5 Acid base balance

Question 1

sources of H+ gain

Answer 1

1. from CO2 in tissue (aerobic respiration)
2. metabolism of protein and other organic molecules
3. loss HCO3- in diarrhoea
4. loss of HCO3- in urine

Question 2

sources of H+ loss

Answer 2

1. H+ + HCO3- -> CO2+ H20 (excretion through lungs)
2. utilisation of H+ in metabolism and organic anions
3. urine
4. vomitting

Question 3

mechanisms of pH homeostasis

Answer 3

1. buffers by phosphates and proteins incl Hb
2. ventilation
3. renal regulation of H+ and HCO3- (slow)

Question 4

how do kidneys contribute to the homeostasis of extracellular H+?

Answer 4

1. excreting or reabsorbing H⁺
   - phosphate and ammonia buffers
2. regulating plasma [HCO₃^-]
   - excretion of filtered HCO₃^-
   - addition of new HCO₃^- to blood

Question 5

explain the reabsorption of HCo3- in proximal tubule

Answer 5

completely filterable

reabsorption of HCo3- involves secretion of H+

no net gain of HCo3-

also reabsorbed at thick ascending limb and collecting duct

Question 6

how can HCo3- be used to correct alkalosis?

Answer 6

Hco3- reabsorption is reduced

Na+/3HCO3- transporter on basolateral membrane is the mechanism by which changes in plasma bicarbonate are sensed by the cells

Question 7

what is the major renal adaptive response to acidosis

Answer 7

ammonium excretion

Question 8

ammoniagenesis

where does it happen

Answer 8

addition of new Hco3- in blood via ammoniagenesis

glutamine metabolism

proximal

Question 9

where does ammonia diffuse to after ammoniagenesis

Answer 9

distal tubule- gets protonated

Question 10

diffusion/ ammonia trapping

Answer 10

1. NH4+ produced and secreted by proximal epithelium- ammoniagenesis
2. early in nephron, most secreted H+ is used to reabsorb bicarbonate. most important in late distal tubule and corticol collecting duct
3. NH4+ reabsorbtion by thick limb of loop of Henle into medullary interstitium- exists as NH3 or NH4+
4. NH3 diffuses into lumen of collecting duct: NH3 + H+ -> NH4+ excreted

Question 11

explain the process of renal adaptation to acidosis

Answer 11

1. addition of HCo3- via ammoniagenesis
2. diffusion and trapping of ammonia (secreted H+ in urine)
3. addition of new Hco3- to blood via phsophate buffers and ammoniagenesis

loss of H+, increased urine [NH4+] and [H2PO4-]

Question 12

what happens to kidneys when there is alkalemia

Answer 12

Kidneys compensate by inhibiting H⁺ secretion (¯HCO₃^- reabsorption), so excreting HCO₃^- in urine leads to increased­ plasma [H⁺]

Question 13

Answer 13