Physiology: Acid-Base Balance

Question 1

what does acidosis cause to the CNS

Answer 1

depression

Question 2

what does alkalosis do to the CNS

Answer 2

overexcitability

Question 3

what does fluctuations in H+ affect?

Answer 3

CNS
enzyme activity
K+ levels

Question 4

how is H+ continually added to the blood?

Answer 4

• carbonic acid formation
• inorganic acids produced during breakdown of nutrients
• organic acids resulting from metabolism

Question 5

define buffer

Answer 5

system that works to keep a stable environment when a change occurs

Question 6

what does the buffer system do when acid is added?

Answer 6

equilibrium shifts to the left

excess H+ is mopped up by A- forming more HA

Question 7

what does the buffer system do if a base is added?

Answer 7

equilibrium shifts to the right

HA is formed so HA dissociates increasing free H+

Question 8

how do the kidneys control HCO3-?

Answer 8

reabsorb some filter and add new HCO3- to the blood

Question 9

how do the kidneys add ‘new’ HCO3- to the blood?

Answer 9

secreted H+ combines with another buffer e.g. phosphate or ammonium

Question 10

what is the phosphate buffer excreted as?

Answer 10

H2PO4- which can be measure as a TA using NaOH

Question 11

what is the first step when acid-base balance is disturbed?

Answer 11

pH is to be returned to normal irrespective of what happens to CO2 and HCO3-

Question 12

define respiratory acidosis

Answer 12

retention of CO2 by the body

Question 13

causes of respiratory acidosis

Answer 13

chronic bronchitis or emphysema
airway restriction (bronchial asthma, tumour)
chest injuries
respiratory distress

Question 14

what does retention of CO2 by the body cause? (respiratory acidosis)

Answer 14

generates acidosis by production of H+ (HCO3- also rises)

Question 15

biochemical result of uncompensated respiratory acidosis

Answer 15

pH <7.35

pCO2 >45mmHg

Question 16

renal compensation of respiratory acidosis

Answer 16

excretes excess H+ and HCO3- while adding new HCO3- to the blood via TA and NH4+

correction of pCO2 requires restoration of normal ventilation

Question 17

define respiratory alkalosis

Answer 17

excessive removal of CO2 from the body

Question 18

causes of respiratory alkalosis

Answer 18

• los inspired pO2 at altitude (hypoxia stimulates peripheral chemoreceptors, hyperventilation lowers pCO2)
• hyperventilation (fever, brainstem damage)
• hysterical over-breathing

Question 19

biochemical result of uncompensated respiratory alkalosis

Answer 19

pH >7.45

pCO2 <35mmHg

Question 20

kidney compensation of respiratory alkalosis

Answer 20

low CO2 causes no H+ secretion and no reabsorption of HCO3-. It is excreted and urine is alkaline

correction requires restoration of normal ventilation

Question 21

define metabolic acidosis

Answer 21

excess of H+ from any source other than CO2

Question 22

causes of metabolic acidosis

Answer 22

• ingestion of acids or acid-producing foods
  excessive metabolic
• production of H+ (lactic acid during exercise or ketoacidosis)
• excess loss of base from the body (diarrhoea- loss of HCO3-)

Question 23

what happens in the body during metabolic acidosis

Answer 23

HCO3- is depleted due to buffering excess H+

Question 24

biochemical result of uncompensated metabolic acidosis

Answer 24

pH <7.35

HCO3- is low

Question 25

compensation for metabolic acidosis

Answer 25

decrease in plasma pH stimulates peripheral chemoreceptors so ventilation is increased blowing off excess CO2

correction requires reabsorption of HCO3- and excretion of H+ to produce TA and NH4+ (this cannot be done immediately so respiratory compensation is essential)

Question 26

define metabolic alkalosis

Answer 26

excessive loss of H+ from the body

Question 27

causes of metabolic alkalosis

Answer 27

loss of HCl from the stomach (vomiting)
ingestion of alkali or alkali-producing food
aldosterone hyper-secretion causing Na+/H+ exchange (acid secretion)

Question 28

biochemical indication of uncompensated metabolic alkalosis

Answer 28

pH >7.45

HCO3- high

Question 29

compensation of metabolic alkalosis

Answer 29

slowed ventilation due to detection by peripheral chemoreceptors leading to retention of CO2 and H+ rises

correction requires HCO3- excretion