Acid-base regulation Flashcards
What are the 3 main mechanisms to minimise changes in pH?
Buffer systems
Respiratory regulation
Renal regulation
What is a buffer?
Any substance that can reversibly bind H+
What are the 4 main buffer systems?
Bicarbonate buffer system
Phosphate buffer system
Protein buffer system
Ammonia buffer system
Does the bicarbonate buffer system take place intracellular or extracellular?
Extracellular
Does the phosphate buffer system take place intracellular or extracellular?
Intracellular, and in urine
Does the protein buffer system take place intracellular or extracellular?
Mainly intracellular
What is the chemical reaction of the bicarbonate buffer system?
H+ + HCO3- = H2CO3 (carbonic acid) = CO2 + H2O
What is the chemical reaction of the phosphate buffer system?
HPO42- + H+ = H2PO4-
What is the chemical reaction of the protein buffer system?
Pr- + H+ = HPr
Is urine usually acidic or alkaline? What causes this?
Acidic – due to excretion of H+ from non-volatile acid production
What are the 2 main processes by which the kidneys regulate extracellular fluid pH?
Reabsorption of filtered HCO3-
Excretion of H+
Describe how HCO3- is reabsorbed in the PCT.
It cannot be absorbed directly. H+ is secreted into the tubule lumen by a Na+/H+ antiporter. The H+ combines with bicarbonate to form carbonic acid (H2CO3). Carbonic anhydrase then converts carbonic acid into CO2 and H2O. The CO2 diffuses across the cell membrane into the PCT cell, where it combines with H2O to form carbonic acid, which then dissociates into H+ and HCO3-. The HCO3- is transported across the basolateral membrane into the bloodstream via Na+/HCO3- co transporter. The H+ is secreted back into the tubule lumen, continuing the cycle
The secretion of H+ in the late distal tubule and collecting ducts occurs through the action of which cells?
Type A intercalated cells
Via which 2 mechanisms is H+ secreted in the late distal and collecting tubules?
H+ ATPase
H+/K+ATPase
What are the 2 main urinary buffers?
Phosphate
Ammonia
In urine, phosphate exists in which two forms?
Monohydrogen phosphate (HPO42-)
Dihydrogen phosphate (H2PO4-)
Draw the formula for the urinary ammonia buffer.
NH3 + H+ = NH4+
Ammonia is synthesised from what?
Glutamine
What 4 things stimulate H+ secretion by the kidneys?
Increase in pCO2 of the extracellular fluid
A decreased pH of the extracellular fluid
Increased aldosterone levels
Hypokalaemia
What is respiratory acidosis?
Low pH due to increased CO2
Over what general time frame and how is respiratory acidosis compensated for?
Slowly (days) by the kidneys to increase the production of bicarbonate
What is metabolic acidosis?
Low pH due to decreased HCO3-
What are the 3 main mechanisms which cause metabolic acidosis?
Addition of exogenous acid (e.g. methanol)
Addition of endogenous acid (e.g. lactic or keto acids)
Failure of H+ excretion or loss of HCO3- (e.g. severe prolonged diarrhoea)
Over what general time frame and how is metabolic acidosis compensated for?
Rapidly by the lungs to increase ventilation and thus decrease CO2
