Physiology 7+8: Acid Base Balance

Question 1

what is the pH of arterial blood

Answer 1

7.45

Question 2

what is the pH of venous blood

Answer 2

7.35 (more acidic from CO2)

Question 3

what affect does acidosis and alkalosis have on the CNS

Answer 3

acidosis = depression, alkalosis = over-excitability

Question 4

what are sources of H+ from metabolic pathways

Answer 4

carbonic acid formation/ breakdown of nutrients to inorganic products/ organic acids from metabolism eg lactic acid

Question 5

what endocrine condition can cause build up of H+

Answer 5

diabetes mellitus

Question 6

how do strong and weak acids act in solution

Answer 6

weak acids partly dissociate and strong acids fully dissociate

Question 7

what does a buffer system do

Answer 7

manages equilibrium of solution ie yields free H+ when [H] decreases and binds to H+ when [H] increases

Question 8

what is the general buffer equation

Answer 8

HA H+ + A- (HA = acid, A = base).

Question 9

what effect does adding acid to a solution have on a buffer

Answer 9

the A- base will mop up the H+ to form HA

Question 10

what effect does decreasing H+ in a solution have on the buffer

Answer 10

more HA will dissociate to form H+

Question 11

what is the buffer dissociation constant equation

Answer 11

K = ([H+] x [A-]) / [HA]

Question 12

what is the buffer equation

Answer 12

pH = pKa + log([A-]/[HA])

Question 13

what catalyses CO2 + H2O to H2CO3 (carbonic acid)

Answer 13

carbonic anhydrase

Question 14

how does carbonic acid (H2CO3) work as a buffer in the body

Answer 14

dissociates to hydrogen ions and bicarbonate: H2CO3 H+ + HCO3-

Question 15

which organ controls bicarbonate levels in the body

Answer 15

kidneys

Question 16

which organ controls CO2 levels in the body

Answer 16

lungs

Question 17

how is bicarbonate (HCO3-) reabsorbed from the filtrate (what does it bind too and what is it reabsorbed as)

Answer 17

binds to H+ to become H2CO3 then is reabsorbed as CO2 and H2O

Question 18

what drives HCO3- reabsorption

Answer 18

H+ secretion (increased secretion = increased reabsorption)

Question 19

why is reabsorption of HCO3- needed

Answer 19

prevent acidosis

Question 20

what available buffers are also in filtrate if HCO3- not available

Answer 20

phosphate –> TA

ammonia –> ammonium

Question 21

what is the normal concentration of HCO3

Answer 21

25 mmol/l

Question 22

what is the normal arterial PCO2

Answer 22

40 mmHg

Question 23

what is compensation of acid-base (AB) vs correction of AB

Answer 23

compensation = restore pH to 7.4 irrespective of what happens to HCO3 and PCO2 // correction = pH, HCO3, CO2 all restored

Question 24

what are the 4 causes of AB disruptions

Answer 24

resp acidosis, resp alkalosis, metabolic acidosis, metabolic alkalosis

Question 25

what is pH proportional to in terms of HCO3- and CO2

Answer 25

[HCO3-] / [CO2)

Question 26

what is respiratory acidosis

Answer 26

retention of CO2 by body

Question 27

what causes resp acidosis

Answer 27

HYPOVENTILATION, COPD, airway restriction (asthma, tumour), chest injury, resp depression

Question 28

how does increased CO2 cause acidosis

Answer 28

CO2 + H20 H2CO3 H+ + HCO3- //// increased CO2 drives equilibrium to the right which increases H+ and HCO3-

Question 29

what pH and PCO2 levels would indicate uncompensated acidosis

Answer 29

pH < 7.35 and PCO2 > 45 mmHg

Question 30

how do the kidneys compensate for resp acidosis (3)

Answer 30

1) increased PCO2 drives H+ secretion 2) all HCO3 is reabsorbed to mop up H+ 3) TA and ammonium buffers are created

Question 31

in compensated resp acidosis, what levels of pH, PCO2 and HCO3 would you expect

Answer 31

normal pH // PCO2 raised // HCO3 raised

Question 32

how would correction of resp acidosis be achieved

Answer 32

normal ventilation to lower PCO2

Question 33

what is respiratory alkalosis

Answer 33

excessive removal of CO2 by the body

Question 34

what causes resp alkalosis

Answer 34

low inspired PO2 at altitude (hypoxia), hyperventilation (over breathing, fever)

Question 35

how does decreased PCO2 cause alkalosis

Answer 35

CO2 + H20 H2CO3 H+ + HCO3- //// decreased CO2 drives equilibrium to the left which also decreased H+ and HCO3-

Question 36

what levels of pH and PCO2 would be seen in uncompensated resp alkalosis

Answer 36

pH > 7.45 and PCO2 < 35 mmHg

Question 37

how do the kidneys compensate resp alkalosis (3)

Answer 37

1) reduces H+ secretion 2) HCO3- is excreted into the urine 3) no ammonium or TA formed

Question 38

what levels of pH, PCO2 and HCO3 are seen in compensated resp alkalosis

Answer 38

normal pH (increased H), decreased PCO2 and decreased HCO3

Question 39

what does correction of resp alkalosis require

Answer 39

normal ventilation and increased PCO2

Question 40

what is metabolic acidosis

Answer 40

increased H+ in the body (not from increased CO2)

Question 41

what can cause metabolic acidosis

Answer 41

ingestion of acids, excessive metabolic production of H+ (exercise, DKA), excessive base loss (diarrhoea)

Question 42

what happens to pH and HCO3- in metabolic acidosis

Answer 42

CO2 + H20 H2CO3 H+ + HCO3- /// increased pH and decreased HCO3- as not enough to mop up excess CO2

Question 43

how do the lungs compensate metabolic acidosis

Answer 43

increased ventilation and more CO2 blown off

Question 44

what levels of PCO2, pH and HCO3- are seen in compensated met acidosis

Answer 44

normal pH (H decrease) and low HCO3 and PCO2

Question 45

how is metabolic acidosis correction achieved by kidneys (4)

Answer 45

HCO3- reabsorbed, H+ secreted and TA and ammonium can create new HCO3-, acid excreted, normal ventilation

Question 46

what is metabolic alkalosis

Answer 46

excessive loss of H+ (nor as common as acidosis)

Question 47

what can cause metabolic alkalosis

Answer 47

vomiting HCL from stomach, ingestion of alkali, aldosterone hyper-secretion (Na/H exchange)

Question 48

what happens to pH, PCO2 and HCO3- in metabolic alkalosis

Answer 48

pH increased (decreased H+), increased HCO3-, normal PCO2

Question 49

how do lungs compensate metabolic alkalosis

Answer 49

slow ventilation to increase CO2 --> H+

Question 50

what happens to pH, PCO2 and HCO3- in compensated metabolic alkalosis

Answer 50

normal pH (increased H+), increased PCO2 and HCO3-

Question 51

how do the kidneys correct metabolic alkalosis

Answer 51

no HCO3- reabsorbed, no TA or ammonium generated