Lecture 21 - Epithelia and cell junctions

Question 1

What are epithelia

Answer 1

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

Question 2

What does Epithelium mean in latin

Answer 2

Epi - Upon
Thelium - To Cover

Question 3

Where do epithelial cells cover

Answer 3

cover both the internal and external surfaces of the body

Question 4

What are some common modified forms of epithelia

Answer 4

glandular structures (exocrine glands)

Question 5

What are the types of epithelia

Answer 5

Simple, Stratified, columnar, cuboidal, squamous

Question 6

What is an example of simple cuboidal cells

Answer 6

Kidney tubules

Question 7

What is an example of simple columnar epithelial cells

Answer 7

Small intestine

Question 8

What is an example of Squamous epithelial cells

Answer 8

Lung alveolus

Question 9

What is an example of stratified epithelia

Answer 9

Oesophagus

Question 10

What are the functions of epithelia

Answer 10

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)

Question 11

What are the two sides of an epithelia

Answer 11

Apical and Basal

Question 12

What are epithelial held together by

Answer 12

Cell junctions

Question 13

What are cell junctions

Answer 13

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

Question 14

What are the classifications of cell junctions

Answer 14

Anchoring
Occluding
Channel-forming
singal-relaying

Question 15

What do anchoring junctions do

Answer 15

Linking cells together or to the extracellular matrix

Question 16

What do occluding auctions do

Answer 16

Seal gaps between cells

Question 17

What do channel-forming junctions do

Answer 17

create passageways linking the cytoplasm of adjacent cells

Question 18

What do single-relaying junctions do

Answer 18

allow signals to be communicated from cell to cell

Question 19

What are some examples of anchoring/strengthening junctions

Answer 19

Adheren junctions
Desmosome
Hemidesmosome
Focal Adhesion

Question 20

What do adherents do and what are they composed of

Answer 20

Bridge between epithelial cells

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

Question 21

What do focal adhesions do and what are they composed of

Answer 21

Attach epithelial cell to basal lamina

Actin filaments
integrin
Focal adhesion kinase
(Slide 15)

Question 22

What do hemidesmosomes do and what are they composed of

Answer 22

Attach epithelial cell to basal lamina

intermediate filaments
integrin/collagen
Dystonin
(Slide 15)

Question 23

What do desmosomes do and what are they composed of

Answer 23

Strengthen gaps between cells

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

Question 24

What do cadherins do

Answer 24

Mediate cell-cell attachment
(slide 16)

Question 25

What do Adherens do

Answer 25

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

Question 26

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

Answer 26

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

Question 27

What do desmosomes do

Answer 27

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

Question 28

What do integrins do

Answer 28

Mediate cell-matrix contacts (slide 21)

Question 29

What is an example of a disease with defective desmosomes

Answer 29

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

Question 30

What are occluding junctions specialised for

Answer 30

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

Question 31

What do some occluding and tight junctions help do

Answer 31

Maintain cell polarity

Question 32

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

Answer 32

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)

Question 33

What do channel-forming junctions allow

Answer 33

ions and small molecules to pass directly from cell to cell

Question 34

What is an example of channel-forming junctions

Answer 34

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)

Question 35

What are some inherited disorders from abnormal gap junctions

Answer 35

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

Question 36

What are channel-forming junctions in plants called

Answer 36

Plasmodesmata

Question 37

structure of signal-relaying junctions

Answer 37

SLIDE 32!!!!!

Question 38

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

Answer 38

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

Question 39

How are epithelial tubes formed

Answer 39

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