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Cell Biology > Epithelia and Cell Junctions > Flashcards

Epithelia and Cell Junctions Flashcards

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1
Q

Epithelia

Definition

A
  • Avascular tissues composed of cells, usually organised into sheets or tubules, attached to an underlying ECM basement membrane.
  • Epithelia cover both the internal and external surfaces of the body
  • Some epithelia are modified to form glandular structures.
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2
Q

Types of epithelia

(5)

A
  • Simple
  • Stratified
  • Columnar
  • Cuboidal
  • Squamous
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3
Q

Functions of Epithelia

(7)

A
  1. Mechanical protection
  2. Permeability barrier
  3. Absorption
  4. Filtration
  5. Secretion
  6. Diffusion of gases or fluids
  7. Sensory
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4
Q

How are epithelia polarised?

A

Polarised in terms of morphology.
Might have specialised apical surface for example.
Distribution of cellular components in the apical and basal-lateral regions are distinct.

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5
Q

How is the physical integrity of the epithelium maintained?

A

Cell Junctions

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6
Q

What are cell junctions?

A

Specialised sites on a cell at which it is attached to another cell, or to the ECM.
They hold the epithelia together, and control its function.

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7
Q

Types of cell junctions

(4)

A
  • Anchoring junctions
  • Occluding junctions
  • Channel-forming juctions
  • Signal-relaying junctions
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8
Q

Anchoring junctions

A

Link cells together or to the extracellular matrix.
* Adherens
* Desosomes
* Focal adhesions
* Hemidesmosomes

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9
Q

Adherens junctions

A
  • Interact with actin filaments, connecting the filaments in neighboring cells.
  • Wrap around cell in the apical region
  • Each cadherin is tethered to actin filaments via several linker proteins
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10
Q

Actin is contractile so…

Adherens

A

… pulls cells closer together.
This allows for the epithelial sheets to form tubes or vesicles.

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11
Q

Desosomes

A
  • Form spot-like structures
  • Cadherins link to keratin.
  • Interact with intermediate filaments in the cytoskeleton
  • Strengthen cells against streching forces
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12
Q

Core components of desosomes

(2)

A

plakoglobin and desmoplakin

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13
Q

Cadherins mediate…

A

… cell-cell attachments.
These are homophilic mechanisms

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14
Q

Integrin molecules play a central role in …

A

… mediating cell-matrix contacts

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15
Q

Focal Adhesions

A

Allow the cell to hold on to the ECM and exert a pull on it.

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16
Q

Hemisdesmosomes

A
  • Interact with intermediate filaments
  • Integrin molecules do the “holding on”
  • Adaptor complex of proteins - plaque
  • Anchor epithelial cells to the basal lamina
17
Q

Pemphigus Vulgaris

A

Autoimmune disorder that causes the destruction of desmosomal proteins.
Causes severe blistering, dehydration, infection, and death.

18
Q

Occluding (tight) junctions

A
  • Define boundary between basolateral and apical membranes
  • Made of claudin and occludin
  • Have a barrier and a fence function
  • Form networks of strands across the cells, which press the cells together.
  • No space for proteins to pass through
19
Q

Claudin and occludin

A

Proteins that make up occluding junctions.
They undergo homodimerisation and physically interact.

20
Q

Barrier function

Occluding junctions

A

Occluding junctions regiulate the passage of ions, water and macromolecules.

21
Q

Fence function

Occluding junctions

A

Maintains cell polarity.

22
Q

Problems with barrier functions cause…

A

… Crohns disease, which causes inflammation of the bowels. This is a permeability disorder.

23
Q

Problems with the fence function can be caused by…

A

… cancer. It causes a loss of cell polaroty and cell contacts and increases motility, which causes metastasis

24
Q

Channel-forming (gap) junction

A
  • Made of connexins
  • Two connexons on neighbouring cells bind to each other.
  • Allow ions through, but not larger molecules.
  • Homophillic interactions
25
Q

Connexins

Channel-forming junctions

A

6 connexins make a connexon, these are like tubes and can open and close.

26
Q

Abnormal gap junctions

A

Cause some inherited disorders, such as cataracts and Vohwinkel syndrome

27
Q

Channel-forming junctions in plants

A

Cell walls prevent these kind of connections between cells.
A channel-forming junctions exists called a plasmodesmata which are regions where the cytoplasm of two cells are directly connected via a pore.

28
Q

Signal-relaying junctions

A
  • Allow communication of signals between cells.
  • Contains specialised protein components which form pairs which effect each other - control things like spacing.
  • Establish an area where communication between cells can take place using vesicles.
  • Allows for transport of species larger than ions.
29
Q

Myasthenia gravis

A

An autoimmune destruction of the neuromuscular junctions. Causes severe muscle muscle weakness

Cell Biology (16 decks)

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