary pressure and intrapleural pressure
fluctuate with the phases of breathing
Intrapulmonary pressure always eventually
equalizes itself with atmospheric pressure
Intrapleural pressure is always less than
intrapulmonary pressure and atmospheric pressure
Chapter 22, Respiratory System
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Pressure Relationships
Two forces act to pull the lungs away from the
thoracic wall, promoting lung collapse
Elasticity of lungs causes them to assume smallest
possible size
Surface tension of alveolar fluid draws alveoli to
their smallest possible size
Opposing force – elasticity of the chest wall pulls
the thorax outward to enlarge the lungs
Chapter 22, Respiratory System
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Pressure Relationships
Chapter 22, Respiratory System
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Figure 22.12
Lung Collapse
Caused by equalization of the intrapleural pressure
with the intrapulmonary pressure
Transpulmonary pressure keeps the airways open
Transpulmonary pressure – difference between the
intrapulmonary and intrapleural pressures
(Ppul – Pip)
Chapter 22, Respiratory System
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Pulmonary Ventilation
A mechanical process that depends on volume
changes in the thoracic cavity
Volume changes lead to pressure changes, which
lead to the flow of gases to equalize pressure
Chapter 22, Respiratory System
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Boyle’s Law
Boyle’s law – the relationship between the pressure
and volume of gases
P 1 V1 = P 2 V2
P = pressure of a gas in mm Hg
V = volume of a gas in cubic millimeters
Subscripts 1 and 2 represent the initial and resulting
conditions, respectively
Chapter 22, Respiratory System
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Inspiration
The diaphragm and external intercostal muscles
(inspiratory muscles) contract and the rib cage rises
The lungs are stretched and intrapulmonary volume
increases
Intrapulmonary pressure drops below atmospheric
pressure (1 mm Hg)
Air flows into the lungs, down its pressure gradient,
until intrapleural pressure = atmospheric pressure
Chapter 22, Respiratory System
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Inspiration
Chapter 22, Respiratory System
Figure
22.13.1
62
Expiration
Inspiratory muscles relax and the rib cage descends
due to gravity
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
Chapter 22, Respiratory System
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Expiration
Chapter 22, Respiratory System
64
Figure 22.13.2
Physical Factors Influencing Ventilation:
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
Chapter 22, Respiratory System
65
Physical Factors Influencing Ventilation:
Airway Resistance
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
Chapter 22, Respiratory System
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Airway Resistance
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
Chapter 22, Respiratory System
67
Alveolar Surface Tension
Surface tension – the attraction of liquid molecules
to one another at a liquid-gas interface
The liquid coating the alveolar surface is always
acting to reduce the alveoli to the smallest possible
size
Surfactant, a detergent-like complex, reduces
surface tension and helps keep the alveoli from
collapsing
Chapter 22, Respiratory System
68
Lung Compliance
The ease with which lungs can be expanded
Specifically, the measure of the change in lung
volume that occurs with a given change in
transpulmonary pressure
Determined by two main factors
Distensibility of the lung tissue and surrounding
thoracic cage
Surface tension of the alveoli
Chapter 22, Respiratory System
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Factors That Diminish Lung Compliance
Scar tissue or fibrosis that reduces the natural
resilience of the lungs
Blockage of the smaller respiratory passages with
mucus or fluid
Reduced production of surfactant
Decreased flexibility of the thoracic cage or its
decreased ability to expand
Chapter 22, Respiratory System
70
Factors That Diminish Lung Compliance
Examples include:
Deformities of thorax
Ossification of the costal cartilage
Paralysis of intercostal muscles
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Chapter 22, Respiratory System
71
The Respiratory System
Physiology
Chapter 22, Respiratory System
22
72
Respiratory 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)
Chapter 22, Respiratory System
73
Respiratory Capacities
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)
Chapter 22, Respiratory System
74
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
Chapter 22, Respiratory System
75
Pulmonary Function Tests
Spirometer – an instrument consisting of a hollow
bell inverted over water, used to evaluate respiratory
function
Spirometry can distinguish between:
Obstructive pulmonary disease – increased airway
resistance
Restrictive disorders – reduction in total lung
capacity from structural or functional lung changes
Chapter 22, Respiratory System
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Pulmonary Function Tests
Total ventilation – total amount of gas flow into or
out of the respiratory tract in one minute
Forced vital capacity (FVC) – gas forcibly expelled
after taking a deep breath
Forced expiratory volume (FEV) – the amount of
gas expelled during specific time intervals of the
FVC
Chapter 22, Respiratory System
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Pulmonary Function Tests
Increases in TLC, FRC, and RV may occur as a
result of obstructive disease
Reduction in VC, TLC, FRC, and RV result from
restrictive disease
Chapter 22, Respiratory System
78
Alveolar Ventilation
Alveolar ventilation rate (AVR) – measures the flow
of fresh gases into and out of the alveoli during a
particular time
AVR
(ml/min)
=
frequency
(breaths/min)
X
(TV – dead space)
(ml/breath)
Slow, deep breathing increases AVR and rapid,
shallow breathing decreases AVR
Chapter 22, Respiratory System
79
Nonrespiratory Air Movements
Most result from reflex action
Examples include: coughing, sneezing, crying,
laughing, hiccupping, and yawning
Chapter 22, Respiratory System
80
Basic Properties of Gases:
Dalton’s Law of Partial Pressures
Total pressure exerted by a mixture of gases is the
sum of the pressures exerted independently by each
gas in the mixture
The partial pressure of each gas is directly
proportional to its percentage in the mixture
Chapter 22, Respiratory System
81
What is Composition of Air?
Air = 21% O2, 78% N2 and .04% CO2
Alveolar air = 14% O2, 78% N2 and 5.2% CO2
Expired air = 16% O2, 78% N2 and 4.5% CO2
Observations
alveolar air has less O2 since absorbed by blood
mystery-----expired air has more O2 & less CO2 than
alveolar air?
Anatomical dead space = 150 ml of 500 ml of tidal volume
Chapter 22, Respiratory System
82
Basic Properties of Gases: Henry’s Law
When a mixture of gases is in contact with a liquid,
each gas will dissolve in the liquid in proportion to
its partial pressure
The amount of gas that will dissolve in a liquid also
depends upon its solubility
Various gases in air have different solubilities:
Carbon dioxide is the most soluble
Oxygen is 1/20th as soluble as carbon dioxide
Nitrogen is practically insoluble in plasma
Chapter 22, Respiratory System
83
Hyperbaric Oxygenation
Clinical application of Henry’s law
Use of pressure to dissolve more O2
in the blood
treatment for patients with anaerobic bacterial infections (tetanus and
gangrene)
anaerobic bacteria die in the presence of O2
Hyperbaric chamber pressure raised to 3 to 4 atmospheres so that
tissues absorb more O2
Used to treat heart disorders, carbon monoxide poisoning,
cerebral edema, bone infections, gas embolisms & crush injuries
Chapter 22, Respiratory System
84
Composition of Alveolar Gas
The atmosphere is mostly oxygen and nitrogen,
while alveoli contain more carbon dioxide and water
vapor
These differences result from:
Gas exchanges in the lungs – oxygen diffuses from
the alveoli and carbon dioxide diffuses into the
alveoli
Humidification of air by conducting passages
The mixing of alveolar gas that occurs with each
breath
Chapter 22, Respiratory System
85
External Respiration: Pulmonary Gas
Exchange
Factors influencing the movement of oxygen and
carbon dioxide across the respiratory membrane
Partial pressure gradients and gas solubilities
Matching of alveolar ventilation and pulmonary
blood perfusion
Structural characteristics of the respiratory
membrane
Chapter 22, Respiratory System
86
Partial Pressure Gradients and Gas
Solubilities
The partial pressure oxygen (PO2) of venous blood
is 40 mm Hg; the partial pressure in the alveoli is
104 mm Hg
This steep gradient allows oxygen partial pressures
to rapidly reach equilibrium (in 0.25 seconds), and
thus blood can move three times as quickly (0.75
seconds) through the pulmonary capillary and still
be adequately oxygenated
Chapter 22, Respiratory System
87
Partial Pressure Gradients and Gas
Solubilities
Although carbon dioxide has a lower partial pressure
gradient:
It is 20 times more soluble in plasma than oxygen
It diffuses in equal amounts with oxygen
Chapter 22, Respiratory System
88
Partial Pressure Gradients
Chapter 22, Respiratory System
Figure
22.17
89
Chapter 22, Respiratory System
90
Oxygenation of Blood
Chapter 22, Respiratory System
91
Figure 22.18
Ventilation-Perfusion Coupling
Ventilation – the amount of gas reaching the alveoli
Perfusion – the blood flow reaching the alveoli
Ventilation and perfusion must be tightly regulated
for efficient gas exchange
Changes in PCO2 in the alveoli cause changes in the
diameters of the bronchioles
Passageways servicing areas where alveolar carbon
dioxide is high dilate
Those serving areas where alveolar carbon dioxide
is low constrict
Chapter 22, Respiratory System
92
Ventilation-Perfusion Coupling
Chapter 22, Respiratory System
93
Figure 22.19
Surface Area and Thickness of the Respiratory
Membrane
Respiratory membranes:
Are only 0.5 to 1 m thick, allowing for efficient
gas exchange
Have a total surface area (in males) of about 60 m2
(40 times that of one’s skin)
Thicken if lungs become waterlogged and
edematous, whereby gas exchange is inadequate
and oxygen deprivation results
Decrease in surface area with emphysema, when
walls of adjacent alveoli break through
Chapter 22, Respiratory System
94
Internal Respiration
The factors promoting gas exchange between
systemic capillaries and tissue cells are the same as
those acting in the lungs
The partial pressures and diffusion gradients are
reversed
PO2 in tissue is always lower than in systemic
arterial blood
PO2 of venous blood draining tissues is 40 mm Hg
and PCO2 is 45 mm Hg
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Chapter 22, Respiratory System
95
Oxygen Transport
Molecular oxygen is carried in the blood:
Bound to hemoglobin (Hb) within red blood cells
Dissolved in plasma
Chapter 22, Respiratory System
96
Oxygen Transport: Role of Hemoglobin
Each Hb molecule binds four oxygen atoms in a
rapid and reversible process
The hemoglobin-oxygen combination is called
oxyhemoglobin (HbO2)
Hemoglobin that has released oxygen is called
reduced hemoglobin (HHb)
Lungs
HbO2 + H+
HHb + O2
Tissues
Chapter 22, Respiratory System
97
Hemoglobin (Hb)
Saturated hemoglobin – when all four hemes of the
molecule are bound to oxygen
Partially saturated hemoglobin – when one to three
hemes are bound to oxygen
The rate that hemoglobin binds and releases oxygen
is regulated by:
PO2, temperature, blood pH, PCO2, and the
concentration of BPG (an organic chemical)
These factors ensure adequate delivery of
oxygen to tissue cells
Chapter 22, Respiratory System
98
Influence of PO2 on Hemoglobin Saturation
Hemoglobin saturation plotted against PO2 produces
a oxygen-hemoglobin dissociation curve
98% saturated arterial blood contains 20 ml oxygen
per 100 ml blood (20 vol %)
As arterial blood flows through capillaries, 5 ml
oxygen are released
The saturation of hemoglobin in arterial blood
explains why breathing deeply increases the PO2 but
has little effect on oxygen saturation in hemoglobin
Chapter 22, Respiratory System
99
Hemoglobin Saturation Curve
Hemoglobin is almost completely saturated at a PO2
of 70 mm Hg
Further increases in PO2 produce only small
increases in oxygen binding
Oxygen loading and delivery to tissue is adequate
when PO2 is below normal levels
Chapter 22, Respiratory System
100
Hemoglobin Saturation Curve
Only 20–25% of bound oxygen is unloaded during
one systemic circulation
If oxygen levels in tissues drop:
More oxygen dissociates from hemoglobin and is
used by cells
Respiratory rate or cardiac output need not increase
Chapter 22, Respiratory System
101
Hemoglobin Saturation Curve
Chapter 22, Respiratory System
102
Figure 22.20
Other Factors Influencing Hemoglobin
Saturation
Temperature, H+, PCO2, and BPG
Modify the structure of hemoglobin and alter its
affinity for oxygen
Increases of these factors:
Decrease hemoglobin’s affinity for oxygen
Enhance oxygen unloading from the blood
Decreases act in the opposite manner
These parameters are all high in systemic capillaries
where oxygen unloading is the goal
Chapter 22, Respiratory System
103
Factors That Increase Release of Oxygen by
Hemoglobin
As cells metabolize glucose, carbon dioxide is
released into the blood causing:
Increases in PCO2 and H+ concentration in capillary
blood
Declining pH (acidosis), which weakens the
hemoglobin-oxygen bond (Bohr effect)
Metabolizing cells have heat as a byproduct and the
rise in temperature increases BPG synthesis
All these factors ensure oxygen unloading in the
vicinity of working tissue cells
Chapter 22, Respiratory System
104
Hemoglobin and Oxygen Partial Pressure
Blood is almost fully saturated
at pO2 of 60mm
people OK at high
altitudes & with some
disease
Between 40 & 20 mm Hg, large
amounts of O2 are released
as in areas of need like
contracting muscle
muscle
tissues
lungs
Chapter 22, Respiratory System
105
pCO2 & Oxygen Release
As pCO2 rises with
exercise, O2 is released
more easily
CO2 converts to carbonic
acid & becomes H+ and
bicarbonate ions &
lowers pH.
Chapter 22, Respiratory System
106
Acidity & Oxygen Affinity for Hb
As H+ increases (decrease
in pH), O2 affinity for
Hb decreases
Bohr effect allows the blood
to unload oxygen
H+ binds to hemoglobin &
alters it
O2 left behind in needy
tissues
Chapter 22, Respiratory System
107
Temperature & Oxygen Release
As temperature
increases, more O2 is
released
Metabolic activity &
heat increases
Chapter 22, Respiratory System
108
Hemoglobin-Nitric Oxide Partnership
Nitric oxide (NO) is a vasodilator that plays a role in
blood pressure regulation
Hemoglobin is a vasoconstrictor and a nitric oxide
scavenger (heme destroys NO)
However, as oxygen binds to hemoglobin:
Nitric oxide binds to a cysteine amino acid on
hemoglobin
Bound nitric oxide is protected from degradation by
hemoglobin’s iron
Chapter 22, Respiratory System
109
Hemoglobin-Nitric Oxide Partnership
The hemoglobin is released as oxygen is unloaded,
causing vasodilation
As deoxygenated hemoglobin picks up carbon
dioxide, it also binds nitric oxide and carries these
gases to the lungs for unloading
Chapter 22, Respiratory System
110
Carbon Dioxide Transport
Carbon dioxide is transported in the blood in three
forms
Dissolved in plasma – 7 to 10%
Chemically bound to hemoglobin – 20% is carried
in RBCs as carbaminohemoglobin
Bicarbonate ion in plasma – 70% is transported as
bicarbonate (HCO3–)
Chapter 22, Respiratory System
111
Transport and Exchange of Carbon Dioxide
Carbon dioxide diffuses into RBCs and combines
with water to form carbonic acid (H2CO3), which
quickly dissociates into hydrogen ions and
bicarbonate ions
CO2
Carbon
dioxide
+
H2O
Water
H2CO3
Carbonic
acid
H+
Hydrogen
ion
+
HCO3–
Bicarbonate
ion
In RBCs, carbonic anhydrase reversibly catalyzes
the conversion of carbon dioxide and water to
carbonic acid
Chapter 22, Respiratory System
112
Transport and Exchange of Carbon Dioxide
Chapter 22, Respiratory System
Figure
22.22a
113
Transport and Exchange of Carbon Dioxide
At the tissues:
Bicarbonate quickly diffuses from RBCs into the
plasma
The chloride shift – to counterbalance the outrush
of negative bicarbonate ions from the RBCs,
chloride ions (Cl–) move from the plasma into the
erythrocytes
Chapter 22, Respiratory System
114
Transport and Exchange of Carbon Dioxide
At the lungs, these processes are reversed
Bicarbonate ions move into the RBCs and bind
with hydrogen ions to form carbonic acid
Carbonic acid is then split by carbonic anhydrase to
release carbon dioxide and water
Carbon dioxide then diffuses from the blood into
the alveoli
Chapter 22, Respiratory System
115
Transport and Exchange of Carbon Dioxide
Chapter 22, Respiratory System
Figure
22.22b
116
Haldane Effect
The amount of carbon dioxide transported is
markedly affected by the PO2
Haldane effect – the lower the PO2 and hemoglobin
saturation with oxygen, the more carbon dioxide can
be carried in the blood
Chapter 22, Respiratory System
117
Haldane Effect
At the tissues, as more carbon dioxide enters the
blood:
More oxygen dissociates from hemoglobin (Bohr
effect)
More carbon dioxide combines with hemoglobin,
and more bicarbonate ions are formed
This situation is reversed in pulmonary circulation
Chapter 22, Respiratory System
118
Haldane Effect
Chapter 22, Respiratory System
Figure
22.23
119
Influence of Carbon Dioxide on Blood pH
The carbonic acid–bicarbonate buffer system resists
blood pH changes
If hydrogen ion concentrations in blood begin to
rise, excess H+ is removed by combining with
HCO3–
If hydrogen ion concentrations begin to drop,
carbonic acid dissociates, releasing H+
Chapter 22, Respiratory System
120
Influence of Carbon Dioxide on Blood pH
Changes in respiratory rate can also:
Alter blood pH
Provide a fast-acting system to adjust pH when it
is disturbed by metabolic factors
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Chapter 22, Respiratory System
121
Control of Respiration:
Medullary Respiratory Centers
The dorsal respiratory group (DRG), or inspiratory
center:
Is located near the root of nerve IX
Appears to be the pacesetting respiratory center
Excites the inspiratory muscles and sets eupnea
(12-15 breaths/minute)
Becomes dormant during expiration
The ventral respiratory group (VRG) is involved in
forced inspiration and expiration
Chapter 22, Respiratory System
122
Control of Respiration:
Medullary Respiratory Centers
Chapter 22, Respiratory System
Figure
22.24
123
Control of Respiration:
Pons Respiratory Centers
Pons centers:
Influence and modify activity of the medullary
centers
Smooth out inspiration and expiration transitions
and vice versa
The pontine respiratory group (PRG) – continuously
inhibits the inspiration center
Chapter 22, Respiratory System
124
Respiratory Rhythm
A result of reciprocal inhibition of the
interconnected neuronal networks in the medulla
Other theories include
Inspiratory neurons are pacemakers and have
intrinsic automaticity and rhythmicity
Stretch receptors in the lungs establish respiratory
rhythm
Chapter 22, Respiratory System
125
Depth and Rate of Breathing
Inspiratory depth is determined by how actively the
respiratory center stimulates the respiratory muscles
Rate of respiration is determined by how long the
inspiratory center is active
Respiratory centers in the pons and medulla are
sensitive to both excitatory and inhibitory stimuli
Chapter 22, Respiratory System
126
Medullary Respiratory Centers
Chapter 22, Respiratory System
Figure
22.25
127
Depth and Rate of Breathing: Reflexes
Pulmonary irritant reflexes – irritants promote
reflexive constriction of air passages
Inflation reflex (Hering-Breuer) – stretch receptors
in the lungs are stimulated by lung inflation
Upon inflation, inhibitory signals are sent to the
medullary inspiration center to end inhalation and
allow expiration
Chapter 22, Respiratory System
128
Depth and Rate of Breathing: Higher Brain
Centers
Hypothalamic controls act through the limbic
system to modify rate and depth of respiration
Example: breath holding that occurs in anger
A rise in body temperature acts to increase
respiratory rate
Cortical controls are direct signals from the cerebral
motor cortex that bypass medullary controls
Examples: voluntary breath holding, taking a deep
breath
Chapter 22, Respiratory System
129
Depth and Rate of Breathing: PCO2
Changing PCO2 levels are monitored by
chemoreceptors of the brain stem
Carbon dioxide in the blood diffuses into the
cerebrospinal fluid where it is hydrated
Resulting carbonic acid dissociates, releasing
hydrogen ions
PCO2 levels rise (hypercapnia) resulting in increased
depth and rate of breathing
Chapter 22, Respiratory System
130
Depth and Rate of Breathing: PCO2
Chapter 22, Respiratory System
Figure
22.26
131
Depth and Rate of Breathing: PCO2
Hyperventilation – increased depth and rate of
breathing that:
Quickly flushes carbon dioxide from the blood
Occurs in response to hypercapnia
Though a rise CO2 acts as the original stimulus,
control of breathing at rest is regulated by the
hydrogen ion concentration in the brain
Chapter 22, Respiratory System
132
Depth and Rate of Breathing: PCO2
Hypoventilation – slow and shallow breathing due to
abnormally low PCO2 levels
Apnea (breathing cessation) may occur until PCO2
levels rise
Chapter 22, Respiratory System
133
Depth and Rate of Breathing: PCO2
Arterial oxygen levels are monitored by the aortic
and carotid bodies
Substantial drops in arterial PO2 (to 60 mm Hg) are
needed before oxygen levels become a major
stimulus for increased ventilation
If carbon dioxide is not removed (e.g., as in
emphysema and chronic bronchitis), chemoreceptors
become unresponsive to PCO2 chemical stimuli
In such cases, PO2 levels become the principal
respiratory stimulus (hypoxic drive)
Chapter 22, Respiratory System
134
Depth and Rate of Breathing: Arterial pH
Changes in arterial pH can modify respiratory rate
even if carbon dioxide and oxygen levels are normal
Increased ventilation in response to falling pH is
mediated by peripheral chemoreceptors
Chapter 22, Respiratory System
135
Peripheral Chemoreceptors
Chapter 22, Respiratory System
Figure
22.27
136
Depth and Rate of Breathing: Arterial pH
Acidosis may reflect:
Carbon dioxide retention
Accumulation of lactic acid
Excess fatty acids in patients with diabetes mellitus
Respiratory system controls will attempt to raise the
pH by increasing respiratory rate and depth
Chapter 22, Respiratory System
137
Respiratory Adjustments: Exercise
Respiratory adjustments are geared to both the
intensity and duration of exercise
During vigorous exercise:
Ventilation can increase 20 fold
Breathing becomes deeper and more vigorous, but
respiratory rate may not be significantly changed
(hyperpnea)
Exercise-enhanced breathing is not prompted by an
increase in PCO2 or a decrease in PO2 or pH
These levels remain surprisingly constant during
exercise
Chapter 22, Respiratory System
138
Respiratory Adjustments: Exercise
As exercise begins:
Ventilation increases abruptly, rises slowly, and
reaches a steady state
When exercise stops:
Ventilation declines suddenly, then gradually
decreases to normal
Chapter 22, Respiratory System
139
Respiratory Adjustments: Exercise
Neural factors bring about the above changes,
including:
Psychic stimuli
Cortical motor activation
Excitatory impulses from proprioceptors in muscles
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Chapter 22, Respiratory System
140
Respiratory Adjustments: High Altitude
The body responds to quick movement to high
altitude (above 8000 ft) with symptoms of acute
mountain sickness – headache, shortness of breath,
nausea, and dizziness
Chapter 22, Respiratory System
141
Respiratory Adjustments: High Altitude
Acclimatization – respiratory and hematopoietic
adjustments to altitude include:
Increased ventilation – 2-3 L/min higher than at sea
level
Chemoreceptors become more responsive to PCO2
Substantial decline in PO2 stimulates peripheral
chemoreceptors
Chapter 22, Respiratory System
142
Pneumothorax
Pleural cavities are sealed
cavities not open to the
outside
Injuries to the chest wall
that let air enter the
intrapleural space
causes a pneumothorax
collapsed lung on same
side as injury
surface tension and recoil
of elastic fibers causes
the lung to collapse
Chapter 22, Respiratory System
143
Smokers Lowered Respiratory Efficiency
Smoker is easily “winded” with moderate exercise
nicotine constricts terminal bronchioles
carbon monoxide in smoke binds to hemoglobin
irritants in smoke cause excess mucus secretion
irritants inhibit movements of cilia
in time destroys elastic fibers in lungs & leads to emphysema
trapping of air in alveoli & reduced gas exchange
Every thirteen seconds someone dies from a smoking-related
disease.
Chapter 22, Respiratory System
144
Chapter 22, Respiratory System
145
Chapter 22, Respiratory System
146
Chronic Obstructive Pulmonary Disease
(COPD)
Exemplified by chronic bronchitis and obstructive
emphysema
Patients have a history of:
Smoking
Dyspnea, where labored breathing occurs and gets
progressively worse
Coughing and frequent pulmonary infections
COPD victims develop respiratory failure
accompanied by hypoxemia, carbon dioxide
retention, and respiratory acidosis
Chapter 22, Respiratory System
147
Chronic Obstructive Pulmonary Disease
progressive airflow limitations
caused by an abnormal
inflammatory reaction to the
chronic inhalation
of particles
chronic bronchitis and emphysema
Signs of COPD are consequences of
the anatomical changes caused by
the disease:
barrel chest
pursed-lip breathing
productive cough
cyanosis.
Chapter 22, Respiratory System
148
Pathogenesis of COPD
Chapter 22, Respiratory System
Figure
22.28
149
Asthma
Characterized by dyspnea, wheezing, and chest
tightness
Active inflammation of the airways precedes
bronchospasms
Airway inflammation is an immune response caused
by release of IL-4 and IL-5, which stimulate IgE and
recruit inflammatory cells
Airways thickened with inflammatory exudates
magnify the effect of bronchospasms
Chapter 22, Respiratory System
150
Tuberculosis
Infectious disease caused by the bacterium
Mycobacterium tuberculosis
Symptoms include fever, night sweats, weight loss, a
racking cough, and splitting headache
Treatment entails a 12-month course of antibiotics
Chapter 22, Respiratory System
151
Lung Cancer
Accounts for 1/3 of all cancer deaths in the U.S.
90% of all patients with lung cancer were smokers
The three most common types are:
Squamous cell carcinoma (20-40% of cases) arises
in bronchial epithelium
Adenocarcinoma (25-35% of cases) originates in
peripheral lung area
Small cell carcinoma (20-25% of cases) contains
lymphocyte-like cells that originate in the primary
bronchi and subsequently metastasize
Chapter 22, Respiratory System
152
Developmental Aspects
Olfactory placodes invaginate into olfactory pits by
the 4th week
Laryngotracheal buds are present by the 5th week
Mucosae of the bronchi and lung alveoli are present
by the 8th week
By the 28th week, a baby born prematurely can
breathe on its own
During fetal life, the lungs are filled with fluid and
blood bypasses the lungs
Gas exchange takes place via the placenta
Chapter 22, Respiratory System
153
Respiratory System Development
Chapter 22, Respiratory System
154
Figure 22.29
Developmental Aspects
At birth, respiratory centers are activated, alveoli
inflate, and lungs begin to function
Respiratory rate is highest in newborns and slows
until adulthood
Lungs continue to mature and more alveoli are
formed until young adulthood
Respiratory efficiency decreases in old age
Chapter 22, Respiratory System
155