11-1: Oxygen Transport

Front 1

Dissolved O2 comprises ___% of total O2 in blood.

Is this enough to meet demands of tissues?

Back 1

2%--although small, this is the only O2 that produces a partial pressure and that drives O2 diffusion!!

Not enough to meet demands of tissues.

Front 2

O2 bound to Hgb comprises ___% of total O2 in blood.

Back 2

98% of total O2 in blood is bound to HgB

Front 3

HgBA:
List subunits
Oxygenated, Deoxygenated forms

What state must iron be in to bind O2?

Back 3

HgbA: alpha-2, beta-2, each binding one molecule of O2

When oxygenated-->oxyhemoglobin
When deoxygenated-->deoxyhemoglobin

Iron must be in FERROUS STATE (Fe2+) to bind oxygen

Front 4

What is methemoglobin? How is it formed?

Back 4

Methemoglobin is iron in its ferric (Fe3+) state; inc'd O2-binding affinity-->won't deliver O2 to tissues

Can be caused by nitrites, sulfonamides, or congenital deficiency of methemoglobin reductase (normally keeps Fe reduced)

Front 5

Which subunits in Hgb S are affected? How does this affect O2 affinity?

Back 5

beta-subunits abnormal-->lower O2 affinity

Front 6

Equation for O2 content of blood.

Back 6

O2 Content = (O2-binding capacity x %Saturation) + Dissolved O2

Front 7

What is O2-binding capacity?

Back 7

maximum amount of O2 that can be bound to Hgb per volume of blood (assuming Hgb is 100% saturated)

Front 8

Equation for determining O2-delivery.

Back 8

O-2 Delivery = Cardiac Output x (Dissolved O2 + O2-Hgb)

Note: Dissolved O2 + O2-Hgb = O2-Content (=O2 binding capacity x %saturation)

Front 9

Percent saturation of Hgb is a function of _____ of blood.

Back 9

PO2

Front 10

The relationship between percent saturation and PO2 is ______.

Back 10

Sigmoidal, not linear!!

Front 11

Why is the relationship between percent saturation and PO2 sigmoidal?

Back 11

Positive cooperativity: when first O2 molecule bound, there's inc'd affinity for second O2 molecule to bind, etc.

Front 12

What is P50? What do decreases in P50 correlate with?

Back 12

P50 = PO2 at which Hgb is 50% saturated (2 of 4 heme groups bound to O2).

Decreases in P50-->increases in affinity for O2

Front 13

What type of blood has the highest affinity for O2?

Back 13

Arterial blood (highest PO2)

Front 14

What type of blood has the lowest affinity for O2?

Back 14

Mixed venous blood

Front 15

A PO2 of 40mmHg corresponds to ____% saturation.

Back 15

75%

Front 16

A PO2 of 100mmHg corresponds to _____% saturation.

Back 16

100%

Front 17

What is the affinity for oxygen like in the lungs? How does this affect the partial pressure gradient?

Back 17

Affinity for O2 is high in lungs, and O2 is bound (lower PO2 of pulmonary capillary bc less O2 is dissolved). Since lower than PO2 of alveolus, O2 flows into capillary.

Front 18

What is % saturation at tissue levels? How does this affect the partial pressure gradient?

Back 18

75%--decreased affinity facilitates oxygen unloading

O2 more likely to be dissolved in blood (inc'd PO2 than tissue PO2), driving O2 into tissue.

Front 19

What is a right shift?
Under what conditions does it occur?

Back 19

Right shift: dec'd affinity, increase in P50 (need higher values of PO2 for 50% saturation);

Occurs when unloading of O2 needed.

Front 20

Right/Left Shift:
Exercise

Why?

Back 20

Right Shift (dec'd affinity)

Exercise --> Inc'd metabolic activity

Inc'd PCO2
Dec'd pH
Inc'd Temp
Inc'd 2,3-DPG

Front 21

What is the Bohr effect?

Back 21

Inc'd CO2-->Dec'd pH-->dec'd O2 affinity

Front 22

What is 2,3-DPG? What are its effects on O2 affinity?

When is it produced?

Back 22

2,3-DPG = byproduct of glycolysis in RBCs. Binds beta chains of deoxyhemoglobin and reduces their affinity for O2.

Inc'd underhypoxic conditions, such as living in HIGH ALTITUDES

Front 23

Under what conditions would you expect a left shift? What is affinity like?

Back 23

Left Shift:
Inc'd affinity, dec'd P50; more difficult to unload O2

Decreases in PCO2 and increases in pH cause left shift, i.e., decreased tissu metabolism and decreased O2 demand

Front 24

Why does HgF differ from HgA? Structurally and mechanistically.

Back 24

HgF has 2 alpha and 2 gamma chains.

2,3-DPG doesn't bind as avidly to gamma chains of HgbF as it does to HgbA. Less 2,3-DPG binding-->Inc'd O2 affinity

Front 25

Carbon monoxide:
Left/Right shift
Why?
Effect on P50?

Back 25

CO decreases O2 bound to Hgb and causes a LEFT shift

CO binds Hgb with 250x the affinity of O2 to form carboxyhemoglobin. Heme groups NOT bound to co have INCREASED affinity.

P50 is decrease--more difficult for O2 to unload.

Front 26

In a case of acute CO poisoning, how would you determine percent of Hgb sites occupied by CO?

Back 26

Measure %O2 saturation.

Ex: %O2 saturation = 60%; thus, 40% of Hgb sites must be occupied by CO.

Front 27

In a case of acute CO poisoning, PaO2 was 660mmHg. Is this enough to meet tissue oxygen demands?

Back 27

No, extremely high PaO2 does little to improve O2 delivery because solubility of O2 in blood is so low.

Front 28

What are the 3 forms of CO2 in the blood? Which is most prominent?

Back 28

1) Dissolved CO2--5% of CO2 in blood
2) Carbaminohemoglobin--3% of total CO2
3) HCO3- (90% of total CO2)

Front 29

What is the Haldane Effect?

Back 29

When less O2 bound, affinity of Hgb for CO2 increases.

So: release of O2 from Hgb increases affinity for O2 production in tissues.

Front 30

Describe the events that occur when CO2 is bound to a RBC as H2CO3.

Back 30

H2CO3 dissociates into H+ and HCO3-

H+ remains in RBC, buffered by deoxyhemoglobin
HCO3- transported into plasma in exchange for Cl-

Inc'd H+ causes right shift of O2-->Hgb unloads O2 more readily

HCO3- carried to lungs in plasma of venous blood and all of reactions occur in reverse:
H+ released from deoxyhemoglobin, HCO3- enters RBCs in exchange for Cl-, H+ and HCO3- combine to form H2CO3-->CO2 and H2O-->expired

Front 31

Band Three Protein:
Function

Back 31

Cl- HCO3- exchange

Front 32

Carbonic Anhydrase:
Function

Back 32

CO2 + H2O<-->H2CO3<-->H+ + HCO3-