Proximal Tubular reabsorption and secretion

Question 1

Where is the PCT mainly found?

Answer 1

Cortex

Question 2

What increases surface area for reabsorption of the proximal tubule?

Answer 2

Microvilli on luminal surface

Question 3

What does the proximal tubule reabsorb?

Answer 3

Na+
Cl-
Glucose
Protein/AA
HCO3-
Water

Question 4

What is paracellular reabsorption?

Answer 4

Leakiness of tight junctions

Question 5

What is transcellular reabsorption?

Answer 5

Dependent on presence of transporters

Question 6

How do solutes move from the lumen to the interstitial fluid?

Answer 6

Concentration gradients
Electrochemical gradients
Na+K+ ATPase pump

Question 7

How do solutes move from the interstitial fluid to vasculature?

Answer 7

Passive diffusion
Oncotic pressure

Question 8

How is Na+ cleared?

Answer 8

Freely filtered, actively reabsorbed, not secreted

Question 9

How is Na+ reabsorbed in the first half of the PCT?

Answer 9

With HCO3- and glucose

Question 10

How is Na+ reabsorbed in the second half of the PCT?

Answer 10

With Cl- and glucose

Question 11

Where is Na+K+ATPase pump restricted to?

Answer 11

Basolateral side of the cell

Question 12

How does Na+ enter the cell from the lumen in the first half of PCT?

Answer 12

Via the Na+-H+ antiporter

Question 13

How does Na+ enter the ISF from the cell in the first half of PCT?

Answer 13

Na+/K+ATPase pump
Na+-HCO3- symporter

Question 14

How is the lumen negative potential difference across cells in early PCT created?

Answer 14

By Na+ cotransporters - bring net +ve charge into cell leaving -ve charge behind

Question 15

How is glucose reabsorbed in PCT?

Answer 15

Na+ dependent - no transepithelial or electrochemical gradient present for glucose

Question 16

How does glucose enter the cell from the lumen?

Answer 16

SLGT2 symporters

Question 17

How does glucose enter the ISF from the cell?

Answer 17

Glucose uniporters (GLUT2)

Question 18

Why does tubular Cl- fluid rise along length of PCT?

Answer 18

More water being reabsorbed than Cl-
Preferential reabsorption of Na+ with HCO3-

Question 19

How does Cl- enter the cell from the lumen in the second half of PCT?

Answer 19

Cl- anion antiporter

Question 20

How does Cl- enter the ISF from the cell in the second half of the PCT?

Answer 20

K+-Cl_ symporter

Question 21

What are the glucose transporters in the second half of the PCT?

Answer 21

SGLT1
GLUT1

Question 22

How is water reabsorbed in the PCT?

Answer 22

Aquaporin water channels on apical and basolateral membrane

Question 23

What is solvent drag in the PCT?

Answer 23

Osmotic water flow results in reabsorption of some solutes, eg. K+, Ca2+ and Mg2+, by solvent drag along paracellular routes

Question 24

What does the PT secrete?

Answer 24

Organic anions and cations (metabolism products)
Exogeneous organic compounds (drugs and toxic chemicals)

Question 25

Where do secreted substances originate from?

Answer 25

Crossing epithelial layer from renal interstitium Synthesis within epithelial cells

Question 26

Does paracellular secretion occur?

Answer 26

No

Question 27

What is tubular secretion coupled to?

Answer 27

Reabsorption of Na+

Question 28

Where does tubular secretion move substances from?

Answer 28

Peritubular capillaries into tubular lumen

Question 29

How are anions moved into the cell from the ISF?

Answer 29

Basolateral OAT antiporters move anions in exchange for endogenous dicarboxylic acid eg. alpha ketoglutarate

Question 30

How do alpha ketoglutarate move into the cell?

Answer 30

Via sodium dicarboxylate symporters (NaDC3)

Question 31

How are anions transported across apical membrane?

Answer 31

By OAT and MRP proteins along conc. gradients

Question 32

What can cause gout?

Answer 32

Elevated plasma conc. of urate

Question 33

What is apical cation transport fuelled by?

Answer 33

Na+/K+ATPase pump

Question 34

What drives H+ out of the cell into the lumen?

Answer 34

Sodium gradient by NHE3

Question 35

How are small cations moved out of the cell into the lumen?

Answer 35

Apical OCTN proteins in exchange for H+

Question 36

How are larger cations transported out of the cell?

Answer 36

Via MDR1 ATPase transporter on apical membrane

Question 37

How are cations transported across basolateral membrane?

Answer 37

Passive diffusion Different OCT proteins along conc. gradients

Question 38

What is the transport maximum of a system?

Answer 38

Amount of solute delivered to the tubule per minute that just saturates its transport process

Question 39

What is the Tm for glucose?

Answer 39

380mg/min