7. Acid-Base Balance

Question 1

What are the three fixed sources of hydrogen?

Answer 1

Anaerobic breakdown of glucose

Metabolism of cystine

Oxidation of phosphoproteins

Question 2

What two proximal tubule transporters are responsible for carrying bicarbonate through the basolateral membrane?

Answer 2

Bicarbonate exits the cells of the proximal tubule via a bicarbonate sodium symporter, or a bicarbonate chloride antiporter.

Question 3

What are the four buffer systems discussed in this lecture?

Answer 3

Bicarbonate

Hemoglobin

Phosphoric acid (H₂PO₄)

Plasma proteins (albumin)

Question 4

What are the symptoms of respiratory alkalosis?

Answer 4

Often tachypnea (the cause) is the only sign.

Lightheadedness,

Confusion,

Peripheral and circumoral paresthesias,

Cramps,

Syncope.

Question 5

What are the causes of high anion gap metabolic acidosis?

Answer 5

Methanol, Uremia, DKA, Paraldehyde, Isoniazid, Lactic acidosis, Ethanol (or ethylene glycol), Rhabdomyolysis, Salicylates

(MUDPILERS are high.)

Question 6

What causes chronic respiratory acidosis?

Answer 6

Anything that makes breathing difficult chronically.

(COPD is a good example)

Question 7

How does phosphate buffering in the tubular lumen help reclaim bicarbonate?

Answer 7

It is possible for carbonic anhydrase to break carbonic acid down into a bicarbonate and hydrogen, but then for that hydrogen to leave the apical surface via the sodium/hydrogen exchanger, and bind to sodium phosphate. That sodium phosphate allows us to clear the hydrogen, resulting in a net gain of one bicarbonate.

Question 8

What is the general pathological mechanism of type II renal tubular acidosis?

Answer 8

Impaired bicarbonate reabsorption the proximal tubule

Question 9

How does ammonia clear hydrogen ions from the nephron?

Answer 9

It sits in an equilibrium between ammonia and ammonium in the medullary interstitial fluid. The uncharged ammonia is capable of entering the intratubular fluid by passing through the cells of the collecting duct. This ammonia binds there with hydrogen, and drags it out to be excreted in the urine.

Question 10

What is the general pathological mechanism of type IV renal tubular acidosis?

Answer 10

Low plasma aldosterone, or a failure to respond to it.

This increases intracellular potassium, which for some reason decreases ammonia synthesis in the cells of the proximal tubule. This decreased ammonia synthesis means less ammonia is available to bind hydrogen and create bicarbonate. This results in metabolic acidosis.

Question 11

How does the body compensate for metabolic acidosis?

Answer 11

In the short-term, we hyperventilate – decreasing carbon dioxide.

In the long-term, the kidneys increase production of ammonia and phosphate – which can clear hydrogen ions, and (thereby) create bicarbonate.

Question 12

What is the response from the kidneys to respiratory acidosis?

Answer 12

The kidneys want to create more bicarbonate, so they increase production of ammonia and phosphate.

Question 13

What is the general pathological mechanism of type I renal tubular acidosis?

Answer 13

The alpha intercalated cells of the distal tubule and collecting duct failed to secrete hydrogen appropriately. This all decreases the amount of available bicarbonate by decreasing the amount of hydrogen available for phosphate and ammonia buffering.

Question 14

What is the typical pH of the intracellular compartment?

Answer 14

7.1 pH

Question 15

How do we calculate carbonic acid concentration (HA)?

Answer 15

.03 x partial pressure of CO2 in mmHg

Question 16

What is the Henderson Hasselbalch equation?

Answer 16

pH = pK + log ([A -] / [HA])

Question 17

Compare the rates of the four slow mechanisms of pH balance.

Answer 17

Lungs: minutes to hours

Ionic shifts: 2-4 hours

Kidneys: hours-days

Bone: hours-days

Question 18

What transporter is responsible for the reabsorption of ammonium from the thick ascending limb into the medullary interstitial fluid?

Answer 18

NKCC2 receptor – ammonium takes the place of the potassium

Question 19

What are the primary causes of respiratory acidosis?

Answer 19

CNS depression

Airway obstruction

Neuromuscular disorders

Severe pneumonia, embolism, edema

(They sell acidic air in CANS)

Question 20

What are the two volatile sources of hydrogen?

Answer 20

Oxidation of glucose

Oxidation of fat

Question 21

What helps make type IV renal tubular acidosis more common than the other types?

Answer 21

ACE inhibitors decrease angiotensin II formation, which can decrease aldosterone.

Toxic levels of ACE inhibitors can therefore cause type IV renal tubular acidosis.

Question 22

What is the typical pH range for urine?

Answer 22

4.5 to 8.0 pH

Question 23

What are the causes of metabolic alkalosis?

Answer 23

Post-hypercapnia, Diuretics, Contraction, Licorice, Endo, Vomiting, Excess alkaline, Re-feeding alkalosis.

People who are basic think they are Pretty Darn CLEVER

Question 24

What are the causes of the non-anion gap acidosis?

Answer 24

Hyperalimentation, Acetazolamide, Renal tubular acidosis, Diarrhea, Ureteropelvic shunt, Post-hypocapnia, Spironolactone

(The not-high are HARDUPS)

Question 25

Where are principal cells, alpha intercalated cells, and beta intercalated cells found?

Answer 25

In the collecting ducts

Question 26

What is the pK of the bicarbonate/carbonic acid buffer reaction?

Answer 26

6.1

Question 27

What are the symptoms of chronic respiratory alkalosis and acidosis?

Answer 27

Usually these are well tolerated.

Question 28

What four organs/mechanisms are responsible for “slow” regulation of blood pH?

Answer 28

Lungs (elimination of CO2)

Ionic shifts (exchange of hydrogen for potassium and sodium through cell membranes)

Kidneys (bicarbonate reabsorption, phosphate buffering, ammonia formation)

Bone (exchanges of calcium, phosphate, and carbonate)

Question 29

In terms of hydrogen and bicarbonate clearance, what are the responsibilities of the alpha-intercalated cells and the beta-intercalated cells, respectively?

Answer 29

Alpha-intercalated cells excrete acid (hydrogen)

Beta-intercalated cells excrete bicarbonate

Question 30

What causes symptoms of metabolic alkalosis?

Answer 30

Increased bicarbonate in the bloodstream binds calcium, causing hypocalcemia.

Also, less hydrogen ions in the bloodstream allows more calcium to bind albumin, also causing hypocalcemia.

Hypocalcemia results in neuromuscular excitability, headache, lethargy, delirium, tetany, and seizures.

Question 31

What should you expect if the patient has acidemia, a normal anion gap, normal serum creatinine, and no diarrhea?

Answer 31

Renal tubular acidosis