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WEEK 17:
Chemical control of ventilation:
| Question | Answer |
|---|---|
| gradients of partial pressure allowing O2 and CO2 to diffuse | PaO2 > PvO2 and PACo2 < PvCO2 |
| a | arterial blood |
| A | alveolar |
| v | venous blood |
| PaO2 | 13.3 kPa |
| PaCO2 | 5.3 kPa |
| what is the BBB impermeable to | HCO3- and H+ |
| what is the BBB permeable to | CO2 |
| explain how central chemoreceptors (CCRs) on the medulla work when there is a high PCO2 | CO2 diffuses out of blood vessels into the CSF and is converted into H+. CCRs detect the H+ leading to hyperventilation to decrease PCO2 in blood and CSF |
| equation for CO2 to H+ | CO2 + H2O <-> H2CO3 <->HCO3- + H+ |
| when do peripherical chemoreceptors (PCRs) become stimulated | ONLY during decreased arterial O2, where PO2 falls below 13.3 kPa leading to hyperventilation |
| where are PCRs found | aortic arch and carotid arteries |
| difference between CCRs and PCRs | CCRs work in both high and low CO2 conditions but PCRs only work in low conditions |
| which PCRs are stimulated when there is a fall in pH | carotid PCRs |
| how does the kidney respond when there is hypoventilation (respiratory acidosis) | increase H+ excretion in urine and increase reabsorption of HCO3- |
| how does the kidney respond when there is hyperventilation (respiratory alkalosis) | increase H+ reabsorption and increase HCO3- excretion |
| uncontrolled diabetes could lead to what | metabolic acidosis |
| explain the compensation for metabolic acidosis | increase ventilation which decreases PaCO2 |
| vomiting could lead to what | metabolic alkalosis |
| explain the compensation for metabolic alkalosis | decrease ventilation which increases PaCO2 |
| order of priority responses (3) | PCO2, pH, PO2 |
| why are PCO2 the first priority | to avoid acid-base problems |
| what level do CCRs control PCO2 changes to | 0.3kPa |
| what level do PCRs control PCO2 changes to | 1.3 kPa |
| cheyne-stokes respiration | ineffective detection of changes of O2 and CO2 levels |
| where does cheyne stokes respiration occur | in individuals with CNS disease, head trauma, and increased intercranial pressure |
| explain what you would see in cheyne stokes respiration | rapid breathing (increases PO2 and decreases PCO2) then apnoea (not breathing due to delay in message relay) to try increase PCO2 and decrease PO2 to normal levels, then rapid breathing again |
Created by:
kablooey
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