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4/23/13
Functions
Respiratory System
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Keri Muma
Bio 6
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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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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
Respiratory Pressures
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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Respiratory pressures are described relative
to atmospheric pressure @ sea level
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Patm = 760 mm Hg
Negative pressure: -1mm Hg = 759 mm Hg
Positive pressure: + 1 mm Hg = 761 mm Hg
0 mm Hg = 760 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
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
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
Boyle’s law – the relationship between the
pressure and volume of gases
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P1V1 = P2V2
P = pressure of a gas in mm Hg
V = volume of a gas in cubic millimeters
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Respiratory Pressures
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Intrapulmonary pressure and
intrapleural pressure fluctuate
with the phases of breathing
Phases of Ventilation
Two phases
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Inspiration – flow of air into
lung
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Expiration – air leaving
lung
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Events of Inspiration
Factors Effecting Ventilation
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Lung Compliance - the ease with which the lungs
can be expanded
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Reduced by factors that produce resistance to
distension of the lung tissue and surrounding
thoracic cage
Reduced by pulmonary edema, fibrosis, surface
tension of the alveoli
Intrapulmonary P decreases
as thoracic cavity expands;
air moves in
Intrapulmonary P increases
as lungs recoil; air moves out
Events of Expiration
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
Elasticity – how readily the lungs recoil after
stretching
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Elastic CT and surface tension of the alveoli
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Factors Affecting Ventilation
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Airway Resistance
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:
F=
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Affected by:
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ΔP
R
Autonomic Nervous System – controls diameter of
bronchioles
  Sympathetic
– bronchodilation decreases resistance
– bronchoconstriction increases resistance
  Parasympathetic
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Chronic Obstructive Pulmonary Diseases: asthma,
bronchitis, emphysema
Testing Respiratory Function
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Respiratory capacities are measured with a
spirometer
Spirometer – an instrument consisting of a hollow
bell inverted over water, used to evaluate respiratory
function
Spirometry can distinguish between:
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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)
Obstructive pulmonary disease – increased airway
resistance
Restrictive disorders – reduction in lung compliance and
capacity from structural or functional lung changes
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)
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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
Air that actually reaches the respiratory zone ~350
ml
Respiratory Capacities
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Functional volume
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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)
Testing Respiratory Function
Vital capacity (VC) – the total amount of
exchangeable air (TV + IRV + ERV)
Total lung capacity (TLC) – sum of all lung
volumes (approximately 6000 ml)
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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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Testing Respiratory Function
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Restrictive vs. Obstructive diseases
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Obstructive disease - increase in RV, decrease in
ERV
Restrictive disease -reduction in VC, TLC, and IRV
(respiratory rate X tidal volume)
Example: 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
External Respiration
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External respiration – gas exchange between
pulmonary blood 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
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External Respiration
Dalton’s Law – partial pressure gradients
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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
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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
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
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
Factors Influencing External Respiration
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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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
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Factors Influencing External Respiration
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Ventilation and perfusion are matched for
efficient gas exchange
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Local Controls of Ventilation & Perfusion
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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When alveolar CO2 is high and O2 is low: Bronchioles will
dilate and arterioles constrict
When alveolar CO2 is low and O2 is high: Bronchioles will
constrict and arterioles will dilate
Local Controls of Ventilation & Perfusion
Factors Influencing External Respiration
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Structural characteristics of the respiratory
membrane:
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Pathological conditions that reduce
ventilation and gas exchange
Are only 0.5 to 1 µm 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
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
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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?
Factors Affecting Saturation of Hemoglobin
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Increases in the following factors decreases
hemoglobin’s affinity for oxygen
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Factors Affecting Saturation of Hemoglobin
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
Temperature
H+ (acidity)
PCO2,
2,3-biphosphoglycerate (BPG) (a.k.a diphosphoglycerate)
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
Summary of factors contributing to total
oxygen content of arterial 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–)
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Transport 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
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Exchange of Carbon Dioxide
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At the tissues:
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Exchange of Carbon Dioxide
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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
Gas Transport in the Blood
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
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
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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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Depth and Rate of Breathing
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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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Three chemical factors affecting ventilation:
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Example: breath holding that occurs in anger,
hyperventilation from anxiety
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PCO2 Levels
A rise in PCO2 levels
(hypercapnia) increases
ventilation
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Changing PCO2 levels are
monitored by 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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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
Carbon dioxide levels- main regulatory chemical for
respiration
  ↑ CO2 = ↓ blood pH
  Increased CO2 increases respiration
  Changes in CO2 act on central chemoreceptors 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
Quickly flushes carbon dioxide from the blood
Occurs in response to hypercapnia
PO2 Levels
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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)
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Arterial pH Levels
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Arterial pH Levels
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
Acidosis may reflect:
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Carbon dioxide retention
Accumulation of lactic acid
Excess fatty acid metabolism in patients with
diabetes mellitus
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Respiratory system controls will attempt to raise
the pH by increasing respiratory rate and depth
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Depth and Rate of Breathing: Reflexes
Depth and Rate of Breathing
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Other 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
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Respiratory Adjustments: High Altitude
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 in response to
low PO2
High-altitude cerebral edema – increased cerebral
blood flow and permeability of cerebral endothelium
when expose to hypoxia
Upon inflation, inhibitory signals are sent to the
medullary inspiration center to end inhalation and
allow expiration
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Acclimatization to the 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)
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