PSC2002/L04 Structure & Function of Epithelia

Question 1

Describe the structure of epithelia. (3)

Answer 1

Sheet-like structure
Line external and internal surfaces
Internal called endothelium

Question 2

What percentage of human cancers originate from epithelial origin?

Answer 2

85%

Question 3

Give 3 functions of epithelia.

Answer 3

Protection
Filtration (kidney tubule lining)
Exchange (alveoli)
Absorption (intestine)
Sensation (taste)
Secretion (gland lining)

Question 4

What is the function of simple squamous epithelia? (3)

Answer 4

Absorption
Filtration
Minimal barrier to diffusion

Question 5

Where is simple squamous epithelium found? (2)

Answer 5

Capillaries
Abdominal and pleural cavities (mesothelium)

Question 6

What is the function of simple cuboidal epithelia? (2)

Answer 6

Secretion
Transportation

Question 7

Where is simple cuboidal epithelium found? (3)

Answer 7

Glands & ducts
Kidney tubules
Ovaries

Question 8

Which kind of epithelium can be ciliated or non-ciliated?

Answer 8

Simple columnar

Question 9

What is the function of simple columnar epithelia? (3)

Answer 9

Absorption
Protection
Secretion

Question 10

Where is simple columnar epithelium found?

Answer 10

Digestive tract

Question 11

What is the function of stratified squamous epithelia?

Answer 11

Protection

Question 12

Where is stratified epithelium found? (4)

Answer 12

Skin
Mouth
Upper throat
Oesophagus

Question 13

Which kind of epithelia can be keratinised or non-keratinised?

Answer 13

Stratified squamous

Question 14

What is the function of pseudostratified columnar epithelia? (2)

Answer 14

Absorption
Protection

Question 15

Where is pseudostratified columnar epithelium found? (2)

Answer 15

Upper respiratory tract
Trachea

Question 16

Where is transitional epithelia found? What is its function?

Answer 16

Bladder
Stretchable layer

Question 17

How do epithelia form a functional unit?

Answer 17

Attached to extracellular matrix of basal lamina

Question 18

Give 3 specialised structures that link epithelial cells to one another.

Answer 18

Tight junctions
Anchoring junctions
Channel forming junctions

Question 19

Describe tight or occluding junctions. (3)

Answer 19

Membrane proteins seal adjacent cells together
Ensure molecules cannot leak freely between cells
Prevent lateral migration of membrane proteins (creating membrane domains/polarity)

Question 20

What is the difference between claudins and occludins?

Answer 20

Claudins have multiple isoforms
Claudins create physical barrier that regulate permeability
Occludins are single type of protein
Role of occludins less clear

Question 21

What does the resistance of epithelia correlate to?

Answer 21

Leakiness of epithelia
High resistance = tight junction

Question 22

What defines whether an epithelial junction is tight or leaky?

Answer 22

Presence of Cld3 or Cld2 with Cld1
Cld1 + Cld3 = tight
Cld1 + Cld2 = leaky

Question 23

How is Claudin-2 introduced into Madin-Darby Canine Kidney I cells?

Answer 23

Using mRNA

Question 24

What is the function of anchoring junctions? (3)

Answer 24

Provide mechanical stability
Anchor cells to basal lamina and other cells
Allows functioning as a cohesive unit

Question 25

What are anchoring junctions categorised by?

Answer 25

Type of cytoskeletal filament they interact with

Question 26

What are: a) cell-cell b) cell-basal lamina actin junctions called?

Answer 26

a) Adherens junction b) Focal adhesion

Question 27

What are a) cell-cell b) cell-basal lamina intermediate junctions called?

Answer 27

a) Desmosomes b) Hemidesmosomes

Question 28

Describe the basal lamina. (2)

Answer 28

40-120nm thick Strong, flexible foundation underlying all epithelia

Question 29

What 4 materials make up the basal lamina?

Answer 29

Laminin Type IV collagen Entactin Perlecan

Question 30

What is the basement membrane?

Answer 30

Combination of basal lamina and reticular lamina

Question 31

What is the reticular lamina mainly composed of?

Answer 31

Type II collagen

Question 32

What is the function of gap/channel-forming junctions? (2)

Answer 32

Allow diffusion between cells Enable cell-cell communication

Question 33

What is an Ussing chamber used for? (2)

Answer 33

Measure resistance of ion transport Determine what ion channels are present (and concentration/expression)

Question 34

Why is frog skin a good model system?

Answer 34

Frogs are able to absorb Na+ from salty water across skin

Question 35

What happens when frog skin is dissected and mounted as a flat sheet containing solution of identical composition?

Answer 35

Transepithelial potential difference due to active transepithelial movement

Question 36

What happens when an epithelial cell is polarised?

Answer 36

Transepithelial voltage generated

Question 37

What is the equation for transepithelial voltage?

Answer 37

V(te) = V(bl) - V(ap)

Question 38

What is the voltage outside and inside of the epithelia?

Answer 38

Apical -158mV Basolateral 0mV

Question 39

What is the voltage inside of the epithelia?

Answer 39

-92mV

Question 40

What is amiloride used for?

Answer 40

Chemical probe for apical Na+ channel?

Question 41

What is ouabain used for?

Answer 41

Na+/K+ ATPase inhibitor

Question 42

What is barium used for?

Answer 42

Blocking K+ channels