Exam #4: Acid & Base Regulation Flashcards
What is the normal pH of the blood?
7.4
How does the pH change in a patient with acidosis?
Decrease in pH
How does the pH change in a patient with alkalosis?
Increase in pH
Describe how the ventilation rate (and thus PO2) changes with changes in pH.
Increase in ventilation rate will increase pH & a decrease in ventilation rate will decrease pH
Define respiratory acidosis.
- Acidosis is any disease process that acts to lower blood pH
- Respiratory acidosis is a decrease in pH from a decrease in ventilation
Define respiratory alkalosis.
- Alkalosis is any disease process that acts to raise blood pH
- Respiratory alkalosis is an increase in pH from an increase in ventilation
Define metabolic acidosis.
Any process that acts to lower pH other than hypoventilation
Define metabolic alkalosis.
Any process that acts to increase pH other than hyperventilation
What is acidemia?
Blood pH less than 7.35
What is alkalemia?
Blood pH above 7.45
Describe how the kidneys compensate for metabolic acidosis.
1) Remember that the lungs will act first; there will first be an increase in ventilation to compensate for metabolic acidosis
2) On a longer timescale, the kidneys will compensate by excreting acidic urine AND by reabsorbing all of the filtered bicarbonate & adding it to the plasma
- 90% of this happens in the proximal tubule
- 10% happens in the collecting ducts
Describe how the kidneys compensate for respiratory acidosis.
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Describe how the kidneys compensate for metabolic alkalosis.
1) Remember that the lungs will act first; there will first be a decrease in ventilation to compensate for metabolic alkalosis
2) On a longer timescale, the kidneys will compensate by excreting basic or alkaline urine i.e. urine containing bicarbonate
Describe how the kidneys compensate for respiratory alkalosis.
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Describe the effect of a chemical buffer when a strong acid or strong base is added to a body fluid.
- **Remember that a buffer is any substance that can reversibly bind hydrogen ions
- Strong acid= increasing amounts of H+ bind to the buffer
- Strong base= H+ is increasingly dissociated from the buffer
Briefly describe the important buffer systems of the body. Where is each most useful? (ECF, ICF, in the kidney tubules)
1) Bicarbonate buffer= ECF (Base= bicarb.; Acid= carbonic acid)
2) Phosphate= urine & ICF
Protein= intracellular
Ammonia
Describe the process of bicarbonate reabsorption.
1) Bicarboante is filtered by the glomerulus into the tubular lumen & H+ is secreted into the tubular lumen by a Na+/H+ exchanger
2) Bicarbonate & H+ combine in the tubular lumen to form carbonic acid (H2CO3)
3) Carbonic acid dissolved into CO2 & water in the lumen
4) CO2 diffuses into the renal tubule cell, combines with H20 again, and reforms carbonic acid via the enzyme carbonic anhydrase
5) In the renal tubule cell, carbonic acid breaks down into Bicarbonate & H+ again
6) Bicarbonate then moves down its concentration gradient across the basolateral membrane of the renal tubule cell (via facilitated diffusion) into the ISF & then into the peritubular capillaries
What is secreted in the process of bicarbonate reabsorption?
1 H+ ion is secreted for every bicarbonate reabsorbed
What is excreted in the process of bicarbonate reabsorption?
Water
How can bicarbonate reabsorption compensate for acidosis? Alkalosis?
Acidosis
- Increased CO2 from respiratory acidosis= increased diffusion of CO2 into the tubular cells
- CO2 combines with water to form carbonic acid, which dissociates into Bicarboante & H+
- Bicarbonate is reabsorbed into the blood & H+ is secreted into the tubular lumen
- In the tubular lumen, H+ combines with filtered bicarbonate, which is reabsorbed
Alkalosis:
- In contrast to acidosis, alkalosis is fairly simply: reabsorb less filtered bicarbonate so more base is excreted
Describe phosphate buffering in respiratory acidosis.
- ***The phosphate buffer system removes H+ ion when the bicarbonate system has been saturated in situations of severe acidosis
- Available phosphate in the lumen will bind to H+ & be excreted
Describe glutamine-NH4+ buffering in severe respiratory acidosis.
- **In situations where we have reabsored all of the bicarbonate and excreted all of the phosphate buffer, this system (gluatmine-NH4+) kicks in
- In the proximal tubule, GLUTAMINE is metabolized to BICARBONATE & NH4+ (ammonium ion)
- BICARBONATE is added to the blood
- Ammonium ion is excreted in the urine
Sketch a Davenport diagram and label the x and y axis. Put in the 40 PaCO2 line and show where it intercepts the line for normal pH.
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Draw a Davenport diagram label the sections where a patient would be in metabolic acidosis, metabolic alkalosis, respiratory acidosis and respiratory alkalosis.
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Draw a Davenport diagram be able to match points on the diagram with clinical scenarios (e.g. patient in uncompensated and compensated respiratory acidosis or alkalosis , metabolic acidosis or alkalosis).
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