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38 Cards in this Set
- Front
- Back
oxidation in living cells serves what functions |
to provide energy for endergonic cellular processes; to transform dietary materials into cellular constituents; the end point for O2 is the mito; a major use of the energy derived from biological oxidation is to maintain the body in a state remote from equilibrium |
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the partial pressure of any gas is |
the product of the ambient pressure in the proportion of total gas composition made up of the specific gas of interest; for example air is composed of approx 21% O2 assuming there's a total pressure of 760 mmHg sea level and no water vapor pressure the partial pressure of O2 is 0.21(760=160 mmHg |
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the 4 gases to consider in pulmonary physio |
nitrogen, oxygen, CO2, and water vapor; the tractional pressures of these gases sum up in any mix of gases |
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the partial pressure of a given gas is defined as |
the pressure exerted by that gas alone |
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calculation of partial pressures- gas mixtures |
in a mix of gases the partial pressure of a given gas is directly proportional to the volume that gas contributes to the total volume; that is if we define the fraction of any gas, Fx, as the ratio of the volume of that gas, Vx, to the total volume of all gases: Fx=Vx/Vtotal then the partial pressure contributes by that gas, Px, is simply that fraction multiplied by the total pressure, or Px=Fx(Ptotal) |
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calculation of partial pressures- vapors |
when a gas is in contact with a liquid and is in equilibrium (saturated) with the liquid the partial pressure of the gas is a function of temp; the one gas to which this applies in a normal respiration is water; the lungs and airways are always moist and inspired gas is rapidly saturated with water vapor in the upper segments of the resp system; the temp in the airways and lungs is almost identical with deep body temp; at this temp water vapor has a partial pressure of 47 mmHg; 760-47=713 so PO2=0.21(713)=150 mmHg and PN2=0.79(713)=563 mmHg |
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calculation of partial pressures- dissolved gases |
when a gas is dissolved in a liquid its partial pressure is determined by the components of the solution which bind or combine with the gas, and the total constant or concentration of the gas in the liquid; such a relation between partial pressure and content is termed a saturation or dissociation curve; each gas has a particular saturation curve determined by the physical and chemical properties of the solution; when discussing the transport of gases in the blood one must consider in detail the saturation curves for O2 and CO2 |
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partial pressure and altitude |
the concentration of O2 doesn't change with altitude but the pressure does so PO2=0.21(whatever the barometric pressure is) |
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the pressure exerted by water vapor depends only on |
temp; if you increase the temp to 100 degrees celcius the partial pressure of water vapor increases to 760 mmHg; the boiling point is defined as the temp at which the saturated vapor pressure of a liquid is equal to the surrounding atmospheric pressure |
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partial pressure of O2 in moist air |
0.21(760-47)=150 mmHg; assuming room temp |
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if a liquid and a gas are at equilibrium then the partial pressures |
of all gases in the liquid are equal to their partial pressures in the air (Pgas in liquid=Pgas in air); if the temp stays constant increasing the pressure will increase the amount of dissolved gas; remember that partial pressure is NOT equivalent to content because it also depends on the solubility of the gas in that liquid; the amount of gas that dissolves (Cgas)=sgas(Pgas) Cgas=gas concentration sgas=solubility of gas in liquid Pgas= partial pressure of the gas |
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the solubility of O2 in water= |
0.45/150=0.003 mL/(dl mmHg) |
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why can't we use O2 in solution to provide the aerobic needs of the tissues |
solubility of O2 in water=0.003; PO2 in arterial blood=100 mmHg; therefore the [O2] dissolved in arterial blood=100(0.003)=3 mL/L; CO=30 L/min; max O2 available by this mechanism is therefore 90 mL/min but the O2 requirements for respiring tissues is 3000 mL/min |
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the 3 forms of hemoglobin |
HbA, HbF, and HbS |
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HbA |
adult hemoglobin |
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HbF |
fetal hemoglobin; fetus's are born with this isotype; it is replaced by HbA after a few months postpartum; HbF has a high affinity for O2; this makes sense since fetus' develop in a low O2 atmosphere |
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HbS |
sickle cell hemoglobin; mutation of E6V (Glu #6 --> Val); causes hemoglobin to polymerize at low PO2 |
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O2 binding induces substantial structural changes in hemoglobin |
this happens primarily at the iron site; the 3D structure of hemoglobin is best described as a pair of identical alphabeta dimers; these 2 dimers are linked by an extensive interface that includes the C-terminus of each dimer; the deoxy form represents the T state; binding of O2 results in a substantial change from T to R |
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How does O2 lead to this structural change? |
when the iron ion moves in the plane of the porphyrin ring the His residue moves with it; the C-terminal end of the alpha helix connected to this His IS the interface between subunits; consequently the structural transition at the iron ion is transmitted through the subunit interface to the rest of the molecule |
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myoglobin |
delivers O2 to the muscles; single protein chain with one prosthetic group (heme); does not display cooperative O2 binding (unaffected by changes in O2 pressure) |
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the oxygen dissociation curve |
the amount of O2 combined with hemoglobin depends on the pO2; the right side of the curve is the loading section and the left is the unloading portion; a large change in pO2 at the loading end produces only a small change in O2 concentration (or % Hb saturation)(note the almost flat slopes); in contrast small changes in pO2 at lower values produce large changes in O2 concentration (this section has a steep slope favoring unloading with O2 moving into the tissues); note that even at a pO2 of 600 mmHg there is only a minimal increase in content |
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advantages to this sigmoid shape |
at high altitude and the PO2 falls to 60 mm Hg there is still a large amount of O2 attached to HbA; the steep part is also valuable in venous blood when you extract O2 the fall in PO2 for a given amount of O2 extracted is low |
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values to remember for hemoglobin saturation |
97% when PO2=100 mmHg (arterial); 75% when PO2=40 mmHg (typical venous); the P-50 (when 50% (half saturation) occurs) PO2=27 mmHg |
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the O2 capacity |
the max amount of O2 that can be combined with hemoglobin; one gram of Hb can combine with 1.39 mL of O2 and normal CBC values for blood=HbA concentration of 15 g/dL therefor the normal O2 capacity is 1.39(15)=20.8 |
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calculating the [O2] in blood |
O2 concentration is the total amount of O2 in the blood (that combined with HbA plus dissolved); [O2 capacity x O2 saturation] + [0.003 x PO2]= [1.39(15)(97/100)] + [0.003(100)]=20.2+0.3= 20.5; so 20.2 bound and 0.3 dissolved |
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polycythemia |
marrow makes too may RBC; a [HbA]=20, 100 mm Hg, the saturation is 100% but there is a considerable larger amount of O2 dissolved in the blood because of the larger amount of HbA |
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anemia |
the [Hb} is reduced to 10, Hb=10, at 100 mmHg, saturation is still 100% but the O2 concentration is less |
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at high altitude |
reduced pO2 to 60 mmHg, O2 saturation will be reduced, and the amount of O2 in the blood is also reduced |
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shifts of the O2 dissociation curve |
there are 4 factors that shift the curve to the right or reduce the affinity of O2 for HbA; PCO2, [H+] (acid), DPG, and temp (all of these increase with exercise); in other words CADET |
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the 3 mechanisms to transport CO2 in the blood |
dissolved in the blood, as bicarbonate, as a carbamino compound |
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solubility of CO2 in the blood |
0.067 (way greater than O2s 0.003) and as a result in arterial blood there is 5% CO2 dissolved; when CO2 has been released to the alveolar gas about 10% of the CO2 is dissolved in the blood |
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formation of bicarbonate |
this occurs via the hydration of CO2; CO2+H2O<-->H2CO3 (kinetically slow reaction) H2CO3<-->H+ + HCO3- (spontaneous); however the enzyme carbonic anhydrase is red blood cells can facilitate the conversion of CO2; the H+ are mopped up by the reduced HbA in the blood so the lower the saturation in the blood the better able it is to take up CO2 through mass action; this increases the osmolar properties of the RBC so water comes in; bicarbonate is pumped out of the cell so Cl- is pumped into the cell to balance it |
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formation of carbamino compounds |
CO2 can bind to the amino terminus of some proteins; the most important is reduced HbA |
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the effect of 2,3 bis-phosphoglycerate (DPG) |
if you look at O2 binging in purified hemoglobin vs hemoglobin in RBCs you notice a dramatic difference of affinity; O2 affinity of purified hemoglobin is much higher than that in RBCs; this compound exists in RBCs at roughly the same concentration as does hemoglobin (2 mM); without this small anionic compound in RBCs it would be difficult to wrench the O2 form hemoglobin's grasp; an example of heterotropic allostery; this is only present in the T form of hemoglobin (the deoxy form) stabilizing it; the effect is to reduce O2 affinity |
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transport of carbon monoxide |
carbon monoxide has a very high affinity for HbA (about 240 times that of O2); if you have a small partial pressure of CO in the blood then it is able to tie up the HbA binding sites; for a very small partial pressure of CO it can saturate the available Hb very easily; CO makes it difficult for O2 to be released from Hb; it shifts the dissociation curve to the left which impedes unleading of O2 |
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surfactant |
a material that reduces the surface tension of the alveolar lining; made up of 90% phospholipid and 10% protein; alveolar type II cells secrete it; aka DPPC; increases the compliance of the lung, increases the stability of the lung, reduces the tendency of pulmonary edema |
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martian weather forecast (Sol 872 MSL); current max temp=1 degreeC; current atmospheric pressure=6.8 mmHg; atmospheric composition 95% CO2, 2.7% N2, 1.6% Ar, 0.13% O2, 0.035% water vapor; what is the current partial pressure of O2 on Mars? a. 0.00884 mmHg b. 5.51 mmHg c. 0.884 mmHg d. 1.18 Pa |
0.0013(6.8)=0.00884 mmHg |
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the presence of hemoglobin in normal arterial blood increases its O2 concentration by how many times? a. 10 b. 30 c. 50 d. 70 e. 90 |
70; 20.5/0.3=about 70 |