Lecture #16: Tubular Reabsorption and Secretion Flashcards Preview

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Where is aquaporin-2 found in the tubules of the kidneys?

Present in apical membranes of collecting tubule cells .
Aquaporin-2 is controlled by ADH.


Which aquaporin is controlled by ADH?



Where is aquaporin-1 located in the kidneys?

It is widespread, including the renal tubules.


For a substance to be reabsorbed, it must first be transported through what two layers?

Reabsorbed across the tubular epithelial membranes into the renal interstitial fluid.

Reabsorbed through the peritubular capillary membrane back into the blood.


What are the two different routes that water is transported from the tubular cells into the interstitium?

Transcellular Route by Osmosis

Paracellular Routes by Osmosis


Is the paracellular or transcellular pathway the most common osmosis pathway for water?



ATPases establish ionic graadients across nephron cell membranes. What is this ion gradient used for within the kidney?

Gradients drive reabsorption or secretion of many other solutes.

These are then transported by way of "secondary" active transport.


Where is the ENaC channel and what opens and closes it?

ENaC channel is found in apical membrane of nephron cells.

Closed by drug amiloride.

Opened by a number of hormones.


We know that ENaC channels are found in the apical membrane of nephron cells, but what other two channels are also found in some segments of apical membranes of the nephron?

CFTR (Cl-) channels

Potassium (K+) channels


What type of transport occurs through channels or uniporters?

Facilitated Transport (i.e., glucose transport)


What type of transport is directly coupled to an energy source?

Active Transport


What type of transport is coupled indirectly to an energy source (i.e., ion gradient)

Secondary Active Transport


Almost 90 percent of glucose reabsorption occurs in the early proximal tubule. Which of the following mechanisms is responsible for moving glucose from the tubular lumen into the cytoplasmic compartment?

A) Primary active transport via a glucose ATPase pump.
B) Secondary Active Transport via a sodium/glucose co-transporter.
C) Secondary active transport via a sodium/glucose antiporter.
D) Diffusion due to concentration differences between tubular fluid and cytoplasm.

B) Secondary active transport via a sodium/glucose co-transporter.


Name some common ATPases we are studying?

Na/K ATPase

H+ ATPase

H/K ATPase

Ca ATPase


What is the charge in mV in the tubular lumen? Also, what is the charge inside of the tubular epithelial cell?

-3 mV

-70 mV


Where are sodium-glucose co-transporters located on tubule cells? Also, what is the name of these co-transporters?

Located on brush border of proximal tubule cells.



Where is the sodium/glucose co-transporter, SGLT2, located and what percentage of glucose does it transport?

SGLT2 -> reabsorbs 90% of glucose in early proximal tubule.


Where is the sodium/glucose co-transporter, SGLT1, located and what percentage of glucose does it reabsorb?

SGLT1 -> reabsorbs 10% of glucose in late proximal tubule.


What are the two substances that are actively secreted into the renal tubules?

> Creatinine

> Para-aminohippuric acid


What is the transport maximum for glucose?

375 mg/min


What is the filtered load for glucose?

125 mg/min


An increase in which of the following factors will result in an increase in glomerular hydrostatic pressure?

A) arterial pressure
B) afferent arteriolar resistance
C) efferent arteriolar resistance
D) both B and C
E) all of the above

B) afferent arteriolar resistance


Of the reasons listed below, which one best describes why some passively reabsorbed substances do not have a transport maximum?

a) The rate of diffusion is determined by electrochemical gradient of the substance.

b) The permeability of the membrane for the substance.

c) Time that the fluid containing the substance remains within the tubule.

d) all of the above

D) all of the above


Where is aquaporin-3 located in the kidney tubules?

Present in basolateral membranes of collecting tubule cells.


What does the rate of transport depend on?

1) The electrochemical gradient

2) Time the substance is in the tubule
- which depends on tubular flow rate


What is "solvent drag"?

Solvent drag is another mechanism that will reabsorb or move some of the solutes.

*Osmotic movement of water can also carry some solutes.....this is solvent drag.


True or False:

Passive water reabsorption by osmosis is coupled mainly to sodium reabsorption.



You know that the kidney couples reabsorption of water, chloride, and urea with sodium reabsorption. With that being said, what happens to the lumen potential when sodium is reabsorbed?

There's an increase in lumen negative potential, thus leading to the passive reabsorption of Chloride.


We know that sodium reabsorption leads to water reabsorption too, but what effect does this have on luminal chloride concentration?

Increases luminal chloride concentration, thus causing passive reabsorption of chloride.


We know that the reabsorption of sodium leads to the reabsorption of water, but what effect does this have on urea concentration in the lumen?

Increases luminal urea concentration, thus leading to the passive reabsorption of urea.