Where in the tubule does resorption of bicarbonate happen?
How is bicarbonate resorption important in controlling acid base balance in the body?
Bicarbonate resorption determines the acidity or alkalinity of the blood
Bicarbonate is freely filtered by the glomerulus
Needs to be reabsorbed
Is bicarbonate resorption an active process?
Yes - uses a lot of energy
What is the normal concentration of bicarbonate in the urine?
What causes proximal renal tubular acidosis?
Disease in PCT
Means there is innapropriate reabsorption of bicarbonate ions
Bicarbonate will be present in the blood at low concentrations
What causes acute respiratory acidosis?
Decreased CNS stimulation - sedative drugs
Neuromuscular ventilatory failure
Structural/ mechanical ventilatory failure
Airway obstruction - asthma and inhaled foreign object
What causes chronic respiratory acidosis?
Decreased CNS stimulation - cerebral disease
Neuromuscular ventilatory failure - ALS, DMD
Structural/ mechanical ventilatory failure - obesity, thoracic deformities
Chronic airway obstruction - COPD
What causes acute respiratory alkalosis?
Increased CNS stimulation - anxiety or drugs
Mechanical over-ventialtion of an intubated patient
What causes chronic respiratory alkalosis?
Increased CNS stimulation - stroke
Increased hypoxic drive - high altitude
How does the PCT reabsorb bicarbonate?
Apical surface - NHE transporter (sodium hydrogen exchanger)
Sodium enters and hydrogen leaves the cell
Hydrogen is pumped out and combines with bicarbonate ions at the brush border
Carbon dioxide is formed from the carbonic acid produced
Carbon dioxide formed enters the cell
Carbon dioxide combines with the water to form protons and bicarbonate ions
Protons are transported out via NHE
Bicarbonate ions are reabsorbed into the basolateral membrane
What catalyses the breakdown of carbonic acid into carbon dioxide and water?
What powers the sodium hydrogen exchanger (NHE)?
Sodium potassium ATPase
Sodium enters down its concentration gradient
How does the blood maintain its acid base balance?
Via the intercalated cells
What are the two cells that form the collecting duct called?
The principal cell
The intercalated cell
What is the role of the principal cell in the collecting ducts?
To regulate salt and water concentration
What is the role of intercalated cells?
To maintain acid base balance
How does the alpha intercalated cell work?
Carbon dioxide inside the cell is hydrated by carbonic anhydrase to form protons and bicarbonate ions
Protons are pumped out in an energy-dependent manner by ATPase into the urine
Bicarbonate ions are pumped into the blood via anion exchanger 1
What does the anion exchanger 1 do?
Exchanges bicarbonate inside the cell for chlorine inside the blood
What is distal renal tubular acidosis caused by?
Pathology to any of the two transporters in the alpha intercalated cells
Draw process bicarbonate reabsorption in PCT
Draw process of bicarbonate reabsorption in the collecting duct