Acid-Base balance I

Question 1

What is pH?

Answer 1

pH = log 1/H

Question 2

What is the pH of arterial blood?

Answer 2

7.45

Question 3

What is the pH of venous blood?

Answer 3

7.35

Question 4

What is the pH of the ECF controlled close to?

Answer 4

7.4

Question 5

What can acidosis do?

Answer 5

lead to depression of CNS

Question 6

What can alkalosis do?

Answer 6

over-excitability of peripheral NS or later the CNS

Question 7

What does H influence?

Answer 7

enzyme activity and K levels in the body

Question 8

How is H continually added to the body fluids?

Answer 8

metabolic activity
carbonic acid formation
inorganic acids from breaking down nutrients
organic acids from metabolism

Question 9

What is the dissociation constant for acids and bases?

Answer 9

K = [H][A]/HA

Question 10

What is pK equal to?

Answer 10

pK=-logK

Question 11

What is the henderson-hasselbach equation?

Answer 11

H = K x HA/A
OR
pH = pK + log [A]/[HA]

Question 12

What are some physiological buffers?

Answer 12

HCO3-CO2

Question 13

Why is the HCO3-CO2 buffer so important?

Answer 13

HCO3 is controlled by kidneys, PCO2 is controlled by lungs

Question 14

How does the HCO3-CO2 buffer influence physiological pH?

Answer 14

pH = pK + log [HCO3]/pCO2 x 0.03 solubility coefficient
Normal conditions HCO3 = 24 mmol, pCO2 is 40 mmHg
pH = 6.1 + log 24/40.0.03 = 7.4

Question 15

What is the role of the kidney in control of HCO3?

Answer 15

variable reabsorption of filtered HCO3

Kidneys can add new HCO3 to the blood

Question 16

What does the kidneys control of HCO3 depend upon?

Answer 16

H secretion into the tubule

Question 17

How much HCO3 is filtered per day?

Answer 17

4320 mmol/day

Question 18

How does HCO3 get back into the interstitial fluid?

Answer 18

Doesn’t do it as an ion
takes H from NHE -> H2CO3 which is converted to CO2 which diffuses into epithelial cell where converted back to HCO3 which goes to interstitial fluid via Na/HCO3 cotransporter

Question 19

How does the kidney form new HCO3 when HCO3 is low?

Answer 19

secreted H binds with next most plentiful buffer in filtrate - phosphate

Question 20

How does phosphate act as a buffer?

Answer 20

binds H and HPO4 to make H2PO4 which is an acid that is excreted so there is a net gain of HCO3

Question 21

What is titratable acid?

Answer 21

the amount of H excreted as H2PO4 can be measured

Question 22

What is the maximum amount of titratable acid that can be excreted per day?

Answer 22

40mmol/day

Question 23

What happens if 40mmol/day is added as titratable acid then how much HCO3 is gained by the circulation?

Answer 23

40mmol/day

Question 24

How does ammonia act as a tubular buffer?

Answer 24

NH3 binds H to make ammonium ion that is excreted causing net gain of HCO3

Question 25

How is ammonia secreted into the tubule?

Answer 25

glutamine from the liver -> glutaminase -> NH3 in tubule

Question 26

What is the usual excretion of NH4?

Answer 26

20mmol/day

Question 27

What may happen in acidosis?

Answer 27

NH4 excretion increases to 5-600mmol/day

Question 28

What are the three actions of H?

Answer 28

drives HCO3 reabsorption - 4300mmol/day
Forms acid phosphate 20 mmol/day
Forms ammonium ion - 40 mmol/day

Question 29

What is the total H secretion per day?

Answer 29

sum of all the HCO3 reabsorption and TA and NH4 excretion - 4360mmol/day

Question 30

What is the total H excretion per day?

Answer 30

sum of Ta and NH4 excretion - 60 mmol/day

Question 31

What is the total amount of new HCO3 generated a day?

Answer 31

60mmol/day