Physiology III Flashcards
Why is PaO2 slightly less than PAO2?
Because of what is known as a physiologic shunt, in which all of the blood that passes the capillary is not oxygenated and continues to arterial circulation
T or F. A normal A-a gradient is positive
T.
Does the diffusion gradient vanish in diffusion or perfusion limited gas exchange?
ONLY perfusion-limited (thus, diffusion-limited is better overall for moving gas)
What physiologic conditions show perfusion-limitation?
- O2 and CO2 binding normally
- N2O binding
What pathological conditions show diffusion-limitation?
- emphysema
- fibrosis
- CO
- strenuous exercise
- altitude
T or F. Normally, O2 diffusion is perfusion-limited
T.
Why is O2 diffusion diffusion-limited in fibrosis?
the alveolar wall thickens
T or F. For the subunits of Hb to bind oxygen, the iron in heme must be ferric
F. It must be Fe2+ (ferrous)
What is methemoglobin?
Hb with Fe3+
What things can convert Hb to methemoglobin?
- nitrites
- sulfonamides
- congenital deficiency of methemoglobin reductase
What is O2 content? Eqn?
the actual amount of O2 per volume of blood
= (O2 binding capacity* % saturation) + dissolved O2
What is the eqn for O2 delivery to tissue?
Cardiac output* O2 content
What is % saturation?
the amount of hemoglobin saturated with O2
Percent Saturation to PaO2
25-10 35-20 50-25 75-40 90-60 100-98
What is the PaO2 when hemoglobin is 50% saturated?
25 mm Hg
What is the %saturation in venous blood where PaO2 is ~40mmHg?
roughly 75%
What things cause a right shift in the Hb binding curve?
increased Co2, temp and 2,3-DPG
Why does HbF bind O2 better than Hb?
because 2,3-DPG does not bind as avidly to the y chains of hemoglobin F as it binds to the B chains of hemoglobin A
How does CO poisoning affect the Hb curve?
- decreased max
- left shift
Why would CO poisoning cause a left shift?
the heme groups NOT bound to CO have an increased affinity for O2. Thus, it cant be unloaded as well
What would be the treatment for CO poisoning?
Give 100% O2
Where is EPO made?
the kidneys (and some in the liver)
How is EPO stimulated to be produced?
Low O2 to kidneys stimulates production of hypoxia-induced factor 1a which induced EPO production
How much of the total Co2 in blood is dissolved?
~5% compared to 2% of O2
T or F. Co2 can bind to Hb
T. Although at different sites from O2 (and its binding reduced affinity of Hb to O2)
What is the Haldane effect?
Increased O2 binding to Hb actually increases the affinity to bind Co2 (opposite of the Bohr effect)
What is the major form of CO2 in blood?
HCO3- (90%)
How is CO2 transformed into HCO3-?
It diffuses passively from tissue into RBCS, is transformed to carbonic acid by carbonic anhydrase and then dissociates. The H+ remains in the red cell and HCO3- is transported to plasma in exchange for Cl-
What happens to the H+ in the red cells?
it is buffered by deoxyhemoglobin
What protein facilitates the exchange of HCO3- out of the cell and Cl- into RBCs?
band three protein
