Diffusion and Perfusion

Question 1

What is the equation for arterial oxygen content?

Answer 1

C(a[O2]) = Hb-bound O2 + freely-dissolved O2

Question 2

The P(a[O2]) represents only ________.

Answer 2

the dissolved oxygen, not the oxygen bound to hemoglobin

Question 3

The pressure gradient that drives oxygen into the capillaries is driven by __________.

Answer 3

the concentration of free oxygen in the blood, not that which is bound to hemoglobin

Question 4

Exercise leads to a shallower oxygenation curve, because ___________.

Answer 4

blood moves faster through the capillaries, thus there is less time for oxygen to diffuse into the blood

Question 5

Disorders of diffusion can affect ________ but not __________.

Answer 5

oxygen concentration; CO2 concentration

Question 6

Minute perfusion is __________.

Answer 6

the amount of blood going through the lung capillary network in one minute (so = cardiac output)

Question 7

Low oxygen concentration in the blood causes the pulmonary vessels to ________.

Answer 7

constrict (allowing for slower flow and hence more diffusion)

Question 8

Factors that influence perfusion include _________.

Answer 8

gravity, capillary recruitment, and oxygen tension

Question 9

What is the V/Q ratio?

Answer 9

The ratio of ventilation to perfusion in a lung unit

Question 10

A lung unit with an obstructed airway would have a ______ V/Q ratio.

Answer 10

low

Question 11

A lung unit with an obstructed capillary would have a ______ V/Q ratio.

Answer 11

high

Question 12

If one lung unit has a low V/Q ratio, then the body will ___________.

Answer 12

increase the V/Q ratio in another unit to compensate

Question 13

_________ saturation limits how much oxygen can be added by increasing the V/Q ratio.

Answer 13

Hemoglobin

Question 14

V/Q mismatch will affect ______ levels but not _________ levels.

Answer 14

P(a[O2]); P(a[CO2])

Question 15

Gravity can cause V/Q mismatch, because perfusion at the bottom of the lungs is ______ than the top, while ventilation at the bottom is only ______ than the top.

Answer 15

6 times greater; 2.5 times greater

Question 16

To correct for abnormally high V/Q, the body can ___________.

Answer 16

bronchoconstrict to decrease V or vasodilate to increase Q

Question 17

High V/Q ratios lead to __________ CO2 in the alveoli.

Answer 17

decreased

Question 18

A shunt is a __________.

Answer 18

blocked alveoli (such as from pneumonia or other infiltrate)

Question 19

What is the conversion between mM and Pa(O2) Torr?

Answer 19

0.0013 mM/Torr

Question 20

What is Fick’s law?

Answer 20

Flux(of gas) = ∆P x (A/d) x k 
∆P = difference in pressure across membrane
A = surface area
d = membrane thickness
k = diffusion constant

Question 21

The diffusible area of the lungs = ________.

Answer 21

roughly 100 m^2

Question 22

Under resting conditions in a healthy individual, the Pa(O2) is 100 Torr when the blood is _______ through the capillary bed of the lungs.

Answer 22

halfway through

Question 23

Both emphysema and interstitial lung disease are considered _______ disorders, because _________.

Answer 23

diffusion; emphysema destroys the surface area through which gas exchange occurs (A) and interstitial lung disease increases the distance (d)

Question 24

Exercise causes the pulmonary blood vessels to _________.

Answer 24

dilate

Question 25

For a healthy person, Ca(O2) is roughly _________.

Answer 25

9.1 mM or 20.7 ml O2 / 100 ml blood

Question 26

One lung has about ______ alveoli.

Answer 26

300 million

Question 27

______ is the most important vasoconstrictor in the pulmonary blood vessels and ______ is the most important vasodilator.

Answer 27

Thromboxane; prostacyclin

Question 28

Increasing the V/Q ratio to much greater than 1 does not ___________.

Answer 28

increase Ca(O2) because hemoglobin is saturated when V/Q is 1

Question 29

There are two local controls of V/Q mismatch: _____________.

Answer 29

high V/Q leads to decreased alveolar P(CO2), which leads to bronchoconstriction, thus decreasing V/Q; and low V/Q leads to low P(O2) which causes vasoconstriction and subsequent raising of V/Q