23.5 pysical properties of gas exchange Flashcards
diffusion of gases through the respiratory membrane depends on 4 things. what are they?
membrane thickness
diffusion coefficient of gasses (how easily a gas diffuses through a liquid or tissue)
surface area
partial pressure difference
how does membrane thickness affect the diffusion rate of gases?
the thicker the membrane, the slower the diffusion rate
what is the diffusion coefficient of a gas?
how easily a gas diffuses through a liquid or tissue
which is more diffusable, CO_2 or O_2?
CO_2 is 20x more diffusable than O_2
what affects the diffusion coefficient of a gas?
surface areas of the membrane (damage)
partial pressure of gases in alveoli and bl
what can affect the surface area of the lungs?
diseases like emphysema and lung cancer can decrease the available surface area
how do partial pressure differences affect gas exchange?
gases move from areas of high partial pressure to areas of low partial pressure
what is the total pressure of the atmosphere (at sea level)?
760 mmHg
what is partial pressure?
the pressure exerted by each type of gas in a mixture
in a mixture of gases, the percentage of each gas is proportionate to its _________
partial pressure
what is H_2O vapor pressure?
pressure exerted by gaseous H_2O in a mixture of gases
what does air in the resp system contain humidity?
mucous linings of the system
what determines the [ ] of a gas in a liquid?
its partial pressure + solubility coefficient
draw the simple gas exchange picture
DO IT
how is O_2 transported?
- 5% is dissolved in plasma
1. 5% dissolved in plasma
what does the O_2-Hgb dissociation curve describe?
the % of Hgb fully saturated with O_2 at any given PO_2
what does the O_2-Hgb dissociation curve show about O_2 saturation at rest?
that Hgb is almost completely saturated with O_2 when PO_2 is 80 mmHg or higher. At lower PO_2, the O_2 dissociates from Hgb
draw the O_2-Hgb dissociation curve
DO IT
what is the environment of the tissue vs that of the lungs in regards to the O_2-Hgb dissociation curve?
TISSUE lower pH 7.0 ish (more acidic) increased CO_2 increased Temp LUNGS higher pH lower CO_2 lower Temp
how do the tissues favor Hgb unbinding (dissociating)?
lower pH 7.0 ish (more acidic)
increased CO_2
increased Temp
how do the lungs favor Hgb binding?
higher pH
lower CO_2
lower Temp
which direction does the O_2-Hgb dissociation curve move in an environment that is low in pH, high in CO_2, and high in temp?
to the right (Hgb becomes “fully” saturated only at higher PO_2
how much O_2 is released to the tissues at rest?
23%
how is CO_2 transported?
70% as bicarbonate ions
23% bound to Hgb
7% in sol’n with plasma
when does Hgb bind more readily to CO_2?
when the Hgb has released its O_2
give the CO_2 to bicarbonate ion (HCO_3^-) rxn
Where does this take place?
CO_2 + H_2O <> H_2CO_3 <> H^+ + HCO_3
maybe write it on paper
arrows to the R happen at the tissue level
arrows to the L happen at alveoli
describe the Chloride shift
at the tissue capillaries: as CO_2 enters RBC, it reacts with H_2O to form HCO_3^- and H^+ ions
Cl^- ions enter the RBC as HCO_3^- leaves (balance of ion mvmt)
what happens to the H+ ions after they split from carbonic acid (H_2CO_3) to form H^+ and bicarbonate (HCO_3^-)?
H^+ ions combine with Hgb
what promotes the conversion of CO_2 to HCO_3^-?
HCO_3^- leaving the cell
and
H^+ binding to the Hgb
what does CO_2 react with to form H_2CO_3?
H_2O and carbonic anhydrase
what is H_2CO_3?
carbonic acid
what is HCO_3^-?
bicarbonate ion
explain what happens with CO_2 transport at the pulmonary capillaries
CO_2 leaves RBCs, which results in the formation of additional CO_2 from carbonic acid (H_2CO_3)
bicarbonate ions are exchanged for Cl^- and the H^+ ions are released from the Hgb
release of the H^+ from Hgb means O_2 can bind at the alveolus, exactly where the conditions favor it (more basic pH, lower Temp, lower CO_2)
how does the resp system regulate bl pH?
increased plasma CO_2 levels lower bl pH bc as plasma CO_2 increases, so do H^+ levels, which decreases the pH (more acidic, more H^+)
how does ventilation rate affect plasma CO_2 levels?
hyperventilation decreases plasma CO_2 levels
hypoventilation increases plasma CO_2 levels
what is the Bohr effect?
the effect of pH on the O_2-Hgb dissociation curve
as pH of bl decreases (becomes more acidic), the amount of O_2 bound to Hgb at any given PO_2 also decreases
what causes the Bohr effect?
it occurs bc a decreased pH yields an increase in H^+ ions that combine with Hgb, change its shape and O_2 cannot bind
