Phys - O2 transport Flashcards
Two forms of O2 transport in blood
- Dissolved (alpha = 0.003, so not very much dissolved)
2. Bound to Hb (98.5% of transported O2)
Iron state in heme that binds O2?
Ferrous iron (Fe2+)
Subunits of adult Hb
alpha2beta2
What is methemoglobin?
Iron is in ferric state (Fe3+) which can NOT bind O2
What causes cyanosis
Unsaturated Hb is purple; low Hb saturation in surface capillaries causes bluish color of skin
What accounts for the sigmoidal shape of the oxygen hemoglobin dissociation curve?
Positive cooperativity - once an O2 binds to one heme, the affinity of the other heme molecules increases
Subunits of fetal Hb
alpha2gamma2
Normal arterial PO2; venous?
100 mmHg
60 mmHg
What is the “loading” portion of the O2-Hb dissociation curve?
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)
What is the “unloading” portion of the O2-Hb dissociation curve?
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)
Where does the curve flatten? What does this mean?
~60mmHg/90% Hb sat
Large range of PO2 lead to same saturation (safety net)
What is P50?
PO2 at which 50% of Hb is saturated
P50 normally ~ 20mmHg
Increased P50 = ___ affinity
Decreased
more PO2 required to saturate HB
Decreased P50 = ___ affinity
Increased
less PO2 required to saturate HB
The dissolved O2 in blood determines:
O2 diffusion
Does O2 bound to Hb contribute to pressure gradient?
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
How is the diffusion gradient favoring O2 transfer from lungs to blood maintained despited very large transfer of O2?
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.
How is the diffusion gradient favoring O2 transfer from blood into cells maintained despited very large transfer of O2?
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.
Relative to Hb saturation, how is more O2 delivered to tissue during exercise?
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).
Right shift of curve means:
Decreased affinity of Hb for O2
4 things that can cause right shift:
- Increased PCO2
- Low pH/increased H+
- Increased temperature
- Increased 2,3-DPG
Explain the Bohr effect
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+.
How does a rise in body temp right shift the curve?
Changes the confirmation of Hb such that its affinity for O2 decreases
What is 2,3-DPG?
Glycolytic metabolite of RBCs
How does 2,3-DPG right shift the curve?
Binds preferentially to deoxygenated Hb
When would you expect to see increased 2,3-DPG?
Hypoxemia - less O2 = less ATP = more glycolysis = more 2,3-DPG
Left shift means:
Increased affinity
5 things which left shift curve:
- Decreased PCO2
- High pH/low H+
- Decreased temperature
- Decreased 2,3-DPG
- Fetal Hb/gamma subunit
Why does fetal Hb need to have a left shifter curve?
Low placental O2; need to be able to fully saturate Hb at lower PO2
What effect does CO have on Hb affinity for O2?
Decreases it because Hb binds CO with 250x more affinity
CO poisoning buzzword
Cherry red
Right shift facilitates:
Unloading, usually due to tissue factors (where unloading occurs)
Left shift facilitates:
Loading, usually due to lung problem (where loading occurs)
