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

Overview Overview of oxygen and carbon dioxide exchange and transport CO2 O2 Alveoli of lungs Airways Pulmonary circulation Cellular respiration ATP Nutrients Cells Systemic Oxygen exchange at cells Oxygen transport CO2 exchange at alveolar-capillary interface CO2 transport 1 2 3 4 5 6 Figure 18-1

Diffusion and Solubility Diffusion Rate : Surface area x Concentration Gradient x Membrane Permeability Membrane Thickness Surface area Constant Concentration gradient Most important factor Membrane thickness Diffusion distance Thus, Diffusion Rate is proportional to Concentration Gradient

Movement of Gases Pressure gradient Solubility of gas in liquid Temperature (in body, relatively constant)

Behavior of Gases in Solution PO2 = 100 mm Hg PO2 = 0 mm Hg PO2 = 100 mm Hg [O2] = 5.20 mmol/L 0.15 mmol/L (a) (b) (c) Initial state: no O2 in solution Oxygen dissolves. At equilibrium, PO2 in air and water is equal. Low O2 solubility means concentrations are not equal. Figure 18-2a–c

Behavior of Gases in Solution PO2 = 100 mm Hg PO2 = 0 mm Hg (a) Initial state: no O2 in solution Figure 18-2a–c (1 of 3)

Behavior of Gases in Solution PO2 = 100 mm Hg PO2 = 0 mm Hg (a) (b) Initial state: no O2 in solution Oxygen dissolves. Figure 18-2a–c (2 of 3)

Behavior of Gases in Solution PO2 = 100 mm Hg PO2 = 0 mm Hg PO2 = 100 mm Hg [O2] = 5.20 mmol/L 0.15 mmol/L (a) (b) (c) Initial state: no O2 in solution Oxygen dissolves. At equilibrium, PO2 in air and water is equal. Low O2 solubility means concentrations are not equal. Figure 18-2a–c (3 of 3)

Behavior of Gases in Solution Figure 18-2c–d

Gas Exchange at the Alveoli and Cells PLAY Animation: Respiratory System: Gas Exchange Figure 18-3

Partial Pressures

Gas Exchange

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

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

Alveolar Ventilation Figure 18-4b

Alveolar Ventilation 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 Figure 18-5

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

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

Oxygen Transport The role of hemoglobin in oxygen transport Figure 18-7a

Oxygen Transport Figure 18-7b

Oxygen Transport Figure 18-7c

The Hemoglobin Molecule The amount of oxygen bound to hemoglobin depends on the PO2 of plasma Figure 18-8

Oxygen-Hemoglobin Dissociation Curve Figure 18-9

Oxygen Binding Physical factors alter hemoglobin’s affinity for oxygen Figure 18-10a

Oxygen Binding Figure 18-10b

Oxygen Binding Figure 18-10c

2,3-diphosphoglycerate (intermediate in glycolysis pathway) lowers Hb binding affinity 2,3-DPG alters hemoglobin’s affinity for oxygen Figure 18-11

Oxygen Binding Differences in oxygen-binding properties of maternal and fetal hemoglobin Figure 18-12

Oxygen Binding Factors contributing to the total oxygen content of arterial blood Figure 18-13

Carbon Dioxide Transport Dissolved: 7% Converted to bicarbonate ion in rbc: 70% Bound to hemoglobin: 23% Hemoglobin also binds H+, Hb and CO2: carbaminohemoglobin

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

Carbon Dioxide Transport in the Blood CO2 Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Capillary endothelium Cell membrane Figure 18-14 (1 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Capillary endothelium Cell membrane Figure 18-14 (2 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Red blood cell Capillary endothelium Cell membrane Figure 18-14 (3 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb•CO2 (23%) Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Red blood cell Capillary endothelium Cell membrane Figure 18-14 (4 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb•CO2 (23%) CO2 + H2O Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (5 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb•CO2 (23%) CO2 + H2O HCO3– H+ + Hb Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (6 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb•CO2 (23%) CO2 + H2O HCO3– H+ + Hb Hb•H Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (7 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb•CO2 (23%) CO2 + H2O HCO3– HCO3– in plasma (70%) H+ + Hb Hb•H Cl– Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (8 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb•CO2 (23%) CO2 + H2O HCO3– HCO3– in plasma (70%) H+ + Hb Hb•H Cl– Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Transport to lungs Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (9 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb•CO2 (23%) CO2 + H2O HCO3– HCO3– in plasma (70%) H+ + Hb Hb•H Cl– Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Transport to lungs Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (10 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb + CO2 Hb•CO2 (23%) Hb•CO2 CO2 + H2O HCO3– HCO3– in plasma (70%) H+ + Hb Hb•H Cl– Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Transport to lungs Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (11 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb + CO2 Hb•CO2 (23%) Hb•CO2 CO2 + H2O HCO3– HCO3– in plasma (70%) H+ + Hb Hb•H Cl– Cellular respiration in peripheral tissues VENOUS BLOOD Alveoli Transport to lungs Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (12 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb + CO2 Hb•CO2 (23%) Hb•CO2 CO2 + H2O HCO3– HCO3– in plasma (70%) in plasma H+ + Hb Hb•H Cl– Cellular respiration peripheral tissues VENOUS BLOOD Alveoli Transport to lungs Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (13 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb + CO2 Hb•CO2 (23%) Hb•CO2 CO2 + H2O HCO3– HCO3– in plasma (70%) in plasma H+ + Hb Hb•H Cl– Cellular respiration peripheral tissues VENOUS BLOOD Alveoli Transport to lungs Red blood cell Capillary endothelium Cell membrane H2CO3 CA Figure 18-14 (14 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb + CO2 Hb•CO2 (23%) Hb•CO2 CO2 + H2O H2CO3 HCO3– HCO3– in plasma (70%) in plasma H+ + Hb Hb•H Cl– Cellular respiration peripheral tissues VENOUS BLOOD Alveoli Transport to lungs Red blood cell Capillary endothelium Cell membrane CA Figure 18-14 (15 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb + CO2 Hb•CO2 (23%) Hb•CO2 CO2 + H2O H2O + CO2 H2CO3 HCO3– HCO3– in plasma (70%) in plasma H+ + Hb Hb•H Cl– Cellular respiration peripheral tissues VENOUS BLOOD Alveoli Transport to lungs Red blood cell Capillary endothelium Cell membrane CA Figure 18-14 (16 of 17)

Carbon Dioxide Transport in the Blood CO2 Dissolved CO2 (7%) CO2 + Hb Hb + CO2 Hb•CO2 (23%) Hb•CO2 CO2 + H2O H2O + CO2 H2CO3 HCO3– HCO3– in plasma (70%) in plasma H+ + Hb Hb•H Cl– Cellular respiration peripheral tissues VENOUS BLOOD Alveoli Transport to lungs Red blood cell Capillary endothelium Cell membrane CA Figure 18-14 (17 of 17)

Gas Transport: Summary PLAY Animation: Respiratory System: Gas Transport Figure 18-15

Reflex Control of Ventilation Figure 18-16

Regulation of Ventilation Respiratory neurons in medulla control inspiration and expiration Neurons in the pons modulate ventilation Rhythmic pattern of breathing arises from a network of spontaneously discharging neurons Ventilation is subject to modulation by chemoreceptor-linked reflexes and by higher brain centers

Regulation of Ventilation Neural activity during quiet breathing Figure 18-17

Regulation of Ventilation Peripheral chemoreceptors Located in carotid and aortic arteries Specialized glomus cells Sense changes in PO2, pH, and PCO2 Central chemoreceptors Changes in CO2

Regulation of Ventilation Carotid body oxygen sensor releases neurotransmitter when PO2 decreases Figure 18-18

Regulation of Ventilation Central chemoreceptors monitor CO2 in cerebrospinal fluid Figure 18-19

Regulation of Ventilation Chemoreceptor response to increased PCO2 PLAY Animation: Respiratory System: Control of Respiration Figure 18-20

Regulation of Ventilation Protective reflexes Irritant receptors Bronchoconstriction Sneezing Coughing Hering-Breuer inflation reflex

Summary Diffusion and solubility of gases Gas exchange Gas transport Transport of oxygen and carbon dioxide Factors affecting oxygen-hemoglobin binding Carbonic anhydrase and chloride shift

Summary Regulation of ventilation Central pattern generator Dorsal versus ventral respiratory groups Peripheral versus central chemoreceptors