CHAPTER 22: RESPIRATORY SYSTEM (3): GAS EXCHANGEHuman Anatomy and Physiology II – BIOL153

Processes of Respiration

Pulmonary ventilation

External respiration

Transport

Internal respiration

Respiratorysystem

Circulatorysystem

Goals/Objectives

State Dalton’s law of partial pressures and Henry’s law

Describe how atmospheric and alveolar air differ in composition, and explain these differences

Relate Dalton’s law and Henry’s laws to events of external and internal respiration

Describe how oxygen is transported in blood, and explain how temperature, pH, BPG, and PCO2

affect oxygen loading and unloading

Describe carbon dioxide transport in blood

Basic Properties of Gases: Dalton's Law of Partial Pressures

Total pressure exerted by mixture of gases = sum of pressures exerted by each gas

Partial pressure Pressure exerted by each gas in mixture Directly proportional to its percentage in

mixture

Basic Properties of Gases: Henry's Law

Gas mixtures in contact with liquid Each gas dissolves in proportion to its

partial pressure At equilibrium, partial pressures in two

phases will be equal Amount of each gas that will dissolve

depends on Solubility–CO2 20 times more soluble in

water than O2; little N2 dissolves in water Temperature–as temperature rises,

solubility decreases (higher temp = gas state)

External Respiration

Influenced by:• Thickness and surface

area of respiratory membrane

• Partial pressure gradients and gas solubilities

• Ventilation-perfusion coupling

Steep partial pressure gradient for O2 in lungs• Drives oxygen flow to

blood

Ventilation-Perfusion Coupling Perfusion-blood flow reaching alveoli

Ventilation-amount of gas reaching alveoli

Ventilation and perfusion matched (coupled) for efficient gas exchange Never balanced for all alveoli due to

Regional variations due to effect of gravity on blood and air flow

Some alveolar ducts plugged with mucus

Ventilation-Perfusion Coupling

Ventilation less than perfusion Ventilation greater than perfusion

Mismatch of ventilation and perfusion ventilation and/or perfusion of alveolicauses local P and PCO2 O2

Mismatch of ventilation and perfusion ventilation and/or perfusion of alveolicauses local P and PCO2 O2

O2 autoregulatesarteriolar diameter

O2 autoregulatesarteriolar diameter

Pulmonary arteriolesserving these alveoliconstricts

Pulmonary arteriolesserving these alveolidilate

Match of ventilationand perfusion ventilation, perfusion

Match of ventilationand perfusion ventilation, perfusion

Transport of Respiratory Gases by Blood

Pulmonary ventilation

External respiration

Transport

Internal respiration

Respiratorysystem

Circulatorysystem

Internal Respiration

Clicker Question

The pressure exerted by each gas in a mixture is proportional to its percentage. This is _______.

a) Dalton's law of partial pressuresb) Boyle's law of partial pressuresc) Henry's law of gas percentagesd) the law of gas proportionality

Clicker Question

Why is the rate of CO2 exchange roughly equivalent to that of O2 despite its less steep pressure gradient?

a) CO2 diffuses much more rapidly out of the cells.

b) CO2 binds to O2 and moves across the respiratory membrane simultaneously.

c) CO2 is more soluble in water than is O2.

d) CO2 is actively transported into the alveoli.

Goals/Objectives

State Dalton’s law of partial pressures and Henry’s law

Describe how atmospheric and alveolar air differ in composition, and explain these differences

Relate Dalton’s law and Henry’s laws to events of external and internal respiration

Describe how oxygen is transported in blood, and explain how temperature, pH, BPG, and PCO2

affect oxygen loading and unloading

Describe carbon dioxide transport in blood

O2 Transport

Molecular O2 carried in blood 1.5% dissolved in plasma 98.5% loosely bound to each Fe of hemoglobin (Hb) in RBCs

Clicker Question

The maximum molecule(s) of O2 that can be transported by one hemoglobin molecule is:

a) oneb) twoc) threed) four

Globin chains

Hemegroup

Globin chains

Hemoglobin consists of globin (two alpha and two betapolypeptide chains) and four heme groups.

Iron-containing heme pigment.

Hemoglobin (Hb) - Structure

oxyhemoglobindeoxyhemoglobin

Hemoglobin attached to carbon dioxide = carbaminohemoglobin

O2 and Hemoglobin

Loading and unloading of O2 facilitated by change in shape of Hb

As O2 binds, Hb affinity for O2 increases

As O2 is released, Hb affinity for O2 decreases

Fully saturated (100%) if all four heme groups carry O2

Partially saturated when one to three hemes carry O2

O2 and Hemoglobin

In the lungs, here

PO2 is high (100

mm Hg), Hb is almost fully saturated (98%) with O2.

If more O2 is present,

more O2 is bound.

However, because of Hb’s properties (O2 binding

strength changes with saturation), this is an S-shaped curve, not a straight line.

In the tissues of other

organs, Where PO2 is

low (40 mm Hg), Hb is less saturated (75%) with O2.

This axis tells you how muchO2 is bound to Hb. At 100%,

each Hb molecule has 4 boundoxygen molecules.

Hemoglobin

Oxygen

100

80

60

40

20

0

0 20 40 60 80 100

Perc

en

t O

2 s

atu

rati

on

of

hem

og

lob

in

P (mm Hg)

This axis tells you the relativeAmount (partial pressure) ofO2 dissolved in the fluid

Surrounding the Hb.

•

•

O2

O2 and Hemoglobin

In the lungs

100

80

60

40

20

00 20 40 60 80

Perc

en

t O

2 s

atu

rati

on

of

hem

og

lob

in

100PO2

(mm Hg)At high PO2

, large changes in PO2 cause only

small changes in Hb saturation. Notice that thecurve is relatively flat here. Hb’s properties produce a safety margin that ensures that Hb is almost fully

saturated even with a substantial PO2 decrease. As a result,

Hb remains saturated even at high altitude or with lung disease.

At high altitude, there is less O2.

At a PO2 in the lungs of only 80

mm Hg, Hb is still 95% saturated.

At sea level, there is lots of O2.

At a PO2 in the lungs of 100 mm Hg,

Hb is 98% saturated.

98%

95%

O2 and Hemoglobin

In the tissues

100

80

60

40

20

0

Perc

ent O

2 sat

urat

ion

of h

emog

lobi

n

0 20 40 60 80 100PO2

(mm Hg)At low PO2

, large changes in PO2 cause large

changes in Hb saturation. Tissues other than

lungs have a low PO2 because they consume O2.

Notice that the curve is relatively steep at low PO2.

Hb’s properties ensure that oxygen is deliveredwhere it is most needed—when tissues need more, they get more.

In metabolically active tissues (e.g.,

exercising muscle), the PO2 is even lower.

At a PO2 of 20 mm Hg, Hb is only 40%

saturated—an additional 35% of O2 has

been unloaded for tissue use.

In resting tissues, at a PO2 of 40 mm Hg,

Hb is 75% saturated—only 23% of O2

carried by Hb is released.

75%

40%

Other Factors Influencing Hemoglobin Saturation

Increases in temperature, H+, Pco2, and BPG Modify structure of hemoglobin;

decrease its affinity for O2

Occur in systemic capillaries Enhance O2 unloading from blood Shift O2-hemoglobin dissociation

curve to right Decreases in these factors shift

curve to left Decreases oxygen unloading from

blood

Other Factors That Effect Hemoglobin Saturation

Perc

en

t O

2 s

atu

rati

on

of

hem

oglo

bin

10ºC

20ºC38ºC

43ºC

0

20

40

60

80

100

Normal bodytemperature

Perc

en

t O

2 s

atu

rati

on o

f hem

oglo

bin

0

20

40

60

80

100

Decreased carbon dioxide(PCO2

20 mm Hg) or H+ (pH 7.6)

Normal arterialcarbon dioxide(PCO2

40 mm Hg)

or H+ (pH 7.4)

Increased carbon dioxide

(PCO2 80 mm Hg)

or H+ (pH 7.2)

20 40 60 80 100P (mm Hg)O2

Factors that Increase Release of O2 by Hemoglobin

As cells metabolize glucose and use O2

Pco2 and H+ increase in capillary blood

Declining blood pH and increasing Pco2

Bohr effect - Hb-O2 bond weakens oxygen unloading where needed most

Heat production increases directly and indirectly decreases Hb affinity for O2 increased oxygen unloading to active tissues

Transport and Exchange of CO2

Globin chains

Hemegroup

Globin chains

Hemoglobin consists of globin (two alpha and two betapolypeptide chains) and four heme groups.

Iron-containing heme pigment.

CO2+Hb↔HbCO2

CO2 transported in blood in three forms 7 to 10% dissolved

in plasma 20% bound to globin

of hemoglobin (carbaminohemoglobin)

70% transported as bicarbonate ions (HCO3

–) in plasma

Transport and Exchange of CO2

CO+HbHbCO