Physiology III

Question 1

Why is PaO2 slightly less than PAO2?

Answer 1

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

Question 2

T or F. A normal A-a gradient is positive

Answer 2

T.

Question 3

Does the diffusion gradient vanish in diffusion or perfusion limited gas exchange?

Answer 3

ONLY perfusion-limited (thus, diffusion-limited is better overall for moving gas)

Question 4

What physiologic conditions show perfusion-limitation?

Answer 4

• O2 and CO2 binding normally

- N2O binding

Question 5

What pathological conditions show diffusion-limitation?

Answer 5

• emphysema
• fibrosis
• CO
• strenuous exercise
• altitude

Question 6

T or F. Normally, O2 diffusion is perfusion-limited

Answer 6

T.

Question 7

Why is O2 diffusion diffusion-limited in fibrosis?

Answer 7

the alveolar wall thickens

Question 8

T or F. For the subunits of Hb to bind oxygen, the iron in heme must be ferric

Answer 8

F. It must be Fe2+ (ferrous)

Question 9

What is methemoglobin?

Answer 9

Hb with Fe3+

Question 10

What things can convert Hb to methemoglobin?

Answer 10

• nitrites
• sulfonamides
• congenital deficiency of methemoglobin reductase

Question 11

What is O2 content? Eqn?

Answer 11

the actual amount of O2 per volume of blood

= (O2 binding capacity* % saturation) + dissolved O2

Question 12

What is the eqn for O2 delivery to tissue?

Answer 12

Cardiac output* O2 content

Question 13

What is % saturation?

Answer 13

the amount of hemoglobin saturated with O2

Question 14

Percent Saturation to PaO2

Answer 14

25-10
35-20
50-25
75-40
90-60
100-98

Question 15

What is the PaO2 when hemoglobin is 50% saturated?

Answer 15

25 mm Hg

Question 16

What is the %saturation in venous blood where PaO2 is ~40mmHg?

Answer 16

roughly 75%

Question 17

What things cause a right shift in the Hb binding curve?

Answer 17

increased Co2, temp and 2,3-DPG

Question 18

Why does HbF bind O2 better than Hb?

Answer 18

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

Question 19

How does CO poisoning affect the Hb curve?

Answer 19

• decreased max

- left shift

Question 20

Why would CO poisoning cause a left shift?

Answer 20

the heme groups NOT bound to CO have an increased affinity for O2. Thus, it cant be unloaded as well

Question 21

What would be the treatment for CO poisoning?

Answer 21

Give 100% O2

Question 22

Where is EPO made?

Answer 22

the kidneys (and some in the liver)

Question 23

How is EPO stimulated to be produced?

Answer 23

Low O2 to kidneys stimulates production of hypoxia-induced factor 1a which induced EPO production

Question 24

How much of the total Co2 in blood is dissolved?

Answer 24

~5% compared to 2% of O2

Question 25

T or F. Co2 can bind to Hb

Answer 25

T. Although at different sites from O2 (and its binding reduced affinity of Hb to O2)

Question 26

What is the Haldane effect?

Answer 26

Increased O2 binding to Hb actually increases the affinity to bind Co2 (opposite of the Bohr effect)

Question 27

What is the major form of CO2 in blood?

Answer 27

HCO3- (90%)

Question 28

How is CO2 transformed into HCO3-?

Answer 28

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-

Question 29

What happens to the H+ in the red cells?

Answer 29

it is buffered by deoxyhemoglobin

Question 30

What protein facilitates the exchange of HCO3- out of the cell and Cl- into RBCs?

Answer 30

band three protein