acid-base balance

Question 1

acid

Answer 1

chemical that releases H+ ions

Question 2

base

Answer 2

chemical that takes up H+ ions

Question 3

buffer

Answer 3

substances or mechanisms that act to minimise changes in pH when H+ concentration is altered

Question 4

pH

Answer 4

-log[H+], indicates degree of acidity or alkalinity

Question 5

normal pH in urine, gastric acid, pancreatic fluid, ECF and cells

Answer 5

urine = 4.5-8 depending on diet Gastric acid: 1 Pancreatic fluid: 7.8 ECF (blood): 7.35-7.45 Cells: 7.1 as metabolism makes acids

Question 6

acidosis definition, causes and symptoms

Answer 6

Blood pH lower than 7.35

Caused by excess diarrhoea as bicarbonate from bile is being removed and H+ is being left behind

Respiratory dysfunction, drowsiness, coma

Question 7

alkalosis definition, causes and symptoms

Answer 7

Blood pH higher than 7.45

Caused by excess vomiting as HCl from stomach acid is being removed and bicarbonate is left behind

Headache, drowsy, convulsions

Question 8

what causes gain of H+ (decrease in pH)

Answer 8

generation of H+ from CO2 in blood

production of non-volatile acids from metabolism of proteins and other organic molecules

loss of HCO3- from bile in diarrhoea and urine

Question 9

loss of H+ (increase in pH)

Answer 9

Utilisation of H+ in metabolism of various organic anions

Loss of H+ in vomitus

Loss of H+ in urine

Hyperventilation

Question 10

why must be regulate pH

Answer 10

have to keep it within very tight limits as too high (8) or low (7) pH is lethal

correct pH is important for enzyme activity, ion transport, cell metabolism

Question 11

how is pH regulated

Answer 11

buffering and excretion

Question 12

3 main buffers for controlling H+ from non-volatile acids

Answer 12

bicarbonate, protein and phosphate

Question 13

how is H+ buffered while being transported in blood

Answer 13

Mostly buffered by Haemoglobin

H+ formed by dissolution of CO2 in water is soaked up by Hb so there is very little change in pH from CO2 produced

H+ dissociates from Hb in lungs so CO2 can form and be breathed out

Question 14

respiratory acidosis

Answer 14

Too little ventilation –> CO2 not removed so excess H+ accumulates

Kidneys would compensate by excreting more H+ and synthesising more bicarbonate

Question 15

respiratory alkalosis

Answer 15

Too much ventilation —> excess CO2 removed so decreased H+

Kidneys would compensate by excreting less/ holding on to H+ and synthesising less bicarbonate

Question 16

what does kidney do with bicarbonate

Answer 16

reabsorb it

replace HCO3- consumed in excretion of non-volatile acids

excrete excess HCO3-

Question 17

reabsorption of HCO3-

Answer 17

in epithelial cell, H2O + CO2 produced by metabolism is converted to carbonic acid by carbonic anhydrase. Carbonic acid dissociates to HCO3- and H+, HCO3- is reabsorbed into interstitial fluid. H+ is transported into tubular lumen via antiport Na+ exchanger. H+ binds HCO3- in tubular lumen, forms carbonic acid which dissociates into H2O and CO2. We do not produce any new HCO3-

Question 18

replacement of HCO3- consumed in excretion of non-volatile acids

Answer 18

in epithelial cell, H2O + CO2 produced by metabolism is converted to carbonic acid by carbonic anhydrase. Carbonic acid dissociates to HCO3- and H+, HCO3- is reabsorbed into interstitial fluid. H+ is transported into tubular lumen via antiport Na+ exchanger. H+ binds HPO4^2- which forms H2PO4^- which is excreted

Question 19

generation of new HCO3- using glutamine

Answer 19

glutamine is synthesised under low HCO3- conditions or
acidosis which dissociates into HCO3- and NH4+. NH4+ is then excreted and HCO3- is absorbed

Question 20

metabolic alkalosis

Answer 20

Increased HCO3-, more to buffer acid in transport and non-volatile acids

Respiratory compensation by hypoventilating to increase CO2 and, decrease pH

Kidneys would compensate by excreting less/ holding on to H+ and synthesising less bicarbonate

Question 21

metabolic acidosis

Answer 21

Decreased HCO3-, less to buffer acid in transport and non-volatile acids

Respiratory compensation by hyperventilating to remove CO2

Kidneys would compensate by excreting more H+ and synthesising more bicarbonate