Epithelia and cell junctions

Question 1

What are epithelia?

Answer 1

Avascular tissues composed of cells

Question 2

What are epithelia usually organised into?

Answer 2

Sheets or tubules

Question 3

What are the sheets/tubules that epithelia are organised into connected to?

Answer 3

An underlying extracellular matrix basement membrane

Question 4

What are the five main types of epithelia?

Answer 4

Simple, stratified, columnar, cuboidal and squamous

Question 5

What is an example of simple cuboidal epithelia?

Answer 5

Kidney tubules

Question 6

What is an example of simple columnar epithelium?

Answer 6

Small intestine

Question 7

What is an example of squamou epithelium?

Answer 7

Lung alveolus

Question 8

What is an example of stratified epithelium?

Answer 8

Oesphagus

Question 9

What are the functions of epithelia in the small intestine?

Answer 9

Permeability barrier and absorption

Question 10

What are some other functions of epithelia?

Answer 10

Filtration, secretion, diffusion of gases or fluids and mechanical protection

Question 11

What are epithelia held together by?

Answer 11

Cell junctions

Question 12

What is a cell junction?

Answer 12

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

Question 13

What are the four functional groups of cell junctions?

Answer 13

Anchoring, Occluding, Channel-forming and Signal-relaying

Question 14

What do anchoring junctions do?

Answer 14

Link cells together or to the extracellular matrix

Question 15

What do occluding junctions do?

Answer 15

Seal the gaps between cells

Question 16

What do channel-forming junctions do?

Answer 16

Create passageways linking the cytoplasm of adjacent cells

Question 17

What so signal-relaying junctions do?

Answer 17

Allow signals to be communicated from cell to cell

Question 18

Role of adherens junctions?

Answer 18

Link cadherins to the actin filaments of the cytoskeleton

Question 19

Role of desmosomes?

Answer 19

They link cadherins to intermediate filaments of the cytoskeleton

Question 20

What is the role of focal adhesions?

Answer 20

They interact with actin filaments within the cell, and anchor the cell to the basal lamina

Question 21

What do cadherins mediate?

Answer 21

cell-cell attachment

Question 22

How do cadherins mediate cell-cell attachment?

Answer 22

A cytoskeletal filament is attached to a linker protein, which is in turn attached to a cadherin molecule. Cadherin molecules then attach to each other in the extracellular space

Question 23

How do epithelial sheets form a tube or vesicle?

Answer 23

They bend

Question 24

How do occluding junctions help maintain cell polarity?

Answer 24

They seal cells in a way that prevents small molecules from passing through the barrier–> maintains concentrations of molecules on either side of the barrier

Question 25

What do channel junctions allow ions and small molecules to do?

Answer 25

Pass directly from cell to cell

Question 26

Example of channel forming junctions in an organ?

Answer 26

Gap junctions allow the passage of ions through them–> permits changes in membrane potential pass from cell to cell–> rhythmic contraction of the heartbeat

Question 27

What are channel forming junctions in plants called?

Answer 27

Plasmodesmata

Question 28

What do signal relaying junctions allow?

Answer 28

Communication of signals between cells

Question 29

Tight junction?

Answer 29

Seals neighbouring cells together in an epithelial sheet to prevent leakage of molecules between them

Question 30

Adherens junction?

Answer 30

Joins an actin bundle in one cell to a similar bundle in a neighbouring cell

Question 31

Desmosome?

Answer 31

Joins the intermediate filaments in one cell to those in a neighbour

Question 32

Gap junctions?

Answer 32

Forms channels that allow small water-soluble molecules, including ions, to pass from cell to cell

Question 33

Hemidesmosome?

Answer 33

Anchors intermediate filaments in a cell to the basal lamina