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BB10005 > Epithelia and cell junctions > Flashcards

Epithelia and cell junctions Flashcards

1
Q

What are epithelia?

A

avascular tisses with cells organised into sheets/tubules, attached to underlying ECM basement membrane

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2
Q

Types of epithelia

A

Simple, stratified, columnar, cuboidal, squamous

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3
Q

cuboidal

A

kidney tubules

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4
Q

columnar

A

small intestine

tall and thin

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5
Q

squamous

A

lung alveolus

flat, like paving slabs

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6
Q

stratified

A

oesophagus
thicker, multiple layers of cells
only bottom layer in contact with basement / basal lamina
Proliferative cell constantly renewing cells above- stratified differentiated across

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7
Q

Functions of epithelia

A

mechanical protection (skin), permeability barrier (small intestine), absorption (small intestine), filtration (epi of renal corpuscle), secretion (sweat glands), diffusion of gases/fluids (lung alveoli), sensory (retina)

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8
Q

Epithelial cells are polarised

A

Top of the cell is a zone where cells are in direct contact- held close together
Basolateral membrane in contact with basal lamina- secreted by these cells
Membrane at apical vs basolateral membrane different- composition of lipids, membrane proteins

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9
Q

Gut specific example of cell polarisation

A

Microvilli on apical membrane. Goblet cells secreting mucus on apical side

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10
Q

How is physical integrity of epithelium maintained

A

cells held together by cell junctions

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11
Q

Cell junctions

A

specialised site on a cell at which it is attached to another cell or the ECM

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12
Q

Anchoring junctions

A

Linking cells together or to to ECM

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13
Q

Occluding junctions

A

Seal gaps between cells

Prevent things moving across epithelium (between cells)

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14
Q

Channel forming junctions

A

create passageways linking cytoplasm of adj cells

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15
Q

signal relaying junctions

A

Allow signals to be communicated from cell to cell

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16
Q

Adherens junction

A

associated with actin filaments
cell-cell
actin(cytoskeleton)-linker-cadherin-cadherin-linker-actin
Linkers intracellular, cadherins across plasma membrane
Linkers are alpha-catenin and beta-catenin

17
Q

Desmosome junction

A

cell-cell
associated with intermediate filaments
also have cadherins
Plakoglobin/desmoplakin are electron dense plaques (type of linker?)

18
Q

Types of anchoring junction

A

Adherens, desmosome, focal adhesion, hemidesmosome

19
Q

Focal adhesion

A

cell-ECM
integrins instead of cadherins, used to hold onto ECM
Integrins have a specialised receptor for components outside the cell
Associated with actin filaments
Kinase allows attachment to be controlled (plaques?)

20
Q

Hemidesmosomes

A

Cell-ECM
intermediate filaments
integrins
Dystonin plaques- allow linking of integrins to cytoskeleton

21
Q

Homophilic mechanism

A

2 molecules which are the same pair up eg cadherins pair up, both calcium dependent

22
Q

adhesion belts

A

many adheren junctions

23
Q

invagination

A

sheet bends due to organised tightening along adhesion belts
Epithelial tube pinches of
If 1 cell contracts, exert force on adjacent cells because cytoskeletons connected by adherens

24
Q

Pemphis Vulgaris

A

autoimmune destruction of desmosomal protein
blistering, dehydration, infection and death
Gaps open up between cells and barrier function of skin fails

25
Q

Occluding junctions

more detail

A

seal gaps between epithelial cells
2 transmembrane proteins at core of junction: claudin and occludin- pair ie claudin-claudin
Barrier (no diffusion, leakage of molecules), Fence (maintaining apical polarity) function

26
Q

Loss of barrier function of occluding junctions

A

Crohn’s disease: inflammation of bowels, permeability disorder

27
Q

Loss of fence function

A

Cancer: loss of cell polarity and cell contacts (epithelial- mesenchymal transition-EMT) incr in motility and eventually metastasis (cancer spreading to new part of the body)
EMT: change from being tightly held to dispersed

28
Q

Channel forming junctions

more detail

A

Gap junctions made of connexin proteins (T proteins)
Connexon composed of 6 subunits, have a hollow tube between then, join up with another 6 on neighbouring cell- forms channel

29
Q

cardiac muscle channel forming junctions example

A

gap junctions allow passage of ions which means changes in mem potential can pass cell to cell- rhythmic contraction of heartbeat

30
Q

what are channel forming junctions in plants called

A

plasmodesmata
cytoplasm physically
connected
Smooth ER desmotubule projects across

31
Q

Signal relaying junctions more detail

A

Communication between cells
eg connection between axon and its target cell/ another axon
NT release to signal to adj cell and stimulate it
Proteins holding membranes and appropriate distance so electrical transmission can occur

32
Q

What happens when signal relaying junctions are lost?

A

Myasthenia Gravis
Autoimmune destruction of neuromuscular junction
Droopy eye
Severe muscle weakness

BB10005 (27 decks)

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