Respiratory System Gas Transport by the Blood

Xinping Yuexyue@lsuhsc.edu

Department of PhysiologyLSUHSC-NO

At Standard Barometric Pressure

Dry Atmospheric Gas (P)

Inspired Gas (PI)

Alveolar Gas (PA)

Mixed Expired Gas (PE)

Po2 159.0 mmHg 149.0 mmHg 104.0 mmHg 120.0 mmHg

Pco2 0.3 mmHg 0.3 mmHg 40.0 mmHg 27.0 mmHg

PN2 600.6 mmHg 564.0 mmHg 569.0 mmHg 566.0 mmHg

PH2O 0 mmHg 47.0 mmHg 47.0 mmHg 47.0 mmHg

O2 = 150 torrCO2 = 0 torr

O2 = 150 torrCO2 = 0 torr

O2 = 100 torrCO2 = 40 torr

O2 = 100 torrCO2 = 40 torr O2 = 100 torrCO2 = 40 torr

O2 = 40 torrCO2 = 45 torrO2 = 40 torrCO2 = 45 torr

Gas Transport

Transport of O2 by the bloodTransport of O2 by the blood

Physically dissolved

•At 37°C, 1 ml of plasma contains 0.00003 ml O2/mm Hg PO2

•Normal arterial blood contains 0.3 ml O2/100 ml

Chemically combined to hemoglobin

•1 gram of hemoglobin can combine with 1.34 ml of O2 when fully saturated

•A person with 15 g Hb/100 ml of blood can carry 20.1 ml O2/100 ml blood

% Hb saturation = x 100%O2 bound to Hb

O2 capacity of Hb

Hemoglobin, human, adult(heterotetramer, (αβ)2)

The protein's α and β subunits are in red and blue, and

the iron-containing heme groups in green

Heme b group

Oxyhemoglobin Dissociation CurveOxyhemoglobin Dissociation Curve

Bohr effect

Hem

oglo

bin

satu

ratio

n, %

Hem

oglo

bin

satu

ratio

n, %

Partial pressure of oxygen, mm HgPartial pressure of oxygen, mm Hg

2020

4040

6060

8080

100100

20

40 60 80 100 120 140 160

P50P50

50%50%

Pco2 , pH

temp, BPG

Pco2 , pH

temp, BPG

Cyanosis

• Occurs when more than 5 grams of hemoglobin/100 ml of arterial blood are in the “deoxy” state

• Absence of cyanosis does not rule out hypoxemia (anemia)

• Presence of cyanosis does not always indicate hypoxemia (polycythemia)

Transport of CO2 by the bloodTransport of CO2 by the blood

Physically dissolved (5-10%)

•At 37°C, 1 ml of plasma contains 0.0006 ml CO2/mm Hg PCO2

•Normal arterial blood contains 2.4 ml CO2/100 ml

Carbamino compounds (5-10%)

Bicarbonate (80-90%)

CO2 + H2OCO2 + H2O H2CO3H2CO3 H+ + HCO3H+ + HCO3

CarbonicAnhydraseCarbonic

Anhydrase-

CO2CO2 (Gas phase)

(Dissolved in the aqueous phase)

R - N + CO2 R - N + H+R - N + CO2 R - N + H+

H

H

H

H

H

COO-

H

COO-

Terminal amine group

Carbamino compoundCarbamino compound

Carbamino CompoundCarbamino Compound

Carbon Dioxide Dissociation CurveCarbon Dioxide Dissociation Curve

Haldane effect

A Classification of the Causes of HypoxiaA Classification of the Causes of HypoxiaIncreased

FIo2

helpful?Classification PAo2

Pao2 Cao2 Cvo2Pvo2

Hypoxic hypoxia

Low alveolar Po2

Diffusion impairment

Right to left shunts

V/Q mismatch

Anemic hypoxia

CO poisoning

Hypoperfusion hypoxia

Histotoxic hypoxia

Low

Norm

Norm

Norm

Norm

Norm

Norm

Norm

Low

Low

Low

Low

Norm

Norm

Norm

Norm

Low

Low

Low

Low

Low

Low

Norm

Norm

Low

Low

Low

Low

Low

Low

Low

High

Low

Low

Low

Low

Low

Low

Low

High

Yes

Yes

No

Yes

No

Possibly

No

No