Acid Base Nonsense Flashcards
What is the normal pH of arterial blood?
7.4
What are the two sources of H+?
Respiratory Acid
Metabolic Acid
- inorganic acids such as H2SO4 and phosphoric acids
- organic acids such as lactic acid and fatty acid
What are the sources of alkali in the body?
Oxidation of organic anions such as citrate
What is the role of buffers?
To minimise changes in pH when H+ ions are added or removed
What is the ratio of HCO3- to H2CO3 in blood?
20:1
What is the concentration of HCO3 in blood?
24mmol/l
What is the normal level of pCO2 within the body?
40mmHg/5.3pKa
What occurs if there is an increase in H+ (Acidosis)?
There is an increase in ventilation and a decrease in CO2
What occurs if there is a decrease in H+ (alkalosis)?
There is a decrease in ventilation and an increase in CO2
In the henderson-hasselbalch equation, what is each varient controlled by?
HCO3 - renal regulation
Pco2 - respiratory regulation
What occurs if you decrease the concentration of HCO3?
pH then decreases and so does pCO2
What can act as intracellular buffers?
Proteins, Organic/Inorganic phosphates, Erythrocytes, Haemoglobin
What must occur if H+ ions are buffered by intracellular buffers?
They must be accompanies by Cl- or exchanged for K+
What happens to potassium levels in acidosis?
Hyperkalaemia
How much of metabolic acid is buffered by plasma?
43%
How much of metabolic acid is buffered in cells?
57%
How much respiratory acid is buffered within cells ?
97%
What affects pCO2 ?
Respiratory Disorders
What affects HCO3?
Renal disorders
What occurs in respiratory acidosis?
There is a decrease in pH bc of an increase in pCO2
What causes respiratory acidosis?
Acute - barbituates, opiates
Chronic - Bronchitis, Emphysema, Asthma
What occurs in respiratory alkalosis?
Increase in pH bc of a decrease in CO2
What are the causes of respiratory alkalosis?
Acute - hyperventilation, aspirin, altitude
Chronic - longterm residence at high altitude
What is metabolic acidosis?
An decrease in pH due to a decrease in HCO3
pCO2 then decreases to compensate for acidic conditions
What causes metabolic acidosis?
Increase in H+ production - ketoacidosis, lactic acidosis, failure to excrete normal dietary load of H+, Loss of HCO3 (diarrhoea)
What is metabolic alkalosis?
Increased pH due to increased HCO3
pCO2 then also increases to compensate for alkalotic conditions
What are the causes of metabolic alkalosis?
Increase in H+ ion loss - vomiting, Increase in H+ renal loss, Excess administration of HCO3- in those who are renally impaired, massive blood transfusions
Describe HCO3- reabsorption
- Sodium ions are reabsorbed from filtrate in exchange for H+ via an antiport mechanism in the apical membrane
- Filtered HCO3- reacts with H+ to form H2CO3 which will combine with carbonic anhydrase to form H2O and CO2
- Carbon dioxide enters cell and enters a reaction with H2O (aided by carbonic anhydrase) to form carbonic acid
- Carbonic acid dissociates to form a bicarbonate ion and hydrogen ion
- H+ ions are secreted and HCO3- pass into peritubular capillaries with Na+
What is the min urine pH?
4.5-5
What is the max urine pH?
8
What upregulates the Na/H ion antiporter?
Angiotensin II
- promotes Na+ reabsorption and H+ secretion.
What is the basis of titratable acidity?
- NaHPO4 lies within the lumen. One Na+ is exchanged for an H+ ion
- Carbon dioxide indirectly forms bicarbonate which enters tubule cells and combines with water to form carbonic acid (aided by carbonic anhydrase)
- Carbonic Acid then dissociates to yield H+ and HCO3-
What is the function of titratable acidity?
To make new Bicarbonate and excrete H+
What is the purpose of ammonium excretion?
Response to increased acid loads and forms new bicarbonate AND excretes H+
What occurs in ammonium excretion?
- Deamination of amino acids by glutaminase within renal tubule results in NH3 production
- NH3 leaves tubule lumen and combines with H+ ions to produce NH4+. NH4+ then combines with CL- to produce NH3Cl- and this is excreted
- New H+ions are generated from CO2 in blood
- HCO3- passes with Na+ into peritubular capillaries
What affect does pH have on renal glutaminase?
When intracellular pH decreases (becomes more acidic), renal glutaminase activity increases which increases NH4+ production and excretion
What is the relationship between Hydrogen and SOdium in titratable excretion?
For every H+ excreted, one Na+ is absorbed
What is the relationship between hydrogen, sodium and bicarbonate during HCO3 reabsorption?
For every H+ excreted, Na+ conserved, one bicarbonate is reabsorbed
if pH = 7.25, [HCO3] = 12mmoles/l, Pco2= 25mmHg, why does this indicate impaired renal function?
Damage to nephron means that kidneys are not removing enough acid from the blood stream
Evident that values show metabolic acidosis
if pH = 7.45, [HCO3] = 12mmol/l, Pco2 = 20mmHg, why does this indicate that the patient has been living at high altitude?
pH is only slightly raised yet HCO3 and CO2 are lower than usual. Lower bicarb and carbon dioxide would suggest metabolic acidosis to compensate for the initial respiratory alkalosis
if pH= 7.28, [HCO3]= 36mmol/l, Pco2= 60mmHg, why would the patient be excreting ammonium ions?
acute and chronic acid loads enhance ammonia production in the proximal tubule and secretion into the urine
if pH=7.5, [HCO3]= 45mmol/l. Pco2= 60mmHg. why would the subject be secreting bicarbonate ions?
increased excretion of HCO3− as the filtered load of HCO3− exceeds the ability of the renal tubule to reabsorb it.
