Respiratory System
Chapter 13
Learning Objectives
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Identify the organs of the respiratory system & general
function of each.
Compare the volumes & capacities of air exchanged during
ventilation.
Explain the following gas principles: Dalton’s Law, Boyle’s
Law and Henry’s Law.
Explain how blood transports both oxygen & carbon dioxide.
Describe the factors that affect the binding of hemoglobin &
oxygen.
Compare & contrast the roles of peripheral and central
chemoreceptors in the regulation of respiration.
Functions
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Gas exchange – between the external
environment and the blood
Filters, humidifies, and warms inspired air
Production of sound
Smell
Maintains pH homeostasis
Anatomy Review
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Nose
Pharynx
Larynx
Trachea
Bronchi
Bronchioles
Alveolar ducts
Alveoli
Anatomy Review
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Respiratory Membrane
 Site of gas exchange between the alveoli and the
blood
 Formed by the alveolar wall and the capillary wall
Anatomy Review
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Pleural Sac – double walled membrane surrounding
the lungs
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Visceral pleura - covers the lung surface
Parietal pleura - lines the walls of the thoracic cavity
Pleural fluid fills the area between layers to allow gliding
and resist separation
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↑ pleura → ↑ pressure → lung collapse
↓ pleura → ↑ friction
Respiratory Pressures
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Respiratory pressures are described relative
to atmospheric pressure @ sea level
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Patm = 760 mm Hg
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OR

0 mm Hg = 760 mm Hg
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Negative pressure: -1mm Hg = 759 mm Hg
Positive pressure: + 1 mm Hg = 761 mm Hg
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Respiratory Pressures
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Intrapulmonary pressure (Ppul) – pressure within
the alveoli
Intrapleural pressure (Pip) – pressure within the
pleural cavity
Respiratory Pressures
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Transpulmonary pressure – difference between
the intrapulmonary and intrapleural pressures
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Intrapleural pressure is always less than
intrapulmonary pressure ( -4 mmHg )
Keeps the airways open
Pneumothorax (puncture in
lung wall)
tabbed chest wound, outside air travels in
Ex: edema due to bleeding or fluid build
air from lung travels into pleural cavity
Events of Respiration
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Pulmonary
ventilation
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External respiration
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Gas transport
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Internal respiration
Pulmonary Ventilation
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Pulmonary ventilation – moving air in and out
of the lungs
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Mechanical process that depends on volume
changes in the thoracic cavity
Caused by the contraction/relaxation of intercostal
muscles and the diaphragm
∆ Volume → ∆ Pressure → flow of gases
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Boyle’s law – the relationship between the
pressure and volume of gases
P1V1 = P2V2
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P = pressure of a gas in mm Hg
V = volume of a gas in cubic millimeters
Respiratory Pressures
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Intrapulmonary pressure and
intrapleural pressure fluctuate
with the phases of breathing
Phases of Ventilation
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Two phases
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Inspiration – flow of air into
lung
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Intrapulmonary P decreases
as thoracic cavity expands;
air moves in
Expiration – air leaving
lung
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Intrapulmonary P increases
as lungs recoil; air moves out
Events of Inspiration
Events of Expiration
Factors Affecting Ventilation
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Lung Compliance - the ease with which the lungs
can be expanded
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Elasticity – how readily the lungs recoil after stretch
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Reduced by factors that decease distension of the
lung tissue and surrounding thoracic cage
Reduced by pulmonary edema, fibrosis (scar tissue),
surface tension of the alveoli
Elastic CT and surface tension of the alveoli
Compliance vs. Elasticity
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Ex: Plastic bag vs. Balloon
Factors Affecting Ventilation
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Surface tension
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The attraction of liquid molecules to one another in the
alveolus
The liquid coating 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
Factors Affecting Ventilation
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Airway Resistance
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Friction is the major source of resistance to airflow
The relationship between flow (F), pressure (P), and
resistance (R) is:
Affected by:
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P
F=
R
Autonomic Nervous System – controls diameter of
bronchioles
Sympathetic – bronchodilation decreases resistance
 Parasympathetic – bronchoconstriction increases resistance
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Chronic Obstructive Pulmonary Diseases: asthma,
bronchitis, emphysema
Airway Resistance Example
Normal breathing
COPD- intrapleural pressure
closes off already blocked small
airways
Testing Respiratory Function
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Spirometer – an instrument consisting of a hollow
bell inverted over water, used to evaluate respiratory
function
Spirometry can distinguish between:
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Obstructive pulmonary disease – increased airway
resistance
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Difficulty exhaling
Restrictive disorders – reduction in lung compliance and
capacity from structural or functional lung changes
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Difficulty inhaling
Respiratory Volumes
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Tidal volume (TV) – air that moves into and out
of the lungs during normal breathing (~ 500 ml)
Inspiratory reserve volume (IRV) – air that can
be inspired forcibly beyond the tidal volume
(2100–3200 ml)
Respiratory Volumes
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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)
Respiratory Volumes
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Dead space volume
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Air that remains in conducting zone and never
reaches alveoli ~150 ml
Functional volume
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Air that actually reaches the respiratory zone
~350 ml
Respiratory Capacities
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Inspiratory capacity (IC) – total amount of air that
can be inspired after a tidal expiration (IRV + TV)
Expiratory capacity (EC) - total amount of air that
can be expired after a tidal inspiration (ERV + TV)
Functional residual capacity (FRC) – amount of
air remaining in the lungs after a tidal expiration (RV
+ ERV)
Respiratory Capacities
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Vital capacity (VC) – the total amount of
exchangeable air (TV + IRV + ERV)
Total lung capacity (TLC) – sum of all lung
volumes (approximately 6000 ml) (VC + RV)
Testing Respiratory Function
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Total ventilation – total amount of gas flow
into or out of the respiratory tract in one
minute
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(respiratory rate X tidal volume)
Ex: 12 breaths/min X 500 mL/breath =
6000mL/min
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
Testing Respiratory Function
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Obstructive vs. Restrictive diseases
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Obstructive disease - increase in RV, decrease in
ERV
Restrictive disease -reduction in VC, TLC, and IRV
External Respiration
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External respiration – gas exchange between
pulmonary capillaries and alveoli across the
respiratory membrane
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Oxygen movement from the alveoli into the blood
Carbon dioxide movement out of the blood into the alveoli
External Respiration
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Factors influencing the movement of oxygen
and carbon dioxide across the respiratory
membrane
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Partial pressure gradients and gas solubility
Matching of alveolar ventilation and pulmonary
blood perfusion
Structural characteristics of the respiratory
membrane
Dalton’s Law – partial pressure
gradients
Total pressure exerted by a mixture of gases is the
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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
Percent
Partial Pressure
78% Nitrogen =
593 mmHg
21% Oxygen=
160 mmHg
0.9% Carbon Dioxide = 7 mmHg
Factors Influencing External
Respiration
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Partial Pressure Gradients
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Oxygen movement into the blood from the alveoli
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The alveoli have a higher PO2 than the blood
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Oxygen moves by diffusion towards the area of lower
partial pressure
Carbon dioxide movement out of the blood to the
alveoli
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Blood returning from tissues has a higher PCO2 than the
air in the alveoli
Henry’s Law – gas solubility
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Gas will dissolve into 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:
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Carbon dioxide is the most soluble; 20X more soluble
than oxygen
Nitrogen is practically insoluble in plasma
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Factors Influencing External
Respiration
Hemoglobin acts
as a “storage depot” for O2 by
removing it from the plasma as soon as it is
dissolved
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This keeps the plasma’s PO2 low and prolongs the
partial pressure gradient between the plasma and the
alveoli
Leads to a large net transfer of O2
Factors Influencing External
Respiration
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Ventilation and perfusion are matched for efficient
gas exchange
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Ventilation – the amount of gas reaching the alveoli
Perfusion – the blood flow reaching the alveoli
Changes in PCO2 and PO2 in the alveoli cause local
changes:
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Poor ventilation
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Alveolar CO2 is high and O2 is low: Bronchioles will dilate and arterioles
constrict
Poor perfusion
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Alveolar CO2 is low and O2 is high: Bronchioles will constrict and
arterioles will dilate
Local Controls of Ventilation &
Perfusion
Factors Influencing External
Respiration
 Structural characteristics of the respiratory
membrane:
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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)
Thickening causes gas exchange to be inadequate:
inflammation, edema, mucus, fibrosis
Decrease in surface area with emphysema, when
walls of adjacent alveoli breakdown
Pathological conditions that
reduce ventilation and gas
exchange
Gas Transport in the Blood
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Oxygen transport in the blood
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98% of oxygen is transported attached to hemoglobin
(oxyhemoglobin [HbO2])
A small amount is carried dissolved in the plasma (~2%)
Each Hb molecule binds four
oxygen atoms in a rapid and
reversible process
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Hemoglobin
Saturation/Dissociation
Curve
The
% hemoglobin
saturation depends on the
PO2 of the blood
In the alveoli – 98%
saturation
In the tissues - ~75%
saturation
In an exercising muscle
the PO2 equals ~ 20
mmHg
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What would be the %
saturation of Hb?
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Factors Affecting Saturation of
Hemoglobin
Increases in the following factors decreases
hemoglobin’s affinity for oxygen
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Temperature
H+
PCO2
2,3-diphosphoglycerate (DPG) (byproduct of glycolysis)
These factors modify the structure of hemoglobin and
alter its affinity for oxygen and enhances oxygen
unloading from Hb
These parameters are higher in systemic capillaries
supplying tissues, where oxygen unloading is the goal
Factors Affecting Saturation of
Hemoglobin
Summary of factors contributing
to total oxygen content of
arterial blood:
Internal Respiration
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Exchange of gases between blood and body
cells
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Oxygen diffuses from blood
into tissue
Carbon dioxide diffuses out
of tissue into blood
Gas Transport in the Blood
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Carbon dioxide is transported in the blood in
three forms:
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Dissolved in plasma – 7%
Bound to hemoglobin – 23% is carried in RBCs as
carbaminohemoglobin, at a different binding site
than oxygen
Most is carried as bicarbonate ions in plasma –
70% is transported as bicarbonate (HCO3–)
Transport of Carbon Dioxide
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Carbon dioxide diffuses into RBCs and combines with
water to form carbonic acid (H2CO3), which quickly
dissociates into hydrogen ions and bicarbonate ions
Exchange of Carbon Dioxide
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At the tissues:
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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
Exchange of Carbon Dioxide
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At the lungs, these processes are reversed
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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
Gas Transport in the Blood
Control of Respiration
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Medullary centers:
The dorsal respiratory group (DRG), or
inspiratory center:
 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 expiration
Control of Respiration
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Pons centers – pneumotaxic
and apneustic areas
 Influence and modify activity
of the medullary centers
 Smoothes out inspiration and
expiration transitions
Depth and Rate of Breathing
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Cortical controls are direct signals from the
cerebral motor cortex that bypass medullary
controls (conscious control)
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Examples: voluntary breath holding, taking a deep
breath
Hypothalamic controls act through the limbic
system to modify rate and depth of respiration
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Example: breath holding that occurs in anger,
hyperventilation from anxiety
Depth and Rate of Breathing
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Three chemical factors affecting ventilation:
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Carbon dioxide levels- main regulatory chemical for
respiration
 ↑ CO = ↓ blood pH
2
 Increased CO increases respiration
2
 Changes in CO act directly on central chemoreceptors
2
in the medulla oblongata
Oxygen levels
 Peripheral chemoreceptors in the aorta and carotid
artery detect oxygen concentration changes
 Information is sent to the medulla oblongata via the
vagus nerve
Arterial pH
PCO2 Levels
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A rise in PCO2 levels
(hypercapnia) increases
ventilation
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Changing PCO2 levels are
monitored by central
chemoreceptors of the medulla
Carbon dioxide in the blood
diffuses into the cerebrospinal
fluid where it is hydrated
Resulting carbonic acid
dissociates, releasing hydrogen
ions (decreases pH)
PCO2 Levels
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Hyperventilation – increased depth and rate of
breathing that:
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Occurs in response to hypercapnia
Quickly flushes carbon dioxide from the blood
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Acidosis- do not breath into bag so that you can
reduce CO2
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Anxiety- breath into bag to keep CO2
PCO2 Levels
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Hypoventilation – slow and shallow breathing
due to abnormally low PCO2 levels
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Apnea (breathing cessation) may occur until PCO2
levels rise
PO2 Levels
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Arterial oxygen levels are monitored by peripheral
chemoreceptors in the aortic and carotid bodies
Substantial drop in arterial PO2 (to 60 mm Hg) is 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)
Arterial pH Levels
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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 in the aorta and
carotid body
Arterial pH Levels
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Acidosis may reflect:
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Accumulation of lactic acid
Excess fatty acid metabolism in patients with
diabetes mellitus
Respiratory system controls will attempt to raise
the pH by increasing respiratory rate and depth
Depth and Rate of Breathing:
Reflexes
Depth and Rate of Breathing
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Other Reflexes
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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
Respiratory Adjustments
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High Altitude
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Quick movement to high altitude (above 8000 ft) can
cause symptoms of acute mountain sickness –
headache, shortness of breath, nausea, and dizziness
A more severe illness is high-altitude pulmonary edema
caused by high pulmonary arterial pressure from
constriction of pulmonary arteries (perfusion) in
response to low PO2
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High pressure causes bleeding into alveoli, cough up pink foam
High-altitude cerebral edema – increased cerebral
blood flow and permeability when hypoxic
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Increase BP in brain may lead to death
Respiratory Adjustments: High
Altitude
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Acclimation to hypoxia – respiratory and
hematopoietic adjustments to altitude include:
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Increased ventilation – 2-3 L/min higher than at sea
level
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Chemoreceptors become more responsive to PCO2

Substantial decline in PO2 stimulates peripheral
chemoreceptors
Kidneys accelerate production of erythropoietin
(slower response ~4 days)