Acid-Base Balance

Question 1

What three mechanisms are used to defend against changes in body fluid pH?

Answer 1

Extra- and intracellular buffering

Adjustments in PCO2 by alterations in ventilatory rate

Adjustments in renal acid excretion

Question 2

What is the most important extracellular buffer?

Answer 2

Bicarbonate buffering system, response is virtually instantaneous

*Other extracellular buffers are protein and Phosphate

Question 3

What is intracellular buffering?

Answer 3

Involves H into and out of the cells

Inside the cells it is titrated by Phosphate and proteins

Question 4

How is the respiratory mechanisms mediated?

Answer 4

Chemoreceptors sensing PCO2

Question 5

What three things happen in the renal defense of acidosis?

Answer 5

Increase H secretion

Entire filtered load of bicarb is reabsorbed

Increased production and excretion of ammonia

Question 6

What happens in the renal defense of alkalosis?

Answer 6

Decreased secretion of H

Decreased bicarb reabsorption

Question 7

What is the primary alteration in metabolic acidosis/alkalosis?

Answer 7

Change in ECF bicarb concentration

Question 8

Describe metabolic acidosis

Answer 8

Low plasma bicarb and low pH

Can develop by: addition of nonvolatile acid, Loss of nonvolatile alkali, failure of kidneys to excrete sufficient net acid

Question 9

What is the anion gap?

Answer 9

Represents anions in the plasma that are not measured

Used to help in the differential diagnosis of metabolic acidosis

Normal is 16 (or 12 if K is not used in calculation)

Question 10

What does metabolic acidosis with high anion gap indicate?

Answer 10

Decreased bicarbonate is replaced by unmeasured anions

DKA, salicylate poisoning, Lactic acidosis

Question 11

What does metabolic acidosis with a normal anion gap indicate?

Answer 11

Decreased bicarb is replaced by Cl

Diarrhea, drainage of pancreatic juice

Question 12

Describe metabolic alkalosis

Answer 12

Increased plasma bicarb and pH

Can develop by addition of noonvolatile alkali (antacid ingestion), loss of nonvolatile acid

Question 13

What are the compensation mechanisms for metabolic alkalosis?

Answer 13

Hypoventilation, increased renal excretion of bicarbonate

Question 14

Describe respiratory acidosis

Answer 14

Elevated PCO2 and reduced plasma pH

Can develop by, inadequate ventilation, impaired gas diffusion

Buffering occurs in the intracellular compartment only

Question 15

What is the renal compensation for resp. acidosis?

Answer 15

Increase bicarb reabsorption and ammonium excretion

Takes several days, acute and chronic phases

Question 16

Describe respiratory alkalosis

Answer 16

Reduced PCO2 and elevated plasma pH

Can develop by stimulation of the respiratory centers

Buffering is intracellular

Question 17

What is the renal compensation for resp. alkalosis?

Answer 17

Inhibition of bicarb reabsorption and reduced ammonium excretion

Question 18

What is a combined complex acid-base disorder?

Answer 18

Normal compensation for a primary acid/base disorder

Question 19

What is a combined simple disorder?

Answer 19

Describes a second acid/base disturbance compounding the first acid-base disturbance

E.g. respiratory failure followed by renal failure both resulting in acidosis (IRDS)

or a hyperventilating patient begins severe vomiting

Question 20

What is renal tubular acidosis?

Answer 20

Group of diverse conditions that cause non anion gap metabolic acidosis in the presence of normal GFR

Classified as type 1, 2, and 4

Question 21

What is type 1 RTA?

Answer 21

Distal RTA

Characteristics: impaired H secretion by the distal segments, urine pH>5.3

Renal defect: Decreased H-K ATPase, Increased tubule permeability, allowing H backflow

Etiology: Sjogren syndrome, Rheumatoid arthritis drugs

Question 22

What is type 2 RTA?

Answer 22

Proximal RTA

Characteristics: Impaired proximal Bicarb reabsorption, low plasma bicarb

Renal defect: Nonspecific tubule dysfunction or mutation in genes involved in bicarb reabsorption

Etiology: Fanconi syndrome, CA inhibitors

Question 23

What is type 4 RTA?

Answer 23

Hypoaldosteronism

Characteristics: impaired aldosterone release or response, urine pH < 5.3, hyperkalemia

Renal defect: Impaired Na reabsorption via epithelial Na channel

Etiology: Congenital hypoaldosteronism (addison disease), aldosterone resistance, diabetic nephropathy