Renal Physiology

Question 1

Autoregulation of glomerular filtration

Answer 1

• myogenic reflex (vasoreactive, first line)
• tubuloglomerular feedback (macula densa sensing solute concentration, affects afferent tone)
• RAAS activation

Question 2

MOA of renin

Answer 2

renin secreted by granular cells

ANG -renin - > ANG1 - (via ACE) -> ANG 2

Question 3

Proximal tubule

Answer 3

65% reabsorption of nutrients (glucose, organic acid, calcium/phosphoate, amino acids).
also excrete HCO3, chloride.

Question 4

what water channels are available at the apical and basolateral side of cells at PT?

Answer 4

aquaporin 1

they are constitutively active

Question 5

MOA of counter current multiplication

Answer 5

descending LOH is permeable only to H2O.
ascending LOH is permeable only to solutes (Na,K,Mg, Ca).
This creates solute trapping ( hypertonic environment) in the medulla. This drives water reabsorption in the descending LOH via osmosis.

Question 6

Distal convoluted tubule

Answer 6

reabsorbs 5% of NaCl.

Question 7

Where does thiazides work?

Answer 7

at the distal convoluted tubule

Question 8

Collecting duct

Answer 8

Both cortical and inner medullary CD contribute to 4-5% of filtered Na+.

Question 9

What is vasopressin?

Answer 9

Binds to V2 receptor.
Triggers G protein coupled intracellular signalling
Results in raised cAMP.
Overall results in more H2O channel insertion to apical membrane.
Increased water permeability and thus increase urine concentration.

Question 10

What is aldosterone?

Answer 10

Made by the adrenals.
Regulate [Na+] reabsorption by entering cell from basolateral membrane, by binding to cytoplasmic mineralocorticoid receptor, translocate to nucleus, modulate gene expression causing increased Na reabsorption and increased K+ secretion.

Question 11

Why is spironolactone called K+ sparring diuretic?

Answer 11

because K+ excretion in CD are driven by electrical gradient. Normally, an anion electrical gradient is made when Na+ is reabsorbed without accompanying anion.

When this is blocked, the electrical gradient is lost, so K + can’t be excreted in urine and K+ level is maintained.

This is the same reason why some Abs cause hyperkalaemia.

Question 12

When does urea get recycled?

Answer 12

in the inner medullary collecting duct.

Question 13

What hormone regulate natriuresis in the medullary collecting duct?

Answer 13

atrial natriuretic peptide: produced by atrial myocytes in hypervolemia.

renal natriuretic peptide: made by renal tubular epithelia.