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I've got kidney disease > Lecture 7: Epithelia 1 > Flashcards

Lecture 7: Epithelia 1 Flashcards

1
Q

We can describe epithelia as what two words?

A
  1. barriers

2. separate body compartments

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2
Q

What is the function of epithelia?

A

facilitate movement of. ions and molecules between external and internal environments

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3
Q

What is the purpose of epithelia on the skin?

A

To act as a barrier to protect our body

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4
Q

Epithelia allow the controlled exchange of material between where?

A

the body and the environment

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5
Q

One side of the epithelia always faces what?

A

the outside wall

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6
Q

Epithelia defines the composition of what?

A

the body fluids eg. the intracellular fluid and extracellular fluid

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7
Q

Describe the basic structure of epithelial tissues (3)

A
  • 1 or more layers of epithelial cells
  • basement membrane
  • supporting tissues (extracellular matrix and cells for support)
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8
Q

The structure of the epithelia depends on what?

A

where in the body it is and its function

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9
Q

What is the name of the area that touches the apical membrane (outside of the cell)?

A

the mucosal/luminal solution

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10
Q

What is the name of the area that touches the basolateral membrane?

A

This is the serosal/interstitial fluid

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11
Q

What are some characteristic structures of an epithelium?

A
  • tight junctions
  • apical membrane
  • basolateral membrane
  • basement membrane
  • lateral intercellular space/basolateral space (in between cells)
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12
Q

Where is the basolateral membrane?

A

all membrane except the apical membrane

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13
Q

What are the two different ways what solutes can travel across epithelia?

A
  • transcellular

- paracellular

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14
Q

What is transcellular transport?

A

this is transport through the cells

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15
Q

What is paracellular transport?

A

this is transport in between the cells

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16
Q

What are the basolateral and apical membranes separated by?

A

tight junctions

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17
Q

What is the purpose of tight junctions?

A

These are specific proteins that are binding/sealing neighbouring cells together

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18
Q

What is the purpose of gap junctions?

A

they are for communication because they allow the passage between cells so they facilitate movement of substances between cells

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19
Q

Which membrane bas microvilli/brush border?

A

apical membrane

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20
Q

What is vectorial transport?

A

this is the transport of ions of molecules across an epithelium in only one direction (although this can be from the mucosal to serosal sides or vice versa)

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21
Q

What does vectorial transport involve? What does this mean it depends on?

A

it involves active and passive transport of ions and solutes and so therefore depends on active transport of ions and solutes

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22
Q

Why are epithelial cells capable of electrolyte transport?

A

because they are polarised/asymmetrical cells

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23
Q

Why are epithelial cells polarised/asymmetrical cells?

A

because they have structural asymmetry and functional asymmetry

24
Q

Describe the structural asymmetry of epithelial cells

A

The structure of the membranes are different:

  • the apical membrane has microvilli but the basolateral membrane doesn’t
  • there is a basement membrane on the basolateral side
  • the tight junctions are close to the surface of the epithelia, close to the outside apical membrane
25
Q

Describe the funcitonal asymmetry of epithelial cells

A

Apical and basolateral membranes are functionally different:

- they contain different set of channels and transporters that have properties distinct from each other

26
Q

Describe the common characteristics of the basolateral membrane that result in functional asymmetry

A
  • High K+ permeability relative to Na+ and Cl- so has lots of K+ channels
  • high water permeability so there are lots of aquaporins
  • there are housekeeping transporters such as Na+/K+ ATPase, Ca2+ATPase, Na+/Ca2+ exchanger, Na+/H+ exchanger
27
Q

Describe the common characteristics of apical membrane that result in functional asymmetry

  • it is _____________ permeable to various __________ (the ___________ depends on the type of epithelium such as
  • ________ absorbing epithelia, which has high permeability due to a range of ___________ and __________
  • secretory epithelia which has a high _______ permeability due to ________ channels
  • it does not contains the ________ ATPase or other housekeeping transporters
  • various water permeability due to ________
A
  • it is selectively permeable to various ions (the permeability depends on the type of epithelium such as
  • Na+ absorbing epithelia, which has high permeability due to a range of transporters and channels
  • secretory epithelia which has a high Cl- permeability due to Cl- channels
  • it does not contains the Na+/K+ ATPase or other housekeeping transporters
  • various water permeability due to aquaporins
28
Q

Typical functional features of the basolateral membrane of an epithelial cell are what?

A

it faces the interstitial fluid, it has the Na+/K+ ATPase and is permeable to K+

29
Q

What are the two different types of epithelia?

A
  • absorptive

- secretory

30
Q

How are the two types of epithelia distinguished?

A

by their transport direction

31
Q

What are the two types of absorptive epithelia?

A
  • leaky

- tight

32
Q

What is the net transport for absorptive epithelia?

A

from mucosal to serosal

33
Q

Absorption in absorptive epithelia is driven by what?

A

Na+/K+ ATPase

34
Q

What is the net transport for secretory epithelia?

A

serosal to mucosal

35
Q

Secretion is secretory epithelia is driven by what?

A

active transport of Cl- via NKCC

36
Q

Leaky and tight absorptive epithelia are separated on what basis? (5)

  • __________ properties derived from _________ characteristics
  • _________ membrane ________ pathways
  • _________ conductivity
  • responsiveness to _______
  • location within _________
A
  • transport properties derived from electrical characteristics
  • apical membrane transport pathways
  • hydraulic conductivity
  • responsiveness to hormones
  • location within organs
37
Q

Taking stuff up from outside to supply the body generates what?

A

electrical charge differences across epithelia

38
Q

What is transepithelial voltage?

A

this is the electrical potential difference/the voltage across an epithelium due to the active transport of ions

39
Q

Which has a higher transepithelial voltage, tight or leaky absorptive epithelia?

A

tight

40
Q

What is transepithelial resistance?

A

the electrical resistance to the flow of ions across an epithelium

41
Q

Which has a higher transepithelial resistance, leaky or tight absorptive epithelia?

A

tight

42
Q

What is the reason for the electrical differences between tight and leaky epithelia?

A

Leaky have lots of paracellular transport because the number and structure of tight junctions differs between tight and leaky epithelia.

43
Q

High permeability of the tight junctions to ions = high/low resistance = high/low transport rate

A

low

high

44
Q

High resistance of the tight junctions to ions = high/low transport rate = high/low transepithelial voltage

A

low

high

45
Q

Which type of absorptive epithelia absorbs lots in a short amount of time?

A

leaky epithelia

46
Q

Which type of epithelia is more for fine tuning and is better at being specific about what it picks up?

A

tight epithelia

47
Q

How does the mechanism by which Na+ crosses the apical membrane differ between leaky and tight absorptive epithelia?

A

leaky: uses Na+ dependent cotransporters and/or exchangers
tight: uses Na+ selective channels

48
Q

How does the hydraulic conductivity differ between leaky and tight absorptive epithelia?

A
  • leaky: high hydraulic conductivity to absorb large amounts of isosmotic fluid
  • tight: low hydraulic conductivity under basal conditions (although this increases under hormonal control) to absorb variable amounts of hyperosmotic fluid
49
Q

What is hydraulic conductivity a measure of?

A

how easy it is for water to be transported

50
Q

How do leaky and tight absorptive epithelia differ in their responsiveness to hormones?

A
  • leaky: there is little control by hormones
  • tight: there is high ion and water transport closely regulated by hormones such as aldosterone (regulating Na+ transport) and vasopressin/ADH (regulating water transport)
51
Q

How do leaky and tight absorptive epithelia differ in their location within organs?

A
  • leaky: proximal regions of the organs for bulk transport

- tight: distal regions of organs for fine tuning

52
Q

Leaky absorptive epithelia possess what in their apical membrane?

A

mainly Na+ dependent co-transporters/exchangers

53
Q

What are two mechanisms for apical membrane transport pathways for Na+ in leaky epithelia?

A
  • cotransport, Na+ coupled

- counter transport, Na+ coupled

54
Q

Cotransport in the apical membrane of leaky epithelia are examples of what transport?

A

secondary active

55
Q

Describe how Na_ coupled solute cotransport works

A

Both Na+ and (eg.) glucose bind to the transporter and then it takes them both in. The movement of ions depends on the membrane potential

56
Q

What is electrogenic and electroneutral?

A

electrogenic: when the things that are being brought into the cell have an overall charge that will affect the membrane potential (eg. Na+ coupled to glucose brings an overall 1+ charge in)
electroneutral: when the things that are being brought into the cell have no overall charge (eg. Na+ coupled to Cl- brings no overall charge in)

I've got kidney disease (43 decks)

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