Unit 2, L14 Principles of Tubular Transport

Question 1

Simple Diffusion

Answer 1

Move from high to low concentration, passive transport

Question 2

Channel-mediated transport

Answer 2

Molecules that are specifically selected for those channels will move through when the channels are open, passive transport

Question 3

Transporter-mediated transport

Answer 3

Requires a transporter to move, but is still passive transport as no energy is needed, the molecule is moving down its concentration gradient

Question 4

Active transport

Answer 4

Moving against the concentration gradient of the molecule, requires energy in the form of ATP

Question 5

Transcellular pathways

Answer 5

Moving through the cell itself, by simple diffusion so passive transport

Question 6

Paracellular pathway

Answer 6

Bypassing the cell, doesn’t enter into the cell. There are adhesion junctions that provide some specificity that prevents everything from getting through, but some of the solutes get through

Question 7

If moving using a paracellular pathway, is that against or with its concentration gradient?

Answer 7

With its concentration gradient

Question 8

Primary active transport

Answer 8

Hydrolysis of ATP produced by mitochondria, gives energy that pushes the chemical out, against its concentration gradient

Question 9

Secondary active transport

Answer 9

Movement of the molecule against its concentration gradient, coupled with the movement of a second molecule. Can move in an antiport fashion, which is going against its concentration gradient AND opposite of the second molecule, or in symport fashion, which is going against its concentration gradient and the same direction of the second molecule

Question 10

What is the primary active transporter and what is it transporting

Answer 10

Na/K/ATPase, and moving Na out and K in, both of which is moving against its concentration gradient

Question 11

What functions first, primary or secondary active transport?

Answer 11

Primary

Question 12

Active or passive, carrier mediated, uses metabolic energy, and dependent on Na+ gradient:

Simple Diffusion

Answer 12

Passive, downhill
Not carrier mediated
Does not use metabolic energy
Is not dependent on Na+ gradient

Question 13

Active or passive, carrier mediated, uses metabolic energy, and dependent on Na+ gradient:

Facilitated Diffusion

Answer 13

Passive and downhill
Yes, carrier mediated
No, does not use metabolic energy
No, is not dependent on Na+ gradient

Question 14

Active or passive, carrier mediated, uses metabolic energy, and dependent on Na+ gradient:

Primary active transport

Answer 14

Active and uphill
Yes, is carrier mediated
Yes, directly uses metabolic energy
No, not dependent on Na+ gradient

Question 15

Active or passive, carrier mediated, uses metabolic energy, and dependent on Na+ gradient:

Cotransport

Answer 15

Secondary active (Na+ is transported down hill and one or more solutes are transported uphill)
Yes, carrier mediated
Yes, indirectly uses metabolic energy
Yes, dependent on Na gradient as solutes move in the same direction as Na+ across cell membrane

Question 16

Active or passive, carrier mediated, uses metabolic energy, and dependent on Na+ gradient:

Countertransport

Answer 16

Secondary active (Na+ is transported downhill and one or more solutes are transported uphill)
Yes, carrier mediated
Yes, indirectly uses metabolic energy
Yes, dependent on Na+ gradient as solutes move in opposite direction as Na+ across cell membrane

Question 17

If something is moving by simple diffusion, what is the one thing that can limit its movement

Answer 17

Its concentration

Question 18

At low solute concentrations, what is happening with binding sites and rate of transport

Answer 18

Many binding sites are available and the rate of transport increases steeply as the concentration increases

Question 19

At high solute concentrations, what happens with binding sites and transport

Answer 19

At high solute concentrations, the available binding sites become less available and when all the binding sites are occupied, saturation is achieved

Question 20

What is the transport maximum

Answer 20

When all binding sites are occupied and saturation is achieved

Question 21

What percentage of free filtered glucose is reabsorbed back into the blood?

Answer 21

100%

Question 22

Na-glucose co-transporter (SGLT)

Answer 22

Secondary active transport, it brings Na and glucose into the cell

Question 23

GLUT 1 and GLUT 2 transporters

Answer 23

Enable glucose to move across the basal membrane, only moves glucose

Question 24

With normal diets and being healthy, what is the normal level of glucose

Answer 24

200 mg/dL of glucose

Question 25

At lower concentrations of glucose, what does the reabsorption and filtration amounts look lie?

Answer 25

Reabsorbed parallels filtered, so all filtered glucose is reabsorbed

Question 26

When glucose concentration reaches renal plasma threshold, what happens to the filtered, reabsorbed, and excreted amounts

Answer 26

Filtered still continues in a linear line
Reabsorbed starts to plateau, as we hit the RPT
Excreted begins here, starts to increase and spill over into the urine

Question 27

At the highest plasma glucose concentration, what happens to the excreted line, reabsorbed line, and filtered line

Answer 27

Filtered line continues linearally
Reabsorbed line continues with its plateau
Excreted line continues and becomes parallel with the filtered line, as all the excess is being excreted rather than reabsorbed

Question 28

What is the tubular maximum of glucose transport

Answer 28

Tm = 375 mg/min

Question 29

What is the renal plasma threshold value

Answer 29

RPT = 220 mg/dL

Question 30

When RPT is reached, what type of transporters are saturated

Answer 30

The lowest capacity transporters

Question 31

What is a region of splay (think glucose titration curve_)

Answer 31

Region of splay is defined from the RPT to the plasma concentration when Tm is reached

Question 32

What are the transporters that are the last to saturate and have the highest capacity?

Answer 32

SGLT-1

Question 33

Glucosuria

Answer 33

Whenver the renal plasma threshold for glucose is exceeded, glucose will be found in the urine. This leads to excretion or spilling of glucose in the urine

Question 34

For PAH titration curve, what do the filtered, excreted, and secreted lines look like?

Answer 34

Filtered line is linear
Excreted line is above the filtered line because PAH appearing in urine comes from both filtration and secretion
Secreted line raises linearly until Tm, where it plateaus out

Question 35

Pi for starling forces across peritubular capillary wall

Answer 35

Interstitial hydrostatic pressure

Question 36

P pc for peritubular capillary wall (starling forces)

Answer 36

Peritubular capillary hydrostatic pressure

Question 37

Pi i, starling forces for peritubular capillary wall

Answer 37

Interstitial fluid oncotic pressure

Question 38

Pi PC, starling forces for peritubular capillary wall

Answer 38

Peritubular capillary oncotic pressure

Question 39

In the peritubular capillaries, what happens with the starling forces?

Answer 39

First, solute and water are reabsorbed across apical membrane into the epithelial cell
Second, some solute and water reenter the tubule fluid
Third, most of the solute and water will move into the interstitium space, where it will go into the capillary

Question 40

What is the main driving force for uptake to the peritubular capillaries

Answer 40

oncotic pressure in the peritubular capillaries

Question 41

Major force opposing uptake to the peritubular capilarries

Answer 41

Hydrostatic pressure in peritubular capillaries, its 20

Question 42

Overall, in the peritubular capillaries, what is the direction of fluid movement (starling forces)

Answer 42

Favors driving fluids into the capillaries

Question 43

These starling forces only apply to the _______ and not the rest of the tubule system due to the permeability of water

Answer 43

Proximal tubule

Question 44

Reabsorption of water and salt in the proximal tubule is __________

Answer 44

Isosmotic

Question 45

Glomerulotubular balance

Answer 45

Where Na reabsorption in the proximal tubule varies in parallel with the filtered load, so 2/3 of the filtered Na is reabsorbed in the PT, even if GFR varies

Question 46

What is the pathway for glomerulotubular balance

Answer 46

Increase GFR, leads to increase filtration fraction, leads to increased filtered load, leads to increased peritubular capillary reabsorption

Decrease GFR leads to decrease filtration fration, leading to decreased peritubular capillary reabsorption