Renal Physiology

Question 1

Proximal convoluted tubule
What is absorbed?
What is required for it to function?

Answer 1

Reabsorbs:
- 65% of Na –> H2O resorption

Na co-transport –> re-absorption of:

• Glucose
• Amino acids
• Phosphate
• Uric acid

Requires HCO3 and carbonic anhydrase to shuttle HCO3 to function

Question 2

Thick ascending loop of Henle
What is absorbed?
What is the result?

Answer 2

NO H2O

Na-K-2Cl co-transporter

• -> Net positive charge resorption –> resorption of Mg and Ca
• -> counter-current formation with the descending limb to create concentrated urine

Question 3

Bartter Syndrome

Answer 3

DYSFUNCTION OF THICK ASCENDING LIMB

Loss of K, Mg and Ca in urine
–> metabolic alkalosis and hypokalaemia with low/normal BP

SAME EFFECT AS FRUSEMIDE

Question 4

What is the control of Ca resorption and thus Mg resorption in the TAL?

Answer 4

CaSR - calcium sensing receptor

Ca binds to the CaSR and Na/Cl transporter on the basolateral membrane –> reduction in Ca and Mg resorption

Question 5

Distal convoluted tubule

What is reabsorbed?

Answer 5

NaCl cotransporter - NCCT

Small amount of Ca reabsorption paracellularly - dependant on Na paracellular reabsorption

Question 6

Gitelman Syndrome

Answer 6

Impaired function of the NCCT

Due to decreased intracellular transport paracellular Na transport increases –> increased paracellular Ca transport

Low K, Low Mg and metabolic alkolosis with low/normal BP

SAME AS THIAZIDE DIURETICS

Question 7

Collecting duct
What is Absorbed?
What is secreted?

Answer 7

ENaC channel - controlled by aldosterone –> Na reabsorption

Aquaporins - controlled by ADH –> H2O resorption - requires high intersitial osmolality for water to move into the cells

H+ and K+ excreted in exchange for Na

Question 8

What is renal tubular acidosis?

Answer 8

Disorders characterised by a normal anion gap - hypercholoraemic metabolic acidosis despite a relatively well preserved GFR with either Hypokalaemia or hyperkalaemia

Question 9

What is type 1 RTA?

Answer 9

Inability to secrete H+ in distal tubule

• -> High urinary pH
• -> Hypo K
• -> Renal stones

Caused by SLE, Sjorgens syndrome, PBC, autoimmune hepatitis

Treat with alkali and K+ replacements

Question 10

What is type 2 RTA?

Answer 10

Inability to reabsorb HCO3 in proximal convoluted tubule

• -> Low urinary pH
• -> Hypo K
• -> Fanconi syndrome - loss of glucose, amino acids, uric acid and phosphate

Caused by ACETAZOLAMIDE, myeloma, wilsons disease, tenofovir

Question 11

What is type 4 RTA?

Commonest type of RTA

Answer 11

Decreased production or responsiveness to aldosterone

• -> Decreased secretion of K and H into the urine
• -> hyperkalaemia
• -> High pH urine

Caused by DM, NSAIDs, ACE-Is, Calcineurin inhibitors, K sparing diuretics, and high dose heparin