RS Lec 5 Flashcards
pressure exerted by gas molecules due to
their motion, motion exerts pressure
pressure increases as
temp increases, conc increases
dalton’s law
total pressure= sum of individual pressures (partial pressures)
diffusion
rate of transfer of gas through tissue/unit time
diffusion is proportional to (3)
- tissue area
- difference is gas partial pressure
- diffusion constant
diffusion is inversely proportional to (1)
-tissue thickness
solubility of CO2 and O2
carbon dioxide solubility is much higher than O2 but have similar molecular weight, co2 diffuses 20x faster than o2
Diffusion constant (D) proportional
-to solubility/ square root (molecular weight)
henry’s law
-amount of gas dissolved in a liquid is directly proportional to partial pressure of gas in equilibrium
concentration of gas (in liquid) =
pressure (only gas dissolved in liquid contributes to partial pressure) x solubility
PO2 in air > PO2 in alveoli because (3)
- humidification of air in respiratory tract ↓
- loss of O2 to blood diffusion ↓
- mixing of inspired air with alveolar air (functional residual capacity) ↓
what determines alveolar PO2? (4)
- PO2 in atmosphere
- alveolar ventilation (Va)
- metabolic rate
- perfusion
what determines alveolar PCO2?
- PCO2 in atmosphere
- alveolar ventilation (Va)
- metabolic rate
- perfusion
increasing alveolar ventilation will
- increase alveolar PO2
- decrease alveolar PCO2
Increasing metabolic rate will
- decrease alveolar PO2
- increase alveolar PCO2
partial pressure of gas in alveoli determine
-arterial levels,
cardiac output
-volume of blood pumped by heart per minute (ml blood/min)
systemic circulation
-high pressure system needed to deliver blood to body (high resistance system)
pulmonary circulation
-low pressure system needed to deliver blood to lungs (high pressures= lung edema)
systemic circulation and pulmonary circulation
flow systemic circulation = flow pulmonary circulation
pulmonary low pressure system
-need to pump blood only to the top of the lung, important for avoiding rupture of resp. membran + edema formation
pulmonary low resistance system
-R is less than 1/10 of that in the systemic circulation due to: shorter and wide vessels
pulmonary high compliance vessels
- higher number of arterioles with low resting tone
- due to thin walls and paucity of smooth muscle, can accept large amount of blood
- can dilate in response to modest increases in arterial pressure
pulomonary blood volume
450 ml
capillary blood volume
70 ml at rest
200 ml during exercise
time blood passes through pulmonary capillaries
- at rest: 0.75 s at rest
- cardiac output increases: 0.3 s
if capillary pressyre falls below alv pressure
capillaries close off, diverting blood to other pulmonary capillary beds with higher pressures.
air should be delivered to regions with
blood flow and vice versa
ventilation/perfusion (V/Q) ratio
balance between lung ventilation/ lung perfusion
-affects alv. arterial levels of oxygen + carbon dioxide
lung ventilation
O2 ATM –> alveoli/ CO2 alveoli –> ATM
lung perfusion
O2 alveoli –> blood/CO2 blood –> alveoli
Increase in ventilation
- PO2 + PCO2 in alveoli ≈ PO2 + PCO2 in ATM
Increase in perfusion
- PO2 + PCO2 in alveoli ≈ PO2 + PCO2 in mixed-venous blood
high V/Q ratio
-lack perfusion (alveolar dead space)- aire not reaching the blood
low V/Q ratio
-lack ventilation (airway obstruction –> shunt)
local V/Q ratio determines
-local alveolar PO2 + PCO2
top of the lungs V/Q
- high V/Q
ventilation is greatest
at bottom of the lung
perfusion is greatest
at the bottom of the lung (depends on gravity and posture)
V/Q is not
constant/uniform in healthy lung
apical V/Q
3 x V/Q
basal V/Q
0.6 x V/Q (closer to ideal)
pulmonary hypoxic vasoconstriction
-response of pulmonary capillaries to low O2, diverts blood to oxygen rich alveoli
local perfusion decrease to match local decrease in ventilation
↓ air flow= ↓ PO2 (alveoli) = vasoconstriction= ↓ blood flow
local ventilation decrease to match local decrease in perfusion
↓ blood flow= ↓ PCO2 (alveoli) = bronchoconstriction = ↓ air flow
