Ch41 Transport of O2 and CO2

Question 1

How is oxygen (O2) transported in the blood?

Answer 1

Almost entirely in combination with hemoglobin.

Hemoglobin allows the blood to transport 30 to 100 times more O2 than dissolved O2.

Question 2

What is the role of hemoglobin in oxygen transport?

Answer 2

It increases the blood’s capacity to transport oxygen significantly.

Hemoglobin can carry much more O2 than would be possible if it were dissolved in plasma.

Question 3

What happens to oxygen in the body’s tissue cells?

Answer 3

O2 reacts with foodstuffs to form carbon dioxide (CO2).

Question 4

How does carbon dioxide (CO2) transport compare to oxygen (O2) transport?

Answer 4

CO2 transport increases 15- to 20-fold by combining with chemical substances in the blood.

Question 5

What is the average PO2 of gaseous O2 in the alveolus?

Answer 5

104 mm Hg.

Question 6

What is the average PO2 of venous blood entering the pulmonary capillary?

Answer 6

40 mm Hg.

Question 7

What is the initial pressure difference that causes O2 to diffuse into the pulmonary capillary?

Answer 7

64 mm Hg.

Question 8

During exercise, how much more oxygen may the body require compared to normal?

Answer 8

Up to 20 times the normal amount.

Question 9

What effect does increased cardiac output during exercise have on blood in the pulmonary capillaries?

Answer 9

It may reduce the time blood remains in the capillaries to less than half normal.

Question 10

How does the diffusing capacity for O2 change during exercise?

Answer 10

It increases almost threefold.

Question 11

What factors contribute to increased diffusing capacity for O2 during exercise?

Answer 11

• Increased surface area of capillaries participating in diffusion
• More nearly ideal ventilation-perfusion ratio

Question 12

What is the PO2 of blood leaving the pulmonary capillaries under non-exercising conditions?

Answer 12

Almost saturated with O2, close to 104 mm Hg.

Question 13

What is the PO2 of the blood that enters the left atrium from the lungs?

Answer 13

About 104 mm Hg.

Question 14

What percentage of blood entering the left atrium is oxygenated?

Answer 14

About 98%.

Question 15

What is ‘shunt flow’ in the context of blood circulation?

Answer 15

Blood that is shunted past the gas exchange areas, not exposed to lung air.

Question 16

What is the PO2 of shunt blood after leaving the lungs?

Answer 16

Approximately 40 mm Hg.

Question 17

What determines tissue PO2?

Answer 17

A balance between the rate of O2 transport to tissues and the rate of O2 usage by tissues.

Question 18

What happens to interstitial fluid PO2 when blood flow to a tissue is increased?

Answer 18

The interstitial fluid PO2 increases.

Question 19

What is the range of intracellular PO2 in peripheral tissues?

Answer 19

From as low as 5 mm Hg to as high as 40 mm Hg, averaging 23 mm Hg.

Question 20

How does CO2 diffuse from tissue cells into capillaries?

Answer 20

Due to elevated intracellular PCO2, causing it to move into capillaries.

Question 21

What is the PCO2 of arterial blood entering tissues?

Answer 21

40 mm Hg.

Question 22

What is the PCO2 of venous blood leaving the tissues?

Answer 22

45 mm Hg.

Question 23

What pressure difference causes CO2 to diffuse out of pulmonary capillaries into alveoli?

Answer 23

5 mm Hg.

Question 24

How does CO2 diffusion compare to O2 diffusion?

Answer 24

CO2 can diffuse about 20 times as rapidly as O2.

Question 25

What is the major difference between the diffusion of CO2 and O2?

Answer 25

CO2 can diffuse about 20 times as rapidly as O2 ## Footnote This results in lower pressure differences required for CO2 diffusion compared to O2.

Question 26

What is the intracellular PCO2 and interstitial PCO2?

Answer 26

Intracellular PCO2 is 46 mm Hg; interstitial PCO2 is 45 mm Hg.

Question 27

How does a decrease in blood flow affect peripheral tissue PCO2?

Answer 27

It increases peripheral tissue PCO2 from 45 mm Hg to 60 mm Hg.

Question 28

What happens to interstitial PCO2 when blood flow is increased to six times normal?

Answer 28

Interstitial PCO2 decreases from 45 mm Hg to 41 mm Hg.

Question 29

What is the effect of a 10-fold increase in tissue metabolic rate on interstitial fluid PCO2?

Answer 29

It greatly elevates the interstitial fluid PCO2 at all rates of blood flow.

Question 30

What is the normal saturation of systemic arterial blood with O2?

Answer 30

97% saturation.

Question 31

What is the PO2 in normal venous blood returning from peripheral tissues?

Answer 31

About 40 mm Hg.

Question 32

How much oxygen can 100 ml of blood carry when hemoglobin is 100% saturated?

Answer 32

About 20 ml of O2.

Question 33

What is the utilization coefficient?

Answer 33

The percentage of blood that gives up its O2 as it passes through tissue capillaries.

Question 34

What is the normal value for the utilization coefficient?

Answer 34

About 25%.

Question 35

What causes the hemoglobin to release more O2 to tissues during exercise?

Answer 35

The steep slope of the dissociation curve and increased tissue blood flow.

Question 36

What is the role of hemoglobin as a tissue oxygen buffer system?

Answer 36

It stabilizes the PO2 in tissues.

Question 37

What happens to tissue PO2 when alveolar PO2 decreases?

Answer 37

Tissue PO2 remains relatively constant despite changes in alveolar PO2.

Question 38

What factors can shift the oxygen-hemoglobin dissociation curve?

Answer 38

* Increased CO2 concentration * Increased blood temperature * Increased BPG concentration * Changes in pH.

Question 39

How does a decrease in pH affect the oxygen-hemoglobin dissociation curve?

Answer 39

It shifts the curve to the right.

Question 40

What is the effect of increased BPG on oxygen release from hemoglobin?

Answer 40

It causes O2 to be released at higher tissue O2 pressure.

Question 41

What is the maximum saturation of hemoglobin with O2 at high alveolar PO2?

Answer 41

100% saturation.

Question 42

What is the average amount of O2 delivered to tissues by each 100 ml of blood flow?

Answer 42

About 5 ml of O2.

Question 43

What is the relationship between exercise and oxygen transport?

Answer 43

Oxygen transport can increase significantly during strenuous exercise.

Question 44

Fill in the blank: The blood of a normal person contains about ______ grams of hemoglobin in each 100 ml of blood.

Answer 44

[15] grams.

Question 45

What is the effect of increased H+ concentration on the oxygen-hemoglobin dissociation curve?

Answer 45

It shifts the curve to the right, enhancing O2 release to tissues. ## Footnote This phenomenon is part of the Bohr effect.

Question 46

What is 2,3-Biphosphoglycerate (BPG)?

Answer 46

A metabolically important phosphate compound present in blood that affects hemoglobin's oxygen affinity.

Question 47

What is the Bohr effect?

Answer 47

The rightward shift of the oxygen-hemoglobin dissociation curve due to increased CO2 and H+ levels, enhancing O2 release in tissues.

Question 48

What happens to the oxygen-hemoglobin dissociation curve in the lungs?

Answer 48

It shifts to the left and upward, increasing O2 binding with hemoglobin.

Question 49

What factors contribute to the rightward shift of the oxygen-hemoglobin dissociation curve during exercise?

Answer 49

Increased CO2, H+ concentration, and temperature in muscle capillary blood.

Question 50

What is the critical intracellular PO2 level for normal metabolism?

Answer 50

Above 1 mm Hg.

Question 51

What is the main limiting factor for O2 usage in cells when intracellular PO2 is above 1 mm Hg?

Answer 51

The concentration of adenosine diphosphate (ADP).

Question 52

How does blood flow affect the metabolic use of oxygen?

Answer 52

The total O2 available depends on the quantity transported per 100 ml of blood and the rate of blood flow.

Question 53

What percentage of O2 is normally transported in the dissolved state in blood?

Answer 53

About 3%.

Question 54

What happens to the amount of O2 transported in the dissolved state during strenuous exercise?

Answer 54

It can fall to as little as 1.5%.

Question 55

What is the consequence of breathing O2 at very high alveolar PO2 levels?

Answer 55

It can lead to O2 poisoning, which may cause brain convulsions and death.

Question 56

How does carbon monoxide (CO) affect hemoglobin?

Answer 56

It displaces O2 from hemoglobin and binds with 250 times more tenacity than O2.

Question 57

What is the lethal partial pressure of carbon monoxide (CO) in the alveoli?

Answer 57

0.6 mm Hg.

Question 58

What is the primary method of CO2 transport in the blood?

Answer 58

As bicarbonate ions (HCO3-), dissolved CO2, and bound to hemoglobin.

Question 59

What percentage of CO2 is transported in the dissolved state?

Answer 59

About 7%.

Question 60

What enzyme catalyzes the reaction of CO2 with water in red blood cells?

Answer 60

Carbonic anhydrase.

Question 61

What occurs to carbonic acid (H2CO3) formed in red blood cells?

Answer 61

It dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+).

Question 62

Fill in the blank: The amount of CO2 dissolved in blood at 45 mm Hg is about ______ ml/dl.

Answer 62

2.7

Question 63

True or False: The PO2 of blood can be normal in carbon monoxide poisoning despite reduced O2 content.

Answer 63

True.

Question 64

What is the effect of diffusion distance from the capillary to the cell on oxygen usage?

Answer 64

If cells are too far from capillaries, O2 usage becomes diffusion-limited.

Question 65

What occurs rapidly in red blood cells that allows CO2 to react with water?

Answer 65

The reaction reaches almost complete equilibrium within a small fraction of a second.

Question 66

What does carbonic acid dissociate into in red blood cells?

Answer 66

H+ and bicarbonate ions (HCO3−).

Question 67

What is the role of hemoglobin in relation to H+ ions?

Answer 67

Hemoglobin combines with H+ ions as it is a powerful acid-base buffer.

Question 68

What is the chloride shift?

Answer 68

It is the phenomenon where chloride ions diffuse into red blood cells while bicarbonate ions diffuse out.

Question 69

What percentage of CO2 transport from tissues to lungs is accounted for by the reversible combination of CO2 with water?

Answer 69

About 70%.

Question 70

What happens to CO2 transport when carbonic anhydrase is inhibited?

Answer 70

CO2 transport becomes poor, and tissue PCO2 may rise to 80 mm Hg instead of the normal 45 mm Hg.

Question 71

What is carbaminohemoglobin?

Answer 71

The compound formed when CO2 reacts with amine radicals of the hemoglobin molecule.

Question 72

What percentage of CO2 is normally transported by carbamino combination with hemoglobin and plasma proteins?

Answer 72

About 30%.

Question 73

What is the normal blood PCO2 range in arterial and venous blood?

Answer 73

40 mm Hg in arterial blood and 45 mm Hg in venous blood.

Question 74

What is the effect of oxygen binding with hemoglobin on CO2 transport?

Answer 74

It displaces CO2 from the blood, known as the Haldane effect.

Question 75

How does the Haldane effect enhance CO2 transport?

Answer 75

It causes hemoglobin to become a stronger acid, displacing CO2 and facilitating its release into the alveoli.

Question 76

What is the average blood pH change as blood acquires CO2 in tissue capillaries?

Answer 76

The pH falls from about 7.41 to about 7.37.

Question 77

What is the respiratory exchange ratio (R)?

Answer 77

The ratio of CO2 output to O2 uptake.

Question 78

What is the value of R when a person is using carbohydrates exclusively?

Answer 78

1.00.

Question 79

What is the value of R when a person is using fats exclusively?

Answer 79

As low as 0.7.

Question 80

What does the average value for R represent for a person on a normal diet?

Answer 80

0.825.

Question 81

What happens to blood acidity during CO2 transport in high metabolic activity?

Answer 81

The decrease in pH can be as much as 0.50, causing significant tissue acidosis.