Lecture 22: Pulmonary Blood Flow and Gas Exchange

Question 1

what are the 2 major circulations

Answer 1

pulmonary & bronchial

pulmonary - receives blood from RV, perfuses alveolar capillaries and participates in gas exchange

Bronchial - brings blood from systemic circuit to supply the airways and other structures
- bronchial vessels anastomose w/ pulmonary circulation so they work in conjunction
- this way, if bronchial circulation is obstructed the lung doesn’t die

Question 2

What is the role of Pulmonary circulation?

Answer 2

perfuse alveoli to pu O2 for delivery to the systemic circuit & drop off CO2 returning from systemic circuit into the alveoli

Question 3

alveolar vessels perfuse the alveolar ______

Answer 3

septum
- and are directly exposed to pressure changes that occur during breathing

Question 4

what are the extra alveolar vessels / bronchovascular bundle composed of

Answer 4

pulmonary arteries, veins, and bronchi w/ loose CT
- affected by pleural pressure more so than alveolar pressure

Question 5

the diameter of the blood vessel is a function of ??

Answer 5

the pressure difference b/w the inside and outside of the blood vessel

Question 6

what happens to diameter of vessel during exercise

Answer 6

dilation
pressure within the vessels increase, increasing transmural pressure which causes alveolar vessels to dilate

Question 7

what is transmural pressure

Answer 7

the difference in pressure between the intravascular pressure and the pressure exerted on the outside of the vessel wall.

Question 8

changes in vascular resistance result from changes in ____

Answer 8

vascular transmural pressure

Question 9

changes in vascular resistance result from changes in ______

Answer 9

vascular transmural pressure

Question 10

what causes extra alveolar vessels to dilate

Answer 10

expansion of pleural cavity, generates increased negative pleural pressure which increases transmural pressure

Question 11

as lungs expand, blood vessels also expand, ______ resistance

Answer 11

decreasing

Question 12

what is the strongest control of arterial radii

Answer 12

hypoxia

Question 13

hypoxia leads to _____ of the pulmonary arteries, why?

Answer 13

vasoconstriction
- poorly ventilated alveoli lead to them having low PO2s so there is no benefit in sending blood to those alveoli

vasoconstriction redistributed blood flow to better ventilated regions of the lung

Question 14

what is atelectasis

Answer 14

lung collapse

Question 15

the extent of hypoxic vasoconstriction depends on species and ?

Answer 15

the thickness of pulmonary vascular smooth muscle (VSM)

VSM in small pulmonary arteries varies in thickness b/w species
- cows and pigs have the thickest VSM layers and the strongest response to hypoxic vasoconstriction (HV)

-dogs and sheep have small amounts of VSM (and therefore have a harder time adjusting to high altitude), horses are intermediate

Question 16

pulmonary fibrosis and diffusion distance (L)

Answer 16

interstitial fibrous tissue increases diffusion distance (L)

Question 17

pneumonia effect on diffusion distance

Answer 17

fluid or pus in the alveoli increase diffusion distance

Question 18

congestive heart failure effect on diffusion distance

Answer 18

edema in the lung increases diffusion distance

Question 19

what limits the amount of O2 that can be taken up by the lungs?

Answer 19

O2 uptake is perfusion-limited in healthy animals

the max rate at which blood can be delivered to lungs by heart (cardiac output)

–perfusion limitation hypothesis

Question 20

under what conditions can O2 become diffusion-limited

Answer 20

if there is insufficient time for equilibration to occur bw the blood and alveolar gas (rare in healthy animals) and or if the diffusion capacity (DL) is abnormally low