# Gas Exchange and Transport

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Gas Exchange and Transport
Chapter 18a Gas Exchange and Transport

Diffusion and solubility of gases Gas exchange in lungs and tissues
About this Chapter Diffusion and solubility of gases Gas exchange in lungs and tissues Gas transport in the blood Regulation of ventilation

Overview Oxygen and carbon dioxide move into and out of the blood at pulmonary and systemic capillaries Internal respiration CO2 O2 Airways Alveoli of lungs CO2 O2 6 CO2 exchange at alveolar-capillary interface 1 Oxygen exchange at alveolar-capillary interface CO2 O2 Pulmonary circulation 2 Oxygen transport 5 CO2 transport Systemic circulation CO2 O2 4 CO2 exchange at cells 3 Oxygen exchange at cells CO2 O2 Cellular respiration Cells Nutrients ATP Figure 18-1

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

Pressure gradient Solubility Temperature Movement of Gases
Partial pressure change Solubility Gas into liquid Temperature Higher faster

Gases in Solution PO2 = 100 mm Hg PO2 = 100 mm Hg [O2] = 5.20 mmol/L
(b) (c) Figure 18-2a–c

Solubility difference between O2 and CO2
Gases in Solution P = O2 P = CO2 100 mm Hg 100 mm Hg [O2] = 5.20 mmol/L [CO2] = 5.20 mmol/L P = O2 P = CO2 100 mm Hg 100 mm Hg [O2] = 0.15 mmol/L [CO2] = 3.00 mmol/L (c) (d) Solubility difference between O2 and CO2 Figure 18-2c–d

Gas Diffusion Figure 18-3 Alveoli Alveoli PO2 = 100 mm Hg
PCO2 = 40 mm Hg PO2 = 40 PO2 = 100 PCO2 = 46 PCO2 = 40 Circulatory system Circulatory system PO2 = 40 PO2 = 100 PCO2 = 46 PCO2 = 40 PO2 < 40 mm Hg PCO2 > 46 mm Hg Peripheral tissue Peripheral tissue (a) Oxygen diffusion (b) CO2 diffusion Figure 18-3

Gas Exchange PLAY Interactive Physiology® Animation: Respiratory System: Gas Exchange

Partial Pressures Table 18-1

Gas Exchange Table 18-2

Causes of Low Alveolar PO2
Inspired air has abnormally low oxygen content Altitude Alveolar ventilation is inadequate Decreased lung compliance Increased airway resistance Overdose of drugs What types??

Alveolar Ventilation Pathological conditions that reduce alveolar ventilation and gas exchange Figure 18-4a

Alveolar Ventilation Fewer alveoli Figure 18-4b

Alveolar Ventilation Low compliance Figure 18-4c

Alveolar Ventilation Figure 18-4d

Alveolar Ventilation Figure 18-4e

Gas Exchange Oxygen diffuses across alveolar epithelial cells and capillary endothelial cells to enter the plasma – respiratory membrane Surfactant Alveolar air space Alveolar epithelium O2 Fused basement membranes 0.1–1.5 m Nucleus of endothelial cell O2 Plasma Capillary lumen RBC Figure 18-5

Pathological changes Gas Exchange
Decrease in amount of alveolar surface area emphysema Increase in thickness of alveolar membrane fibrosis Increase in diffusion distance between alveoli and blood pneumonia

Used in cellular respiration
Oxygen Transport Capillary endothelium ARTERIAL BLOOD O2 dissolved in plasma (~PO2) < 2% O2 O2 + Hb Hb•O2 > 98% Red blood cell Alveolus Alveolar membrane Transport to cells Cells Hb•O2 Hb + O2 O2 Used in cellular respiration O2 dissolved in plasma Figure 18-6

Hemoglobin increases oxygen transport by blood
(a) Oxygen transport in blood without hemoglobin. Alveolar PO2 = arterial PO2 Hemoglobin increases oxygen transport by blood PO2 = 100 mm Hg Alveoli O2 molecule Arterial plasma PO2 = 100 mm Hg Oxygen dissolves in plasma. O2 content of plasma = 3 mL O2/L blood O O2 content of red blood cells = 0 Total O2 carrying capacity 3 mL O2/L blood Figure 18-7a

Oxygen Transport Figure 18-7b
(b) Oxygen transport at normal PO2 in blood with hemoglobin PO2 = 100 mm Hg PO2 = 100 mm Hg Red blood cells with hemoglobin are carry- ing 98% of their maximum load of oxygen. O2 content of plasma = 003 mL O2/L blood O2 content of red blood cells = 197 mL O2/L blood Total O2 carrying capacity 200 mL O2/L blood Figure 18-7b

Oxygen Transport Figure 18-7c
(c) Oxygen transport at reduced PO2 in blood with hemoglobin PO2 = 28 mm Hg PO2 = 28 mm Hg Red blood cells carrying 50% of their maximum load of oxygen. O2 content of plasma = mL O2/L blood O2 content of red blood cells = mL O2/L blood Total O2 carrying capacity 100.3 mL O2/L blood Figure 18-7c

The Hemoglobin Molecule
 Chain  Chain Hemoglobin consists of 4 subunits, each centered around Fe2+ Heme group (a) Porphyrin ring (b) R = additional C, H, O groups Figure 18-8

Oxygen-Hemoglobin Dissociation Curve
Figure 18-9

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 Figure 18-10a

Oxygen Binding Figure 18-10b

Oxygen Binding Figure 18-10c

2,3-DPG decreases hemoglobin’s affinity for oxygen
Oxygen Binding 2,3-DPG decreases hemoglobin’s affinity for oxygen Figure 18-11

Maternal and fetal hemoglobin have different oxygen-binding properties
Figure 18-12

Oxygen Binding The total oxygen content of arterial blood depends on the amount of oxygen dissolved in plasma and bound to hemoglobin TOTAL ARTERIAL O2 CONTENT Oxygen dissolved in plasma (PO2 of plasma) Oxygen bound to Hb helps determine is influenced by Oxygen diffusion between alveoli and blood Adequate perfusion of alveoli Composition of inspired air Alveolar ventilation % Saturation of Hb Total number of binding sites x affected by Rate and depth of breathing Airway resistance Lung compliance Surface area Diffusion distance Hb content per RBC Number of RBCs PCO2 pH Temperature 2,3–DPG x Membrane thickness Amount of interstitial fluid Figure 18-13

Carbon Dioxide Transport
Dissolved: 7% Converted to bicarbonate ion: 70% Bound to hemoglobin: 23% Hemoglobin also binds H+ Hb and CO2: carbaminohemoglobin H20 + CO H2CO3 H+ + HCO3-

Carbon Dioxide Transport in the Blood
VENOUS BLOOD CO2 Dissolved CO2 (7%) Cellular respiration in peripheral tissues Red blood cell CO2 + Hb Hb•CO2 (23%) Cl– HCO3– HCO3– in plasma (70%) CO2 + H2O CA H2CO3 H+ + Hb Hb•H Capillary endothelium Cell membrane Transport to lungs Dissolved CO2 Dissolved CO2 CO2 Hb•CO2 Hb + CO2 Cl– Alveoli CA HCO3– in plasma HCO3– H2CO3 H2O + CO2 Hb•H H+ + Hb Figure 18-14

Summary of O2 and CO2 Exchange and Transport
Dry air = 760 mm Hg PO2 = 160 mm Hg PCO2 = 0.25 mm Hg Alveoli PO2 = 100 mm Hg PCO2 = 40 mm Hg CO2 O2 CO2 transport HCO3– = 70% Hb•CO2 = 23% Dissolved CO2 = 7% Arterial blood PO2 = 100 mm Hg Pulmonary circulation PCO2 = 40 mm Hg O2 transport Hb•O2 > 98% Dissolved O2 < 2% (~PO2) Venous blood PO2 = 40 mm Hg PCO2 = 46 mm Hg Systemic circulation CO2 O2 Cells PO2 < 40 mm Hg PCO2 > 46 mm Hg Figure 18-15

Gas Transport PLAY Interactive Physiology® Animation: Respiratory System: Gas Transport