Lecture 21 - Epithelia and cell junctions Flashcards

1
Q

What are epithelia

A

avascular tissues composed of cells, usually organised into sheets or tubules, attached to an underlying ECM basement membrane

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2
Q

What does Epithelium mean in latin

A

Epi - Upon
Thelium - To Cover

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3
Q

Where do epithelial cells cover

A

cover both the internal and external surfaces of the body

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4
Q

What are some common modified forms of epithelia

A

glandular structures (exocrine glands)

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5
Q

What are the types of epithelia

A

Simple, Stratified, columnar, cuboidal, squamous

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6
Q

What is an example of simple cuboidal cells

A

Kidney tubules

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7
Q

What is an example of simple columnar epithelial cells

A

Small intestine

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8
Q

What is an example of Squamous epithelial cells

A

Lung alveolus

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9
Q

What is an example of stratified epithelia

A

Oesophagus

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10
Q

What are the functions of epithelia

A

Mechanical protection (e.g. skin)
Permeability barrier (e.g. small intestine)
Absorption (e.g. small intestine)
Filtration (e.g. epithelium of renal corpuscle)
Secretion (e.g. sweat glands)
Diffusion of gases or fluids (e.g. lung alveoli)
Sensory (e.g. retina)

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11
Q

What are the two sides of an epithelia

A

Apical and Basal

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12
Q

What are epithelial held together by

A

Cell junctions

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13
Q

What are cell junctions

A

A specialised site on a cell at which it is attached to another cell or the extracellular matrix

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14
Q

What are the classifications of cell junctions

A

Anchoring
Occluding
Channel-forming
singal-relaying

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15
Q

What do anchoring junctions do

A

Linking cells together or to the extracellular matrix

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16
Q

What do occluding auctions do

A

Seal gaps between cells

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17
Q

What do channel-forming junctions do

A

create passageways linking the cytoplasm of adjacent cells

18
Q

What do single-relaying junctions do

A

allow signals to be communicated from cell to cell

19
Q

What are some examples of anchoring/strengthening junctions

A

Adheren junctions
Desmosome
Hemidesmosome
Focal Adhesion

20
Q

What do adherents do and what are they composed of

A

Bridge between epithelial cells

Actin filaments
cadherin
Alpha-catenin
Beta-catenin
(slide 15)

21
Q

What do focal adhesions do and what are they composed of

A

Attach epithelial cell to basal lamina

Actin filaments
integrin
Focal adhesion kinase
(Slide 15)

22
Q

What do hemidesmosomes do and what are they composed of

A

Attach epithelial cell to basal lamina

intermediate filaments
integrin/collagen
Dystonin
(Slide 15)

23
Q

What do desmosomes do and what are they composed of

A

Strengthen gaps between cells

Intermediate filaments
Cadherin (desmoglein)
Plakoglobin
Desmoplakin
(Slide 15)

24
Q

What do cadherins do

A

Mediate cell-cell attachment
(slide 16)

25
Q

What do Adherens do

A

Link cadherins to the actin filaments of the cytoskeleton
(slide 17)

26
Q

What features of epithelial sheets make them ideal for an organ such as the small intestine

A

1 cell thick
Can bend to form a tube or a vesicle
(slide 18+19)

27
Q

What do desmosomes do

A

link cadherins to intermediate filaments of the cytoskeleton
(slide 20)

28
Q

What do integrins do

A

Mediate cell-matrix contacts
(slide 21)

29
Q

What is an example of a disease with defective desmosomes

A

Pemphigus Vulgaris

autoimmune destruction of desmosomal protein
severe blistering
dehydration and infection
death
(slide 22)

30
Q

What are occluding junctions specialised for

A

Seal gaps between epithelial cells, typically found in the lumen of the gut
(slide 23)

31
Q

What do some occluding and tight junctions help do

A

Maintain cell polarity

32
Q

What diseases are associated with a loss of function of tight junctions

A

Barrier function:
Crohn’s disease - Inflammation of the bowels, Permeability disorder

Fence function:
Cancer – Loss of cell polarity and cell contacts (epithelial-mesenchymal transition - EMT), increase in motility and eventual metastasis
(slide 26)

33
Q

What do channel-forming junctions allow

A

ions and small molecules to pass directly from cell to cell

34
Q

What is an example of channel-forming junctions

A

Example : cardiac muscle
Gap junctions allow the passage of ions this permits changes in membrane potential to pass from cell to cell = rhythmic contraction of the heartbeat
(slide 28)

35
Q

What are some inherited disorders from abnormal gap junctions

A

Cataracts (connexin 50 affected)
Vohwinkel Syndrome (connexin 26 affected)
(slide 29)

36
Q

What are channel-forming junctions in plants called

A

Plasmodesmata

37
Q

structure of signal-relaying junctions

A

SLIDE 32!!!!!

38
Q

What is a disease associated with a loss of signal-relaying junctions

A

Myasthenia Gravis

autoimmune destruction of neuromuscular junction
first indication of disease is a droopy eye
severe muscle weakness
(slide 33)

39
Q

How are epithelial tubes formed

A

Invagination of epithelial cell sheet caused by an organised tightening along adhesion belts in selected regions of cell sheet

Adhesion belt with associated actin filaments

Epithelial tube pinches off from overlying sheet of cells