pH of the body depends on the ratio of what?
[HCO3] / [H2CO3]
What pH constitutes acidosis?
pH<7.35
How does the body become acidotic?
1) metabolic acidosis: where the pH is < 7.35 where the primary defect is a decrease in plasma [HCO3]
2) respiratory acidosis: This is a pH<7.35 where the primary defect is an increase in the paCO2
What are a few causes of metabolic acidosis?
1) excess acid production like keto acid production in diabetes mellitus
2) severe diarrhoea
3) renal failure
What is the compensatory response to metabolic acidosis?
- buffering in the ECF by HCO3-, Pi, and plasma proteins
- bone releases Ca2+ as salt in exchange for H+ ions
- ICF- H+ is titrated by HCO3-, Pi and histidine groups on proteins
what is the respiratory response to metabolic acidosis?
the plasma HCO3 concentration has decreased, therefore blood pH has fallen and the lungs try to bring about a proportionate decrease in the paCO2- increasing ventilation
What is the renal compensation to metabolic acidosis?
reabsorption of all filtered HCO3-, secretion of H+ by nephron and increased excretion of H+ bound to urinary buffers (Pi and creatinine), increased NH4+ production
what is Kuss Maul breathing?
observed increased respiration due to acidosis
what are the causes of respiratory acidosis?
overall inadequate ventilation
1) depression of respiratory centre
2) paralysis of respiratory muscles
3) lung damage from pulmonary oedema in CV or lung disease
What is the compensatory response to respiratory acidosis?
buffering of H+ mainly in the ICF (acute phase)
when pCO2 rises, CO2 moves into cell where it combines with H2O to form H2CO3, then HCO3, and H+
H+ buffered by intracellular protein
what is the effect of chronic and acute acidosis on K+ excretion?
Acute acidosis = decreases K+ excretion
Chronic acidosis= increases K+ excretion
what is the effect of acidosis on bones?
when chronic, demineralization of bones occurs (osteomalacia)
b/c the Ca2+ is released from bone to exchange for H+ present in the ECF
What pH denotes alkalosis?
pH> 7.45
What is metabolic alkalosis?
the primary defect cuasing pH increase is an increase in plasma HCO3 concentration
what is the cause of respiratory alkalosis?
decrease in paCO2 often due to hyperventilation
what are some causes of metabolic alkalosis?
- vomiting
- ingestion of volatile base (antacids)
- volume contraction (haemorrhage) which increases Na+ reabsorption
what respiratory action compensates for metabolic alkalosis?
1) plasma [HCO3] has increased and therefore blood pH has increased
2) the lungs try to bing out the proportionate increase in paCO2- therefore hypoventilation occurs
What is the renal compensation to metabolic alkalosis?
- reduced reabsorption of HCO3-
- decreased excreton of titratable acid and NH4+
what are some causes of respiratory alkalosis?
hyperventilation (panic attacks)
What is the intracellular and renal response to alkalosis?
intracellular = buffering in the ICF
renal = filtered load and excretion of HCO3- increased, decreased exretion of titratable acid and NH4+
thus, decreased net acid excretion and HCO3- appears in urine
what are some effects of alkalosis?
irritability/confusion - if severe hypocalcaemic tetany
Why does blood alkalosis lead to tetany?
because your albumin wants H+ when it’s in the alkalotic state, but obviously H+ isn’t available, it binds instead to calcium. This decreased free serum Ca2+ increases the neuronal membrane permeability to sodium, so you have an easy initiation of action potentials - leads to tetany
What is trousseaus sign of tetany ?
Why does hyperventilation lead to fainting/dizziness?
the decrease in pCO2 cuases cerebral ischaemia resulting in dizziness and fainting
How do you analyze an acid base disorder nature/origin?
1) examine pH - is it acidic or basic?
2) if acidic- examine the value for pCO2, it will be high if the acisosis is respiratory - examine the value for plasma HCO3 concentration and it will be low if the acidosis is metabolic
3) if alkalosis- examine the value for pCO2- it will be low if the alklaosis is respiratory - examine the value for plasma [HCO3] and it will be high if the alkalosis is metabolic
Analyze the following acid base disorders
patient A= metabolic acidosis
Patient B = metabolic Alkylosis
patient C= respiratory acidosis