Chapter 18a
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Transcript of Chapter 18a
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Chapter 18a
Gas Exchange and Transport
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About this Chapter
• Diffusion and solubility of gases
• Gas exchange in lungs and tissues
• Gas transport in the blood
• Regulation of ventilation
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Figure 18-1
Overview
• Oxygen and carbon dioxide move into and out of the blood at pulmonary and systemic capillaries • Internal respiration
6
5
4 3
CO2 O2
Alveoli of lungs
Airways
CO2
CO2
O2
O2
Pulmonarycirculation
CO2 O2
Cellularrespiration
ATPNutrientsCells
Systemiccirculation
CO2 O2
Oxygen exchangeat cells
Oxygen transport
CO2 exchangeat alveolar-capillaryinterface
Oxygen exchangeat alveolar-capillaryinterface
CO2 exchangeat cells
CO2 transport
2
1
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Diffusion and Solubility
• Constants influencing diffusion in the lungs • Surface area• Contact between air and blood
• Membrane thickness• Alveoli and endothelium
• Diffusion distance• Distance between blood and air
• Concentration gradient • Most important factor as others usually are
constant
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Movement of Gases
• Pressure gradient• Partial pressure change
• Solubility• Gas into liquid
• Temperature• Higher faster
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Figure 18-2a–c
Gases in Solution
(a)
PO2 = 100 mm Hg
PO2 = 0 mm Hg
(b) (c)
PO2 =
100 mm Hg[O2] =5.20 mmol/L
PO2 =
100 mm Hg[O2] =0.15 mmol/L
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Figure 18-2c–d
Gases in Solution
(c)
100 mm Hg[O2] =5.20 mmol/L
[O2] =0.15 mmol/L
(d)
100 mm Hg[CO2] =5.20 mmol/L
[CO2] =3.00 mmol/L
PO2=
100 mm HgPO2
=
PCO2=
100 mm HgPCO2
=
Solubility difference between O2 and CO2
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Figure 18-3
Gas Diffusion
PO2 = 100 mm Hg
Alveoli
Peripheral tissue
Alveoli
Peripheral tissue
(b) CO2 diffusion(a) Oxygen diffusion
Circulatorysystem
Circulatorysystem
PO2 = 40 PO2
= 100
PO2 = 40 PO2
= 100
PCO2 = 46 PCO2
= 40
PCO2 = 46 PCO2
= 40
PO2 < 40 mm Hg– PCO2
> 46 mm Hg–
PCO2 = 40 mm Hg
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Gas Exchange
PLAY Interactive Physiology® Animation: Respiratory System: Gas Exchange
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Table 18-1
Partial Pressures
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Table 18-2
Gas Exchange
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Causes of Low Alveolar PO2
1. Inspired air has abnormally low oxygen content• Altitude
2. Alveolar ventilation is inadequate• Decreased lung compliance• Increased airway resistance• Overdose of drugs• What types??
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Figure 18-4a
Alveolar Ventilation
• Pathological conditions that reduce alveolar ventilation and gas exchange
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Figure 18-4b
Alveolar Ventilation
Fewer alveoli
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Figure 18-4c
Alveolar Ventilation
Low compliance
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Figure 18-4d
Alveolar Ventilation
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Figure 18-4e
Alveolar Ventilation
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Figure 18-5
Gas Exchange
• Oxygen diffuses across alveolar epithelial cells and capillary endothelial cells to enter the plasma – respiratory membrane
Fused basementmembranes
Alveolarair space
Plasma
Alveolarepithelium
0.1–1.5 m
Surfactant
Nucleus ofendothelial
cell
Capillarylumen
RBC
O2
O2
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Gas Exchange
• Pathological changes• Decrease in amount of alveolar surface area• emphysema
• Increase in thickness of alveolar membrane• fibrosis
• Increase in diffusion distance between alveoli and blood• pneumonia
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Figure 18-6
Oxygen Transport
O2
O2
O2 dissolved in plasma (~PO2) < 2%
O2 dissolved in plasma
O2 + Hb Hb•O2
> 98%
Hb + O2Hb•O2
ARTERIAL BLOOD
Alveolarmembrane
Alveolus
Capillaryendothelium
Transportto cells
Red blood cell
Cells
Used incellular
respiration
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Figure 18-7a
Oxygen Transport
• Hemoglobin increases oxygen transport by blood
O
(a) Oxygen transport in blood withouthemoglobin. Alveolar PO2
= arterial PO2
PO2 = 100 mm Hg
PO2 = 100 mm Hg
Alveoli O2 molecule
Arterialplasma
Oxygen dissolves in plasma.
Total O2 carryingcapacity
O2 content of plasma = 3 mL O2/L bloodO2 content of redblood cells = 0
3 mL O2/L blood
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Red blood cells with hemoglobin are carry-ing 98% of their maximum load of oxygen.
(b) Oxygen transport at normalPO2
in blood with hemoglobin
PO2 = 100 mm Hg
PO2 = 100 mm Hg
Total O2 carryingcapacity
O2 content of plasma = 003 mL O2/L bloodO2 content of redblood cells = 197 mL O2/L blood
200 mL O2/L blood
Figure 18-7b
Oxygen Transport
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Red blood cells carrying 50% of theirmaximum load of oxygen.
(c) Oxygen transport at reduced PO2
in blood with hemoglobinPO2
= 28 mm Hg
PO2 = 28 mm Hg
Total O2 carryingcapacity
O2 content of plasma = 000.8 mL O2/L bloodO2 content of redblood cells = 099.5 mL O2/L blood
100.3 mL O2/L blood
Figure 18-7c
Oxygen Transport
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Figure 18-8
The Hemoglobin Molecule
• Hemoglobin consists of 4 subunits, each centered around Fe2+ (a)
Chain
Hemegroup
(b) R = additional C, H, O groups
Porphyrinring
Chain
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Figure 18-9
Oxygen-Hemoglobin Dissociation Curve
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Figure 18-10a
Oxygen Binding• Physical factors alter
hemoglobin’s affinity for oxygen shift curve right or left
• pH• Temperature• pCO2
• BPG• RBCs produce during
hypoxia• Hb type• Fetal HbF
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Figure 18-10b
Oxygen Binding
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Figure 18-10c
Oxygen Binding
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Figure 18-11
Oxygen Binding
• 2,3-DPG decreases hemoglobin’s affinity for oxygen
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Figure 18-12
Oxygen Binding
• Maternal and fetal hemoglobin have different oxygen-binding properties
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Figure 18-13
Oxygen Binding
• The total oxygen content of arterial blood depends on the amount of oxygen dissolved in plasma and bound to hemoglobin
TOTAL ARTERIALO2 CONTENT
Oxygen dissolved inplasma (PO2 of plasma)
Oxygenbound to Hb
Total number ofbinding sites
% Saturationof Hb
Adequateperfusionof alveoli
Oxygen diffusionbetween alveoli
and blood
Diffusiondistance
Surfacearea
Lungcompliance
Amount ofinterstitial fluid
Membranethickness
Composition ofinspired air
Numberof RBCs
x
xAirwayresistance
Alveolarventilation
pHPCO2
affected by
helpsdetermineis influenced by
Rate anddepth of
breathing2,3–DPG Hb content
per RBCTemperature
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Carbon Dioxide Transport
• Dissolved: 7%• Converted to bicarbonate ion: 70%• Bound to hemoglobin: 23% • Hemoglobin also binds H+
• Hb and CO2: carbaminohemoglobin
H20 + CO2 H2CO3 H+ + HCO3-
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Figure 18-14
Carbon Dioxide Transport in the Blood
CO2
CO2
Dissolved CO2
(7%)
Dissolved CO2 Dissolved CO2
CO2 + Hb
Hb + CO2
Hb•CO2 (23%)
Hb•CO2
CO2 + H2O
H2O + CO2
H2CO3
H2CO3
HCO3–
HCO3–
HCO3– in
plasma (70%)
HCO3–
inplasma
H+ + Hb Hb•H
H+ + HbHb•H
Cl–
Cellularrespiration
inperipheral
tissues
VENOUS BLOOD
Alveoli
Transportto lungs
Red blood cell
CA
CA
Capillaryendothelium
Cell membrane
Cl–
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Systemiccirculation
Cells
O2CO2
Venous blood
CO2 transportHCO3
– = 70%Hb•CO2 = 23%
Dissolved CO2 = 7%Pulmonarycirculation
Arterial blood
O2 transportHb•O2 > 98%
Dissolved O2 < 2%
(~PO2)
Dry air = 760 mm HgPO2
= 160 mm HgPCO2
= 0.25 mm Hg
Alveoli
O2CO2
PO2 = 100 mm Hg
PCO2 = 40 mm Hg
PO2 = 100 mm Hg
PCO2 = 40 mm Hg
PO2 = 40 mm Hg
PCO2 = 46 mm Hg
PO2 < 40 mm Hg–
PCO2 > 46 mm Hg–
Figure 18-15
Summary of O2 and CO2 Exchange and Transport
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Gas Transport
PLAY Interactive Physiology® Animation: Respiratory System: Gas Transport