Chapter 22: Respiratory System (#3)

CHAPTER 22:

RESPIRATORY SYSTEM

(3): GAS EXCHANGE

Human Anatomy and Physiology II –

BIOL153

Processes of Respiration

Pulmonary

ventilation

External

respiration

Transport

Internal

respiration

Respiratory

system

Circulatory

system

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 alveoli

causes local P and PCO2 O2

Mismatch of ventilation and perfusion

ventilation and/or perfusion of alveoli

causes local P and PCO2 O2

O2 autoregulates

arteriolar diameter

O2 autoregulates

arteriolar diameter

Pulmonary arterioles

serving these alveoli

constricts

Pulmonary arterioles

serving these alveoli

dilate

Match of ventilation

and perfusion

ventilation, perfusion

Match of ventilation

and perfusion

ventilation, perfusion

Transport of Respiratory Gases by

Blood

Pulmonary

ventilation

External

respiration

Transport

Internal

respiration

Respiratory

system

Circulatory

system

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 pressures

b) Boyle's law of partial pressures

c) Henry's law of gas percentages

d) 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) one

b) two

c) three

d) four

Globin chains

Hemegroup

Globin chains

Hemoglobin consists of globin (two alpha and two beta

polypeptide 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 hemegroups carry O2

Partially saturated when one to three hemes carry O2

O2 and Hemoglobin

In the lungs, here

PO2is 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 PO2is

low (40 mm Hg), Hb is

less saturated (75%)

with O2.

This axis tells you how much

O2 is bound to Hb. At 100%,

each Hb molecule has 4 bound

oxygen molecules.

Hemoglobin

Oxygen

100

80

60

40

20

0

0 20 40 60 80 100

Pe

rc

en

t O

2sa

tu

ra

tio

n o

f h

em

og

lo

bin

P (mm Hg)

This axis tells you the relative

Amount (partial pressure) of

O2 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

ent O

2sa

tu

ra

tio

n o

f h

em

oglo

bin

100

PO

2

(mm Hg)

At high PO2

, large changes in PO2

cause only

small changes in Hb saturation. Notice that the

curve 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 PO2in the lungs of only 80

mm Hg, Hb is still 95% saturated.

At sea level, there is lots of O2.

At a PO2in the lungs of 100 mm Hg,

Hb is 98% saturated.

98%

95%

O2 and Hemoglobin

In the tissues

100

80

60

40

20

0

Per

cent O

2sa

tura

tion o

f hem

oglo

bin

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 PO2because they consume O2.

Notice that the curve is relatively steep at low PO2.

Hb’s properties ensure that oxygen is delivered

where it is most needed—when tissues need more,

they get more.

In metabolically active tissues (e.g.,

exercising muscle), the PO2is even lower.

At a PO2of 20 mm Hg, Hb is only 40%

saturated—an additional 35% of O2 has

been unloaded for tissue use.

In resting tissues, at a PO2of 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

Other Factors That Effect

Hemoglobin Saturation

Perc

ent O

2sa

tu

ra

tio

n o

f h

em

og

lo

bin 10ºC

20ºC

38ºC

43ºC

0

20

40

60

80

100

Normal body

temperatureP

erc

ent O

2satu

ration of hem

oglobin

0

20

40

60

80

100

Decreased carbon dioxide(PCO2

20 mm Hg) or H+ (pH 7.6)

Normal arterial

carbon dioxide

(PCO

2

40 mm Hg)

or H+

(pH 7.4)

Increased carbon dioxide

(PCO280 mm Hg)

or H+ (pH 7.2)

20 40 60 80 100

P (mm Hg)O

2

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

Transport and Exchange of CO2

Globin chains

Hemegroup

Globin chains

Hemoglobin consists of globin (two alpha and two beta

polypeptide 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

(carbaminohemoglobi

n)

70% transported as

bicarbonate ions

(HCO3–) in plasma

Transport and Exchange of CO2

CO+HbHbCO