Lecture 2- Epithelial tissues

Question 1

What are the two main criteria of epithelial classification?

Answer 1

1) SHAPE
    squamous
    cuboidal
    columnar
2) LAYERING
    single layer= simple
    multi-layered= stratified

Question 2

Where can you find simple squamous epithelia and why?

Answer 2

lung alveolar epithelium, mesothelium (lies body cavities) and endothelial lining of blood vessels
- thin = allows exchange to occur

Question 3

Where can you find simple cuboidal epithelia?

Answer 3

kidney collecting duct, other ducts

Question 4

Where can you find simple columnar epithelia?

Answer 4

enterocytes, other absorptive and secretory epithelia

Question 5

What are the two main types of stratified squamous epithelia and where an you find them?

Answer 5

1) Keratining: epidermis (skin) (nuclei are not visible)

2) Non-Keratinising: lining of mouth, oesophagus, anus, cervix, vagina (nuclei are visible)

Question 6

What is pseudo stratified epithelium and where can it be found?

Answer 6

= falsely stratified, looked multi-layered but surface cells have contact with basal lamina
- tracheal/ bronchial epithelium, ducts in the urinary and reproductive tracts

Question 7

What is the importance of epithelial polarity?

Answer 7

• To give directionality to epithelial function
• need plasma membrane polarity for this
• apical vs basolateral domains

Question 8

How is this polarity established?

Answer 8

• Have belt junctions which seal off the paracellular pathway and helps maintain conc gradients
• tight junctions form focal connections between membranes of adjacent cells
• TJ strands interact with proteins (Claudine & occludin)

Question 9

What are the gate and fence functions of tight junctions?

Answer 9

Gate- sealing off the paracellular pathway

Fence- segregating the apical and basolateral polarity

Question 10

How can membrane polarity polarity be maintained?

Answer 10

• Have pumps on only one side= uni-directional flow of ions and molecules
• Have secretory vesicles only on one side
• lots of mitochondria near secretory domain for AT of molecules across membranes

Question 11

What are the major epithelial functions?

Answer 11

• Absorptive epithelium (PCT)
• Fluid transporting (DCT)
• Selectively permeable (Thin limb of LoH)
• Secretory (pancreas)
• Protective

Question 12

What are the features of Transpoting epithelium?

Answer 12

• high conc of ion transporters
• Mitochondria associated with basal membrane to provide energy for AT
• Basal membrane infoldings, increase SA for pumping ions & water
  Ions transported from APICAL -(DCT lumen) -> BASAL (capillary)

Question 13

What are the features of absorptive epithelium?

Answer 13

e. g. Enterocytes
- villi and microvilli to increase SA for absorption
e. g. PCT lumen
- brush border made of microvilli

Question 14

What are the features of secretory epithelium? Give example of where they can be found

Answer 14

Pancreas:
1) Exocrine: secreted into duct
Secretion: BASAL (capillary)–> APICAL (lumen)
- secretory granules found in apical cytoplasm
- RER found in basal
2) Endocrine: secreted into bloodstream
Secretion: APICAL –> BASAL (capillary)
-secretory granules found in basal cytoplasm
- RER found in apical

Question 15

What are the different classes of secretion?

Answer 15

Endocrine vs Exocrine

Constitutive vs Stimulated

Question 16

What are the two different types of protective epithelia?

Answer 16

Keratinising: no nuclei (dry surfaces)

Non-keratinising: nuclei visible in surface cell layers (surface vulnerable to chemical damage)

Question 17

What happens when there are defects in cytokeratins or cell junctions?

Answer 17

Blistering diseases–> damage to fragile epidermal cells

Question 18

What links ECM to cells

Answer 18

Hemidesmosomes

Question 19

Describe how villus cells are regenerated

Answer 19

• New cells produced in Crypt of Leiberkhun by stem cells
• Cells move up along villus
• Cells then die and are lost at the tip of the villus

Question 20

What happens when cell- turnover is unbalanced in the intestines?

Answer 20

Cell loss> proliferation = villi shorten (cancer drugs do this)
Cell proliferation > cell loss = too much tissue (benign tumour, polyp)

Question 21

Describe how epidermal cells are regenerated

Answer 21

• Surface cells are continuously lost
• new cells formed on basal layer which migrate up
• Flatten out and differentiate on the way (e.g. keratinise)

Question 22

What causes a callus?

Answer 22

• constant abrasion stimulates cells to divide
• proliferation > loss
• -> increase in tissue mass

Question 23

Give an example of an infectious agent affecting epidermal turnover

Answer 23

HPV- hijacks cell proliferation machinery

• increased cell proliferation
• –> warts

Question 24

When might changes to steady state be physiologically normal?

Answer 24

1) Mentrual cycle- changes to endometrial epithelial lining

2) Pregnancy- increase in epithelial glands of breast