Chp. 6: Gas Transport by the Blood

Question 1

Henry’s Law

Answer 1

Amount dissolved is proportional to the partial pressure

Question 2

How much O2 is dissolved in blood?

Answer 2

For each mmHg of PO2, there is 0.003mL O2 per 100mL of blood

0.3mL O2 per 100mL of arterial blood

Question 3

Hemoglobin S

Answer 3

Valine instead of glutamic acid in beta-chains

Right shift of dissociation curve

Question 4

Methemoglobin

Answer 4

Ferric form of hemoglobin

Question 5

O2 capacity

Answer 5

Max amount of O2 that can be combined with Hb

When all available binding sites are occupied by O2

Question 6

How much O2 is carried by Hb?

Answer 6

1g of pure Hb can combine with 1.39mL O2

Normal blood has 15g Hb per 100mL, so O2 capacity is 20.8mL O2 per 100mL of blood

Question 7

O2 sat of arterial blood with PO2 100mmHg

Answer 7

97.5%

Question 8

O2 sat of mixed venous blood with PO2 of 40mmHg

Answer 8

75%

Question 9

Is oxygenated Hb relaxed or tense?

Answer 9

Relaxed

Question 10

Physiological advantages of CURVED shape of O2 dissociation curve

Answer 10

• Flat upper portion means that even if PO2 in alveolar gas falls somewhat, loading of O2 will be little affected
• Steep lower part means that peripheral tissues can withdraw large amounts of O2 for only a small drop in capillary PO2

Question 11

Right-shift of O2 Hb curve

Answer 11

O2 affinity of Hb is reduced = more unloading of O2 in a tissue capillary

acidemia
Hypercapnia
hyperthermia
increased 2,3DPG

“An exercising muscle is acidic, hypercarbic, and hot and benefits from increased unloading of O2 from capillary blood”

Question 12

SO2 97%

Answer 12

PO2 100

Question 13

SO2 75%

Answer 13

PO2 40

Question 14

SO2 50%

Answer 14

PO2 27

Question 15

What is the affinity of CO for Hb compared to O2?

Answer 15

240 times

Question 16

What happens if CO binds Hb?

Answer 16

Hb concentration and PO2 of blood may be normal, but O2 concentration is grossly reduced

LEFT SHIFT

Question 17

CO2 carriage forms

Answer 17

dissolved, bicarb, carbamino compounds

Question 18

Solubility of CO2 in blood

Answer 18

24x more soluble than O2

0.067mL/dL/mmHg

Question 19

Chloride shift

Answer 19

To maintain electrical neutrality, Cl- ions move into the cell from the plasma via a chloride-bicarb exchanger

Follows Gibbs-Donnan equilibrium

Question 20

Haldane Effect

Answer 20

Reduced Hb in peripheral blood helps with loading of CO2, whereas oxygenation that occurs in pulmonary capillary assists in unloading

Question 21

Carbamino compounds

Answer 21

Most important protein is globin of hemoglobin

Question 22

CO2 dissociation curve

Answer 22

More linear than O2

Right-shifted by increases in SO2 (Haldane effect)

Question 23

Respiratory Acidosis

Answer 23

When PCO2 rises, bicarb must also increase to some extent because of dissociation of carbonic acid produced

Kidney responds by conserving bicarb

H+ ions excreted in urine as H2PO4- or NH4+ and bicarb is reabsorbed

Question 24

Respiratory Alkalosis

Answer 24

Decrease in PCO2

Renal compensation by increased excretion of bicarb

Question 25

Metabolic Acidosis

Answer 25

HCO3- lowered by accumulation of acids in blood like DKA, after tissue hypoxia, which releases lactic acid, or with loss of bicarb in severe diarrhea Compensation occurs by increase in ventilation due to action of H+ ions on peripheral CRs

Question 26

Metabolic Alkalosis

Answer 26

Excessive ingestion of alkalis and loss of acid gastric secretions by vomiging Respiratory compensation small and may be absent

Question 27

Why is CO2 elimination less of a problem than O2 delivery?

Answer 27

CO2 diffuses 20 times faster than O2

Question 28

Tissue hypoxia

Answer 28

Abnormally low PO2 in tissues caused by low O2 delivery 1) Low PO2 in arterial blood (hypoxic hypoxia) 2) Reduced ability of blood to carry O2, as in anemia or CO poisoning (anemic hypoxia) 3) Reduction in tissue blood flow (circulatory hypoxia) 4) Toxin that interferes with ability of tissue to utilize available O2, like cyanide (histotoxic hypoxia)

Question 29

How is PO2 and O2 concentration of mixed venous blood determined?

Answer 29

Balance between O2 delivery on one hand and tissue O2 utilization on the other

Question 30

KEY CONCEPTS for gas transport by blood

Answer 30

1) Most of O2 is transported bound to Hb. Max amount bound to Hb is called O2 capacity. O2 saturation is amount combined with Hb divided by capacity and is equal to proportion of binding sites occupied by O2. 2) O2 dissociation curve shifted to right (reduced affinity) by increases in PCO2, H+, temperature, and 23DPG. 3) Most of CO2 in blood is in form of bicarb, with smaller amounts dissolved or in form of carbamino compounds 4) CO2 dissociation curve is steeper and more linear than O2 5) Acid-base status of blood determined by H-H equation and especially ratio of bicarb to PCO2. 6) PO2 in some tissues is less than 5mmHg and purpose of much higher PO2 in capillary blood is to provide an adequate gradient for diffusion. Factors determining O2 delivery to tissues include the blood O2 concentration and blood flow.