Chapter 30 - Regulation of Acid-Base Balance

Question 1

Whys is H+ regulation very precise?

Answer 1

Because the H+ influences almost all enzyme systems in the body.

Question 2

What is the normal extracellular concentration of H+?

Answer 2

0.00004 mEq/L

Question 3

What is the definition of a strong acid?

Answer 3

One that rapidly dissociates and releases especially large amounts of H+ in solution

Question 4

What is the pH range of urine?

Answer 4

4.5 to 8 pH.

Question 5

What is the normal pH of arterial blood?

Answer 5

7.4 pH.

Question 6

What is the normal pH of venous blood and interstitial fluid?

Answer 6

7.35 pH.

Question 7

What are the limits of pH that a person can live for more than a few hours?

Answer 7

6.8 to 8 pH.

Question 8

What are the 3 primary systems that regulate the H+ concentration in the body fluids?

Answer 8

1. Chemical acid-base buffer systems of the body fluids
2. Respiratory center
3. Kidneys

Question 9

What is a buffer?

Answer 9

Any substance that can reversibly bind H+.

Question 10

Describe the bicarbonate buffer system.

Answer 10

A water solution of carbonic acid (H2CO3) and bicarbonate salt (NaHCO3)

Question 11

How is carbonic acid made in the body?

Answer 11

CO2 + H2O + Carbonic anhydrase

Question 12

What is the dissociation constant K?

Answer 12

For any acid, the concentration of the acid relative to its dissociated ions

Question 13

Which system has primary control of the bicarbonate concentration?

Answer 13

Kidneys

Question 14

Which system has primary control of the PCO2 in the extracellular fluid?

Answer 14

Rate of respiration

Question 15

What is the difference between a metabolic acidosis and respiratory acidosis?

Answer 15

Metabolic acidosis = decrease in [bicarbonate]

Respiratory acidosis = Increase in [PCO2]

Question 16

What is the role of the phosphate buffer system?

Answer 16

It plays a major role in buffering renal tubular fluid and intracellular fluids

Question 17

How do the changes in extracellular pH change the intracellular pH?

Answer 17

The diffusion of the bicarbonate buffer system thru the cell membrane

Question 18

How do the kidneys regulate extracellular fluid H+ concentration?

Answer 18

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

Question 19

Where does most of the bicarbonate reabsorption and H+ secretion take place in the kidney?

Answer 19

80-90% in the proximal tubule

Question 20

How are hydrogen ions secreted in the kidneys?

Answer 20

1. Thru the sodium-hydrogen counter-transport in the cells of the proximal tubule.
2. Thru the active hydrogen pump of the intercalated cells of the late distal and colleting tubules.

Question 21

How much H+ is secreted in a day?

Answer 21

4400 mEq/day

Question 22

How is bicarbonate reabsorbed?

Answer 22

Indirectly. First combines w/ H+ to form H2CO3 which becomes CO2 + H20. The CO2 easily moves into the tubular cell, which combines w/ water and carbonic anhydrase to form H2CO3 again. Then it dissolves into HCO3- and H+ again (this is all happening inside the cell). The H+ is secreted while the HCO3 is absorbed into the bloodstream.

Question 23

How is the bicarbonate expelled from the tubular cell into the bloodstream?

Answer 23

By Na+ _ HCO3 cotransport and Cl- _ HCO3- exchanger.

Question 24

How much HCO3- is filtered per day?

Answer 24

4320 mEq/day

Question 25

What happens whenever an H+ secreted into the tubular lumen combines w/ a buffer other than HCO3-?

Answer 25

A net gain of a new HCO3- to the blood.

Question 26

What happens whenever a NH4+ is excreted?

Answer 26

A new HCO3- is generated and added to the blood.

Question 27

What is the dominant mechanism by which acid is eliminated in chronic acidosis?

Answer 27

Excretion of NH4+

Question 28

What are the most important stimuli for increasing H+ secretion by the tubules in acidosis?

Answer 28

1. Increase in PCO2 of the extracellular fluid.

2. Increase in H+ concentration of the extracellular fluid (decrease in pH).

Question 29

What values should we expect to increase/decrease in a simple respiratory acidosis after partial renal compensation?

Answer 29

Reduced plasma pH
Increased CO2
Increased HCO3-

Question 30

What values should we expect to increase/decrease in a simple metabolic acidosis after partial respiratory compensation?

Answer 30

Low pH
Low HCO3-
Low PCO2

Question 31

What values should we expect to increase/decrease in a simple respiratory alkalosis after partial renal compensation?

Answer 31

Increased pH
Decreased PCO2
Decreased HCO3-

Question 32

What values should we expect to increase/decrease in a simple metabolic alkalosis after partial respiratory compensation?

Answer 32

Increased pH
Increased HCO3-
Increased PCO2