Lecture 22: Pulmonary Blood Flow and Gas Exchange Flashcards
what are the 2 major circulations
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
What is the role of Pulmonary circulation?
perfuse alveoli to pu O2 for delivery to the systemic circuit & drop off CO2 returning from systemic circuit into the alveoli
alveolar vessels perfuse the alveolar ______
septum
- and are directly exposed to pressure changes that occur during breathing
what are the extra alveolar vessels / bronchovascular bundle composed of
pulmonary arteries, veins, and bronchi w/ loose CT
- affected by pleural pressure more so than alveolar pressure
the diameter of the blood vessel is a function of ??
the pressure difference b/w the inside and outside of the blood vessel
what happens to diameter of vessel during exercise
dilation
pressure within the vessels increase, increasing transmural pressure which causes alveolar vessels to dilate
what is transmural pressure
the difference in pressure between the intravascular pressure and the pressure exerted on the outside of the vessel wall.
changes in vascular resistance result from changes in ____
vascular transmural pressure
changes in vascular resistance result from changes in ______
vascular transmural pressure
what causes extra alveolar vessels to dilate
expansion of pleural cavity, generates increased negative pleural pressure which increases transmural pressure
as lungs expand, blood vessels also expand, ______ resistance
decreasing
what is the strongest control of arterial radii
hypoxia
hypoxia leads to _____ of the pulmonary arteries, why?
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
what is atelectasis
lung collapse
the extent of hypoxic vasoconstriction depends on species and ?
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
pulmonary fibrosis and diffusion distance (L)
interstitial fibrous tissue increases diffusion distance (L)
pneumonia effect on diffusion distance
fluid or pus in the alveoli increase diffusion distance
congestive heart failure effect on diffusion distance
edema in the lung increases diffusion distance
what limits the amount of O2 that can be taken up by the lungs?
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
under what conditions can O2 become diffusion-limited
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
