Lec 26 Flashcards
air is composition of
78% N2
21% O2
0.033% CO2
Dalton LAw
total pressure exerted by mixture is sum of pressures exerted by all individuals gases
pressure exerted by individual gas
partial pressure
P gas in dry air
p atm * %gas in atmosphere
p gas in humid air
(p atm- p H2O) * %gas in atmosphere
P(CO2) and P(O2) in atmosphere
PO2=160 mmhg
PCO2= 0.25 mmhg
alveolar partial pressure
PO2= 100mmhg
PCO2= 40mmhg
because of still air
ventilation can vary to match —- with —-
perfusion with ventilation
O2 and CO2 should pass from what barriers in body
epithelial cells and capillary endothelial cells
diffusion if gas is governed by – law
fick
rate of diffusion directlly proportional to
1- surface area (A)
2- membrane permeability (D)
3- partial pressure gradient
rate of diffusion inversely proportional to
1- diffusion distance (T)
membrane thickness
interstitial fluid
diffusion rate
ADdP/T^2
atmosphere and alveoli pressure gradient
O2 will diffuse inside alveoli (160>100)
CO2 will diffuse outside of alveoli to atmosphere(40>0.25)
pulmonary circulation is btw
alveoli and capillary
systemic circulation is btw
arterial and tissue
P(O2) and P(CO2) arterial blood
100 mmHg
40 MMHg
large partial pressure gradient
P(O2) and P(CO2) venous blood
<40 mmHg
>46 mmHg
Diffusion reaches —- under normal circumstances
Equilibrium
what it mens by diffusion equilibrium
Maximally offload CO2
Maximally upload O2
Hypoxia
not enough O2
Alveolar gas exchange is influenced by
1- adequate perfusion of alveoli
2- gas diffusion btw alveoli and blood
3- O2 reaching alveoli
Factors that decrease O2 reaching the alveoli
1- low O2 content in atm
2- low alveolar ventilation
low alveolar ventilation is caused by
1- decreased lung compliance
2- increased airway resistance
3- CNS depression(drug,alcohol)
pathological conditions leads to hypoxia
1- emphysema
2- asthma
3- fibrotic lung disease
4- pulmonary edema
Emphysema
destruction of alveoli
– less SA for gas exchange
Low SA , PO2 low or normal
asthma
1-bronchioles constricted
2-increase airway resistance
3-decrease alveolar ventilation
Low PO2
fibrotic lung disease
1- build up scar tissue around alveoli
2- thickened alveolar membrane
3- slow gas exchange
4- decrease alveolar ventilation
higher distance, normal or low PO2
pulmonary edema
fluid in interstitial space increases (heart failure)
arterial PCO2 may be normal as soluble in water
higher distance
