Mechanisms of obtaining acid base balance

Question 1

Where in the tubule does resorption of bicarbonate happen?

Answer 1

PCT

TALLH

Collecting duct

Question 2

How is bicarbonate resorption important in controlling acid base balance in the body?

Answer 2

Bicarbonate resorption determines the acidity or alkalinity of the blood

Bicarbonate is freely filtered by the glomerulus

Needs to be reabsorbed

Question 3

Is bicarbonate resorption an active process?

Answer 3

Yes - uses a lot of energy

Question 4

What is the normal concentration of bicarbonate in the urine?

Answer 4

40 mmol/L

Question 5

What causes proximal renal tubular acidosis?

Answer 5

Disease in PCT

Means there is innapropriate reabsorption of bicarbonate ions

Bicarbonate will be present in the blood at low concentrations

Question 6

What causes acute respiratory acidosis?

Answer 6

Decreased CNS stimulation - sedative drugs

Neuromuscular ventilatory failure

Structural/ mechanical ventilatory failure

Airway obstruction - asthma and inhaled foreign object

Question 7

What causes chronic respiratory acidosis?

Answer 7

Decreased CNS stimulation - cerebral disease

Neuromuscular ventilatory failure - ALS, DMD

Structural/ mechanical ventilatory failure - obesity, thoracic deformities

Chronic airway obstruction - COPD

Question 8

What causes acute respiratory alkalosis?

Answer 8

Increased CNS stimulation - anxiety or drugs

Subarachnoid haemorrhage

Mechanical over-ventialtion of an intubated patient

Question 9

What causes chronic respiratory alkalosis?

Answer 9

Increased CNS stimulation - stroke

Increased hypoxic drive - high altitude

Question 10

How does the PCT reabsorb bicarbonate?

Answer 10

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

Question 11

What catalyses the breakdown of carbonic acid into carbon dioxide and water?

Answer 11

Carbonic anhydrase

Question 12

What powers the sodium hydrogen exchanger (NHE)?

Answer 12

Sodium potassium ATPase

Sodium enters down its concentration gradient

Question 13

How does the blood maintain its acid base balance?

Answer 13

Via the intercalated cells

Question 14

What are the two cells that form the collecting duct called?

Answer 14

The principal cell

The intercalated cell

Question 15

What is the role of the principal cell in the collecting ducts?

Answer 15

To regulate salt and water concentration

Question 16

What is the role of intercalated cells?

Answer 16

To maintain acid base balance

Question 17

How does the alpha intercalated cell work?

Answer 17

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

Question 18

What does the anion exchanger 1 do?

Answer 18

Exchanges bicarbonate inside the cell for chlorine inside the blood

Question 19

What is distal renal tubular acidosis caused by?

Answer 19

Pathology to any of the two transporters in the alpha intercalated cells

Question 20

Draw process bicarbonate reabsorption in PCT

Answer 20

Question 21

Draw process of bicarbonate reabsorption in the collecting duct

Answer 21