Ch 30 Acid Base Balance

Question 1

What are the three fundamental ways by which the kidneys regulate extracellular [H+]?

Answer 1

1. Secretion of H+
2. Reabsorption of filtered HCO3-
3. Production of new HCO3-

Question 2

What factors increase net H+ secretion and HCO3- reabsorption?

Answer 2

Incr PCO2
Incr H+ or decr HCO3-
Decr ECF volume
Incr Angiotensin II
Incr Aldosterone
Hypokalemia

Question 3

What factors will decrease H+ secretion and HCO3- reabsorption?

Answer 3

Decr PCO2
Decr H+ or Incr HCO3-
Incr ECF volume
Reduced Angiotensin II
Reduced Aldosterone
Hyperkalemia

Question 4

What are the most important stimuli that will increase H+ secretion by the tubules in ACIDOSIS?

Answer 4

1. Increased PCO2 of the ECF (if resp acidosis)
2. Increased H+ conc in ECF (if resp or metab acidosis)

Question 5

Why does a drop in extracellular fluid volume lead to increased loss of H+ and reabsorption of HCO3-?

Answer 5

Because dropped ECF stimulates aldosterone and angiotensin II.
1. Angiotensin II stimulates the Na/H+ exchanger to increase H+ secretion into pee
2. Aldosterone stimulates increased H+ by the intercalated cells of the cortical collecting tubules

Question 6

Summarize the basic compensatory mechanisms for metabolic acidosis

Answer 6

Blow off CO2 and increase plasma HCO3 by
-Incr ventillation
-Decr HCO3 excretion
-Add more HCO3 to circulation

Question 7

Summarize the basic compensatory mechanisms for metabolic alkalosis

Answer 7

-Decr ventillation
-Incr HCO3 excretion

Question 8

Summarize the basic compensatory mechanisms for respiratory acidosis

Answer 8

Increase plasma HCO3:
-Incr HCO3 addition to circulation
-Decr HCO3 excretion

Question 9

Summarize the basic compensatory mechanisms for respiratory alkalosis

Answer 9

-Incr HCO3 excretion

Question 10

What are the main causes of respiratory acidosis?

Answer 10

Decr ventilation (central dz)
Shunts (V/Q mismatch)
Reduced perfusion
Obstructive airway dz

Question 11

What are the main causes of respiratory alkalosis?

Answer 11

Hyperventilation
Hypoxia : High altitude

Question 12

What are the main causes of metabolic acidosis?

Answer 12

Renal tubular acidosis
Diarrhea (Bicarb loss)
Vomiting intestinal contents
Diabetes mellitus
Acids ingestion (aspirin poisoning)
Chronic renal failure

Question 13

What are the main causes of metabolic alkalosis?

Answer 13

Overuse of diuretics
Hyperaldosteronism
Vomiting gastric contents
Overuse of anti-ulcer drugs

Question 14

Briefly explain how renal tubular acidosis develops

Answer 14

The tubules cannot excrete H+ or reabsorb HCO3, and inability to titrate the phosphate and ammonium, leading to accumulation of acids and loss of bicarb

Question 15

What are anion gaps useful for? How do you interpret them?

Answer 15

They expand on the reason for a metabolic acidosis:
If the anion gap is normal, likely Cl- is high, trying to compensate for fallen HCO3-. Causes include diarrhea and renal tubular acidosis

If the anion gap is high and Cl- is normal, then there are unmeasured anions such as lactate, ketones, uremic acids, phosphate, sulfate, or albumin.
OR could be fallen unmeasured cations such as low Mg, K, or Ca

Question 16

What are differentials for an increased anion gap w/ normochloremia?

Answer 16

Ketoacidosis, lactic acidosis, chronic renal failure, aspirin poisoning, starvation, ethylene glycol poisoning, methanol poisoning

Question 17

What are differentials for metabolic acidosis with a normal anion gap and hyperchloremia?

Answer 17

Diarrhea, renal tubular acidosis, Addison’s , carbonic anhydrase inhibitors