Part 2: Respiratory Physiology
Transcript of Part 2: Respiratory Physiology
4/3/2016
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Respiratory System
Part 2: Respiratory Physiology
Respiration
• Exchange of gases between air and body
cells
• Three steps
1. Ventilation
2. External respiration
3. Internal respiration
Ventilation
• Pulmonary ventilation consists of two phases
1. Inspiration: gases flow into the lungs
2. Expiration: gases exit the lungs
• Relies on pressure gradients
– Atmosphere and alveoli
• Negative pressure breathing
– Thoracic pressures
– Atmospheric pressure
Boyle’s Law
• The relationship between the pressure and
volume of a fixed quantity of gas in a closed
container
• Pressure (P) varies inversely with volume (V):
P1V1 = P2V2
While one increases the other decreases
Ventilation
• Intrapleural pressure is subatmospheric
– Inward elastic recoil of lung tissue
– Outward elastic recoil of chest wallResting lung volume
Ventilation
• Atmospheric pressure (Patm)
– Pressure exerted by the air surrounding the body
– 760 mm Hg at sea level
• Thoracic pressures are described relative to Patm
– Negative respiratory pressure is less than Patm
– Positive respiratory pressure is greater than Patm
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Figure 22.12
Atmospheric pressure
Intrapleural
pressure
756 mm Hg
(–4 mm Hg)
Transpulmonary
pressure
760 mm Hg
–756 mm Hg
= 4 mm Hg
Thoracic wall
Diaphragm
LungIntrapulmonary
pressure 760 mm Hg
(0 mm Hg)
Parietal pleura
Pleural cavity
Visceral pleura
756
760
Ventilation
• Intrapulmonary (intra-alveolar) pressure (Ppul)
– Pressure in the alveoli
– Fluctuates with breathing
– Always eventually equalizes with Patm
Ventilation
• Intrapleural pressure (Pip):
– Pressure in the pleural cavity
– Fluctuates with breathing
– Always a negative pressure (<Patm and <Ppul)
Ventilation
• Negative Pip is caused by opposing forces
– Two inward forces promote lung collapse
• Elastic recoil of lungs decreases lung size
• Surface tension of alveolar fluid reduces alveolar size
– One outward force tends to enlarge the lungs
• Elasticity of the chest wall pulls the thorax outward
Pulmonary Ventilation
• Inspiration and expiration
• Mechanical processes that depend on volume changes in the
thoracic cavity
– Volume changes → pressure changes
– Pressure changes → pressure gradient → gases flow to
equalize pressure
Inspiration
• An active process
– Inspiratory muscles contract
• Thoracic volume increases
• Lungs are stretched and intrapulmonary volume
increases
– Intrapulmonary pressure drops
– Air flows into the lungs, down its pressure gradient
» Ppul = Patm
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Figure 22.13 (1 of 2)
Sequence of events
Changes in anterior-posterior and superior-
inferior dimensions
Changes in lateraldimensions
(superior view)
Ribs are elevatedand sternum flares
as external
intercostalscontract.
Diaphragmmoves inferiorly
during contraction.
Externalintercostalscontract.
Inspiratory muscles contract (diaphragm descends; rib cage rises).
2
1
Thoracic cavity volume increases.
3 Lungs are stretched; intrapulmonary volume increases.
4 Intrapulmonary pressure drops (to –1 mm Hg).
5 Air (gases) flows into lungs down its pressure gradient until intrapulmonary pressure is equal to atmospheric pressure
Question
• What part of the lung tissue expands during
inspiration?
Expiration
• Quiet expiration is normally a passive process
– Inspiratory muscles relax
• Thoracic cavity volume decreases
• Elastic lungs recoil and intrapulmonary volume decreases
– Ppul rises
• Air flows out of the lungs down its pressure gradient until Ppul = 0
Figure 22.13 (2 of 2)
Sequenceof events
Changes in anterior-posterior and superior-
inferior dimensions
Changes inlateral dimensions
(superior view)
Ribs and sternumare depressed
as external
intercostalsrelax.
Externalintercostalsrelax.
Diaphragmmovessuperiorly
as it relaxes.
1 Inspiratory muscles relax (diaphragm rises; rib cage descends due to recoil of costal cartilages).
2 Thoracic cavity volume decreases.
3 Elastic lungs recoil passively; intrapulmonary volume decreases.
4 Intrapulmonary pres-sure rises (to +1 mm Hg).
5 Air (gases) flows out of lungs down its pressure gradient until intra-pulmonary pressure is 0.
Figure 22.14
5 seconds elapsed
Volume of breath
Intrapulmonarypressure
Expiration
Intrapleuralpressure
Trans-pulmonarypressure
InspirationIntrapulmonary pressure. Pressure inside lung decreases as lung volume increases during inspiration; pressure increases during expiration.
Intrapleural pressure.Pleural cavity pressure becomes more negative as chest wall expands during inspiration. Returns to initial value as chest wall recoils.
Volume of breath.During each breath, the pressure gradients move 0.5 liter of air into and out of the lungs.
Air Flow
• Physical factors influencing efficiency of air flow
– Inspiratory muscles overcome three factors that hinder
air passage and pulmonary ventilation
1. Airway resistance
2. Alveolar surface tension
3. Lung compliance
NOTE: Study guide, Respiratory pg 10
6b. Friction is inversely proportional to airway diameter
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Air Flow
• Broncoconstriction
– Smooth muscle contracts
– Reduced air flow
Lung Compliance
• Measure of lung’s ability to stretch and expand
• Diminished by
– Nonelastic scar tissue (fibrosis)
– Reduced production of surfactant
– Decreased flexibility of the thoracic cage
• Emphysema/COPD is associated with increased
compliance
– Due to diminished elastic recoil – patient has no trouble filling lungs with air, but great effort is required for exhalation
Gas Laws
• Dalton’s Law of Partial Pressure
– Describes how a gas behaves when it is part of a mixture
• Partial pressure = pressure exerted by a single gas in the mixture = proportional to the percentage of gas in a mixture
• Total pressure exerted by a mixture of gases is the sum of the pressures exerted by each gas
Gas Laws
• Dalton’s Law of Partial Pressure
– Example:
• Air contains 20.9% O2
• Atmospheric Pressure = 760 mmHg
0.209 P o2 x 760 mmHg = 160 mmHg
= partial pressure of oxygen in the atmosphere
Gas Laws
• Fick’s Law of Diffusion– Gives the rate of diffusion for a given gas across a
membrane
– CO2 has a high diffusion coefficient and diffuses 20 times more rapidly across a membrane than O2
Vg = (A) (P1-P2) (D)
(T)
• A = membrane surface area
• P1-P2 = difference in partial pressures
• D = diffusion coefficient
• T = thickness of membrane
Gas Laws
• Diseases related to gas diffusion– Pulmonary edema
– COPD
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Gas Exchange
• External respiration
– Pulmonary gas exchange
• Internal respiration
– Gas exchange between blood capillaries and
tissues
External Respiration
• Exchange of O2 and CO2 across the respiratory
membrane
– Between lung and blood
Thought Question
• Can you think of some factors that might
influence the exchange of gases between the
lungs and the blood? Hint: remember Fick’s
Law?
External Respiration
• Respiratory membrane
– Site of gas exchange between lung and blood
• Not actually a membrane, but a collection of
associated structures
– Membrane of lung epithelium
– Pulmonary capillary membrane
– Surfactant
– Connective tissue
Figure 22.9c
Capillary
Type II (surfactant-
secreting) cell
Type I cell
of alveolar wall
Endothelial cell nucleus
Macrophage
Alveoli (gas-filled
air spaces)
Red blood cell
in capillary
Alveolar pores
Capillary
endothelium
Fused basement
membranes of the
alveolar epithelium
and the capillary
endothelium
Alveolar
epithelium
Respiratory
membrane
Red blood
cell
O2
Alveolus
CO2
Capillary
Alveolus
Nucleus of type I
(squamous
epithelial) cell
(c) Detailed anatomy of the respiratory membrane
External Respiration
• Partial pressure gradient for O2 in the lungs is
steep
– Venous blood pO2 = 40 mm Hg
– Alveolar pO2 = 104 mm Hg
Oxygen readily diffuses from alveoli to lung
capillaries
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External Respiration
• Partial pressure gradient for CO2 in the lungs
– Venous blood pCO2 = 45 mm Hg
– Alveolar pCO2 = 40 mm Hg
• But…
– CO2 is 20 times more soluble in plasma than
oxygen
– CO2 diffuses in equal amounts with oxygen!
Figure 22.19
Inspired air:
P 160 mm Hg
P 0.3 mm Hg
Blood leaving
lungs and
entering tissue
capillaries:
P 100 mm Hg
P 40 mm Hg
Alveoli of lungs:
P 104 mm Hg
P 40 mm HgO2
Heart
Blood leaving
tissues and
entering lungs:
P 40 mm Hg
P 45 mm Hg
Systemic
veins
Systemic
arteries
Tissues:
P less than 40 mm Hg
P greater than 45 mm Hg
Internal
respiration
External
respiration
Pulmonary
veins (P
100 mm Hg)
Pulmonary
arteries
CO2
O2
CO2
O2
CO2O2
CO2
O2
CO2
O2
Partial
pressure of
O2 in inspired
air is greater
than that of
blood
entering the
lungs
O2 flows out
of alveoli and
into
bloodstream
EXTERNAL
RESPIRATION
Figure 22.19
Inspired air:
P 160 mm Hg
P 0.3 mm Hg
Blood leaving
lungs and
entering tissue
capillaries:
P 100 mm Hg
P 40 mm Hg
Alveoli of lungs:
P 104 mm Hg
P 40 mm HgO2
Heart
Blood leaving
tissues and
entering lungs:
P 40 mm Hg
P 45 mm Hg
Systemic
veins
Systemic
arteries
Tissues:
P less than 40 mm Hg
P greater than 45 mm Hg
Internal
respiration
External
respiration
Pulmonary
veins (P
100 mm Hg)
Pulmonary
arteries
CO2
O2
CO2
O2
CO2O2
CO2
O2
CO2
O2
Partial
pressure of
CO2 in
inspired air is
less than that
of blood
entering the
lungs
CO2 flows out
of
bloodstream
and into
alveoli,
where it is
exhaled
EXTERNAL
RESPIRATION Factors Affecting External Respiration
Anatomical adaptations
• Moist surfaces
• Thickness and surface area
• Narrow capillaries = RBC’s single file
Physiological and physical factors
• Pulmonary disease
• Affect of drugs on minute volume
• Partial pressure changes with altitude
Internal Respiration
• Capillary gas exchange in body tissues
• Partial pressures and diffusion gradients are
reversed compared to external respiration
– pO2 in tissue is always lower than in systemic
arterial blood
– pCO2 in tissue is higher than in systemic arterial
blood
Figure 22.19
Inspired air:
P 160 mm Hg
P 0.3 mm Hg
Blood leaving
lungs and
entering tissue
capillaries:
P 100 mm Hg
P 40 mm Hg
Alveoli of lungs:
P 104 mm Hg
P 40 mm HgO2
Heart
Blood leaving
tissues and
entering lungs:
P 40 mm Hg
P 45 mm Hg
Systemic
veins
Systemic
arteries
Tissues:
P less than 40 mm Hg
P greater than 45 mm Hg
Internal
respiration
External
respiration
Pulmonary
veins (P
100 mm Hg)
Pulmonary
arteries
CO2
O2
CO2
O2
CO2O2
CO2
O2
CO2
O2
Partial
pressure of
O2 in
oxygenated
blood is
greater than
that of
tissues
O2 flows out
of
bloodstream
and into
tissues
INTERNAL
RESPIRATION
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Figure 22.19
Inspired air:
P 160 mm Hg
P 0.3 mm Hg
Blood leaving
lungs and
entering tissue
capillaries:
P 100 mm Hg
P 40 mm Hg
Alveoli of lungs:
P 104 mm Hg
P 40 mm HgO2
Heart
Blood leaving
tissues and
entering lungs:
P 40 mm Hg
P 45 mm Hg
Systemic
veins
Systemic
arteries
Tissues:
P less than 40 mm Hg
P greater than 45 mm Hg
Internal
respiration
External
respiration
Pulmonary
veins (P
100 mm Hg)
Pulmonary
arteries
CO2
O2
CO2
O2
CO2O2
CO2
O2
CO2
O2
Partial
pressure of
CO2 in
oxygenated
blood is less
than that of
tissues
CO2 flows out
of tissues
and into
bloodstream
INTERNAL
RESPIRATION Gas Transport (page 12)
• Oxygen (O2) transport
• Carbon dioxide (CO2) transport
O2 Transport
�Molecular O2 is carried in the blood
� Solubility in plasma low
� Few O2 = partial pressure
� Only 1.5% dissolved in plasma
� paO2 does not include O2 bound to hemoglobin
� Poor measure of total O2
O2 Transport
• Hemoglobin
– Bound O2 does not contribute to partial pressure
• Maintaining partial pressure gradient → diffusion
– 98.5% loosely bound to each Fe of hemoglobin
(Hb) in RBCs
• (4) O2 per hemoglobin
O2 Transport
• Oxyhemoglobin (HbO2)
– Hemoglobin-O2 combination
• Reduced hemoglobin (HHb)
– Hemoglobin that has released O2
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O2 Transport
• Loading and unloading of O2 is facilitated by
change in shape of Hb
– As O2 binds, Hb affinity for O2 increases
• 4 heme groups bound to O2
– Saturated
• 1, 2 or 3 heme groups bound to O2
– Partially saturated
• Measure of oxygen saturation = SO2
O2 Transport
• Rate of loading and unloading of O2 is
regulated by
– pO2
– Temperature
– Blood pH
– pCO2
– Products of metabolism
Modify hemoglobin shape
O2 Transport
• Factors that promote oxyhemoglobin formation
– ↑ pO2
– ↓ pCO2
Conditions found in the lungs promote O2
binding to Hb
O2 Transport
• Factors that promote oxyhemoglobin dissociation
– ↓ pO2
– ↑ temperature
– ↑ pCO2
– ↑ products of metabolism
Conditions found in the tissues promote O2
unloading
Oxyhemoglobin Dissociation
• Influence of pO2 on hemoglobin saturation
– Arterial blood
• paO2 = 100 mm Hg
• Hb is 97-100% saturated
– SO2 100%
– Venous blood (resting tissues)
• pO2 = 40 mm Hg
• Hb is 75% saturated
– Venous blood still contains oxyhemoglobin!
Figure 22.20
Difference in partial
pressures = some O2
unloaded to resting
tissues
LungsExercising
tissues
Resting
tissues
Greater difference
in partial pressures
= Additional O2
unloaded to
exercising tissues
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Oxyhemoglobin Dissociation
– Utilization coefficient
• Difference between arterial and venous SO2
– Example: arterial SO2 = 100%; venous SO2 = 75%
– Utilization coefficient 25%
– ↑ metabolism = ↓ paO2 = larger partial pressure
difference
Oxyhemoglobin Dissociation
• Only 20–25% of bound O2 is unloaded during
one systemic circulation (at rest)
• If O2 levels in tissues drop:
– More oxygen dissociates from hemoglobin and is
used by cells
• Blood flow and heart rate need not increase!
Oxyhemoglobin Dissociation
• Other factors influencing hemoglobin
saturation
• ↑ temperature and ↑ H+
– Conditions found at cells enhance O2 unloading
– Shift the O2-hemoglobin dissociation curve to the
right
Figure 22.21
O2P (mm Hg)
Normal body
temperature
10°C
20°C38°C
43°C
Normal arterial
carbon dioxide
(P 40 mm Hg)
or H+ (pH 7.4)
CO2
Increased carbon dioxide
(P 80 mm Hg)
or H+ (pH 7.2)CO2
Decreased carbon dioxide
(P 20 mm Hg) or H+ (pH 7.6)CO2
(a)
(b)
Factors promoting Oxyhemoglobin dissociation shift curve to the right
CO2 Transport
• CO2 is transported in the blood in three forms
– 7-10% dissolved in plasma
– 20% bound to globin of hemoglobin
• carbaminohemoglobin or HbCO2
– 70% transported as bicarbonate ions (HCO3–) in
plasma
CO2 Transport
H2O + CO2 ↔ H2CO3 ↔ HCO3- + H+
CA
Key
H2O = water
CO2 = carbon dioxide
H2CO3 = carbonic acid
HCO3- = bicarbonate ion
H+ = hydrogen ion
CA = carbonic anhydrase
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CO2 Transport
H2O + CO2 ↔ H2CO3 ↔ HCO3- + H+
CA
• Reaction happens in plasma but is 1,000X faster in the RBC because of CA
• H+ ions = acid = decrease pH = improved O2 unloading from hemoglobin
• HCO3- diffuses out, replaced by Cl- to maintain equilibrium = Chloride Shift
Cl-
Figure 22.22a
Red blood cell
Blood plasma
Slow
Tissue cell Interstitial fluid
Carbonic
anhydrase
CO2
CO2
(a) Oxygen release and carbon dioxide pickup at the tissues
CO2 (dissolved in plasma)
CO2 + H2O H2CO3 HCO3– + H+
FastCO2 + H2O H2CO3
O2 (dissolved in plasma)
CO2 + Hb HbCO2
HbO2 O2 + Hb
(Carbamino-
hemoglobin)
HCO3– + H+
HCO3–
Cl–
Cl–
HHb
Binds to
plasma
proteins
Chloride
shift
(in) via
transport
protein
CO2
CO2
CO2
CO2
CO2
O2
O2
In the tissues
CO2 Transport
• In pulmonary capillaries reaction is reversed
– HCO3– moves into the RBCs and binds with H+ to
form H2CO3
– H2CO3 is split by carbonic anhydrase into CO2 and
water
– CO2 diffuses into the alveoli
H2O + CO2 ↔ H2CO3 ↔ HCO3- + H+
CA
Figure 22.22b
Blood plasma
Alveolus Fused basement membranes
CO2
CO2
CO2
(b) Oxygen pickup and carbon dioxide release in the lungs
CO2
O2
O2 O2 (dissolved in plasma)
Cl–
Slow
CO2 (dissolved in plasma)
CO2 + H2O H2CO3 HCO3– + H+
Red blood cell
Carbonic
anhydrase
FastCO2 + H2O H2CO3
CO2 + Hb HbCO2
O2 + HHb HbO2 + H+
(Carbamino-
hemoglobin)
HCO3– + H+
HCO3–
Cl–
Chloride
shift
(out) via
transport
protein
In the lungs