Exam #4: Acid & Base Regulation

Question 1

What is the normal pH of the blood?

Answer 1

7.4

Question 2

How does the pH change in a patient with acidosis?

Answer 2

Decrease in pH

Question 3

How does the pH change in a patient with alkalosis?

Answer 3

Increase in pH

Question 4

Describe how the ventilation rate (and thus PO2) changes with changes in pH.

Answer 4

Increase in ventilation rate will increase pH & a decrease in ventilation rate will decrease pH

Question 5

Define respiratory acidosis.

Answer 5

• Acidosis is any disease process that acts to lower blood pH
• Respiratory acidosis is a decrease in pH from a decrease in ventilation

Question 6

Define respiratory alkalosis.

Answer 6

• Alkalosis is any disease process that acts to raise blood pH
• Respiratory alkalosis is an increase in pH from an increase in ventilation

Question 7

Define metabolic acidosis.

Answer 7

Any process that acts to lower pH other than hypoventilation

Question 8

Define metabolic alkalosis.

Answer 8

Any process that acts to increase pH other than hyperventilation

Question 9

What is acidemia?

Answer 9

Blood pH less than 7.35

Question 10

What is alkalemia?

Answer 10

Blood pH above 7.45

Question 11

Describe how the kidneys compensate for metabolic acidosis.

Answer 11

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

Question 12

Describe how the kidneys compensate for respiratory acidosis.

Answer 12

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Question 13

Describe how the kidneys compensate for metabolic alkalosis.

Answer 13

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

Question 14

Describe how the kidneys compensate for respiratory alkalosis.

Answer 14

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Question 15

Describe the effect of a chemical buffer when a strong acid or strong base is added to a body fluid.

Answer 15

• **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

Question 16

Briefly describe the important buffer systems of the body. Where is each most useful? (ECF, ICF, in the kidney tubules)

Answer 16

1) Bicarbonate buffer= ECF (Base= bicarb.; Acid= carbonic acid)
2) Phosphate= urine & ICF

Protein= intracellular
Ammonia

Question 17

Describe the process of bicarbonate reabsorption.

Answer 17

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

Question 18

What is secreted in the process of bicarbonate reabsorption?

Answer 18

1 H+ ion is secreted for every bicarbonate reabsorbed

Question 19

What is excreted in the process of bicarbonate reabsorption?

Answer 19

Water

Question 20

How can bicarbonate reabsorption compensate for acidosis? Alkalosis?

Answer 20

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

Question 21

Describe phosphate buffering in respiratory acidosis.

Answer 21

• ***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

Question 22

Describe glutamine-NH4+ buffering in severe respiratory acidosis.

Answer 22

• **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

Question 23

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.

Answer 23

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Question 24

Draw a Davenport diagram label the sections where a patient would be in metabolic acidosis, metabolic alkalosis, respiratory acidosis and respiratory alkalosis.

Answer 24

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Question 25

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).

Answer 25

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