Gas Diffusion Flashcards
Week 4
What is Boyels Law
gas pressure is inversely proportional to volume at a constant temperature
- what is Henry’s law?
the amount of gas in solution is proportional to the partial pressure of the gas
W- hat is Dalton’s law?
gases exert a pressure proportional to their abundance
What is Ficks Law?
Vgas= AD(P1-P2) / T
What layers do gases pass through in the diffusion pathway?
- gas space with alveolus
- alveolar fluid lining
- tissue barrier
- plasma layer
- diffusion into RBC
- O2 uptake by Hb
What factors would make the perfect lung?
- increased SA, coefficient of diffusion, and partial pressure gradient
- decreased thickness
why is alveolar PO2 so much lower than atmospheric atm PCO2?
RV and VD volume = high CO2 = dilutes O2
Increased VD vs VT compromises alveloar pressure
How does Po2 of blood Change in pulmonary circulation?
- loading of arterial blood equilibrates PaO2 with PAO2
-lowered by V/Q mismatch
- diluted by venous blood from bronchial veins
what is oxyhaemoglobin?
deoxyhaemoglobin with 4 O2 molecules
What is Hb saturation?
% heme units containing bound O
how does Hb promote O2 movement from the alevoli to venous blood?
O2 binding lowers PO2 = Boyle’s Law sees increased pressure differential between blood and alveoli = gradient = movement
Where does O2 and CO2 bind to Hb?
- Heme part
- globin part
What is meant to positive cooperativity?
reaction rates increase as more 2 binds to Hb
Arterial PO2 and saturation
= 100mmHG at ARTERIAL end
= 97.5% sat (Hb loaded w O2)
Venous PO2 and saturation
= 40mmHG at VENOUS enf
= 75% sat (O2 unloaded from Hb)
What is the advantage of the plateau region of Oxygen-HB dissociation curve ?
safety margin for maintain O2 saturation
What is the adv of the steep region of Oxygen-HB dissociation curve ?
small changes in Po2 = rapid desaturation
What is the significance of R shift of Oxygen-HB dissociation curve?
decreased Hb sat = decreased PO2 = favours O2 unloading in TISSUES
What is the significance of L shift of Oxygen-HB dissociation curve
increased Hb sat = increased PO2 = favours loading in LUNGS
What factor favour R shift?
increased PCO2
decreased pH
Increased Temp
What are the 3 ways by which CO2 is transported?
- dissolved in plasma
- bound to Hb
- in HCO3
What is the overall function of Chloride shift?
maintains RBC electroneutrality
What is the function of Chloride shift in lungs?
increases HCO3 = CA reaction moves BACKWARDS
Maintains pressure gradient for moving CO2 out of RBCs
What is the function of Chloride shift in Tissues?
influx Cl in RBC echange CO2
decreases HCO3 to keep CA moving FORWARDS
mainatins pressure grandet for moving CO2 INTO RBCs
How is Left Shift created and where does it occur?
decreased H+ and CO2 to HbO2 = favours O2 unloading - L shift
in Lungs (Bohrs effect)
How is right shift created and where does it occur?
Increased binding of H+ and CO2 = favours UNLOADING of O2
in tissues (bohrs efffect)
what is the function of the Haldane effect in the lungs ?
OcyHb binds O2 more readily
loading of O2 favours releae of CO2 and H+
what is the function of the Haldane effect in the tissues
deoxyHb binds CO2 and H= more readily
UNLOADNG of O2 favours binding of CO2 and H+
What are the PO2 partial pressure values in:
a) PiO2
b) Alveolar
c) Tissues?
a) 150mmHg
b) 100mmHg
c) 40mmHg
What are the PO2 partial pressure values in:
a) Arterial Blood
b) venous blood
a) 100mmHg
b) 40mmHg
What are the PCO2 partial pressure values in:
a) PiO2
b) Alveolar
c) Tissues?
a) 150mmHg
b) 40mmHg
c) 46mmHg
What are the PCO2 partial pressure values in:
a) Arterial Blood
b) venous blood
a) 40mmHg
b) 46mmHg
What is pressure due to?
Collision of gas molecules
What is Dalton’s Law?
Gases exert P proportional to their abundance
What is Henry’s law?
Amount of gas in solution is proportional to partial pressure of the gas
Increased P = Increased gas dissolved in fluid
What do membranes need for diffusion to occur in
maintain a partial pressure gradient across all membranes and fluid layers
What three things will increase diffusion according to Fick’s Law?
- increased SA
- Decreased thickness of resp membrane
- increased partial pressure
Describe Coopertivity
Hb shape changes when O2 binds
increases reaction rate:
- as O2 binds it gets easier for subsequent ones to bind
- as O2 is released, it strats of easier but then gets harder
PaO2 =
O2 dissolved in plasma
SaO2 =
% O2 bound to Hb
CaO2 =
= total O2 in blood
What occurs to the Hb dissociation curve at increased Temperature?
Right shift
decreased SaO2
favours unloading O2
Summarise Bohr Effect
Relationship between PO2 and HBO2
how CO2 affects affinity of Hb for O2
Decrease in 1 = increase in another
Summarise Haldene’s Effect
HbO2 + CO2
How O2 affects affinity of Hb for CO2
increase in Hb)2 = decreased Hb affinity for CO2
What is the effect of humidifying inhaled air? normally.
moist environment creates a more favourable environment for O2 to move from lungs to blood
Humidifed air impact at sea level vs high altitude
HA= Fixed partial pressure of humidified air in resp tract (47) displaces other gases, reducing available pressure available for O2. puts strain as already less PO2.
SL: O2 is in abundance to humidification is not as essential.
what are the advantages of of the slow rate at which alveolar air is renewed?
stable gas exchange (composition of air is constant)
prevents sudden changes in blood gas levels
Why is the partial dif between arterial and venous saturation levels much lower for CO2 than O2?
Tissues use O2 faster than the rate that CO2 is produced
Is CO2 or O2 more soluble?
CO2
