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Chapters 23: Respiratory System
Respiratory System:
A. Functional Anatomy
B. Mechanisms of Breathing
C. Gas Exchange
D. Gas Transport
E. Control of Respiration
Today:
A. Gas Exchange
B. Gas Transport
C. Control of Respiration
Mariners
Twins
2
0
Supplies the body
with oxygen and
disposes of carbon
dioxide
Chapters 23: Respiratory System
Gas Exchange:
Physical Properties of Gases:
Chapters 23: Respiratory System
Gas Exchange:
Physical Properties of Gases:
1) Dalton’s Law of Partial Pressures:
0.21 mm Hg
Carbon
Dioxide
• The total pressure of a gas is equal to the sum of the
pressures of its constituents
0.04%
Carbon
Dioxide
159 mm Hg
Oxygen
PAtmosphere = 760 mm Hg
20.94%
Oxygen
PO2 = 0.21 x 760 mm Hg = 159 mm Hg
Partial Pressure
of Dry Room Air
601 mm Hg
Nitrogen
PN2 = 0.79 x 760 mm Hg = 601 mm Hg
79%
Nitrogen
PCO2 = 0.0004 x 760 mm Hg = 0.30 mm Hg
% Composition of Air
Chapters 23: Respiratory System
Chapters 23: Respiratory System
Gas Exchange:
Physical Properties of Gases:
Gas Exchange:
2) Henry’s Law:
• Gases in a mixture dissolve in a liquid in proportion to their
partial pressures
Lung air modified by gas exchange:
Why is alveolar gas high in CO2 and water vapor?
1) O2 into blood; CO2 out of blood
2) Humidification of air (conducting pathways)
3) Mixture of fresh and residual air / breath
• Gases diffuse down pressure gradients
Additional factors affecting gas/liquid interchange:
• Solubility of gas in water
• Carbon Dioxide >> Oxygen >> Nitrogen
Ø “The Bends” (pg 872)
• Temperature
• Solubility inversely related to temperature
0.04%
Carbon
Dioxide
20.94%
Oxygen
H2O = 6.2%
N2 = 74.5%
79%
Nitrogen
% Composition of Air
O2 = 13%
CO2 = 6%
% Composition of Lung Air
Chapters 23: Respiratory System
Chapters 23: Respiratory System
Gas Exchange:
External / Internal Respiration:
1) External Respiration (O2 / CO2 exchange between blood and lungs)
• Pulmonary gas exchange driven by gas partial pressures
• PO2 in alveoli = ~100 mmHg
Net movement into blood
• PO2 in blood = ~40 mmHg
• PCO2 in alveoli = ~40 mmHg
Net movement into alveoli
• PCO2 in blood = ~45 mmHg
Gas Exchange:
External / Internal Respiration:
1) External Respiration (O2 / CO2 exchange between blood and lungs)
• Pulmonary gas exchange driven by gas partial pressures
• PO2 in alveoli = ~100 mmHg
Net movement into blood
• PO2 in blood = ~40 mmHg
• PCO2 in alveoli = ~40 mmHg
Net movement into alveoli
• PCO2 in blood = ~45 mmHg
• Thin, extensive exchange area maximizes exchange rates
• Thickness < 1.0 µm; exchange area ~ 50-70 m2
• Ventilation-perfusion Coupling
Chapters 23: Respiratory System
Chapters 23: Respiratory System
Gas Exchange:
Ventilation-perfusion Coupling:
• Mechanism for matching flow of blood with volume of gas
in alveoli (Autoregulatory homeostasis)
Gas Exchange:
Ventilation-perfusion Coupling:
When PO2 is low and PCO2 is high in alveoli:
1) Ventilation = amount of gas reaching alveoli
2) Perfusion = blood flow in pulmonary capillaries
Bronchioles
Bronchioles
Alveoli
Alveoli
↓ PO2
↑ PCO2
Pulmonary venules
Pulmonary arterioles
Pulmonary venules
Pulmonary arterioles
Pulmonary
capillaries
Pulmonary
capillaries
Chapters 23: Respiratory System
Chapters 23: Respiratory System
Gas Exchange:
Ventilation-perfusion Coupling:
Gas Exchange:
Ventilation-perfusion Coupling:
When PO2 is low and PCO2 is high in alveoli:
1) Bronchioles dilate (↑ ventilation)
When PO2 is low and PCO2 is high in alveoli:
1) Bronchioles dilate (↑ ventilation)
2) Pulmonary arterioles constrict (↓ blood flow)
Bronchioles
Bronchioles
Alveoli
↓ PO2
↑ PCO2
Pulmonary venules
Pulmonary arterioles
Pulmonary
capillaries
Alveoli
↓ PO2
↑ PCO2
Pulmonary venules
Pulmonary arterioles
Pulmonary
capillaries
Chapters 23: Respiratory System
Chapters 23: Respiratory System
Gas Exchange:
Ventilation-perfusion Coupling:
Gas Exchange:
Ventilation-perfusion Coupling:
When PO2 is high and PCO2 is low in alveoli:
When PO2 is high and PCO2 is low in alveoli:
1) Bronchioles constrict (↓ ventilation)
Bronchioles
Bronchioles
Alveoli
Alveoli
↑ PO2
↓ PCO2
↑ PO2
↓ PCO2
Pulmonary venules
Pulmonary arterioles
Pulmonary venules
Pulmonary arterioles
Pulmonary
capillaries
Pulmonary
capillaries
Chapters 23: Respiratory System
Chapters 23: Respiratory System
Gas Exchange:
Ventilation-perfusion Coupling:
Gas Exchange:
External / Internal Respiration:
When PO2 is high and PCO2 is low in alveoli:
1) Bronchioles constrict (↓ ventilation)
2) Pulmonary arterioles dilate (↑ blood flow)
Bronchioles
Alveoli
↑ PO2
↓ PCO2
2) Internal Respiration (O2 / CO2 exchange between blood and tissues)
• Driven by gas partial pressures
• PO2 in blood = ~104 mmHg
• PO2 in tissue = ~40 mmHg
Net movement into tissue
• PCO2 in blood = ~40 mmHg
• PCO2 in tissue = ~45 mmHg
Net movement into blood
Pulmonary venules
Pulmonary arterioles
Pulmonary
capillaries
Gas movements
in body:
Chapters 23: Respiratory System
Respiratory System:
A. Functional Anatomy
B. Mechanisms of Breathing
C. Gas Exchange
D. Gas Transport
E. Control of Respiration
Supplies the body
with oxygen and
disposes of carbon
dioxide
(Figure 23.17)
Chapters 23: Respiratory System
Gas Transport:
Oxygen Transport:
• Most O2 in blood bound to hemoglobin (Hb) (> 98.5%)
• O2 solubility low in plasma (~ 1.5%)
• Hb can bind up to 4 O2 molecules (saturated)
• HHb = deoxyhemoglobin (reduced)
• HbO2 = oxyhemoglobin (oxidized)
HHb
Blood
PO2
PO2
100 mm Hg
40 mm Hg
HbO2
tissues
O2
O2
H+
+
O2 Exchange: Lung → Blood
O2
O2
O2
Red Blood Cell
O2
O2
Tissue
Blood
Chapters 23: Respiratory System
PO2
PO2
40 mm Hg
100 mm Hg
O2 Exchange: Blood → Tissue
O2
HbO2 + H+
HHb + O2
O2
lungs
+ O2
Chapters 23: Respiratory System
Alveoli
Chapters 23: Respiratory System
O2
Gas Transport:
Oxygen Transport:
• O2 association / dissociation with Hb depends on
number of O2 molecules present
• Cooperative binding (lungs)
HHb + O2
O2
HbO2 +
• As each Hb subunit binds 1 O2, the affinity of
the Hb for binding O2 increases.
H+
• Reversible binding (tissues)
• As each Hb subunit releases 1 O2, the affinity of
the Hb for binding O2 decreases.
Red Blood Cell
O2
O2
O2
Chapters 23: Respiratory System
Chapters 23: Respiratory System
Gas Transport:
Oxygen Transport:
• % O2 saturation of Hb depends on PO2
Gas Transport:
Oxygen Transport:
• % O2 saturation of Hb depends on PO2
Oxygen-Hb Dissociation Curve
15
60
10
40
5
20
0
20
40
60
80
100
PO2
• PO2 ~ 100 mm Hg (Alveoli PO2)
• Hb 98% saturated with O2
• 20 ml O2 / 100 ml blood
Oxygen Content = 20 vol %
Oxygen-Hb Dissociation Curve
100
20
80
15
60
10
40
5
20
0
20
40
PO2
Lungs
Tissues
60
80
100
Sigmoid curve
ml O2 / 100 ml blood
80
Sigmoid curve
% O2 saturation of hemoglobin
20
ml O2 / 100 ml blood
% O2 saturation of hemoglobin
100
• PO2 ~ 40 mm Hg (Tissue PO2)
• Hb 75% saturated with O2
• 15 ml O2 / 100 ml blood
Oxygen Content = 15 vol %
Chapters 23: Respiratory System
Chapters 23: Respiratory System
Gas Transport:
Oxygen Transport:
Gas Transport:
Oxygen Transport:
• % O2 saturation of Hb depends on PO2
Volume of O2
unloaded to tissues
20
80
15
60
10
40
5
20
Sigmoid curve
• Hb saturated at 70 mm Hg
ml O2 / 100 ml blood
% O2 saturation of hemoglobin
100
Oxygen-Hb Dissociation Curve
• Adapted for varying PO2
• Only 25% O2 unloaded from
systemic circuit
• Venous reserve
Factors influencing O2 affinity of Hb (modify structure):
1) Temperature
• ↑ temperature = ↓ O2 affinity
(Figure 23.21)
2) pH (Bohr effect)
• ↓ pH = ↓ O2 affinity
3) PCO2
• ↑ PCO2 = ↓ O2 affinity
4) BPG (2,3-biphosphoglycerate)
• Intermediate of anaerobic metabolism
0
20
40
60
80
• ↑ BPG = ↓ O2 affinity
100
PO2
Chapters 23: Respiratory System
Gas Transport:
Oxygen Transport:
“Adaptive Complex”:
• During extreme physical activity:
1) Temperature
2) pH
3) PCO2
All facilitate unloading
of O2 at tissues...
Chapters 23: Respiratory System
Gas Transport:
Oxygen Transport Impairment:
Hypoxia: Inadequate delivery of O2 to tissues
1) Anemic hypoxia (RBC deficiency)
2) Ischemic hypoxia (circulation deficiency)
3) Histotoxic hypoxia (tissue uptake; cyanide)
4) Hypoxemic hypoxia (reduced arterial PO2)
Ø Carbon monoxide poisoning
4) BPG
Chapters 23: Respiratory System
Gas Transport:
Carbon Dioxide Transport:
• CO2 = waste product of aerobic metabolism
• Produced in tissues / expelled in lungs
• CO2 carried in blood 3 ways:
1) Dissolved directly in plasma (7 - 10%)
2) Bound to amino acids of Hb (20 - 30%)
• Carbaminohemoglobin
3) Converted to bicarbonate ion (HCO3-) (60 - 70%)
Chapters 23: Respiratory System
Gas Transport:
Carbon Dioxide Transport:
Hb
Plasma
CA
CO2 + H20
H2CO3
H+ + HCO3-
• Carbon dioxide (CO2) combines with water (H2O) to form
carbonic acid (H2CO3) in RBCs
• Reaction catalyzed by carbonic anhydrase (CA)
• H2CO3 dissociates into hydrogen ion (H+) and bicarbonate
ion (HCO3- )
• HCO3- released into plasma
• H+ binds to Hb (Bohr effect - lowers O2 affinity)
Chapters 23: Respiratory System
Gas Transport:
Carbon Dioxide Transport:
• CO2 transport allows for blood buffering
• HCO3- acts as a proton acceptor (H+) in plasma
• If blood [H+] rises, H+combines with HCO3• If blood [H+] drops, H+ dissociates from H2CO3
Tissue
Blood
Chapters 23: Respiratory System
PCO2
PCO2
45 mm Hg
40 mm Hg
CO2 Exchange: Tissue → Blood
slow
CO2 + H2O
Cl-
CO2
CA
CO2 + H2O
CO2
PCO2
40 mm Hg
45 mm Hg
HbCO2
Red Blood Cell
CO2
Blood
H+ + HCO3-
H2CO3
Hb + CO2
CO2
PCO2
H+ + HCO3Chloride
Shift Cl-
CO2
• Mechanism maintains stable blood pH ~ 7.4
Alveoli
H2CO3
HCO3-
CO2
Chapters 23: Respiratory System
Tissue
Blood
Chapters 23: Respiratory System
CO2 Exchange: Blood → Lung
PO2
PO2
100 mm Hg
O2 / CO2 Exchange Interactions
40 mm Hg
slow
CO2 + H2O
H2CO3
H+ + HCO3-
CO2
PCO2
PCO2
45 mm Hg
40 mm Hg
ClClCA
CO2
CO2 + H2O
CO2
H+ + HCO3-
H2CO3
Hb + CO2
HbCO2
Red Blood Cell
CO2
Lung
PO2
100 mm Hg
CA
CO2
CO2 + H2O
O2
HHb + O2
(Bohr Effect)
CO2
Chapters 23: Respiratory System
PO2
40 mm Hg
O2 / CO2 Exchange Interactions
PCO2
PCO2
40 mm Hg
45 mm Hg
Chapters 23: Respiratory System
Respiratory System:
A. Functional Anatomy
B. Mechanisms of Breathing
C. Gas Exchange
D. Gas Transport
E. Control of Respiration
CO2
O2
CA
CO2 + H2O
H+ + HCO3-
H2CO3
HHb + O2
HbO2 + H+
Red Blood Cell
HbO2 + H+
Red Blood Cell
HCO3-
Blood
H+ + HCO3-
H2CO3
Supplies the body
with oxygen and
disposes of carbon
dioxide
Chapters 23: Respiratory System
Control of Respiration:
Neural Mechanisms:
1) Medullary Respiratory Centers (reticular formation):
• Dorsal Respiratory Group (DRG)
• Inspiratory center (“pacesetter”: 12-15 breaths/min)
• Excites diaphragm (phrenic nerve)
• Excites ext. intercostals (intercostal nerves)
• Ventral Respiratory Group (VRG)
Chapters 23: Respiratory System
Control of Respiration:
Factors Influencing Rate / Depth of Breathing:
1) Pulmonary Irritant Reflexes
• Irritants (mucus/ inhaled debris) stimulate coughing/sneezing
• Triggered by receptors in lungs
2) Inflation (Hering-Breuer) Reflex
• Lung stretch inhibits inspiratory center
• Triggered by stretch receptors in lungs
• Mixed innervation (inspiration/expiration)
• Role in forced expiration?
2) Pons Respiratory Centers
• Modulate respiratory rhythm
Chapters 23: Respiratory System
Control of Respiration:
Higher Brain Center Influences:
1) Hypothalamic Control
• Emotion / pain can modulate respiratory rate
• Acts through limbic system
2) Cortical Control
• Voluntary control (bypasses medullary centers)
Chapters 23: Respiratory System
Control of Respiration:
Chemical Factors Influencing Breathing:
1) [PCO2]
• Most powerful respiratory stimulant
• Mediated through medullary chemoreceptors
• ↑ CO2 = ↑ H+ in cerebrospinal fluid = ↑ ventilation rate
• ↑ CO2 = hypercapnia; ↓ CO2 = hypocapnia
2) [PO2]
• Minor respiratory stimulant
• Mediated through peripheral chemoreceptors (e.g. aorta)
• Stimulated by [PO2] < 60 mm Hg
• ↓ O2 = ↑ respiratory rate
Chapters 23: Respiratory System
Control of Respiration:
Chemical Factors Influencing Breathing:
1) Arterial pH
• Mediated through peripheral chemoreceptors
Chapters 23: Respiratory System
Influences on
respiratory center:
• ↓ pH = ↑ respiratory rate
(Figure 23.25)
Chapters 23: Respiratory System
Homeostatic Imbalances of Respiratory System:
1) Chronic Obstructive Pulmonary Disease
• Obstructive disorders of the airways
2) Asthma
• Acute Inflammation/constriction of airways
3) Tuberculosis
• Bacterial infection invades lungs
4) Lung Cancer
• Aggressive cancer - metastasizes rapidly
• Strongly associated with smoking
Chapters 23: Respiratory System