Renal 4 : Tubular Transport

Question 1

What are the 3 processes involved in urine formation

Answer 1

Ultrafiltration: glomerulus
Reabsorption: water and solutes
Secretion: solutes into tubular fluid

Question 2

How much of filtered urea is excreted/reabsorbed?

Answer 2

50% of filtered load reabsorbed
Filtered: 56
Excreted: 28
Reabsorbed: 28

Question 3

what is the key difference between diffusion and carrier-mediated transport in terms of transport rate?

Answer 3

carrier mediated transport has a higher rate initially, then flattens out at a certain Tm

Question 4

What is the difference between transcellular and paracellular pathways

Answer 4

trans: across cells
para: between cells

Question 5

How is arterial and venous clearance related to oxygen ventilation and flow? (General Fick Principle)

Answer 5

Cao2 - Cvo2 = V*o2 / Q = O2 demand/O2 supply

Question 6

if blood flow is restricted to the kidney, the kidney requires more/less oxygen

Answer 6

less

Question 7

Fick principle in the kidney

Answer 7

reduced arterial blood perfusion does NOT lead to increased o2 extraction
the kidney reduces its oxygen demand in restricted perfusion

Question 8

Reduction of arterial blood perfusion results in increased/decreased oxygen extraction in skeletal muscle.

Answer 8

increased

Question 9

What happens to renal flow rate of oxygen when perfusion increases?

Answer 9

increases

Question 10

What happens to skeletal muscle flow rate of oxygen with increased perfusion?

Answer 10

stays the same (flat line)

Question 11

What happens to oxygen extraction when renal perfusion increases?

Answer 11

sharp decrease and then flatline

Question 12

How is glucose handled

Answer 12

100% reabsorbed normally

Question 13

How do we caculate the tubular transport maximum (Tm)?

Answer 13

Tm = Pa x GFR - U x V*

units: mg/min

Question 14

What is the Renal Plasma Threshold (RPT) with relation to glucose?

Answer 14

The point where glucose first appears urine.

Units: mg/ml

Question 15

What is the kinetic argument for splay?

Answer 15

low Ka for substance-carrier interaction

Question 16

What is the morphological argument for splay?

Answer 16

different Tm values among nephrons.

Question 17

What is the main effect of splay?

Answer 17

For increasing plasma concentrations of substance x, RPTx is reached before Tmx is maximized.

Question 18

At low dose, PAH is mostly reabsorbed/secreted

Answer 18

PAH is over 90% secreted in low dose

S = E-F (R=0)

Question 19

What is the Renal Plasma Threshold (RPT) with relation to PAH?

Answer 19

Point at which secretion slope of PAH first decreases

Question 20

Define osmotic diuresis

Answer 20

Urine flow >1ml/min

Question 21

What is the function of mannitol?

Answer 21

osmotic diuretic. It is filtered but not reabsorbed, and increases urine flow by holding excess water in the tubules via osmotic forces.

Question 22

How can glucose function as an osmotic diuretic?

Answer 22

excess glucose in the tubules holds excess water by osmotic forces. by osmotic diuresis, glucose -> dehydration and thirst.