Acid Base Balance and
related disorders
Monday, 27 September 2021 8:31 AM
Acid-base balance
- Constant loading of acid into our body
- Therefore amount of acid secreted must equal amount produced
Chemical buffer system
- Chemical buffering agents
○ Molecules bind to protons when the pH drops or released
protons when the pH rises
- Can inactivate excess acids and bases momentarily
- Unable to eliminate them from body
○ Lungs and kidneys have critical roles in eliminating acid in the
body
- Carbonic acid bicarbonate buffer system
○ Consists of carbonic acid and sodium bicarbonate
○ Can temporarily regulate pH in our body
§ Cannot eliminate them from the body
□ Lungs and kidneys have critical roles in eliminating
acids
Renal mechanism
- Kidney is the ultimate acid-base regulatory organ to protect internal
environment against acid overload
○ Only renal system can get rid of the bodies non-volatile acids
§ Uric acid / lactic acid / ketone bodies
○ Only renal can regulate alkaline substances in the blood
○ Only renal can restore chemical buffers that are used in
managing proton levels in extracellular fluids
In proximal tubules
- 80% of filtered sodium bicarbonate is reabsorbed by the proximal
tubules
○ Rest absorbed by distal nephrons
- Reabsorbed HCO3 always accompanied by the secretion of protons
and vice versa
- Reabsorption is achieved by sodium bicarbonate cotransporter
- Basolateral membrane
○ sodium bicarbonate co-transporter
, - Reabsorbed HCO3 always accompanied by the secretion of protons
and vice versa
- Reabsorption is achieved by sodium bicarbonate cotransporter
- Basolateral membrane
○ sodium bicarbonate co-transporter
§ Help to reabsorb bicarbonate ion back into circulation
○ Sodium-potassium ATPase
§ Primary active transport
§ Pumps out sodium
□ Sodium depleted in cell
§ Enables sodium to diffuse into epithelial cells
§ Antiport
□ Sodium comes in and hydrogen ion excreted
§ Interconversion of water and co2 into Bicarbonate and
proton
□ Diffuse into cell
□ Done by enzyme carbonic anhydrase
® Present in kidneys
□ Can absorb water and CO2 then converted inside
cell to proton and bicarbonate
§ Intracellular carbonic anhydrase
□ Facilitates generation of protons and bicarbonate
□ Type 2
§ Membrane bound carbonic anhydrase
□ facilitates production of water and CO2 from
carbonic acid
□ Type 4
- Apical membrane
○ Sodium hydrogen exchanger - NHE
§ Antiport
§ Secondary active transport
□ Depends on sodium potassium ATPase channel on
basolateral membrane to function
® To prepare gradient
§ When sodium comes in, it helps to remove the acid
○ Hydrogen ATPase
§ Pumps hydrogen ion into filtrate
§ Depending on ATP
§ Primary active transport
- Generation of new bicarbonate ion in proximal tubules
○ Ammonium synthesis
§ Generates new bicarbonate ions
§ Ammoniagenesis
§ Only in proximal tubular cells
○ Important in acidosis
§ Where body has too many acids so need to generate
related disorders
Monday, 27 September 2021 8:31 AM
Acid-base balance
- Constant loading of acid into our body
- Therefore amount of acid secreted must equal amount produced
Chemical buffer system
- Chemical buffering agents
○ Molecules bind to protons when the pH drops or released
protons when the pH rises
- Can inactivate excess acids and bases momentarily
- Unable to eliminate them from body
○ Lungs and kidneys have critical roles in eliminating acid in the
body
- Carbonic acid bicarbonate buffer system
○ Consists of carbonic acid and sodium bicarbonate
○ Can temporarily regulate pH in our body
§ Cannot eliminate them from the body
□ Lungs and kidneys have critical roles in eliminating
acids
Renal mechanism
- Kidney is the ultimate acid-base regulatory organ to protect internal
environment against acid overload
○ Only renal system can get rid of the bodies non-volatile acids
§ Uric acid / lactic acid / ketone bodies
○ Only renal can regulate alkaline substances in the blood
○ Only renal can restore chemical buffers that are used in
managing proton levels in extracellular fluids
In proximal tubules
- 80% of filtered sodium bicarbonate is reabsorbed by the proximal
tubules
○ Rest absorbed by distal nephrons
- Reabsorbed HCO3 always accompanied by the secretion of protons
and vice versa
- Reabsorption is achieved by sodium bicarbonate cotransporter
- Basolateral membrane
○ sodium bicarbonate co-transporter
, - Reabsorbed HCO3 always accompanied by the secretion of protons
and vice versa
- Reabsorption is achieved by sodium bicarbonate cotransporter
- Basolateral membrane
○ sodium bicarbonate co-transporter
§ Help to reabsorb bicarbonate ion back into circulation
○ Sodium-potassium ATPase
§ Primary active transport
§ Pumps out sodium
□ Sodium depleted in cell
§ Enables sodium to diffuse into epithelial cells
§ Antiport
□ Sodium comes in and hydrogen ion excreted
§ Interconversion of water and co2 into Bicarbonate and
proton
□ Diffuse into cell
□ Done by enzyme carbonic anhydrase
® Present in kidneys
□ Can absorb water and CO2 then converted inside
cell to proton and bicarbonate
§ Intracellular carbonic anhydrase
□ Facilitates generation of protons and bicarbonate
□ Type 2
§ Membrane bound carbonic anhydrase
□ facilitates production of water and CO2 from
carbonic acid
□ Type 4
- Apical membrane
○ Sodium hydrogen exchanger - NHE
§ Antiport
§ Secondary active transport
□ Depends on sodium potassium ATPase channel on
basolateral membrane to function
® To prepare gradient
§ When sodium comes in, it helps to remove the acid
○ Hydrogen ATPase
§ Pumps hydrogen ion into filtrate
§ Depending on ATP
§ Primary active transport
- Generation of new bicarbonate ion in proximal tubules
○ Ammonium synthesis
§ Generates new bicarbonate ions
§ Ammoniagenesis
§ Only in proximal tubular cells
○ Important in acidosis
§ Where body has too many acids so need to generate
