Exam #3 (Acid-Base)

Question 1

Normal range of arterial pH is

Answer 1

7.37 (or 7.35) to 7.42 (or 7.45)

Question 2

Acidemia pH level

Answer 2

pH < 7.37

Question 3

Alkalemia pH level

Answer 3

pH > 7.42

Question 4

Mechanisms of maintaining normal pH

Answer 4

• Buffering of H+ in both ECF & ICF
• Respiratory compensation
• Renal compensation

Question 5

Volatile Acid

Answer 5

CO2

Produced from aerobic metabolism

Question 6

Non-Volatile Acid

Answer 6

Aka fixed acids
Sulfuric acid, phosphoric acid
Ketoacids, lactic acid, Beta-hydroxybutyric acid, glycolic acid, oxalic acid & salicylic acid

Question 7

Function of buffers

Answer 7

Prevents change in pH when H+ ions are added to or removed from a solution

Question 8

When are buffers most effective?

Answer 8

Most effective within 1.0 pH unit of the pK (-ve logarithm of the [H+] at which 1/2 of the acid molecules are dissociated & are undissociated) of the buffer

Question 9

Extracellular buffers include

Answer 9

Mostly HCO3-

Phosphate: most important as a urinary buffer

Question 10

Intracellular buffers include

Answer 10

Organic phosphates: AMP, ADP, ATP, DPG
Proteins
Hemoglobin: major buffer. Deoxyhemoglobin is better buffer than oxyhemoglobin b/c it allows for the binding of H+

Question 11

Henderson-Hasselbalch Equation

Answer 11

Used to calculate pH

pH = -log10[H+]
pK = -ve logarithm of the [H+] at which 1/2 of the acid molecules are dissociated & are undissociated
[A-] = Concentration of base form of buffer; is the H acceptor
[HA] = Concentration of acid form of buffer; is the H donor

Question 12

In the henderson-hasselbalch equation when the concentration of A- & HA are equal,

Answer 12

The pH of the solution = the pH of the buffer

Question 13

In a acid-base titration curve, as H+ ions are added to the solution vs as H+ ions are removed

Answer 13

The titration curve describes how the pH of a buffered solution changes as H ions are added/removed from it. As H+ ions are added to the solution, the HA form is produced. As H+ ions are removed, the A- form is produced.

Question 14

A buffer is most effective in which portion of the acid-base titration curve?

Answer 14

A buffer is most effective in the linear portion of the titration curve, where the addition or removal of H+ causes little change to pH

Question 15

The most effective physiologic buffer will have a pK w/

Answer 15

1.0 pH unit of 7.4 (7.4 ± 1.0)

Question 16

Based on Henderson-Hasselbalch Equation, when the pH of the solution = pK

Answer 16

the concentration of HA & A are equal

Question 17

As the filtered load increases what impact will it have on HCO3-

Answer 17

Increases in the filtered load leads to increased HCO3- reabsorption. If plasma [HCO3-] becomes high (metabolic alkalosis), then filtration will exceed reabsorption & excretion will occur

Question 18

What impact does Pco2 have on filtered HCO3-

Answer 18

Increased Pco2 -> increased HCO3- reabsorption

Decreased Pco2 -> decreased HCO3- reabsorption

Question 19

What impact does ECF volume have on filtered HCO3-?

Answer 19

Expansion of ECF volume -> decreased HCO3- reabsorption

Contraction of ECF volume -> increased HCO3- reabsorption (contraction alkalosis)

Question 20

What impact does Angiotensin II have on filtered HCO3-?

Answer 20

Angiotensin II stimulates Na+ - H+ exchange (proximal tubule) and increases HCO3- reabsorption. Contraction alkalosis

Question 21

Metabolic Acidosis

Answer 21

Over-production or ingestion of fixed acid or loss of base (lower HCO3-) produces & increase in arterial [H+] (acidemia)
Primary disturbance = decreased [HCO3-]
HCO3 is used to buffer the extra acid

Question 22

What is the primary disturbance of metabolic acidosis?

Answer 22

Lower [HCO3-]

Question 23

Compensation mechanism for Metabolic acidosis?

Answer 23

Respiratory compensation = hyperventilation (kussmaul breathing; deep rapid respiration, common in type 1 diabetics due to keto acids)
Renal compensation = increased excretion of H as titratable acid & NH4. increase “new” HCO3 reabsorption
Chronic metabolic acidosis = adaptive increase in NH3 synthesis

Question 24

Metabolic Alkalosis

Answer 24

• Loss of fixed H or gain of base => decrease arterial H (alkalemia)
• Primary disturbance = increase [HCO3-]. eg: vomiting

Question 25

Compensation for Metabolic Alkalosis

Answer 25

Respiratory Compensation = hypoventilation

Renal compensation = increased HCO3 excretion

Question 26

What happens if the ECF volume contracts w/ Metabolic Alkalosis?

Answer 26

If ECF volume contraction occurs, HCO3 reabsorption will increase, worsening the metabolic alkalosis

Question 27

Respiratory Acidosis

Answer 27

Due to decreased respiratory rate & retention of CO2

Primary disturbance = increased arterial CO2 -> increased [H]

Question 28

What is the primary disturbance of Respiratory Acidosis?

Answer 28

Increase arterial CO2 -> increased [H]

Question 29

Compensation mechanism for Respiratory Acidosis

Answer 29

No respiratory compensation**; the lungs cannot compensate for themselves
Renal compensation: increased excretion of H as titratable H & NH4. Increased reabsorption of “new” HCO3

Question 30

Acute vs Chronic Respiratory Acidosis

Answer 30

Renal compensation has not yet occurred w/ acute. Renal compensation occurs w/ chronic.

Question 31

Respiratory Alkalosis

Answer 31

Due to increased respiratory rate (hyperventilation)

Primary disturbance = decreased PCO2

Question 32

What is the primary disturbance of Respiratory Alkalosis?

Answer 32

Decreased PCO2

Question 33

Compensation mechanism for Respiratory Alkalosis

Answer 33

No respiratory compensation

Renal compensation: decrease H+ excretion, increase HCO3 excretion

Question 34

Acute vs Chronic Respiratory Alkalosis

Answer 34

In acute renal compensation has not yet occurred. In chronic renal compensation is present.