Tubular transport

Question 1

Are transport proteins in the epithelia asymmetrically distributed and why?

Answer 1

Yes permits vectorial transport

Question 2

What are the types of transport proteins?

Answer 2

• Pumps
• Carriers
• Channels

Question 3

What are the transport processes?

Answer 3

• Active
• Secondary active
• Passive

Question 4

How do Na/K pumps work?

Answer 4

Through the hydrolysis of ATP it moves 3 Na out of the cell and 2 K into the cell. This is against their concentration gradients

Question 5

How do SGLT cotransporters work?

Answer 5

They use secondary active transport to move Na down its concentration gradient and it brings a glucose with it

Question 6

How do GLUT uniporters work?

Answer 6

Passive transport through the uniporter

Question 7

How is glucose absorbed?

Answer 7

The Na/K pump creates low Na in the cell so that SGLT can move in sodium and glucose on the apical side. On the basolateral side, GLUT allows for the passive movement of glucose into the blood

Question 8

Should there be glucose in the urine?

Answer 8

No, it should all be absorbed in the proximal tubule

Question 9

What is a condition in which you could find glucose in the urine?

Answer 9

Diabetes mellitus, the amount of glucose exceeds the Tm and glucose is excreted

Question 10

What is an important physiological buffer?

Answer 10

HCO3-

Question 11

Reabsorption of filtered HCO3 relies on what?

Answer 11

Na gradient maintained by the Na/K ATPase

Question 12

What inhibits reabsorption of HCO3?

Answer 12

CA inhibitors (acetazolamide)

Question 13

What does the PT efficiently recover?

Answer 13

• Filtered amino acids
• Oligopeptides
• Low molecular weight proteins

Question 14

How is sodium reabsorbed in the proximal tubule?

Answer 14

• Na coupled mechanisms when reabsorbing molecules (transcellular processes)
• Chloride mediated Na transport (paracellular processes)

Question 15

What is chloride-mediated Na transport?

Answer 15

Cl is driven across leaky tight junctions and Na follows. This is because the lumen is negatively charged and the Cl- is repelled

Question 16

Is the PT highly water permeable?

Answer 16

Yes

Question 17

What features facilitate PT solute absorption?

Answer 17

• Subcellular specializations
• Secondary structural features
• Tertiary structural features

Question 18

What are some subcellular specializations of the PT?

Answer 18

• Mitochondrial rich

- Specialized transporters

Question 19

What is a secondary structural feature of PT?

Answer 19

Brush border

Question 20

What are tertiary structural features of PT?

Answer 20

• Convolutions of early PT

- Proximity of all nephronal segments to the vasa recta

Question 21

How is HCO3 reabsorbed?

Answer 21

It is combined with H+ by CA to make CO2 and H2O the Co2 can now diffuse into the cell. The CO2 is then combined with H2O and makes HCO3 again. This is then shuttled out of the cell through Na HCO3 cotransporter

Question 22

How is transport of solutes iso-osmotic?

Answer 22

PT solute and water transport are proportionate

Question 23

How are LMPs absorbed?

Answer 23

They enter through endocytosis and fuses with a lysosome. The lysosome is degraded and fuses with a multivesicular body and then transported to the interstitial space

Question 24

What is Bartter syndrome?

Answer 24

Nacl absorption is impaired so there is no dilution of luminal fluid. There is now low medullary interstitial osmolarity

Question 25

What is different about apical NaCl transporters?

Answer 25

Don’t depend on the presence of K and has different drug sensitivity

Question 26

How is calcium absorbed in the DT?

Answer 26

Ca enters through ion channel and then binds to calbindin. This then releases the Ca at the basolateral membrane and it exits across the membrane via Na Ca exchanger or pumps

Question 27

What is the effect of parathyroid hormone on the DT?

Answer 27

• Increases Ca absorption

- Stimulate Vitamin D production

Question 28

What hormones regulate the collecting duct?

Answer 28

Aldosterone and ADH

Question 29

What do Principle cells in the collecting ducts do?

Answer 29

Absorb Na on apically located Na channel (ENaC)

Question 30

What hormone regulates ENaC?

Answer 30

Aldosterone

Question 31

What blocks ENaC?

Answer 31

Amiloride

Question 32

What is the effect of ADH on principal cells?

Answer 32

Causes an increase the amount of aquaporins (AQP2) are on the apical side and water can flow into the cell

Question 33

What is nephrogenic diabetes insipidus?

Answer 33

Loss of function mutation where the collecting duct can no longer respond to ADH

Question 34

What inhibits the NaK2Cl cotransporter?

Answer 34

Diuretics (lasix, Bumex)

Question 35

How is NaCl transported in the TAL?

Answer 35

There is a sodium gradient made by NaK pump. The NaK2Cl then moves Na down its concentration gradient. On the basolateral side, Cl and Na are pumped out and K is pumped out on the apical side

Question 36

Why do you get dilution of luminal fluid in the TAL?

Answer 36

NaCl is filtered from the lumen but water is impermeable so you are taken solutes out with the solvent staying the same resulting in dilute fluid

Question 37

What are the different cells of the collecting duct?

Answer 37

• Principle cells
• alpha intercalated cells
• beta intercalated

Question 38

Which AQP in the CD is regulated?

Answer 38

AQP2 (apical sde)

Question 39

Which AQP in the CD is constitutive?

Answer 39

AQP3,AQP4 (basolateral side)

Question 40

What do alpha intercalated cells secrete?

Answer 40

Acid (HCO3 secreted back into the blood)

Question 41

What do Beta intercalated cells secrete?

Answer 41

Base (bicarbonate secreted back into the lumen)