S1) Epithelial Transport Flashcards

1
Q

The movement of monosaccharides, ions and amino acids from ultra-filtrate in the nephron is a two-stage transcellular process.

Describe the import stage

A
  • Import of substances from the nephron lumen into the epithelial cells
  • Carried out by membrane transport proteins on the apical surface of nephron cells
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2
Q

The movement of monosaccharides, ions and amino acids from ultra-filtrate in the nephron is a two-stage transcellular process.

Describe the export stage

A
  • Export of substances from the cells into the interstitial fluid surrounding the basolateral surface
  • Carried out by transport proteins on the basolateral plasma membrane
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3
Q

What are the 2 requirements for trans-epithelial transport to occur?

A
  • Epithelial cells must be polarised
  • Different sets of transport proteins localised in the basolateral and apical surfaces
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4
Q

Explain how tight junctions allow for polarised epithelial cells to function

A

Tight junctions are specialised regions of plasma membrane that connect adjacent epithelial cells and help to form a barrier to separate surrounding ECF

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5
Q

Which preventative function do tight junctions have?

A

Prevent diffusion of the membrane proteins and glycolipids between the apical and basolateral regions of the plasma membrane

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6
Q

Why does epithelial paracellular permeability decrease from the PCT to collecting duct in the mammalian kidney?

A

There are changes in the permeability of tight junctions expressed along its length

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7
Q

What is the type of transport mechanism used through the tight junction?

A

Passive paracellular transport driven by electro-osmotic gradients produced by transcellular transport

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8
Q

How is epithelial transport performed through transport and energy coupling?

Identify three mechanisms

A
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9
Q

How is epithelial transport performed by facilitated diffusion?

A
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10
Q

How does epithelial transport vary in number of solutes and direction?

A
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11
Q

Explain what adaptations enable the proximal tubule to reabsorb 1/3 of total fluid through the paracellular pathway

A
  • A leaky epithelium
  • Low transepithelial resistance (TER)
  • High paracellular transport
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12
Q

Identify some important determinants of paracellular transport

A
  • Peritubular protein concentration
  • Renal hydrostatic pressure
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13
Q

Which 3 substances also increase paracellular permeability?

A
  • Nitric oxide
  • Prostaglandins
  • cAMP
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14
Q

What drives paracellular reabsorption of Mg2+ and Ca2+ in the thick ascending limb?

A
  • Driven by a lumen-positive transepithelial voltage
  • Voltage is generated by Na+-K+-2Cl (NaKCC) cotransport and luminal K+ recycling
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15
Q

In terms of epithelial transport, describe the properties of the distal nephron

A
  • Tight epithelium
  • Low passive permeability to cations
  • High transepithelial resistance
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16
Q

In terms of paracellular transport, what is the role of tight junctions in the distal nephron?

A

Tight junctions function as cation barriers to prevent the dissipation of transtubular Na+, K+, and H+ gradients

17
Q

In terms of paracellular transport, what is the role of aldosterone in the distal nephron?

A

Aldosterone regulates the transport of Na+ and K+ in this segment

18
Q

In terms of paracellular permeability, describe the role of tight junctions in the distal nephron

A

Tight junctions of the cortical and distal collecting duct epithelia lead to increased paracellular chloride permeability

19
Q

In terms of paracellular permeability, describe the role of aldosterone in the distal nephron

A

An aldosterone-sensitive interaction regulates Na+ channel activity to increase paracellular permeability