Acid base balance

Question 1

Range blood pH must be maintained

Answer 1

7.35-7.45

Question 2

<7.35

Answer 2

acidosis

Question 3

> 7.45

Answer 3

alkalosis

Question 4

H+ input due to

Answer 4

Diet (fatty acids, amino acids) and respiration (CO2, lactic acids, ketoacids)

Question 5

Regulate pH by

Answer 5

ventilation: fast, changes level of CO2
Renal: slow, Retaining/ losing HCO3- ions

Question 6

pH buffers

Answer 6

HCO3- in extra celullar fluid
Proteins, haemoglobin, phosphates in cells
Phosphates, ammonia in urine

Question 7

Carbonic anhydrase

Answer 7

Catalyses carbonic acid equation both ways

Question 8

Carbonic acid equation

Answer 8

CO2 + H2O –> H2CO3

–> HCO3- + H+

Question 9

Transport of CO2 in the blood at the tissue

Answer 9

Diffuses from cell where it is produced into erythrocyte
Dissolved CO2 carried 3 different ways:
stays as dissolved CO2
or dissolved CO2 + Hb = HbCO2
or CO2 and H2O --> H2CO3 --> HCO3- + H+

Question 10

Total blood CO2

Answer 10

Dissolved CO2, HCO3- and HbCO2

Question 11

CO2 diffusion at the lungs

Answer 11

HbCO2–> Hb + CO2
H2CO3 –> H2O + CO2
CO2 produced diffuses into the alveolus and is expired
Blood CO2> Alveolar CO2 = net diffusion into alveolus

Question 12

What happens to H+?

Answer 12

when O2 is released into the cell from the erythrocyte, affinity for H+ increases

Question 13

What happens if someone hypoventilates?

Answer 13

Prevents normal elimination of CO2
arterial PCO2 and H+ conc would increase
= respiratory acidosis

Question 14

Hyperventilation?

Answer 14

Low arterial PCO2 and decr H+

= respiratory alkalosis

Question 15

Changes in PCO2 and chemoreceptors recap

Answer 15

Peripheral chemoreceptors respond to incr in arterial H+ due to incr in PCO2
Incr in brain PCO2 leads to incr in brain extracellular H+ conc that stimulates central chemoreceptors
Both central and peripheral chemoreceptors stimulate medullary inspiratory neurones to incr ventilation

Question 16

Non-CO2 dependent changes in pH

Answer 16

eg incr in lactic acid
H+ can’t cross BBB so originally only activate peripheral chemoreceptors
Therefore changes in respiratory activity almost entirely due to stimulation of peripheral chemoreceptors

Question 17

Bicarbonate regulation in the kidneys

Answer 17

HCO3- filtered completely at renal corpuscle and lots absorbed at PCT, loop of henle and CCT (cortical collecting duct)
CCT can also secrete HCO3-

Question 18

Renal HCO3- secretion =

Answer 18

Filtered + secreted - absorbed

Question 19

HCO3- reabsorption in PCT

Answer 19

Epithelial cells secreting H+ ions into lumen of PCT
Combines with HCO3- to form H2CO3 then to H2O and CO2, which can diffuse across into the epithelial cell where they reform H2CO3
This H2CO3 produces H+ and HCO3-, HCO3- moves into ISF by facilitated diffusion and H+ pumped into lumen (back to 1st step)
Net result reabsorption of HCO3-

Question 20

Enzymes/ pumps behind reabsorption

Answer 20

ATPase and Na/H+ pump (antiporter) releasing H+ into tubule
CAIV extracellular form attached to epi CSM
CAII intracellular form
HCO3- moves into ISF by NBCe1-a pathway

Question 21

Collecting duct: acidosis

Answer 21

Kidney secretes H+ and reabsorbs HCO3-

Question 22

collecting duct: alkalosis

Answer 22

Kidney secretes K+ and HCO3- and reabsorbs H+

Question 23

What happens when all filtered bicarbonate has been reabsorbed?

Answer 23

Additional buffering with ‘new’ bicarbonate ions, synthesised in the tubule cells, as long as a ‘sink’ for H+ (here HPO4 2- ) is available
Net gain HCO3-
diagram is useful here

Question 24

Glutamine

Answer 24

New bicarbonate ions synthesised from catalysis of glutamine
Metabolised in the cell to make NH4+ and HCO3-
HCO3- moves into bloodstream by sodium dependent pathway and NH4+ moves into lumen, secreted
Glutamine moves in form tubular lumen because been filtered

Question 25

Overall renal response to acidosis

Answer 25

Sufficient H+ secreted to reabsorb all HCO3-
More H+ secreted and adds new HCO3- in the plasma due to nonbicarbonate urinary buffers
Net result: HCO3- in blood incr, compensates for acidosis

Question 26

Overall renal response to alkalosis

Answer 26

Amount of H+ secretion not enough to reabsorb all filtered bicarbonate so this is excreted in urine
Little or no excretion of H+ on nonbicarbonate buffers
Decr tubular glutamate metabolism and ammonium secretion
Net result: plasma bicarbonate decr and compensates for alkalosis