Lecture 4: Gas Exchange Flashcards
what is pulmonary gas exchange?
diffusion of O2 from alveolar air into pulmonary blood
CO2 moves from ____ to ___
pulmonary blood to alveolar air
gases difuse down their ___ gradients
partial pressure
what is systemic has exchange?
excahnge of O2 and Co2 between systemic capillaries and tissue cells
the exchange of O2 and CO2 occurs via ___ diffusion
passive
passive diffusion is governed by what 3 laws?
dalton, henry, Fick
what is Dalton’s law?
the pressure exerted by each gas in a mixture is independent of the pressure exerted by other gases becasue the molecules are so far apart
the pressure of each individiual gas is its ___ pressure
partial
the total pressure of the mix of gases is the sum of ____
all the partial pressures
what is atmospheric pressure?
760mmHg
what is the partial pressure of humidified air? why is it lower than the atmospheric pressure?
500mmHg; because the partial pressure of water has to be subtracted
____ law states that the amount of a gas that dissolves in a liquid is directly proportional to the partial pressure of the gas in which the liquid is in equilibrium
Henry’s
what will happen to the difusion rate as long as Po2 in gas phase is higher than the Po2 in liquid?
there will be a net difusion of O2 into liquid
the concetration of a gas is equal to the ___ and ___ of the gas
pressure and solubility
the more soluble a gas, the ____ its concentration will be at any given pressure
greater
transfer of gases across cell membranes and capillary walls occurs by diffusion, described by _____’s law
Fick
Fick’s Law depends on what variables?
surface area, diffusion coeficient, partial pressure difference, thickness of membrane
what are 3 important parameters for efficient gas exchange in the lungs?
- partial pressure difference
- large surface area
- disatnce needs to be small
what is the driving force of efficient gas exchange according to Fick’s Law?
partial pressure difference
the diffusion coeficient for CO2 is ~ ____x greater than for O2
20
when diffusion is decreased, is hypoxia or hypercapnia likely to happen first?
hypoxia
the rate of O2 diffusing out of the alveoli is great enough that complete ____ is reached well before the blood reaches the end of the alveolar-capillary exchange unit
equilibrium
if there is an abnormal alveolar diffusion barrier, this will impair diffusion and ____ will not be reached
equilibrium
give 2 examples of conditions that impair alveolar diffusion, preventing equilibrium being reached
fibrosis and pulmonary edema
when an alveolar-diffusion barrier such as fibrosis is present it is almost impossible to reach equilibrium when the barometric pressure ____
drops
what are the 2 main parts of hemoglobin?
- globin
2. heme
what is the structure of globin?
protein made of 4 polypeptide chains
what is contained in the heme? what is its function>
Fe, carries O2
how many O2 can be bound to 1 hemoglobin?
4
O2 is not very soluble in water, and therefore also not in our blood, what is used to allow its transport in the body?
hemoglobin
as Po2 increases, more O2 associates with ___
hemoglobin
the oxygen-hemoglobin dissociation curve has what shape?
sigmoidal
the oxygen hemoglobin dissociation curve is an example of ____ cooperativity
positive
between 60-100mmHg the O2 hemoglobin curve hits a plateau. The hemoglobin is ___% saturated with O2. whay does this plateau exist?
90; safety feature, plateau allows pO2 to drop significantly before the effects are truly felt by hemoglobin
the binding of O2 to hemoglobin is both ___ and fully ___
rapid; reversible
what is P50 on the o2 hem curve?
Po2 where Hb is 50% saturated by O2
changes in P50 reflect changes in hb’s ____ for O2
affinity
an increase in P50 means a ____ in Hbs affinity for O2 and vice versa
decrease
the binding of the first O2 to Hb causes a ____ that makes it easier for the second O2 to bind and so on
conformational change
a lower pH causes the affinity of Hb for O2 to ____
decrease
a high blood Co2 causes the affinity of Hb for O2 to ___
decrease
high temperature causes the affinity of Hb for O2 to ___
decrease
addition of BPG/DPG causes the affinity of Hb for O2 to ___
decrease
the affinity of Hb is often decreased by _____ hydrogen ionproduction
increased
CO prevents the binding of ___ to ____
O2 to Hb
CO has a ____x more affinity for Hb than O2
250
cigarette smokers and those who live close to traffic polution have up to __% of their Hb bound to CO. What is the normal % of Hb boud to CO?
10; 1
CO poisoning causes the O2 Hb curve to shift in what direction?
left
CO poisoning _____ the affinity of HB for O2. what is the effect of this?
increases; Hb holds onto it and doesnt let it do its job
in what 3 ways is CO2 carried in the blood?
- dissolved
- bound to carbamino compounds
- in the form of bicarbonate
the majority of CO2 is carried in the blood in what form ?
bicarbonate ions
the enzyme used to make CO2 and H2o into carbonic acid is ____ and is only found in the _____
carbonic anhydrase; RBC (not plasma!)
as blood picks up more Co2, the bicarbonate ions accumulate inside ____
RBC
how can bicarbonate exit the RBC?
by exchanging for Cl (chloride shift)
the ratio of sodium bicarbonate to carbonic acid is ___ . what is this vital to?
20 to 1 ; acid base balance
as long as the ration remains at 20:1, the pH will remain at
7.4
there is a balance between HCo3- governed by ___ and PCO2 governed by ___
renal excretion; ventilation
if a person is hypoventilating or has a lung disease that prevents normal elimination of CO2, there is a ___ in arterial PCO2 and ___ in arterial H+ concentration. This is called respiratory ___
increase; increase; acidosis
if a person is hyperventilating, there is a ___ in arterial CO2 and a ____ in arterial [h+]. This is called respiratory ___
decrease; decrease; alkalosis
H+ in the RBC is buffered by ___
deoxyhemoglobin
