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
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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
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Respiratory System
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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
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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
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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
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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
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Structure of the Nose
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Figure 22.2a
Structure of the Nose
Chapter 22, Respiratory System
Figure
22.2b
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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
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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
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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
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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
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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
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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
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Framework of the Larynx
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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
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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
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Movements of Vocal Cords
Chapter 22, Respiratory System
Figure
22.5
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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
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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
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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
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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
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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
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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
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Respiratory Zone
Chapter 22, Respiratory System
Figure
22.8b
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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
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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
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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
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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
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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
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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
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Breathing
 Breathing, or pulmonary ventilation, consists of two
phases
 Inspiration – air flows into the lungs
 Expiration – gases exit the lungs
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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
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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
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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
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Pressure Relationships
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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)
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Factors That Diminish Lung Compliance
 Examples include:
 Deformities of thorax
 Ossification of the costal cartilage
 Paralysis of intercostal muscles
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The Respiratory System
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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)
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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
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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
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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
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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
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Nonrespiratory Air Movements
 Most result from reflex action
 Examples include: coughing, sneezing, crying,
laughing, hiccupping, and yawning
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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
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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
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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
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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
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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
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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
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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
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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
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Partial Pressure Gradients
Chapter 22, Respiratory System
Figure
22.17
89
Chapter 22, Respiratory System
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Oxygenation of Blood
Chapter 22, Respiratory System
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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
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Ventilation-Perfusion Coupling
Chapter 22, Respiratory System
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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
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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
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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
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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
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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