Physiology IV

Question 1

T or F. All Cardia Output goes to the pulmonary circulation

Answer 1

F. A small amount of coronary venous blood drains directly to the left ventricle through the thesbesian vein

Question 2

How does the pulmonary circulation resistance compare to the systemic resistance?

Answer 2

much lower pressures and resistance (proportional so blood flow remains the same)

Question 3

What mainly determines the resistance of pulmonary vasculature?

Answer 3

O2

Question 4

What is hypoxic vasoconstriction?

Answer 4

decreases in PAO2 produce pulmonary vasoconstriction to reduce “wasting” of blood to alveoli that are not oxygenated

Question 5

How does hypoxic vasoconstriction?

Answer 5

direction action of alveolar PO2 on the vascular smooth muscle of arterioles where voltage-gated Ca2+ channels open, leading to contraction

Question 6

When does this vasoconstriction kick in?

Answer 6

If PAO2 drops below 70 mm Hg

Question 7

What conditions can cause GLOBAL (all of the lung) hypoxic vasoconstriction?

Answer 7

1) high altitude (which increases pressure to compensate (flow=P/R) and can cause right ventricular hypertrophy)
2) Fetal circulation

Question 8

What other molecules can alter pulmonary resistance?

Answer 8

• Thromboxane A2, leukotrienes

- Prostacyclin (PGI2)

Question 9

Capillaries in which lung zone is most likely to be closed? Why?

Answer 9

Zone 1 (top) because they are just held open in normal circumstances by enough Parterial but decreased Parterial due to hemorrhage or increased alveolar pressure can cause them to be compressed and close

Question 10

What is blood flow driven by in Zone 2?

Answer 10

difference between retrial and alveolar pressure, not arterial and venous pressure (as it is in systemic vascular beds)

Pa greater than PA greater than Pv

Question 11

What is bronchial blood flow?

Answer 11

the small amount (less than 2%) of blood that bypasses the alveoli

Question 12

What is the reason that PaO2 will always be slightly less than PAO2?

Answer 12

shunts

Question 13

Do shunts cause a large increase in PaCO2? Why or why not?

Answer 13

No, because central chemoreceptors can sense increased in PaCO2 and increase ventilation rates to give it off

Question 14

Why can PaO2 be affected by shunts more than PaCO2?

Answer 14

Because the O2 chemoreceptors are not active until PaO2 decreased below 60 mm Hg

Question 15

What is a normal ventilation/perfusion ratio?

Answer 15

0.8 (average for whole lung)

Question 16

Where in the vertical lung is V/Q the highest?

Answer 16

Zone 1

Question 17

How does PaO2 change within the vertical lung?

Answer 17

Zone 1- 130 mm Hg
Zone 3- 89 mm Hg

PaCO2 has the opposite distribution but the change is not as great

Question 18

What is the V/Q of ‘dead space’?

Answer 18

infinity. Dead space is ventilation of the lung regions that are not perfused (ventilation is “dead” or wasted)

Question 19

Example of pathology in which V/Q = infinity?

Answer 19

pulmonary embolism