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Phys2 Gas transport
| Question | Answer |
|---|---|
| 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
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