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PHSL 233 > L7 > Flashcards

L7 Flashcards

1
Q

what are epithelia

A

they are barriers

they separate body compartments (organs)

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2
Q

what do epithelia act as

A

to act as gatekeepers

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

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3
Q

what are some areas where epithelia separate internal and external environments

A

Skin

Intestinal tract

Nephrons of the kidneys/urinary tract

Respiratory tract, reproductive tract

Regions of the eye and auditory system

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4
Q

what are the properties of epithelia

A

Separate internal and external environments

Control exchange of material between body and the
environment

Define the composition of the luminal fluid of hollow
organs

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5
Q

what is an example of where epithelia control exchange of material between body and the
environment

A

Intestinal tract and nephron/urinary tract

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6
Q

what are some examples of where epithelia define the composition of the luminal fluid of hollow
organs

A

Reproductive tract, respiratory tract, intestinal tract, kidney nephron, oviduct, and vas deferens, etc.

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7
Q

what is the basic structure of epithelial tissue

A

it has 1 or more layers of epithelial cells, a basement membrane and supporting tissues (extracellular matrix, cells)

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8
Q

the structure of epithelial tissue depends on what

A

where it is located in the body and its function

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9
Q

what is an example of serosal/interstitial fluid

A

blood

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10
Q

what is another name for the intERcellular space

A

the basolateral space

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11
Q

what membrane of the epithelium faces the mucosal solution

A

apical membrane

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12
Q

what does the basement membrane face

A

serosal solution (blood)

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13
Q

what are the 2 ways that substances can cross the epithelium

A

Paracellular = substances can travel between the epithelial cells

Transcellular = through the cells

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14
Q

what is the difference between gap and tight junctions

A

Gap = communication they are a passage and tight junctions are barrier proteins

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15
Q

describe the apical membrane

A

Faces the lumen (outside)
of the organ

it can be called the apical, mucosal, luminal
membrane or brush border

often has microvilli (MV)

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16
Q

describe the basolateral membrane

A

Faces the interstitial fluid
(inside) ‘internal body’

it can be called the basolateral membrane,
serosal membrane

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17
Q

what are the 2 parts of the basolateral membrane

A

Basal membrane (BM)

Membrane lining the lateral
intercellular space (LIS)
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18
Q

where does the basolateral membrane spann from

A

tight junction to tight junction

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19
Q

what is vectorial transport

A

transport in a specific diffection

It involves active and passive transport of ions & solutes and depends on active transport (e.g. Na/K-ATPase) and osmosis

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20
Q

how do we sweat

A

Sweat glands are specialised parts of the skin epithelium. What these glands do is they secrete salt. water follows salt which is how we sweat

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21
Q

what is the natural environment made up of

A

electrical and chemical

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22
Q

why are epithelial cells capable of fluid and electrolyte transport

A

because they are polarised/asymmetrical
cells

they have structural and functional asymmetry

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23
Q

what is meant by structural asymmetry

A

the apical and basolateral membranes are different which makes it polar (because it is different on either side)

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24
Q

why do epithelial cells have functional asymmetry

A

because apical and basolateral membranes are
functionally different

They contain different set of channels and transporters which have properties distinct from each other

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25
Q

what are some common characteristics of the basolateral membrane

A

High K+ permeability relative to Na+, Cl

High water permeability

it also contains housekeeping transporters

Attached to the basement membrane

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26
Q

what is the reason that the basolateral membrane his a high K+ permeability relative to Na+, Cl

A

because it contains lots of K+ channels

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27
Q

why is the basolateral membrane so permeable to water

A

because it contains lots of aquaporins

28
Q

what are some examples of housekeeping transporters located in the basolateral membrane

A

Na+/K+ ATPase

Ca2+ ATPase and Na+/Ca2+ exchanger

Na+/H+ exchanger (NHE-1)

29
Q

what are some common characteristics of the apical membrane

A

Selectively permeable to various ions

no housekeeping transporters

variable water permeability

30
Q

the apical membranes permeability to ions depends on what….

with examples

A

Permeability depends on the type of epithelium and what channels and transporters that membrane has

Na+ absorbing epithelia, high Na + permeability
– Range of transporters and channels

Secretory epithelia, high Cl- permeability
– Cl- channels

Determines the transport properties of the epithelium

31
Q

Typical functional features of the basolateral membrane of
an epithelial cell are:

A. faces the external environment, does not have K+ channels, does
not contain aquaporins.

B. has microvilli, faces the interstitial fluid, touches neighbouring cells.

C. contains Na+ channels, has K+ channels, is permeable to water.

D. faces the interstitial fluid, has Na+-K+-ATPase, is permeable to K+.

A

D

32
Q

there are 2 types of absorptive epithelia

A

lecky and tight

33
Q

what are the characteristics of absorptive epithelium

A

Net transport is from mucosal to serosal solution

Absorption driven by the active transport of Na+
Na/K-ATPase

34
Q

what are some examples of where you can find absorptive epithelium

A

Intestine and nephron

35
Q

what are the characteristics of secretory epithelium

A

Net transport from serosal to mucosal solution

Secretion is driven by the active transport of Cl-
NKCC

36
Q

what are some examples of secretory epithelium

A

Salivary glands, pancreas, sweat glands

37
Q

what are some examples of epithelia that is both secretory and absorptive

A

Small and large intestine, kidney nephron,

airways

38
Q

what is the difference between tight and leaky absorptive epithelia

(5 points)

A

They are separated on basis of….

Transport properties derived from electrical
characteristics

Apical membrane transport pathways

Hydraulic conductivity (relative water flow)

Responsiveness to hormones

Location within organs

39
Q

what is transepithelial voltage

A

Voltage that develops across an epithelium due to active transport of ions

This is talking about going across the whole cell not just across the membrane (thats a mp)

40
Q

what is the transepithelial voltage range for leaky absorptive epithelium

A

0 - 5 mV

41
Q

what is the transepithelial voltage range for tight absorptive epithelium

A

20 - 100 mV

42
Q

what are the electrical characteristics of absorptive epithelium

A

transepithelial voltage and transepithelial resistance

43
Q

what is transepithelial resistance

A

Electrical resistance to flow of ions across an epithelium

Unit: ohms/cm^-2

44
Q

what is the transepithelial resistance range for tight absorptive epithelium

A

Leaky absorptive epithelia
20 - 100 ohms/cm^-2
therefore it is ‘Easy’ for ions to move across epithelium

Tight absorptive epithelia
300 - 10,000 ohms/cm^-2
therefore it is difficult for ions to move across epithelium

45
Q

how many x larger is the resistance for tight absorptive epithelia compeered to lecky

A

15 – 100 x higher

46
Q

what is the reason for the difference in transepithelial resistance between tight and leaky absorptive epithelia

A

Leaky epithelia have lots of paracellular transport because they have less tight junctions

The number and the type of tight junctions in the epithelia determines the electrical resistance

47
Q

electrical resistance is a measure of what

A

Electrical resistance is a measure of how much substances and solutes can pass the epithelium through the paracellular pathway vs the transcellular pathway

48
Q

Why do we have leaky and tight epithelia within the same tissue within the same organ?

with example

A

The distal part of the kidney we have tight epithelium

200L of fluid goes through the kidneys per day and the majority of that is reabsorbed. To reabsorb this we have leaky and tight absorptive epithelium

leaky does bulk (to reduce time and make it more efficient)

tight is for specific things for fine tuning of homeostasis

49
Q

if you have a high resistance what does that mean for the flow of ions

A

that there is a slow rate of transport (flow)

50
Q

how does Na cross the apical membrane in leaky absorptive epithelia

A

Leaky epithelia - Na+ dependent cotransporters

and/or exchangers (counter transporters)

51
Q

how does Na cross the apical membrane in tight absorptive epithelia

A

Tight epithelia - Na+ selective channels (e.g.

ENaC: epithelial Na+ channel)

52
Q

describe hydraulic conductivity in leaky absorptive epithelia

what kind of fluid will it absorb

A

high hydraulic conductivity
as it has a range of aquaporins and tight junctions (number and types)

it absorb large amounts of isosmotic fluid therefore it is efficient and effective

53
Q

describe hydraulic conductivity in tight absorptive epithelia

A

low hydraulic conductivity under basal conditions

increases under hormonal control

absorb variable amounts of hyperosmotic fluid because tight can produce large osmotic gradients as it stops the water from moving back

54
Q

describe the effect of hormones on leaky epithelium

A

has very little effect as leaky have a constant rate of transport

55
Q

describe the effect of hormones on tight absorptive epithelium

A

very responsive to hormones

ion and water transport is closely regulated by hormone

56
Q

what are the 2 hormones which have an effect on tight absorptive epithelia

A

aldosterone and vasopressin

57
Q

what is the effect of aldosterone on tight absorptive epithelia

A

aldosterone, regulates Na+ transport through ENaC

58
Q

what is the effect of vasopressin on tight absorptive epithelia

A

vasopressin also called antidiuretic hormone (ADH)

regulates water transport Aquaporin 2 (AQP2)

59
Q

why do tight and leaky epithelia respond to hormones

A

to regulate blood pressure

60
Q

where is leaky epithelia usually located within organs? why?

A

proximal regions of organs

in these regions because this is where ‘bulk’ transport occurs

61
Q

where is leaky epithelia usually located within the nephron

A

proximal tubule of the nephron

62
Q

where is leaky epithelia usually located within the small intestine

A

duodenum, jejunum and ileum of small intestine

63
Q

where is tight absorptive epithelia usually located within organs? why?

A

distal regions of organs

as this is where ‘fine tuning’ (highly controlled absorption) takes place

64
Q

where is tight absorptive epithelia usually located within the nephron

A

late distal tubule and collecting duct of nephron

65
Q

where is tight absorptive epithelia usually located within the large intestine

A

distal colon of the large intestine

66
Q

Leaky absorptive epithelia

A. have a high transepithelial resistance.

B. can mainly be found in distal parts of organs.

C. do not have tight junctions.

D. have a low hydraulic conductivity.

E. possess mainly Na+ dependent co-transporters/exchangers in their apical membrane.

A

E

PHSL 233 (31 decks)

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