Physiology: Acid-Base Balance Flashcards
what does acidosis cause to the CNS
depression
what does alkalosis do to the CNS
overexcitability
what does fluctuations in H+ affect?
CNS
enzyme activity
K+ levels
how is H+ continually added to the blood?
- carbonic acid formation
- inorganic acids produced during breakdown of nutrients
- organic acids resulting from metabolism
define buffer
system that works to keep a stable environment when a change occurs
what does the buffer system do when acid is added?
equilibrium shifts to the left
excess H+ is mopped up by A- forming more HA
what does the buffer system do if a base is added?
equilibrium shifts to the right
HA is formed so HA dissociates increasing free H+
how do the kidneys control HCO3-?
reabsorb some filter and add new HCO3- to the blood
how do the kidneys add ‘new’ HCO3- to the blood?
secreted H+ combines with another buffer e.g. phosphate or ammonium
what is the phosphate buffer excreted as?
H2PO4- which can be measure as a TA using NaOH
what is the first step when acid-base balance is disturbed?
pH is to be returned to normal irrespective of what happens to CO2 and HCO3-
define respiratory acidosis
retention of CO2 by the body
causes of respiratory acidosis
chronic bronchitis or emphysema
airway restriction (bronchial asthma, tumour)
chest injuries
respiratory distress
what does retention of CO2 by the body cause? (respiratory acidosis)
generates acidosis by production of H+ (HCO3- also rises)
biochemical result of uncompensated respiratory acidosis
pH <7.35
pCO2 >45mmHg
renal compensation of respiratory acidosis
excretes excess H+ and HCO3- while adding new HCO3- to the blood via TA and NH4+
correction of pCO2 requires restoration of normal ventilation
define respiratory alkalosis
excessive removal of CO2 from the body
causes of respiratory alkalosis
- los inspired pO2 at altitude (hypoxia stimulates peripheral chemoreceptors, hyperventilation lowers pCO2)
- hyperventilation (fever, brainstem damage)
- hysterical over-breathing
biochemical result of uncompensated respiratory alkalosis
pH >7.45
pCO2 <35mmHg
kidney compensation of respiratory alkalosis
low CO2 causes no H+ secretion and no reabsorption of HCO3-. It is excreted and urine is alkaline
correction requires restoration of normal ventilation
define metabolic acidosis
excess of H+ from any source other than CO2
causes of metabolic acidosis
- 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-)
what happens in the body during metabolic acidosis
HCO3- is depleted due to buffering excess H+
biochemical result of uncompensated metabolic acidosis
pH <7.35
HCO3- is low
compensation for metabolic acidosis
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)
define metabolic alkalosis
excessive loss of H+ from the body
causes of metabolic alkalosis
loss of HCl from the stomach (vomiting)
ingestion of alkali or alkali-producing food
aldosterone hyper-secretion causing Na+/H+ exchange (acid secretion)
biochemical indication of uncompensated metabolic alkalosis
pH >7.45
HCO3- high
compensation of metabolic alkalosis
slowed ventilation due to detection by peripheral chemoreceptors leading to retention of CO2 and H+ rises
correction requires HCO3- excretion
