Lecture 31

Question 1

T or F? The pulmonary artery carries “deoxygenated,” blood returning from the systemic circulation to the lungs.

Answer 1

True

Question 2

Approximately 11-12% of blood is going to lungs, How much of that is actually involved in gas exchange?

Answer 2

~9-10%

Question 3

The excess fluid in the lungs must be removed from the intrapleural space to maintain the negative ____ that links the movement of the thoracic walls to the alveoli.

Answer 3

Pip

Question 4

Right ventricular pressure ↓rapidly after systole but the pressure in the pulmonary artery ↓far more slowly due to what reason?

Answer 4

Due to the resistance offered by a large number of very fine capillaries where gas exchange occurs and elasticity of the aveoli.

Question 5

What is the average pulmonary capillary pressure?

Answer 5

~7mmHg (systemic is 17mmHg)

Question 6

Approximately ______ mL of blood is found int he lungs, of that, _____ mL is actually flowing through the pulmonary capillaries of ventilated alveoli and so is actually participating in gas exchange.

Answer 6

450mL ; 70mL

Question 7

During hemorrhaging, to compensate, the lungs can store a significant amount of blood. How much blood?

Answer 7

Up to x2 normal: ~ 900mL

Question 8

T or F? Pulmonary vessels passively distend to accommodate a ↑CO/↑BP and narrow with a ↓CO/↓BP.

Answer 8

True

Question 9

T or F? Systemic blood vessels dilate with ↓Po2, (autoregulation), but in the lungs, this has the opposite effect.

Answer 9

True, if the Po2

Question 10

T or F? Lower portions of the body have a decrease in hydrostatic pressure.

Answer 10

False, the lower portions have an increase in hydrostatic pressure due to the effect of gravity on the blood. (~ 23mmHg pressure drop from top to bottom: but only when vertical)

Question 11

What is “zone 1” when referring to the lungs?

Answer 11

Zone 1: no flow at all, (alveolar pressure always > capillary pressure).

Question 12

What is “zone 2” when referring to the lungs?

Answer 12

Zone 2: intermittent flow only during the part of the cardiac cycle when capillary pressure > alveolar pressure, (systole vs. diastole).

Question 13

What is “zone 3” when referring to the lungs?

Answer 13

Zone 3: continuous flow as capillary pressure always exceeds alveolar pressure.

Question 14

Normally we only observe zones 2 and 3 in someone at rest: top of the lungs is zone 2 changing to zone 3 at the bottom, when is zone 1 observed?

Answer 14

Zone 1 is only observed when breathing pressurized gas/air, (SCUBA, etc.), or at very low pulmonary artery pressures.

Question 15

What “zone” is the lungs in when lying down?

Answer 15

Zone 3, when lying down gravity/hydrostatic pressure becomes irrelevant as everything is at the same height and flow throughout the lungs

Question 16

T or F? During heavy exercise, (↑CO), blood flow increases throughout the lungs: the top of the lungs can increase up to ~ x8 whereas the bottom only to about ~ x3 due to the fact that the top of the lungs changes from zone 2 to 3 which the bottom is already at.

Answer 16

True

Question 17

During heavy exercise, the total blood flow through the lungs can ↑x4 to x7 and this is accommodated by what 2 ways?

Answer 17

1. Up to 3x increase in the number of open capillaries
2. Capillaries dilate ~ x2; this decreases the vascular resistance so much that the actual pulmonary arterial pressure does not increase much overall.

Question 18

Approximately what is the left atrial pressure threshold during left atrial “damming”/back pressure before edema occurs?

Answer 18

~23mmHg

Question 19

T or F? What can happen if the pulmonary pressure increases greater than 7-8mmHg?

Answer 19

Pulmonary pressure starts to rise significantly and the chances of edema increase dramatically.

Question 20

At rest, how long does it take blood to pass through the pulmonary capillaries? During exercise?

Answer 20

Rest: ~0.8 sec
Excercise: ~0.3 sec

Question 21

Approximately how much fluid is lost during capillary exchange?

Answer 21

~1%

Question 22

Fluid exchange across the pulmonary capillaries is essentially the same as for the systemic/peripheral circulation, except for?

Answer 22

1. Pulmonary capillary pressure is 7mmHg vs. 17mmHg.
2. Interstitial Fluid[IF]/ECF pressure in the lungs is -8mmHg vs. -5mmHg.
3. Tissue oncotic pressure is ~ 14mmHg, (rest of body typically < ½).
   4- Alveoli are very delicate and can easily be ruptured by any significant increase in IF/ECF pressure > 0mmHg, (= atmospheric): this would allow fluid to accumulate in the alveoli.

Question 23

Why is tissue oncotic pressure higher in the pulmonary capillaries than in the rest of the body?

Answer 23

Pulmonary capillaries are relatively leaky which allows significant amounts of plasma proteins to escape.

Question 24

Small openings or pores between Type __ cells allows any excess fluid to drain into the interstitial space and be removed by the lymphatics.

Answer 24

Type 1 cells

Question 25

T or F? Chronically elevated capillary pressure can cause decrease drainage

Answer 25

False, If chronic, increased drainage via the lymphatics is employed, (drainage can ↑x10!).

Question 26

Why is it bad if excess fluid accumulates in the intrapleural space?

Answer 26

This can reduce the coupling between the pleurae which is essential for an efficient increase in alveolar volume/decrease in pressure necessary for inhalation.