Proximal Tubule Reabsorption Quiz

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Questions and Answers

What type of reabsorption occurs in the proximal tubule with respect to fluid and electrolytes?

Hypertonic reabsorption

Isotonic reabsorption (correct)

Anisotonic reabsorption

Hypotonic reabsorption

How is the transepithelial flux of sodium, water, and other solutes primarily facilitated in the proximal tubule?

Through hormonal regulation

Via aquaporin-1 water channels

By carbonic acid hydration

Through gaps between the cells (the 'shunt' pathway) (correct)

Which water channels in the proximal tubule are not sensitive to hormonal regulation?

Aquaporin-1 (AQP-1) (correct)

Aquaporin-4 (AQP-4)

Aquaporin-2 (AQP-2)

Aquaporin-3 (AQP-3)

What is the primary source of the intracellular H+ ions in the proximal tubule?

Carbonic acid from carbonic anhydrase (A) Signup and view all the answers

What is the primary function of aquaporin-1 (AQP-1) water channels in the proximal tubule?

Enabling isotonic reabsorption of fluid and electrolytes (B) Signup and view all the answers

What is the enzyme responsible for producing carbonic acid in the proximal tubule?

Carbonic anhydrase (B) Signup and view all the answers

How does the 'shunt' pathway primarily contribute to transepithelial flux in the proximal tubule?

By allowing passage of water through the cells (B) Signup and view all the answers

Flashcards

Isotonic Reabsorption

Reabsorption in the proximal tubule where the concentration of solutes and water remain the same.

Shunt Pathway

A process by which sodium, water, and other solutes move across the epithelial cells of the proximal tubule. This movement is facilitated by gaps between the cells.

Aquaporin-1 (AQP-1)

AQP-1 is a type of water channel found in the proximal tubule. Unlike other water channels, it's not controlled by hormones.

Intracellular H+ ions in the proximal tubule

Intracellular H+ ions are produced in the proximal tubule by carbonic acid. This acid is formed by carbonic anhydrase.

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Function of Aquaporin-1 (AQP-1)

AQP-1 water channels help in the isotonic reabsorption of fluid and electrolytes by allowing water to move along with solutes.

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Carbonic Anhydrase

Carbonic anhydrase is an enzyme responsible for converting carbon dioxide and water into carbonic acid in the proximal tubule.

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Shunt Pathway and Transepithelial Flux

The 'shunt' pathway allows water to move through the gaps between the cells of the proximal tubule, contributing to overall transepithelial flux.

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Study Notes

Reabsorption in the Proximal Tubule

The proximal tubule executes isotonic reabsorption, recovering approximately 65-70% of filtered water and electrolytes.
Key electrolytes reabsorbed include sodium, chloride, bicarbonate, and glucose.

Transepithelial Flux Mechanisms

Sodium, water, and other solutes transit via a combination of active transport and passive diffusion, facilitated by:
- Sodium-potassium ATPase pumps on the basolateral membrane.
- Co-transporters and exchangers on the apical membrane.

Water Channels

The aquaporin-1 (AQP-1) water channels operate without hormonal influence, allowing for baseline permeability to water.

Sources of Intracellular H+ Ions

The primary source of intracellular H+ ions is from cellular metabolism, particularly through the oxidation of organic compounds.

Function of Aquaporin-1

The primary role of AQP-1 water channels is to facilitate rapid water reabsorption, ensuring fluid balance in the proximal tubule.

Enzyme for Carbonic Acid Production

The enzyme carbonic anhydrase is responsible for catalyzing the formation of carbonic acid from carbon dioxide and water in the proximal tubule.

Shunt Pathway Role

The 'shunt' pathway contributes to transepithelial flux primarily through paracellular transport, enabling solutes to diffuse between adjacent cells and aiding in Na+ and water reabsorption.

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Description

Test your knowledge on the mechanisms of fluid and electrolyte reabsorption in the proximal tubule of the kidney. Assess your understanding of processes such as carbonic acid conversion, sodium flux, and water reabsorption.