Gas Transport

Question 1

what are the two ways oxygen is transported in blood

Answer 1

1. dissolved in plasma
2. bound to hemoglobin (majority)

Question 2

hemoglobin

Answer 2

heme protein inside RBCs

tetramer - 4 subunits that can each bind O2

Question 3

how does O2 binding affect binding affinity of other subunits

Answer 3

O2 binding increases binding affinity of other subunits

Question 4

O2 capacity

Answer 4

the maximum amount of O2 that could be carried by hemoglobin (mL O2 per dL of blood)

O2 capacity = [hgb] x 1.36

Question 5

Hufner’s constant

Answer 5

average value of mL O2 bound per gram of hgb (not all Hgb are completely filled/bind at max capacity)

1.36 mL/g

Question 6

O2 saturation

Answer 6

actual measurement of O2 bound to hemoglobin (percentage of actual amount bound vs maximum amount that could be bound

SO2 = [(O2 bound) / (O2 capacity)] x 100

Question 7

if PCV = 39% (13 g/dl Hgb) and SO2 = 90%, how much O2 is bound?

Answer 7

O2 capacity = 13 x 1.36 = 17.68

O2 saturation = 90% of 17.68 = 15.9 mL/dL

Question 8

how does anemia affect the O2 binding ability of Hgb

Answer 8

anemia increases O2 binding ability

Question 9

dissolved O2

Answer 9

measures the amount of O2 dissolved in blood

dissolved O2 = PO2 x solubility coefficient

(PO2 can be measured on blood gas)

Question 10

henrys law

Answer 10

concentration of a gas = the partial pressure of the gas x solubility constant

Question 11

solubility coefficient

Answer 11

0.003 mL O2 / dLxmmHg

Question 12

if PO2 = 100 mmhg, how much O2 is dissolved in plasma

Answer 12

dissolved O2 = 100 x 0.003 = 0.3 mL/dL

Question 13

what is the importance of dissolved O2

Answer 13

drives diffusion gradients and determines Hgb-O2 saturation

Question 14

total O2 content

Answer 14

measures the total amount of O2 in the body

C(O2) = (SO2/100 x 1.36 x [Hgb]) + (0.003 x PO2)

sum of the hemoglobin bound and dissolved O2 content

Question 15

Hb-O2 equilibrium curve

Answer 15

shows the relationship between PO2 and SO2

sigmoidal curve - nonlinear due to heme-heme interactions altering affinity based on O2 binding status

Question 16

what determines SO2

Answer 16

PO2 (nonlinear)

as PO2 increases, SO2 increases until fully saturated

Question 17

how are SO2 and C(O2) related

Answer 17

directly related (linear) due to negligible amount dissolved in plasma

can assume total concentration = saturated concentration

Question 18

where on the curve do animals exist in health

Answer 18

upper end of curve
arterial PO2 = 100, SO2 = 98%
venous PO2 = 40, SO2 = 75%

Question 19

how does a decrease in PO2 in the upper range (100 down to 60) affect SO2

Answer 19

minimal effect (minor decrease)

Question 20

how does a decrease in PO2 in the lower range (60 down to 40) affect SO2

Answer 20

significant effect (major decrease)

Question 21

pulse oximeter

Answer 21

probe that measures O2 saturation

emits 2 wavelengths of light that get absorbed differently by free Hgb and Hgb bound to O2

machine reports SpO2 (pulsatile) - can assume equal to SaO2 (arterial)

Question 22

P50

Answer 22

the partial pressure of oxygen (PO2) where Hgb is 50% saturated

low P50 = high affinity
high P50 = low affinity

Question 23

what does it mean if Hgb has a high affinity for O2

Answer 23

• less PO2 required to load
• shifts curve to the LEFT
• caused by decreased PCO2, [H+], temp., and 2,3-BPG
• promotes O2 LOADING in the lungs

Question 24

what does it mean if Hgb has a low affinity for O2

Answer 24

• more PO2 required to load
• shifts curve to the RIGHT
• caused by increased PCO2, [H+], temp., and 2,3-BPG
• promotes O2 UNLOADING in the tissues

Question 25

how much carbon dioxide is there in environmental air

Answer 25

negligible

Question 26

how does CO2 diffuse in the body

Answer 26

via diffusion gradient from tissues –> capillaries –> alveoli

Question 27

what are the 3 ways CO2 is transported in the blood

Answer 27

1. bicarbonate (majority)
2. dissolved in plasma
3. carbamino compounds

Question 28

carbamino compounds

Answer 28

carbon dioxide combined with amino groups

mostly bound to hemoglobin (some other proteins)

Question 29

how does Hgb binding to O2 affect CO2 binding

Answer 29

Hgb NOT bound to O2 (reduced) has a HIGHER affinity for CO2 binding

Haldane effect
- unloading of O2 promotes CO2 carrying (deoxygenated blood carries more CO2)

• loading of O2 inhibits CO2 carrying

Question 30

does arterial or venous blood have a higher proportion of CO2 transported on carbamino compounds

Answer 30

venous blood

also has a higher amount of dissolved CO2
(bicarbonate is still the majority of transport)