Tubular reabsorption and secretion - Loop of Henle Flashcards

1
Q

What are the parts of the loop of Henle?

A

Thin descending limb

Thin ascending limb

Thick ascending limb

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2
Q

What is reabsorbed in the thin descending limb?

A

Water

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3
Q

How is water reabsorbed in the thin descending limb?

A

Aquaporin1 channel on apical domain of epithelial cell
Water passes through it from the tubular lumen into the cell
Aquaporin1 channel on basolateral domain of epithelial cell
Water passes through it from the cell into the interstitial fluid

Also moves through paracellular route but less

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4
Q

How does the osmolality change across the length of the thin descending limb? Why?

A

Increases
ions and molecules become more concentrated in tubular lumen
as water is reabsorbed without them

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5
Q

What is reabsorbed in the thin ascending limb?

A

Sodium ions

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6
Q

How are sodium ions reabsorbed in the thin ascending limb?

A

Move through paracellular route from tubular lumen into interstitial fluid down its concentration gradient, so by passive diffusion

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7
Q

What causes the concentration gradient of sodium ions in the thin ascending limb?

A

High concentration of sodium ions in tubular lumen from thin descending limb

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8
Q

What is the main primary active transporter in the thick ascending limb?

A

Na+ K+ ATPase

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9
Q

Where is the Na+ K+ ATPase located on the epithelial cell in the thick ascending limb?

A

Basolateral domain

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10
Q

What does the Na+ K+ ATPase in the thick ascending limb do?

A

Actively transports 3 sodium ions from the epithelial cell into interstitial fluid

Actively transports 2 potassium ions from the interstitial fluid into the epithelial cell

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11
Q

What is the electrochemical gradient of sodium ions in the thick ascending limb?

A

High concentration of sodium ions in tubular lumen, positive charge in tubular lumen

Low concentration of sodium ions in epithelial cell, negative charge in epithelial cell

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12
Q

What is the importance of the electrochemical gradient of sodium ions in the thick ascending limb?

A

It is used in reabsorption of other substances by secondary active transport

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13
Q

What is reabsorbed in the thick ascending limb?

A

Sodium ions

Potassium ions

Chloride ions

Calcium ions

Magnesium ions

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14
Q

How are potassium and chloride ions reabsorbed in the thick ascending limb?

A

NKCC2 transporter on apical domain of epithelial cell
Moves one sodium ion, one potassium ion and two chloride ions from the tubular lumen into the epithelial cell
Potassium ion is moving against its concentration gradient, but the sodium and chloride ions are moving down their concentration gradient, so is secondary active transport

CIC-KB channel on basolateral domain of epithelial cell
Chloride ions move through it from the cell into the interstitial fluid down their concentration gradient, so by facilitated diffusion

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15
Q

What happens to the potassium ions in the epithelial cell in the thick ascending limb?

A

ROMK channel on apical domain of epithelial cell
Potassium ions move through it from the epithelial cell back into the tubular lumen down their concentration gradient, so by facilitated diffusion

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16
Q

What is the importance of the potassium ions in the epithelial cell in the thick ascending limb diffusing back into the tubular lumen?

A

To maintain the concentration of potassium ions in the tubular lumen
so that the NKCC2 transporter can keep working

17
Q

How are calcium and magnesium ions reabsorbed in the thick ascending limb?

A

Potassium ions in the epithelial cell diffusing back into the tubular lumen give a positive charge in the tubular lumen
Magnesium and calcium ions move through the paracellular route from the tubular lumen into the interstitial fluid down their electrical gradient, so by passive diffusion

18
Q

How much of the filtered sodium, potassium and chloride ions are reabsorbed in the thick ascending limb?

A

25%

19
Q

What happens to the osmolality across the length of the thick ascending limb?

A

Decreases to less than plasma osmolality
ions become less concentrated in the tubular lumen
because they are reabsorbed without reabsorbing water