12 Acid Base Regulation Flashcards
When does net H+ production occur?
ATP hydrolysis
lactate production
ketone production (DM)
Acid ingestion
What happens to the H+ we produce?
What problem is associated with this?
it is reacted with HCO3- to form CO2, which can then be excreted
HCO3- can run out if we have too much H+!
In what 2 ways does the kidney regulate pH?
reabsorbing filtered HCO3-
producing HCO3-
How is HCO3- reabsorbed in the kidney?
bicarbonate reacts with secreted H+ (CA) , so it can then diffuse in as H2O and CO2
HCO3- then leaves the basolateral membrane down its’ own gradient, cotransporting Na+ out
How is a HCO3- excess corrected in the kidney?
they kidney is unable to reabsorb so much HCO3-, as it is limited by the amount of H+ in the PCT and the Na+/H+ exchanger
How does the kidney produce net bicarbonate?
if the CO2 is coming from the vesa recta, is can diffuse into the cellls of the PCT then form an equilibrium
the H+ goes into the filtrate via Na+/H+ cotransporter, the HCO3- then leaves the basolateral membrane, having lost an H+
How does the DCT secrete H+?
H+/K+ ATPase
H+ ATPase
in specialised alpha-intercalated cells
Why is phosphate important?
it is used to buffer the XS H+ in the urine to prevent it from getting too low
if all the bicarbonate it being reabsorbed in the PCT, the urine doesn’t have another pH buffer, so it relies on phosphate
When plasma pH is 7.4, what does this tell us about phosphates?
HPO4(2-) predominates
When urinary pH is 5, what does this tell us about phosphates?
Why?
H2PO4(-) predominates
along the tubule, phosphate is pickup up additional hydrogen ions, which it carries out (this is how it acts as a buffer)
When might the kidney secrete ammonium?
the PCT releases ammonium into the filtrate as a way of getting rid of hydrogen ions
How does the kidney secrete ammonium?
glutamine from the liver is converted into glutamic acid in the PCT cells
this is then converted to alpha-ketogluterate, expelling NH3 into the flitrate
the NH3 then binds with H+ expelled by an H+ATPase
this then acts as a reservoir for H+ in the filtrate
What happens to the pH by the end of the PCT?
it has usually fallen to about 6.9 (although is highly variable)
What is the cause of respiratory acidosis?
hypoventilation
What happens in respiratory acidosis?
an increase in CO2 decreases pH
How is respiratory acidosis compensated for?
the kidney increases HCO3- production, to increase pH
What is the cause of respiratory alkalosis?
hyperventilation or high altitude
What happens in respiratory alkalosis?
Co2 decreases, so pH rises
How is respiratory alkalosis compensated for?
the kidney decreases the production or recovery of HCO3- to decrease pH
What are the possible causes metabolic acidosis?
renal failure
lactic acidosis
ketoacidosis
aspirin poisoning…
What happens in metabolic acidosis?
H+ increases causing HCO3- to decrease
OR
HCO3- decreases, so H+ increases
How is metabolic acidosis accounted for?
CNS increases ventilation to decrease CO2, increasing pH
What causes metabolic alkalosis?
vomiting (loss of acid)
contraction alkalosis
What happens in metabolic alkalosis?
H+ decreases so HCO3_ increases
OR
HCO3- increases so H+ decreases
How is metabolic alkalosis accounted for?
CNS decreases ventilation rate to increase CO2, decreasing pH to normal
How is the anion gap usually calculated?
[Na+] - [Cl-] - [HCO3-]
cations - anions
What does an increased anion gap suggest?
there is a high concentration of anions not being counted - acidosis
What might cause an increased anion gap?
lactate
ketones
sulphates, phosphates, urates, and hippurate (renal failure)
aspirin overdose
i.e. several causes of metabolic acidosis change the anion gap
