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Phys2 Gas transport

QuestionAnswer
What are the two ways O2 is carried in the BL? 1.Dissolved (0.3ml per 100 ml BL). 2.Hemoglobin bound (20.8ml per 100 ml BL)
What is the main function of Hb? Facilitates diffusion of O2 from the alveoli into the plasma and INCREASES the total amount of O2 in the BL for the same PO2. **Affects O2 content, but not PO2
How much O2 is dissolved in plasma at PO2 of 100mmHg? 0.3ml per 100ml of BL. **it is not very soluble, therefore builds up a back flow quickly
2 important regions on an oxygen dissociation curve 1.Steep region (PO2 10-40): Hb dumps O2 fast at lower PO2 (small change in PO2 will cause Inc dumping, key at BL-CELL interface, tissue gets O2). 2.Plateau (PO2 70-120): no Hb sat change w/ change in PO2 (in the lung at BL-gas int, 100% sat with hypovent
What is the difference b/w an oxygen dissociation curve that is just Hb saturation Vs BL O2 content? 1.Hb sat: only the O2 bound to Hb, will be SLIGHTY lower at plateau. 2.BL O2 content: represents the TOTAL O2 both Hb bound and plasma dissolve. Has a slightly higher plateau.
Why should caution be used when interpreting Hb saturation values obtained from PULSE OXIMETRY? 1.Anemia: Hb will dec in number and thus total O2 content will decrease greatly BUT it will still be 97% saturated. 2.Carbon Monoxide: Hb will still be 97% b/c it measures the BOUND-Hb (not what binds to it), total O2 content will be greatly decreased.
Which molecule has a higher affinity to Hb: O2 or CO? CO. **CO poisoning will reduce the total O2 content in the blood. However, b/c the PO2 reflects the ‘back pressure’ exerted by O2 molecules that have diffused into the plasma, the PO2 will be normal.
Carbonmonoxide poisoning: Hb sat%? PO2? Total O2 content? 1.Hb sat%: Normal, 97%. 2.PO2: Normal, 100mmHg. 3.Total O2: DECREASED!!
Bohr Effect Rightward shift on the O2 dissociation curve. Hb gives up O2 more readily. **Lower Hb saturation for a given PO2. INC P50
3 molecules that cause a Right shift on the HbO2 dissociation curve (Bohr effect) 1.Inc H+. 2.Inc PCO2. 3.Inc 2,3BPG. **Good b/c tissue needs O2 during exercise or inc metabolism.
Left shift on HbO2 dissociation curve Hb holds on to O2 more readily (higher Hb sat at a given PO2). DEC P50 **Dec H+, PCO2, 2,3BPG
Hb saturation: Right shift? Left shift? Right: Lower. Left: Higher. **P50 value is what is changing the most.
HbO2 dissociation curve in venous Vs arterial BL? venous curve is Right-shifted due to more CO2.
PO2 and Hb sat% in Pulmonary veins (Arterial BL)? PO2: 100mmHg. Hb sat%: 97%
PO2 and Hb sat% in Pulmonary Arteries (venous BL)? PO2: 40mmHg. Hb sat%: 75% **b/c of CO2 molecules bound to Hb
What is P50? what is its normal value? The PO2 at which the Hb is 50% saturated. Normal: PO2 27mmHg
What are the 3 forms of CO2 transport in the BL? 1.Bicarbonate (HCO3-): 60%, from carbonic acid. 2.Carbamino: 30%, CO2 bound to protein (majority is Hb). 3.Dissolved: 10%, higher than O2 b/c CO2 is much more soluble.
Why are RBC the main facilitator of CO2 transport? 2 reasons 1.Hb is the principle protein for carbamino transport (30%). 2.Large amount of Carbonic Anhydrase in the RBC allows CO2->Carbonic Acid->bicarbonate + H+ (60%)
2 ways CO2 dissociation curve differs from O2 dissociation curve 1.Steeper: allows it to unload CO2 more rapidly at lower PCO2 % with a smaller PCO2 difference. 2.Linear (NO PLATEAU) **Explains why 46mmHg and 40mmHg is a sufficient gradient at the BL-gas interface.
Haldane Effect Oxygenation (Inc PO2) of BL DECREASES the ability to carry CO2. **Creates a downward shift of CO2 dissociation curve (highest at PO2 0mmHg, lowest at PO2 100mmHg).
Why is the Haldance Effect advantageous? Good for unloading CO2 in the lungs due to Inc PO2 as well as loading CO2 in the tissue due to dec PO2.
Reduced hemoglobin Deoxygenated hemoglobin
How does PCO2 affect BL pH? B/c CO2 in the bL leads to the formation of HCO3 and H+ ions, the pH of the blood is dependent on both the [CO2] in the BL & the [HCO3-]
Equation for PCO2 affect on BL pH pH = 6.1 + log([HCO3-]/[CO2]) **[CO2]: 0.03xPCO2. **[HCO3-]: 24mEq/L **Normally: Log (20)
What will cause a change in [HCO3-] METABOLIC CHANGES **nothing to do with ventilation
What will cause a change in [CO2] VENTIALATION CHANGES (Hypo or hyperventilation) **nothing to do with metabolism.
When is BL pH 7.4? Normally, as long as [HCO3-]/[CO2] equals 20. *HCO3- (24mEq/L). *CO2 (0.03x40)
Inc PCO2 1.[HCO3-]/[CO2]: <20. 2.pH: <7.4 3.Effect: Respiratory acidosis 4.Compensation: Metabolic alkalosis.
Dec PCO2 1.[HCO3-]/[CO2]: >20. 2.pH: >7.4 3.Effect: Respiratory alkalosis. 4.Compensation: metabolic acidosis
Inc HCO3- 1.[HCO3-]/[CO2]: >20. 2.pH: >7.4. 3.Effect: Metabolic alkalosis. 4.Compensation: Respiratory acidosis.
Dec HCO3- 1.[HCO3-]/[CO2]: <20. 2.pH: <7.4. 3.Effect: Metabolic acidosis. 4.Compensation: Respiratory alkalosis.
Patient found unconcious, BL pH of 7.24, PaCO2 of 56mmHg? Respiratory acidosis
Patient w/ severe diarrhea for several days. BL pH of 7.28, PaCO2 of 32mmHg? Compensated metabolic acidosis
Patient with Dec pH, Inc PCO2? Repsiratory acidosis. **expect Inc HCO3-
Patient with Dec pH, Dec PCO2? compensated metabolic acidosis. **expect dec HCO3-.
Patient with Inc pH, Inc PCO2? compensated metabolic alkalosis. **expect Inc HCO3-
Patient with Inc pH, Dec PCO2? Respiratory alkalosis. **expect dec HCO3-.
Created by: WeeG