Transport of O2 and CO2 in Transport of O2 and CO2 in blood and tissue fluidsblood and tissue fluids

Dr. Walid DaoudDr. Walid DaoudMBBCh, MSc, MD, FCCPMBBCh, MSc, MD, FCCP

Director of Chest DepartmentDirector of Chest Department , ,

Shifa Hospital, Shifa Hospital, A. Professor of Chest MedicineA. Professor of Chest Medicine

Transport of O2 from lungs to body fluidsTransport of O2 from lungs to body fluids____________________________________________________________________________

PO2 is higher in alveoli (104 mmHg) than in PO2 is higher in alveoli (104 mmHg) than in pulmonary capillaries (40 mmHg) so O2 pulmonary capillaries (40 mmHg) so O2 diffuses from alveoli to blood. Also PO2 is diffuses from alveoli to blood. Also PO2 is higher in tissues capillaries so O2 diffuses to higher in tissues capillaries so O2 diffuses to tissue cellstissue cells..

PCO2 is higher in pulmonary capillaries (45 PCO2 is higher in pulmonary capillaries (45 mmHg) than in alveoli (40 mmHg) so CO2 mmHg) than in alveoli (40 mmHg) so CO2 diffuses to the alveoli. Also PCO2 is higher in diffuses to the alveoli. Also PCO2 is higher in

tissue cells so CO2 diffuses to bloodtissue cells so CO2 diffuses to blood . .

Uptake of O2 by pulmonary blood during Uptake of O2 by pulmonary blood during exerciseexercise____________________________________________________________________________

During strenuous exercise, a person needs 20 During strenuous exercise, a person needs 20 times O2times O2::

Increased cardiac outputIncreased cardiac output

Increased O2 diffusing capacity 3-folds due to Increased O2 diffusing capacity 3-folds due to increased surface area of capillaries and increased surface area of capillaries and ideal VA/QT in upper part of lungsideal VA/QT in upper part of lungs..

Blood can still become fully oxygenated despite Blood can still become fully oxygenated despite short time of exposure in the capillariesshort time of exposure in the capillaries

Transport of O2 in arterial bloodTransport of O2 in arterial blood____________________________________________________________________________

98%98% of blood enter left atrium from lungs and of blood enter left atrium from lungs and becomes fully oxygenated (PO2 104 mmHg)becomes fully oxygenated (PO2 104 mmHg)..

2%2% of blood enter left atrium from bronchial of blood enter left atrium from bronchial vessels and not exposed to lung air or not vessels and not exposed to lung air or not

oxygenated (shunt flow)oxygenated (shunt flow) . .

This blood is venous (PO2 40 mmHg) causing This blood is venous (PO2 40 mmHg) causing venous admixture causing arterial PO2 to venous admixture causing arterial PO2 to

drop from 104 mmHg to 95 mmHgdrop from 104 mmHg to 95 mmHg . .

Diffusion of O2 from peripheral capillaries Diffusion of O2 from peripheral capillaries to tissue fluidto tissue fluid____________________________________________________________________________

PO2 in capillaries still 95 mmHgPO2 in capillaries still 95 mmHg

PO2 in interstitial fluid 40 mmHgPO2 in interstitial fluid 40 mmHg

PO2 leaves the tissue capillaries and enter PO2 leaves the tissue capillaries and enter systemic veins 40 mmHgsystemic veins 40 mmHg

Increased rate of blood flow in tissue, greater O2 Increased rate of blood flow in tissue, greater O2 is transported to tissueis transported to tissue

44--folds increase in blood flow, PO2 increase folds increase in blood flow, PO2 increase from 40 to 66 mmHgfrom 40 to 66 mmHg . .

Increased tissue metabolism will decreased PO2 Increased tissue metabolism will decreased PO2 in interstitial fluidin interstitial fluid . .

Diffusion of O2 from peripheral capillaries Diffusion of O2 from peripheral capillaries to tissue cellsto tissue cells____________________________________________________________________________

Normal intracellular PO2 5-40 mmHgNormal intracellular PO2 5-40 mmHg

))average 23 mmHgaverage 23 mmHg((

Only 1-3 mmHg of O2 is normally required for Only 1-3 mmHg of O2 is normally required for oxygenation in the mitochondria of the celloxygenation in the mitochondria of the cell..

So the low intracellular PO2 (23 mmHg) is So the low intracellular PO2 (23 mmHg) is more than adequate and provides a large more than adequate and provides a large

safety factorsafety factor . .

Diffusion of CO2 from peripheral tissue cells Diffusion of CO2 from peripheral tissue cells into cap & from capillaries into alveoliinto cap & from capillaries into alveoli__________________________________________________________________________

Cellular oxidation results in CO2 formationCellular oxidation results in CO2 formation

Intracellular PCO2 (46 mmHg) is higher than in Intracellular PCO2 (46 mmHg) is higher than in interstitial fluid (45 mmHg) and higher than tissue interstitial fluid (45 mmHg) and higher than tissue capillaries (40 mmHg) so CO2 diffuses from cell to capillaries (40 mmHg) so CO2 diffuses from cell to tissue capillaries then from venous blood (PCO2 tissue capillaries then from venous blood (PCO2 becomes 45 mmHg) to alveoli (PCO2 40 mmHg)becomes 45 mmHg) to alveoli (PCO2 40 mmHg)

Decreased blood flow PCO2 increase to 60 mmHg. Decreased blood flow PCO2 increase to 60 mmHg. Increase blood flow decrease PCO2 in interstitial Increase blood flow decrease PCO2 in interstitial fluid to 41 mmHg. Increased metabolism increase fluid to 41 mmHg. Increased metabolism increase

PCO2 in interstitial fluidPCO2 in interstitial fluid . .

O2 transport in bloodO2 transport in blood__________________________________________________________________________

11 . .In physical solutionIn physical solution::

3%3% of O2 is dissolved in plasmaof O2 is dissolved in plasma

22 . .In chemical combination with hemoglobinIn chemical combination with hemoglobin::

97%97% of O2 is carried by hemoglobinof O2 is carried by hemoglobin

O2 molecule combines loosely and reversibly with the O2 molecule combines loosely and reversibly with the heme portion of hemoglobinheme portion of hemoglobin..

When PO2 is high at pulmonary capillariesWhen PO2 is high at pulmonary capillaries , ,

O2 binds with HBO2 binds with HB

When PO2 is low in tissue capillaries, O2 is released When PO2 is low in tissue capillaries, O2 is released from HBfrom HB . .

Oxygen-hemoglobin dissociation curveOxygen-hemoglobin dissociation curve__________________________________________________________________________

At PO2 leaving the lung is 95 mmHg and O2 At PO2 leaving the lung is 95 mmHg and O2 saturation in systemic arterial blood is 97%saturation in systemic arterial blood is 97%

PO2 in normal venous blood returning from PO2 in normal venous blood returning from peripheral tissue is 40 mmHg and O2 peripheral tissue is 40 mmHg and O2

saturation of hemoglobin is 75%saturation of hemoglobin is 75% . .

Oxygen-hemoglobin dissociation curveOxygen-hemoglobin dissociation curve__________________________________________________________________________

O2 capacityO2 capacity::

Each 1 gm of HB can bind 1.34 ml O2 and HB is 100% Each 1 gm of HB can bind 1.34 ml O2 and HB is 100% saturated with O2saturated with O2..

Arterial blood contain 15 gm HB/100 ml blood = 15 x 1.34 Arterial blood contain 15 gm HB/100 ml blood = 15 x 1.34 = 20 ml O2= 20 ml O2..

O2 contentO2 content::

Arterial (PO2 95 mmHg, sat O2 97%) = 19.4 mlArterial (PO2 95 mmHg, sat O2 97%) = 19.4 ml

Venous (PO2 40 mmHg, sat O2 75%) =14.4 mlVenous (PO2 40 mmHg, sat O2 75%) =14.4 ml

Normally 5 ml of O2 is transported from lungs to tissues Normally 5 ml of O2 is transported from lungs to tissues by each 100 ml of blood flowby each 100 ml of blood flow . .

O2-hemoglobin dissociation curveO2-hemoglobin dissociation curve

Oxygen-hemoglobin dissociation curveOxygen-hemoglobin dissociation curve__________________________________________________________________________

O2 transport during strenuous exerciseO2 transport during strenuous exercise::

O2 uptake by tissue is increased 3 times normal (15 ml O2 uptake by tissue is increased 3 times normal (15 ml instead of 5 ml) or (19.4 - 4.4 ml)instead of 5 ml) or (19.4 - 4.4 ml)::

PO2 drop from 40 to 15 mmHg in interstitial fluidPO2 drop from 40 to 15 mmHg in interstitial fluid

Utilization coefficientUtilization coefficient::

% %of blood that gives O2 as it passes through tissue of blood that gives O2 as it passes through tissue capillaries = 25% at rest & increases to 75-85% during capillaries = 25% at rest & increases to 75-85% during strenuous exercise & approachstrenuous exercise & approach

100%100% when blood flow is very slow or metabolic rate is when blood flow is very slow or metabolic rate is very high (all O2 is given to tissue)very high (all O2 is given to tissue)..

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