Proximal Tubule

Front 1

Is para-aminohippuric acid (PAH) mostly filtered or secreted into urine?

Back 1

Mostly secreted

Front 2

Why do the kidneys accumulate urea?

Back 2

To create osmotic pressure for bringing water out of the filtrate

Front 3

What are the two methods of ion transport from the lumen to peritubular capillaries?

Back 3

Transcellular and paracellular transport

Front 4

What is the plasma membrane of the tubule called facing the filtrate?

Facing the interstitial space?

Back 4

Luminal membrane

Basolateral membrane

Front 5

In the proximal tubule, how is glucose brought through the luminal membrane and into tubular cells?

Back 5

Na/Glucose symporter

Front 6

In the proximal tubule, how is glucose moved through the basolateral membrane and out into the interstitial space?

Back 6

Glucose uniporter

Front 7

What transport protein in the proximal tubular cell facilitates a low intercellular sodium concentration?

Back 7

Na/K ATPase

(3 sodium goes out / 2 potassium goes in)

Front 8

How many different kinds of Na/Glucose symporters are there in the proximal tubule and where are each concentrated?

Back 8

2 types:

- SGLT-2 early in the PCT

- SGLT-1 later in the PCT

Front 9

What transport protein in the proximal tubular cell facilitates a low intercellular sodium concentration to create a chemical gradient for driving glucose in from the filtrate?

Back 9

Na/K ATPase

Front 10

How many different kinds of amino acid/sodium symporters are there in the PCT?

Back 10

3

Front 11

How many different kinds of phosphate/sodium symporters are there in the PCT?

Back 11

2

Front 12

How many different kinds of sodium/proton antiporters are there?

Back 12

1

Front 13

How is filtered protein reabsorbed by the proximal tubule?

Back 13

Receptor mediated endocytosis

Front 14

To what luminal membrane receptors do proteins bind in the PCT? (2)

Back 14

Megalin and Cubulin

Front 15

What happens to the proteins that have been endocytosed into tubular cells?

Back 15

They are degraded to amino acids and released basolaterally

Front 16

How is 25-OH Vitamin D transported into tubular cells?

Back 16

Also by endocytosis

Front 17

Where in the cell is 25-OH Vitamin D converted to 1,25-(OH)2 Vitamin D?

Back 17

Mitochondria

Front 18

Why is chloride not absorbed in the early proximal tubule?

Back 18

It is absorbed paracellularly, so its concentration must increase further down the nephron for it to diffuse out.

Front 19

Does the filtrate decrease in osmolarity as it traverses down the proximal tubule?

Back 19

No, since water is also moving out at the same rate as sodium

Front 20

What drives water's movement from filtrate to interstitial space?

How does it move?

Back 20

Osmotic pressure from the movement of sodium causes water to move both transcellularly and paracellularly

Front 21

On what is the movement of water and solutes from interstitial space to peritubular capillaries dependent?

Back 21

Starling forces

Front 22

Describe the hydrostatic and oncotic pressure in peritubular capillaries.

Back 22

Low hydrostatic pressure and high oncotic pressure

Front 23

What is glomerulotubular balance?

Back 23

Concept that the proximal tubule reabsorbs a constant percentage of filtrate (~67%)

Front 24

Why is glomerulotubular balance so important?

Back 24

It prevents wild fluctuations of fluid volume to distal parts of the nephron

(so you don't pop the Loop of Henle)

Front 25

What effect does an increase in efferent arteriole resistance have on proximal tubule reabsorption?

Back 25

When the efferent arteriole contracts, it drops the hydrostatic pressure of the peritubular capillaries, because more water is filtered out into the glomerulus. This drives up PCT reabsorption.

Front 26

What effect does an increase in efferent arteriole resistance have on peritubular capillary hydrostatic and oncotic pressure?

Back 26

Hydrostatic pressure goes down;

oncotic pressure goes up.

Front 27

What are the drawbacks to in vivo micropuncture of nephrons? (2)

Back 27

- Change in ascending and descending Loop of Henle not differentiated

- Only cortical nephrons can be examined

Front 28

What term refers to the maximum capacity of tubular transport from filtrate?

Back 28

Tubular transport maximum (Tm)

Front 29

What equation gives the amount filtered for a given solute?

Back 29

Filtered load = GFR x Plasma conc of solute

FL = GFR x [Solute]plasma

Front 30

What equation gives the amount excreted?

Back 30

Amount excreted = V x urine solute conc

(where V is the urine flow rate)

Front 31

What is threshold?

Back 31

The point where a normally reabsorbed solute begins to appear in urine due to saturation of transport proteins.

Front 32

What is splay?

Back 32

The slight variance in Tm between nephrons

Front 33

Is glucose in the urine of diabetes mellitus patients a compensatory mechanism for high blood glucose levels?

Back 33

No, it is a sign of glucose transporter saturation

Front 34

What part of the nephron does most tubular secretion take place?

Back 34

Proximal tubule

Front 35

What transporters on the basolateral side of the tubular cells bring anions into the cell? (2)

What molecule is simultaneous kicked out?

Back 35

Organic Anion Transporters (OAT) 1, 3

alpha-ketoglutarate

Front 36

What brings alpha-ketoglutarate into the cell in the PCT from the interstitial space?

Back 36

Na/alpha-KG symporter

Front 37

What allows a sodium gradient that would promote the inward draw of the Na/alpha-KG symporter?

Back 37

Na/K ATPase

(3 Na out / 2K in)

Front 38

What transport proteins move anion into the tubular lumen? (2)

Back 38

MRP2 and OAT4

Front 39

What does OAT4 bring in as it kicks an anion out into the lumen of the PCT?

Back 39

alpha-ketoglutarate

Front 40

What transporters bring cations from the interstitial space across the basolateral membrane and into the cell?

Back 40

OCT-1,2,3 uniporter

Front 41

What transporters bring the cation from inside the cell across the luminal membrane and into the tubular lumen? (2)

Back 41

OCTN and MDR1

Front 42

What does OCTN bring in as it kicks a cation out into the lumen?

Back 42

Proton

Front 43

How does PAH help increase penicillin concentration in blood?

Back 43

Penicillin would normally be secreted into the proximal tubule, but coadministration of PAH leads to PAH competing with penicillin for transport proteins ultimately reducing the amount of penicillin excreted in urine.

Front 44

Name a couple of substances that are neither reabsorbed nor secreted by tubules

Back 44

Inulin and creatinine

Front 45

What equation gives the clearance rate of a substance?

Back 45

C=UV/P

(V = urine flow rate; U=urine concentration; P=plasma concentration)

Front 46

What do the clearance rate of inulin and creatinine tell us?

Back 46

GFR

Front 47

If a random substance has less clearance than the same concentration of inulin, what does that mean?

Back 47

It is being reabsorbed

Front 48

If a random substance has more clearance than the same concentration of inulin, what does that mean?

Back 48

It is being secreted

Front 49

How can renal plasma flow be calculated using PAH?

Back 49

RPF = (Urine PAH x V) / Plasma PAH

Front 50

How is renal blood flow calculated from renal plasma flow?

Back 50

RBF = RPF/(1-Hct)

(Hct = Hematocrit)