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30 Cards in this Set
- Front
- Back
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Dissolved oxygen
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Gas dissolved in plasma. Accounts for 2% of total blood O2 content.
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Arterial content of dissolved O2
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100mmHg x 0.003mlO2/100ml = 0.3mlO2/100ml of blood
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Delivery of dissolved O2
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Being more like flow, units are in ml/min.
Cardiac output x O2 content = 5000 ml/min x 0.3 ml O2/100ml = 15 ml O2/min Vastly inadequate for O2 consumption of 250 ml/min at rest. |
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Oxygen bound to hemoglobin
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98% of total blood O2 content.
1 g HbA can bind up to 1.34 ml O2, normal blood HbA = 15 g/100 ml |
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Arterial content of O2 bound to hemoglobin
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With 100% Hb saturation: 15 g/100 ml X 1.34 ml/g = 20.1 ml O2/100 ml of blood
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Delivery of O2 bound to hemoglobin
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5,000 ml/min x 20.1 ml/100 ml = ~1,000 ml O2/min
4 times in excess of oxygen consumption of 250 ml/min at rest Can be increased with increased cardiac output |
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Heme
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An iron-binding porphyrin which in turn can bind and release oxygen.
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Adult Hb
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HbA, α2β2
Globular, 4 subunits Each subunit has O2-binding heme moiety |
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Fetal Hb
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HbF, α2γ2
Higher O2 affinity Replaced by HbA during 1st year |
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Sickle cell Hb
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HbS, mutation in beta chains
Deoxygenated form polymerizes Distorts RBCs, small vessels occluded, hypoxia |
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Oxygen binding
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Determined by oxygen partial pressure
Percent saturation Average of all Hb molecules Increases sharply then levels Normal arterial saturation: 100% |
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Hb affinity for oxygen
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Positive cooperativity
Measure by P50 value |
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Positive cooperativity
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Each time an O2 binds a Hb molecule, it makes it easier for subsequent O2 molecules to bind; of course up to the point of saturation of 4 O2 molecules per Hb.
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P50 Value
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Refection of the affinity of Hb for O2; defined as the partial pressure needed for Hb molecules on average to be 50% saturated; a lower P50 means increased affinity as 50% saturation requires less O2 pressure; a higher P50 means decreased affinity as 50% saturation requires more O2 pressure.
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Oxygen unloading
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As cells in the tissues take up O2, the partial pressure drops; this causes Hb to release O2 to the tissues.
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Oxygen loading
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Conveniently in the pulmonary capillary blood the PO2 is around 100 mm Hg; this causes Hb to bind O2 up to 100% saturation.
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Normal metabolism
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Requires about 250 ml of O2/min; since Hb normally transports about 1,000 ml of O2/min, only 25% is needed by the tissues.
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Factors that may decrease the affinity of Hb for O2 in tissues
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-Bohr effect: increased PCO2 and decreased pH
-Increased temperature -Increased 2,3-DPG |
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2,3-DPG
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Byproduct of glycolysis in RBCs; binds the beta chains of Hb causing a conformation shift in the protein such that the affinity for oxygen is reduced; high altitude stimulates production of 2,3-DPG.
2,3-DPG binds HbA more avidly than HbF. This accounts for the higher oxygen affinity of HbF. |
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Dissociation curve when affinity for O2 decrease
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-Shifts to the right
-Increased P50 value |
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Factors that may increase the affinity of Hb for O2 in the lungs
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-Bohr effect: decreased PCO2 and increased pH
-Decreased temperature -Decreased 2,3-DPG |
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Dissociation curve when affinity for O2 increases
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-Shifts to the left
-Decreased P50 value |
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Carbon monoxide and the O2-Hb dissociation curve
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The hemoglobin heme moieties have a 250 times higher affinity for carbon monoxide than oxygen. Very small partial pressures of CO may displace substantial amounts of oxygen from hemoglobin.
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Lethal amounts of CO
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CO can compete equally with oxygen to bind Hb if its pressure reaches only 0.4 mm Hg!!! A pressure of 0.6 mm Hg may be lethal.
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CO binding Hb causes a _____ shift
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Leftward shift in the dissociation curve, making O2 unloading in the tissues more difficult.
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Dissolved CO2
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About 5% of total CO2 content
Exerts partial pressure |
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Bicarbonate
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More than 90% of total CO2 content
Reversibly converted in RBCs Role of carbonic anhydrase |
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Carbaminohemoglobin
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About 3% of total CO2 content
CO2 binds terminal amino groups of Hb and serum proteins Haldane effect |
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Reversible conversion to and from bicarbonate
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CO2 diffuses into RBCs; combines with water to produce carbonic acid (catalyzed by carbonic anhydrase); carbonic acid dissociates partially into H+ and HCO3-; H+ binds to Hb while bicarbonate is transported out of the cell into the blood (through exchange with Cl-); whole process reversed in the lungs.
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Haldane effect
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When less O2 is bound to Hb, the affinity of the terminal amino groups of Hb for CO2 increases; this condition would be present in the tissues and makes sense in terms of loading CO2.
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