About this Chapter

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

About this Chapter

Diffusion and solubility of gases

Gas exchange in lungs and tissues

Gas transport in the blood

Regulation of ventilation


CO2 O2

Alveoli of lungs

Airways

CO2

CO2

O2

O2

Pulmonarycirculation

CO2 O2

Cellularrespiration

ATPNutrients

Cells

Systemiccirculation

CO2 O2

Oxygen exchange at cells

Oxygen transport

CO2 exchangeat alveolar-capillaryinterface

Oxygen exchangeat alveolar-capillaryinterface

CO2 exchange at cells

CO2 transport

1

2

34

5

6

Overview

Overview of oxygen and carbon dioxide exchange and transport

Figure 18-1


Diffusion and SolubilityDiffusion Rate : Surface area x Concentration Gradient x Membrane Permeability

Membrane Thickness

Surface area

Constant

Concentration gradient

Most important factor

Membrane thickness

Constant

Diffusion distance

Constant

Thus, Diffusion Rate is proportional to Concentration Gradient


Movement of Gases Pressure gradient

Solubility of gas in liquid

Temperature (in body, relatively constant)

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-2a–c

Behavior of Gases in Solution

PO2 = 100 mm Hg

PO2 = 0 mm Hg

PO2 = 100 mm Hg

[O2] = 5.20 mmol/L

PO2 = 100 mm Hg

[O2] = 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.

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-2a–c (1 of 3)


PO2 = 100 mm Hg

PO2 = 0 mm Hg

(a) Initial state:no O2 in solution



PO2 = 100 mm Hg

PO2 = 0 mm Hg

(a) (b)Initial state:no O2 in solution

Oxygen dissolves.



PO2 = 100 mm Hg

PO2 = 0 mm Hg

PO2 = 100 mm Hg

[O2] = 5.20 mmol/L

PO2 = 100 mm Hg

[O2] = 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.

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-2c–d


Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-3

Gas Exchange at the Alveoli and Cells

Animation: Respiratory System: Gas ExchangePLAY


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

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-4a

Alveolar Ventilation

Pathological conditions that reduce alveolar ventilation and gas exchange

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-4b


Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-4c


Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-4d


Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-4e



Gas Exchange

Oxygen diffuses across alveolar epithelial cells and capillary endothelial cells to enter the plasma


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

O2

O2

O2 dissolved in plasma (~ PO2) < 2%

O2 dissolved in plasma

O2 + Hb Hb•O2

> 98%

Hb + O2Hb•O2

ARTERIAL BLOOD

Alveolar membrane

Alveolus

Capillaryendothelium

Transportto cells

Red blood cell

Cells

Used incellular

respiration


Oxygen Transport

The role of hemoglobin in oxygen transport


Oxygen Transport


Oxygen Transport


The Hemoglobin Molecule

The amount of oxygen bound to hemoglobin depends on the PO2 of plasma


Oxygen-Hemoglobin Dissociation Curve


Oxygen Binding

Physical factors alter hemoglobin’s affinity for oxygen


Oxygen Binding


Oxygen Binding


2,3-diphosphoglycerate (intermediate in glycolysis pathway) lowers Hb binding affinity

2,3-DPG alters hemoglobin’s affinity for oxygen


Oxygen Binding

Differences in oxygen-binding properties of maternal and fetal hemoglobin


Oxygen Binding

Factors contributing to the total oxygen content of arterial blood


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

CO2

Dissolved CO2

(7%)

Dissolved CO2 Dissolved CO2

CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2O

H2O + CO2H2CO3

HCO3–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

CA

H2CO3

CA

Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Figure 18-14 (1 of 17)


CO2

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli


Cell membrane



CO2 Dissolved CO2

(7%)Cellular

respirationin

peripheraltissues

VENOUS BLOOD

Alveoli


Cell membrane



CO2 Dissolved CO2

(7%)

CO2

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane



CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane



CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2O

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

H2CO3

CA



CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

–

H+ + Hb

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

H2CO3

CA



CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

–

H+ + Hb Hb•H

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

H2CO3

CA



CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

– HCO3– in

plasma (70%)H+ + Hb Hb•H

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Red blood cell


Cell membrane

H2CO3

CA



CO2 Dissolved CO2

(7%)

CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

– HCO3– in


Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA



CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb Hb•CO2 (23%)

CO2 + H2OHCO3

– HCO3– in


Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA



CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2OHCO3

– HCO3– in


Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA



CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2OHCO3

– HCO3– in


Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA



CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2OHCO3

–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA



CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2OHCO3

–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA



CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2O

H2CO3

HCO3–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA



CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2O

H2O + CO2H2CO3

HCO3–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

CA



CO2

CO2

Dissolved CO2

(7%)


CO2 + Hb

Hb + CO2

Hb•CO2 (23%)

Hb•CO2

CO2 + H2O

H2O + CO2H2CO3

HCO3–

HCO3–

HCO3– in

plasma (70%)

HCO3–

inplasma

H+ + Hb Hb•H

H+ + HbHb•H

Cl–

Cl–

Cellularrespiration

inperipheral

tissues

VENOUS BLOOD

Alveoli

Transportto lungs

Red blood cell


Cell membrane

H2CO3

CA

CA


Gas Transport: Summary

Animation: Respiratory System: Gas TransportPLAY


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



Neural activity during quiet breathing



Peripheral chemoreceptors Located in carotid and aortic arteries

Specialized glomus cells

Sense changes in PO2, pH, and PCO2

Central chemoreceptors

Changes in CO2



Carotid body oxygen sensor releases neurotransmitter when PO2 decreases



Central chemoreceptors monitor CO2 in cerebrospinal fluid



Chemoreceptor response to increased PCO2

Figure 18-20

Animation: Respiratory System: Control of RespirationPLAY



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

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