Acid-Base

Question 1

Define acid and base

Answer 1

Acid = molecules that can release H+
Base = ion or molecule that can accept H+

Question 2

What is the arterial blood pH?

Answer 2

7.35-7.45

Question 3

What is urine pH and why does it range?

Answer 3

4.5 - 8
Ranges depending acid-base status of EFC
In order to tightly regulate body pH

Question 4

What are the pH limits a person can live for a few hours?

Answer 4

6.8 - 8

Question 5

Define acidosis

Answer 5

Arterial pH below 7

Question 6

Define alkalosis

Answer 6

Arterial pH above 7.4

Question 7

What systems regulate the body pH?

Answer 7

Kidneys
Lungs

Question 8

Define a buffer

Answer 8

Substance that can bind or release H+ to keep pH of solution relatively constant despite addition of considerable acid or base

Question 9

Name 4 buffers

Answer 9

H2CO3
H2PO4-
HProt
HHb

Question 10

What does amino acid metabolism create?

Answer 10

Releases NH4+ and H2SO4 (sulfuric acid)

Question 11

How does the kidney regulate acid-base balance?

Answer 11

Excretes acids
Conserves HCO3-

Question 12

Where does H+ secretion and HCO3- reabsorption NOT occur?

Answer 12

THIN segment of loop of Henle

Question 13

What effects do carbonic anhydrase inhibitors have?

Answer 13

Decrease proximal tubular H+ secretion»>Increase fluid excretion»>Increase loss of bicarbonate and Na+

Question 14

What cells are found in the DCT?

Answer 14

Type A Intercataled cells

Question 15

How is HCO3- reabsorbed in the DCT?

Answer 15

HCO3- / Cl- exchanger

Question 16

How is H+ secreted in the DCT?

Answer 16

Mainly H+ ATPase mediated by ALDOSTERONE
H+/K+ ATPase

Question 18

What happens when urine pH reaches 4.5?

Answer 18

Limiting pH = further H+ secretion is not possible

Question 19

What is the role of buffering systems in terms of urine pH?

Answer 19

3 systems bind H+ in the urin
Allow more H+ secretion
Delay reaching limiting pH

Question 20

What are the 3 buffering systems in urine?

Answer 20

Bicarbonate buffer system
Phosphate buffer system
Ammonia buffer system

Question 21

Where does each buffering system in urine occur?

Answer 21

Bicarbonate = mostly PCT
Phosphate = DCT & CT
Ammonia = PCT & DCT

Question 22

What is the ratio between HCO3- and phosphate?

Answer 22

New HCO3- is returned to the blood for each NaHPO4 rate reacts with a secreted H+

Question 23

How does the ammonia buffer work?

Answer 23

Glutamine is taken up by the proximal tubular cell
It splits into 2HCO3- and 2NH4-
The NH4+ is secreted into tubular lumen by NH4- / Na+ exchanger
NH4+ joins with Cl-

Question 24

What factors interfere with H+ secretion and HCO3- reabsorption?

Answer 24

CO2
Ang II
Aldosterone
Serum K+ levels
ECF volume

Question 25

Why does high CO2 increase H+ secretion and HCO3- reabsorption?

Answer 25

Increases the carbonic acid levels = enhanced H+ secretion

Question 26

How does increased aldosterone increase H+ secretion and HCO3- reabsorption?

Answer 26

Stimulates H+ secretion by Type A intercalated cells of the DCT

Question 27

How does decrease in ECF volume increase H+ secretion and HCO3- reabsorption?

Answer 27

Activates RAAS -> increasing H+ secretion -> alkalosis

Question 28

How does increase in Ang II increase H+ secretion and HCO3- reabsorption?

Answer 28

Ang II enhances the activity of the sodium-hydrogen exchanger (NHE3) located on the luminal membrane of PCT cells Leading to increased secretion of H+

Question 29

How does ventilation regulate acid-base balance?

Answer 29

Increase ventilation = eliminates CO2 = decrease in H+ concentration

Question 30

How is bicarbonate lost and what does this cause?

Answer 30

Metabolic acidosis Diarrhoea Renal tubular acidosis type 2 (RTA2)

Question 31

How is metabolic acidosis caused?

Answer 31

Ingestion of acidifying salts = NH4Cl and CaCl2 Decreased H+ excretion = renal failure or RTA1 Increased H+ production = diabetic ketosis and lactic acid generation

Question 32

What are the causes of metabolic alkalosis?

Answer 32

Loss of H+ = vomiting & diuretics Ingestion of HCO3- = ex-antacids

Question 33

What are the causes of respiratory acidosis?

Answer 33

Decreased ventilation = due to lung diseases or neuromuscular problems (leading to respiratory muscle weakness) Severe pneumonia / asthma

Question 34

What are the causes of respiratory alkalosis?

Answer 34

Increased ventilation = due to hyperventilation of physiology Physiology = high altitudes so low O2 level stimulates respiration

Question 35

What happens in chronic acidosis?

Answer 35

Regardless of what type of acidosis = increased production of NH4+ which contribute to excretion of H+ and addition of new HCO3- to the extracellular fluid

Question 36

What limits respiratory compensation of metabolic alkalosis?

Answer 36

Size of this compensation is limited by carotid and aortic chemoreceptor mechanisms As pO2 should be maintained

Question 37

What are other compensatory mechanisms for metabolic acidosis?

Answer 37

Decreased glomerular filtration of HCO3-

Question 38

What are other compensatory mechanisms for metabolic alkalosis?

Answer 38

Decreased renal H+ secretion Reduced HCO3- reabsorption If levels are very high HCO3- can be excreted in urine

Question 39

Why may compensation be complete or incomplete?

Answer 39

Compensatory mechanisms may not have time to form in severe acute disturbances If acid-base disorder slowly develops = compensation will happen more effectively