L23: Pulmonary Circulation & Gas Exchange Flashcards
high pressure - low flow
thoracic aorta –> bronchial arteries —>
trachea, bronchial tree, adventitia CT
low pressure - high flow
pulmonary artery and branches —> alveoli
what are the two circulations of the lung
high pressure; low flow
low pressure; high flow
the wall thickness of the pulmonary artery is 1/3 that of the aorta, thus
the pulmonary arterial tree has higher compliance
allowing pulmonary arteries to accommodate SV output of right ventricle
how much blood is w/in pulmonary circulation
450 ml
9%
failure of left side of heart causes _____ to build in pulmonary circulation
pressure
increases blood vol by 100% and increased bp
normal pulmonary arterial pressure =
24/9 mmhg
mean pulmonary arterial pressure =
15
left atrium pressure =
8
mean lap = 2
pressure gradient in pulmonary system =
7 mmhg
agents that constrict pulmonary arterioles
norepinephrine
angiotensin II
prostaglandins
agents that dilate pulmonary arterioles
isoproterenol
ACH
when standing, little blood flow goes to the ____ of the lungs, whilst the _____ of the lungs gets 5x as much
top gets little
bottom get 5x
agents that constrict pulmonary venules
serotonin
histamines
e coli endotoxin
effect of heavy exercise on blood flow thru lungs
- -flow increases 4-7x
- -increase # of open capillaries by 3x
- -increase pulmonary arterial pressure
because of all the pulmonary compensations during exercise, arterial pressure will ?
increase very little even during max exercise
what is physiologic shunt in the lungs
2% of blood in systemic arteries is blood that has bypassed the pulmonary capillaries
what are the 3 zones of blood flow in the lungs
- no flow
- intermittent flow
- continuous flow
relate the 3 zones of blood flow to specific lung areas
top = zone 2
middle, lower = z3
what effect does exercise have on blood flow zones to lungs?
converts top lungs from z2 to z3
pulmonary capillary pressure =
7 mmhg
peripheral tissue capillary pressure =
17 mmhg
interstitial fluid pressure in lungs is more _____ than peripheral is
more negative
pulmonary capillaries are leaky to _____ molecules because colloid osmotic pressure = ____. when peripheral = ?
proteins
= 14
peripheral <7
alveolar walls can be ruptured by any ____ pressure in the ______ _____ greater than alveolar air pressure
positive press.
interstitial spaces
capillaries –> pulmonary interstitium
total outward force
total inward force into capillaries
out = 29
in = 28
mean filtration pressure =
29 - 28 = 1 mmhg
excess fluid in the lungs is carried away by
lymphatics
left atrial pressure is normally never above
+6 mmhg
in left heart failure, left atrial pressure rises to ?
40-50 mmhg
normal = 6
left atrial pressure above 8 =
causes equal increases in pulmonary arterial pressure
left atrial pressure above 30 =
pulmonary edema
pulmonary edema occurs when pulmonary capillary pressure
greater than 25
most common causes of pulmonary edema
left side failure
mitral valve disease
damage to lung capillaries
pleural effusion
pumping of fluid from pleural space by the lymphatics creates a normal pressure in pleural space = -7
pleural effusion is edema of the
pleural cavity
hypoxia increases pressure in the
pulmonary artery
declines in pH produce _____ of other tissues
vasodilation
what are the results of bronchial obstruction or hypoxia on blood flow?
–constriction of vessels supply afflicted alveoli
–reduction of blood flow to that portion of lung
what are the factors that control oxygen conc. in the alveoli
- -rate of O2 absorption into blood
- -rate of new o2 entry into lungs
why alveolar ventilation cannot increase pO2 above 149 under normal circumstances?
because 149 mmhg is the max pCO2 in humidified air at normal atm air at sea level
what are the factors that control CO2 conc. in the alveoli?
rate of co2 excretion
alveolar ventilation
rate of co2 excretion
alveolar pCO2 increases in direct proportion to rate of excretion
alveolar pCO2 is _____ related to alveolar ventilation
inversely
list factors that determine how rapidly a gas will pass thru the respiratory membrane
memb. thickness
memb. surface area
diffusion coefficient of gas
partial pressure difference of gas
Va/Q ratio is the
ventilation-perfusion ratio
= alveolar ventilation/blood flow
normal Va/Q ratio =
0.8
pulmonary = 5 L/min ventilation = 4 L/min
Va/Q = 0 when
Va = 0
but there is still perfusion
Va/Q = infinite when
Q = 0
but there is still ventilation but no gas is exchanged
alveoli partial pressures for normal vs. ventilation obstructions
po2 = 149
pco2 = 0
for obstructions
normal
po2 = 104
pco2 = 40
shunted blood - when Va/Q is below normal a fraction of venous blood
passing thru pulmonary capillaries does not become oxygenated
the greater the physiologic shunt the greater
the amount of blood that fails to be oxygenated
when ventilation of alveoli is great but alveolar blood flow is low ?
there is more o2 in alveoli than can be transported in blood
thus ventilation of these alveoli is wasted
