Acid - base balance

Question 1

Normal plasma [H+]

Answer 1

40 nM

Question 2

Sulfur containing amino acids

Answer 2

Cysteine, methionine

Question 3

What amino acids make HCl?

Answer 3

Lysine, arginine and histidine

Question 4

The bicarbonate system

Answer 4

H+ + HCO3 - = CO2 + H2O

Question 5

The phosphate system

Answer 5

H+ +HPO4 2- = H2PO4 -

Question 6

The protein buffers

Answer 6

H+ + Pr- = HPr

Question 7

What is a buffer?

Answer 7

It is a solution that minimizes the change in [H+].

Question 8

What ratio is important in the bicarbonate buffer system?

Question 9

Plasma [CO2]

Answer 9

Is proportional to the partial pressure of CO2 in plasma

Question 10

How do you measure pH?

Answer 10

Arterial Blood Gas (ABG)

Question 11

What does pK represent?

Answer 11

The Equilibrium constant of the reaction

Question 12

When do Buffers resist change?

Answer 12

[Base] = [acid]

Question 13

When are Buffers the most effective?

Answer 13

When 1 pH is on either side of pK.

Question 14

What controls PCO2?

Answer 14

Alveolar ventillation

Question 15

What controls the [HCO3-] ECF ?

Answer 15

Independent regulation

Question 16

How kidneys control acid-base levels?

Answer 16

By excretion of an acidic or basic urine

Question 17

What are the primary renal mechanisms involved in regulating acid and base levels?

Answer 17

“Reabsorption” and secretion of HCO3 -
Formation of new HCO3-
Secretion of [H+] into tubular fluid
Buffer system within tubule that react with secreted [H+]

Question 18

What are the 3 ratios important for buffering?

Answer 18

NH3:NH4+ HPO4 2-:H2PO4- HCO3-:H2CO3

Question 19

What does Carbonic anhydrase do?

Answer 19

Convert H2CO3 to make CO2 and H2O

Question 20

Where does HCO3- get absorbed?

Answer 20

85-90% is absorbed in the proximal tubule. Also, a good place to secrete [H+]

Question 21

What happens in the distal tubule and collecting duct in the bicarbonate system?

Answer 21

H+-ATPase pump more important in this part of nephron

In distal part of nephron [HCO3-] is low and H+ react with other buffers

Question 22

Role of the Respiratory system

Answer 22

Chemosensitive area in medulla regulates respiration
Monitors [H+] of plasma via CSF indirectly
Charged ions can’t cross Blood brain barrier but CO2

Question 23

Metabolic acidosis

Answer 23

Increase ECF [H+] or decrease ECF [HCO3-]

Question 24

What causes metabolic acidosis?

Answer 24

Severe sepsis or shock = Lactic acid
Uncontrolled diabetes - overproduction of 3-OH-butyric aid & other ketoacids
Diarrhea = loss of HCO3- from GI tract

Question 25

Metabolic alkalosis

Answer 25

High pH caused by Increase ECF [HCO3-] or decrease [H+]

Question 26

What causes Metabolic alkalosis?

Answer 26

Excessive diuretic (thiazide0 use = chronic loss of Cl-, Na+ &K+ = increases H+ secretion
Vomiting = loss of H+ from GI tract
Ingestion of alkaline antacids
Hypokalemia

Question 27

What are the 3 mechanisms that change pH?

Answer 27

Intra- and extra- cellular buffering
Respiratory adjustment of ECF PCO2
Renal adjustment of ECF [HCO3-]

Question 28

Acidosis

Answer 28

Plasma pH <7.4

Question 29

Alkalosis

Answer 29

Plasma pH >7.4

Question 30

How do you produce the NH3?

Answer 30

Glutamine with the enzyme glutaminase

Question 31

Phosphate system carried on

Answer 31

Further H+ secreted into Lumen buffered by HPO4 2-

Very effective buffer because pK=6.8 (close to pH of filtrate)