Gas exchange - L4 Flashcards
What is total pressure the sum of?
Total pressure is the sum of all the indiviual gases the Partial Pressures
Ptotal = P1 + P2 + P3 + … Pn
What does partial pressure of a gas depend on?
Fractional concentration of the gas - quantity of gas relative to total quantity of gas in mixture
Total pressure of gas mixture
Formula for P gas?
Pgas = % gas x Ptotal
Composition of air:
79% Nitrogen
21% Oxygen
Trace amounts: carbon dioxide, helium, argon, etc.
Water can be a factor - depending on humidity (i.e. at
100% humidity then water takes 6.2% of air)
What is PN2 at sea level with 0% humidity?
At sea level our pressure is 760mmHg and assuming 0% humidity, the partial pressure of nitrogen is 600 mm Hg
PN2 = 0.79 x 760 = 600 mmHg
What is PO2 at sea level with 0% humidity?
PO2 = 0.21 x 760 mm Hg = 160 mm Hg
What is the pressure of air at sea level with 0% humidity
P air = 760 mm Hg = PN2+PO2
PCO2? at sea level with
Air is only 0.03% CO2
PCO2 = 0.0003 x 760 mm Hg = 0.23mm Hg
at 100% humidity P air?
P air = 760 mm Hg = PN2+PO2+PH20
PN2 at 100% humidity?
PN2 = 0.741 x 760 mm Hg = 563 mm Hg
PO2 at 100% humidity?
PO2 = 0.196 X 760 mm Hg = 149 mm Hg
PH20 at 1005 Humidity?
H20 = 0.062 x 760 = 47 mmHg
PCO2 at 100% humidity?
PCO2 = 0.00027 x 760 = 0.21 mmHg
Is alveoli pressure different to atmospheric?
Yes
Is the partial pressure higher or lower in the interstitial fluid surrounding the capillaries?
The interstital fluid surrounding capillaries partial pressure is lower, because the respiratory tissue consume oxygen and PCO2 is higher around 46 and PO2 is around 40 or lower
What happens when O2 and CO2 diffuses down pressure gradients?
when o2 and co2 diffuse down pressure gradients, o2 goes from blood to tissues and co2 moves from tissue to blood
What m is considered moderate altitude
2,000m considered moderate altitude
Fick’s law of diffusion
Diffusion rate V gas through a sheet of tissue depends on partial pressure gradient of gas, the surface rate of respirtaoyr membrane, thckness of emmbrane through which gas is diffused and diffsuion constant
exercise - fick’s law?
surface area increased as pulmonary blood pressure is raised by increased cardiac output - previous closed pulmonary capillaries are forced open
alveoli membrants are stretched further due to larger and deeper breaths
can increase with pathologies
what is the diffusion constant related to? which is higher CO2/O2?
solubility to the gas and to its molecular weight - inversely
CO2 is higher than that of O2
approx 20 times of O2
What is the diffusion process affected by?
Exercise and the thickening of the blood-gas barrier
Due to the diffusion process it is affected by exercise what do highly trained athletes face a risk of?
Risk of exercised induce arterial hypoxemia (EAIH)
PULMONARY OEDEMA - what is it characterised by?
Fluid accumulation in alveoli and/or interstitial space
treatment for pulmonary oedema
administering oxygen and diuretics
emergency case of treatment for pulmonary oedema
reduce altitude as fast as possible
What 4 things does this fluid accumulation that characterises pulmonary oedema do?
- Impairs diffusion (higher distance from alveoli to blood)
- Leakage in unprotected capillaries
- Increases work of breathing (decreased lung compliance)
- Arterial blood shows lower PO2 and higher PCO2
What are the causes of pulmonary oedema? 2 reasons
Increased capillary pressure via left heart failure which has an inability to supply sufficient BF
Reduced atmospheric pressure at high altitude
What happens to the body at 3000m altitude?
3,000m altitude inspired oxygen already down to 95 and PO2 is approx 60% - dangerous zone in this altitude, Oxyhametoxylin goes very steep curve and with a small increase in altitude from then on you will lose quite a lot of o2 so very challenging if above this altitude.
What is the highest m that humans live at and what happens to the body here?
5,000m altitude - highest that humans live at - arterial PO2 down to around 50 - body has adaptative responses such as making more RBCs so that we can eventually survive here
What is located greater than 5000m? What happens to the body here?
Greater than this -
Highest mountain summits: MT Everest: 8800m - recorded PO2 values is about 25 mm Hg - very low - must properly acclimitiase to get to this altitude - unliveable really
What is the air in alveoli saturated with and does this take up more or less of the gas available?
air in alveoli is saturated with water vapour so air is going to take more of the concentration of available gas
Changes of gases occurring continuously between alveoli air and capillary blood, what happens upon respiration and where?
Upon respiration, fresh atmospheric air mixes with air rich in CO2 and relatively poor in O2 in dead space of conducting zone
