Phys - O2 transport

Question 1

Two forms of O2 transport in blood

Answer 1

1. Dissolved (alpha = 0.003, so not very much dissolved)

2. Bound to Hb (98.5% of transported O2)

Question 2

Iron state in heme that binds O2?

Answer 2

Ferrous iron (Fe2+)

Question 3

Subunits of adult Hb

Answer 3

alpha2beta2

Question 4

What is methemoglobin?

Answer 4

Iron is in ferric state (Fe3+) which can NOT bind O2

Question 5

What causes cyanosis

Answer 5

Unsaturated Hb is purple; low Hb saturation in surface capillaries causes bluish color of skin

Question 6

What accounts for the sigmoidal shape of the oxygen hemoglobin dissociation curve?

Answer 6

Positive cooperativity - once an O2 binds to one heme, the affinity of the other heme molecules increases

Question 7

Subunits of fetal Hb

Answer 7

alpha2gamma2

Question 8

Normal arterial PO2; venous?

Answer 8

100 mmHg

60 mmHg

Question 9

What is the “loading” portion of the O2-Hb dissociation curve?

Answer 9

PO2 60-100 mmHg
(think: PO2 ~ 100mmHg in arterial blood where Hb needs to be saturated; increased PO2 = increased affinity of Hb for O2 = O2 can move onto Hb)

Question 10

What is the “unloading” portion of the O2-Hb dissociation curve?

Answer 10

PO2 40-60 mmHg
(think: venous PO2 ~ 40 mmHg; O2 needs to leave Hb to enter tissues; decreased PO2 = decreased Hb affinity for O2 = O2 able to enter tissues)

Question 11

Where does the curve flatten? What does this mean?

Answer 11

~60mmHg/90% Hb sat

Large range of PO2 lead to same saturation (safety net)

Question 12

What is P50?

Answer 12

PO2 at which 50% of Hb is saturated

P50 normally ~ 20mmHg

Question 13

Increased P50 = ___ affinity

Answer 13

Decreased

more PO2 required to saturate HB

Question 14

Decreased P50 = ___ affinity

Answer 14

Increased

less PO2 required to saturate HB

Question 15

The dissolved O2 in blood determines:

Answer 15

O2 diffusion

Question 16

Does O2 bound to Hb contribute to pressure gradient?

Answer 16

No; only the dissolved O2 equilibrates; when pressure difference is greater in blood, O2 will diffuse into cells and more O2 can unload from Hb; thus Hb determines the total amount of O2 that can diffuse

Question 17

How is the diffusion gradient favoring O2 transfer from lungs to blood maintained despited very large transfer of O2?

Answer 17

98.5% of O2 binds Hb, which is not available for diffusion. Only 1.5% O2 dissolves, so the pressure gradient favoring transfer into blood is maintained.

Question 18

How is the diffusion gradient favoring O2 transfer from blood into cells maintained despited very large transfer of O2?

Answer 18

Less O2 in cells than dissolved in blood; O2 can dissociate from Hb and dissolve but will always be at higher PO2 in blood than cells.

Question 19

Relative to Hb saturation, how is more O2 delivered to tissue during exercise?

Answer 19

Muscle consumes more O2 during exercise, creating a greater pressure gradient across blood/cells. Thus, more O2 can become available from the reserve that is bound to Hb (also perfusion increases to provide more O2).

Question 20

Right shift of curve means:

Answer 20

Decreased affinity of Hb for O2

Question 21

4 things that can cause right shift:

Answer 21

1. Increased PCO2
2. Low pH/increased H+
3. Increased temperature
4. Increased 2,3-DPG

Question 22

Explain the Bohr effect

Answer 22

Increased CO2 production by tissues causes increased H+ (carbonic acid equilibrium), which right shifts the O2-Hb curve. This facilitates unloading of O2 such that increased CO2 leads to more O2 delivery to tissues via H+.

Question 23

How does a rise in body temp right shift the curve?

Answer 23

Changes the confirmation of Hb such that its affinity for O2 decreases

Question 24

What is 2,3-DPG?

Answer 24

Glycolytic metabolite of RBCs

Question 25

How does 2,3-DPG right shift the curve?

Answer 25

Binds preferentially to deoxygenated Hb

Question 26

When would you expect to see increased 2,3-DPG?

Answer 26

Hypoxemia - less O2 = less ATP = more glycolysis = more 2,3-DPG

Question 27

Left shift means:

Answer 27

Increased affinity

Question 28

5 things which left shift curve:

Answer 28

1. Decreased PCO2
2. High pH/low H+
3. Decreased temperature
4. Decreased 2,3-DPG
5. Fetal Hb/gamma subunit

Question 29

Why does fetal Hb need to have a left shifter curve?

Answer 29

Low placental O2; need to be able to fully saturate Hb at lower PO2

Question 30

What effect does CO have on Hb affinity for O2?

Answer 30

Decreases it because Hb binds CO with 250x more affinity

Question 31

CO poisoning buzzword

Answer 31

Cherry red

Question 32

Right shift facilitates:

Answer 32

Unloading, usually due to tissue factors (where unloading occurs)

Question 33

Left shift facilitates:

Answer 33

Loading, usually due to lung problem (where loading occurs)