RENAL 05: PRINCIPLES OF TUBULAR TRANSPORT

Question 1

transcellular transport

Answer 1

A molecule goes across cell (like actually gets into the cell and moves across it before moving out of the ccell on the other side)

Question 2

Paracellular transport

Answer 2

A molecule moves just kinda like around a cell in between adherins junctions to get to the other side of a barrier / tissue

Question 3

Primary active transport

Answer 3

Use ATP to yeet something across a barrier

Question 4

Secondary active transport

Answer 4

Use energy from something else to yeet something unfavorable across a barrier

Question 5

At low solute concentrations, what is the consequence of crrier mediated transport

Answer 5

lots of available spots but maybe not a huge drive to occupy them

Question 6

At very high solute concentrations what is the consequence of carrier mediated transport

Answer 6

you have a large drive to occupy the spots but they could be oversaturated, and at this saturation point we hit transport maximum

Question 7

Kinetics of diffusion vs carrier mediated transport

Answer 7

Carrier mediated transport is not linear due to fast saturation whereas diffusion is linear and does not saturate

Question 8

Ideally what proportion of free glucose that is filtered will be reabsorbed into the blood

Answer 8

100%

Question 9

what affects the reabsorption of glucose back into the blood

Answer 9

1. NKA pumping on basalateral membrane
2. Na/Glucose transporter (SGLT) across apical membrane (secondary active transport)
3. GLUT1 and GLUT2 transporters - they are uniporters which will bring glucose through basalateral membrane into blood

Question 10

For glucose, how does it fit into the F+S=R+E and why?

Answer 10

R=F-E
It isn’t secreted so we lose S

It isn’t a good measure of GFR because ideally we reabsorb everything

Question 11

At low concentration of glucose, the reabsorption and filtration curves should _____

Answer 11

be parallel / match perfectly

Question 12

When glucose concentration reaches the renal plasma threshold, what begins to hapen?

Answer 12

Glucose begins to spill into the urine, and the reabsorption line deviates bellow the filtered line (because you have saturated your ability to reabsorb, it’s transport mediated so this is a consequence of that high concentration)

Question 13

at extremely high plasma glucose, what is happening to glucose? What does the excretion line look like?

Answer 13

Way more is getting excreted. It’s going to actually have the excretion line parallel the filtered line because it’s just getting yeeted now at a constant rate (as long as GFR is remaining constant it will match that point at a given high concentration of glucose)

Question 14

What is the RPT?

Answer 14

The point at which the lowest capacity tranporters are saturated - this is when the excretion line appears on the graph

Question 15

What ist he Tm

Answer 15

the point at which all transporters are saturated - this is when the reabsorption line becomes fully horizontal

Question 16

What is the region of splay

Answer 16

The concentrations of glucose between the RPT and the Tm (where we still have some, but not all transporters active in transport of glucose)

Question 17

To rule out a patient having diabetes or being pregnant, what do we generally have a patient do before examining their pee?

Answer 17

Fast

Question 18

PAH load relationship with F+S=R+E

Answer 18

S=E-F

we secrete a lot of it.

Question 19

PAH titration curve

Answer 19

You have some PAH in plasma but the majority should be excreted and you do secrete it. therefore the excretion line will be steeper than the filtration line, because you need to add in the secretion portion . The Tm is going to be the point at which the transporters it uses (a subset of OATs) is saturated At the point the Tm is hit, the secretion line goes horizontal and the excretion line hits a less steep slope that parallels the filtration because it now depends on filtration rate to excrete.

Question 20

Implication of using PAH for RPF - why do we need to use low concentrations?

Answer 20

So we don’t hit the Tm

Question 21

Starling forces along peritubular capillaries are more similar to skeletal muscle, or glomerular capillaries

Answer 21

skeletal muscle

Question 22

Starling forces in peritubular capillaries favor reabsorption or filtration

Answer 22

reabsorption

Question 23

Glomerulotubular balance

Answer 23

sodium reabsorption in proximal tubule varies in parallel with filtered load

Therefore, without rapid adustments to Na reabsorption, urinary excretion would fluctuate and disturb balance (also chagne extracellular fluid volume, which is bad)

Therefore, mechanotransduction of microvilli of proximal tubule cells can lead to filtered load increase and therefore peritubular capillary reabsorption increase.