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SFIII Test 3 > Sodium and Water Transport > Flashcards

Sodium and Water Transport Flashcards

1
Q

How is sodium reabsorbed in the proximal tubule?

A

Coupled with the secretion of H+ via the NHE3 antiporter

Additional sodium enters in symport with glucose, AA’s, and phosphate

Transport across the BL membrane consists mostly of NA-K pump, with some bicarbonate symport

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2
Q

How is chloride reabsorbed in the proximal tubule?

A

Transcellular - enters via antiport with organic base and leaves via Cl channels in the BL membrane

However, a significant amount is reabsorbed paracellularly

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3
Q

How is water reabsorbed in the proximal tubule?

A

Transcellularly and Paracellulary via aquaporins

Permeability to water is so great that it keeps pace with active sodium reabsorption

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4
Q

Describe glomerulotubular balance as it relates to sodium.

A

Changes in GFR result in a proportional change in the filtered load of Na

The PT reabsorbs a constant fraction of the filtered load of salt and water

However, the absolute quantity will change depending on the GFR

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5
Q

What is osmotic diuresis?

A

Increased urine flow that is due to extra amount of non-reabsorbed solute within the tubular lumen

E.g. mannitol and severe DM

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6
Q

What are the differences in reabsorption between the descending and ascending loop of Henle?

A

Descending - only reabsorbs water

Ascending - Only Sodium and Chloride

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7
Q

What is the Na-K-Cl symporter (NKCC)?

A

Major transporter in the thick ascending limb

Target for loop diuretics

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8
Q

How is K transported in the thick ascending limb?

A

NKCC

Channels in both membrances that recycle K from the cell interior to the lumen and interstitium

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9
Q

What is Bartter’s syndrome?

A

Charachterized by very large urinary losses of NACl, hypokalemia

Caused by mutations of genes encoding proteins that transport ions in the thick ascending limb

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10
Q

How are sodium and chloride transported in the distal tubule?

A

Apical membrane contains a Na-Cl symporter (NCC) and sodium channels

Sodium leaves the BL membrane via Na-K ATPase, chloride via channels

*NCC is the target for thiazide diuretics

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11
Q

What is Gitelman’s syndrome?

A

Charachterized by increased excretion of Na, MG, Cl, and K

Caused by mutations int he gene that codes for the NCC in the distal tubule

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12
Q

How are sodium, chloride and water absorbed in the collecting tubule?

A

Sodium and water are absorbed via channels

Chloride reabsorption here is passive and paracellular

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13
Q

What is the role of aldosterone and ADH in the collecting tubule?

A

Aldosterone stimulates sodium channels being added to the apical membrane

ADH stimulates aquaporins

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14
Q

What is Liddle’s syndrome?

A

Caused by mutations in the gene that codes for epithelial sodium channel in the principal cells of the collecting duct

Characterized by severe hypertension, low plasma renin activity, metabolic alkalosis due to hypokalemia and hypoaldosteronism

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15
Q

What is obligatory water loss?

A

Water loss that must happen to be able to dissolve solutes in the urine

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16
Q

What is the function of the loop countercurrent multiplier system?

A

Increase the osmotic concentration of the medullary intersititum

17
Q

What is the role of urea in the kidney?

A

Urea contributes to the hyperosmolarity of the renal medullary intersitium and to a concentrated urine

18
Q

How does the kidney handle urea?

A

PT- passively reabsorbed (about 50%)

LH - Secreted into the tubule due to high concentration in medulla

DT - very low permeability

CD - In the presence of ADH (stimulates UT-AI transporter), urea is highly permeable and reabsorbed

19
Q

What is the recirculation of urea?

A

Urea reabsorbed in the collecting duct diffuses into the thin LoH, passes through the DT, and then finally back to the CD.

The net affect is to trap urea in the renal medulla and contribute to the hyperosmolarity

20
Q

What is the role of the vasa recta?

A

Countercurrent exchangers

Completely passive exchange of solute and water depending on where it is located in the medulla

Helps protect the medullary gradient

21
Q

What is free water and how does it affect urine?

A

Water generated in the ascending loop of henle (impermeable)

Low ADH - water not reabsorbed, hyposmotic urine

High ADH - free water is reabsorbed, hyperosmotic urine

22
Q

What is free water clearance?

A

Used to compare the rate of solute excretion with the rate of water excretion

23
Q

When is free water clearance greater than 0?

A

Urine is dilute to plasma

Free water is being lost from the boyd

Plasma is being concentrated

24
Q

When is free water clearance less than 0?

A

Relatively more solute than water is being excreted

Water is being conserved and returned to plasma

SFIII Test 3 (12 decks)

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