Epithelia I, II, III

Question 1

7 general functions of Epithelia

Answer 1

1. Barrier
2. Selective absorption and transport of molecules
3. Selective secretion
4. Movement of particles and mucous
5. Biochemical modification
6. Communication to/from tissues/organs
7. Reception of sensory stimuli

Question 2

How does the naming convention of epithelia occur?

Answer 2

Epithelia classified on:

1. # layers
2. cell shape relative to apical basal sides
3. Stratified epithelia are named based on outermost layer of epithelia
   (e. g. stratified squamous epithelia have a squamous outer layer, though inner cells are often cuboidal))

Question 3

Describe structural arrangement/polarity of epithelia

Answer 3

surface that faces lumen = apical surface
surface that faces towards CT = basal surface

Most epithelial cells have polarity -
-molecular/protein comp on apical and basal side are diff due to tight junctions

Question 4

What does the polarity of epithelia allow for?

Answer 4

transcytosis: The endocytosis of substances from one membrane region, followed by trans-cellular transport of the vesicles and their exocytosis from another membrane

Question 5

Describe pseudostratified epithelium

Answer 5

consists of a falsely-stratified single layer of epithelia

• appear stratified bc cells have diff heights
• all cells sit on basement membrane, but not all reach apical surface
• nuclei are staggard

examples: trachea, vas deferens, epididymus

Question 6

general structural relationships (orientation) to other structures

Answer 6

• The basal surface of the epithelia overlies and is attached to the basal lamina
• The epithelia and basal lamina also attaches to CT.
• CT contains blood vessels, muscles and nerves

Question 7

Are epithelial cells highly vascular or have no vascular supply?

Answer 7

No inbuilt vascular supply.

-Blood needs to diffuse through the connective tissue to reach the epithelia.

Question 8

Describe epithelial-to-mesenchymal transition

-why is this important in cancer studies?

Answer 8

during development, primitive epithelial cells become mesenchymal cells, infiltrate the epithelial layer and migrate through the body to form new regions of epithelia

• tumors do this - reactivate mesenchymal transition, migrate through the body, and metastasize their evil little hearts out

Question 9

List the different types of cell junctions

Answer 9

1. Tight junctions (zonula occludens)
2. Adherence junctions ( zonula adherens)
3. Desmosomes (macula adherens)
4. Gap junctions

Question 10

Tight junctions

Answer 10

Zonula occludens
- made of occludins and claudins

• Wraps all around cell
• Hold adjacent epithelial cells together
• provides highly selective barrier that limits/prevents diffusion of membrane proteins
• the basis of impermeability of epithelia: it forces substances in the lumen (water, ions, etc) to go through the cells as opposed to between them to get into the basal surfaces.

Question 11

Adherence junctions

Answer 11

zonula adherens
-made of cadherins that link to actin filaments

• promote attachment and polarity of membrane

Question 12

Desmosomes

Answer 12

macula adherens

-made of cadherins (diff from that of adherence junctions) that link to intermediate filaments

Question 13

cadherins

Answer 13

Make up adjacent junction and desmosomes.
transmembrane proteins with extracellular domains that interact with eachother in presence of calcium

cytoplasmic tails that bind adapters and controls various aspects of epithelial polarity , development, and function

Question 14

gap junctions

Answer 14

small “tunnel” or channel between 2 adjacent cells.

promotes rapid communication between epithelial cells through diffusion of ions/small molecules (signaling molecules)

Question 15

types and functions of different cell surface modifications on epithelial cells

Answer 15

1. microvilli: cell surface protrusions containing actin meant to increase surface area (more efficient membrane transport/secretion)
2. cilia: protrusions containing microtubules powered by dynein. Moves substances by rhythmic motion.

Question 16

stereocilia

Answer 16

unusual type of microvillus found in epididymus and sensory cells in ear.

• extremly long, actin filled microvilli
• NOT related to cilia

Question 17

3 kinds of cilia

Answer 17

1. primary cilium: promote signal transduction
   - non motile
2. motile cilia: cilia wave like boat oar to move shit
3. sensory cilia: sensory reception
   - non motile

Question 18

basal laminae structure

Answer 18

thin sheet of extracellular material formed by special fibrous protein, collagen, interwoven with glycoproteins.

Question 19

7 functions of basal laminae

Answer 19

1. mediate attachment of epi to underlying CT
2. selective filtration of substances diffusing to/from epithelia
3. necessary for establishment/maintenance of epithelial cell polarity
4. serve as “highways” for migration of cells through CT
5. barrier to invading microbes/cancer
6. control gene expression
7. controls development, morphogenesis, organization, repair by providing scaffold

Question 20

How do epithelial cells directly connect to basal laminae?

Answer 20

by attachment to hemidesmosomes and focal adhesions on basal surface via integrins

Question 21

Integrins of hemidesmosomes and focal adhesions connect to ______

Answer 21

• integrins of hemidesmosomes connect to intermediate filament
• integrins of focal adhesions connect to actin

Question 22

How did exocrine glands develop?
- How do they secrete material?
(What membrane do they HAVE to cross to get ‘outside’ of epithelial cells?)

Answer 22

Simple invaginations of epithelium (still in contact with epi)

• Secrete molecules onto epithelial surface
  via Apical membrane using secretory units
  (unidirectional)

Question 23

types of exocrine secretions

Answer 23

1. mucus secretions

2. serous secretions (watery, sweat, saliva)

Question 24

How did endocrine glands develop?

How do they secrete material?

Answer 24

Invaginations of epithelium that pinch off from epithelial surface (surrounded by blood vessels in CT)

-secrete molecules (hormones) into blood supply by crossing BASAL surface

Question 25

Secretions from both exocrine and endocrine glands are generally regulated by what?

Answer 25

Autonomic nervous system

Question 26

How are epithelial tissues maintained and regulated?

Answer 26

1. Most epithelia have self-renewing potential via stem cells at the base of crypts
2. new cells push up old cells and old cells migrate towards apical direction
3. Regulation via signaling pathways:
   
   • ie: Wnt proteins (which can stimulate/inhibit differentiation depending on location)

Question 27

What protein inhibits Wnt pathway? What happens to epithelial cell regulation if the protein is knocked out.

Answer 27

APC.

if it is knocked out, cell proliferation can occur

Question 28

Key principles of signaling pathways

Answer 28

1. each pathway is used by multiple, distinct stem cell systems in different organs/tissues
2. single signaling pathway often triggers different developmental outcomes in different stem cell lineages

Question 29

Term for all cancer of epithelial origin

-how are they used in diagnosis

Answer 29

carcinoma

(most common cancers by far are derived from epithelial tissue)

-often retain some properties of their tissue of origin: diagnosis aided by histological appearance

Question 30

Term for cancers derived from glandular epithelia

Answer 30

adenocarcinoma

Question 31

What are carcinomas believed to be a result of?

Answer 31

Carcinomas result from defect in regulatory pathways that control epithelial stem cells or their progeny during tissue development and maintenance.

Question 32

how are tissue sections made?

Answer 32

1. tissue sample is cut (very thinly)
2. put in saline buffer
3. fix to slides

Question 33

In histology stains, anything that doesn’t bind will appear how?

Answer 33

it will not show up dark

-no stain

Question 34

Describe staining with antibodies (immunohistology).

Answer 34

1. after fixing and staining, apply “primary antibody” (antibody that sticks to the protein you want to look at).
2. Wash off the excess, then add “secondary antibody” (antibody that sticks to the primary antibody, which is also linked to either a fluorescent tag or an enzyme that produces a colored product).
3. Then you wash off the unbound secondary enzyme, and look at either the fluorescence or the color against the background of the cells.

Question 35

Common tissue layer framework?

Answer 35

1. Mucosa - carries outer epithelium and a underlying CT layer (lamina propria). Immune function
2. Submucosa - deeper, denser, CT with embedded tissues. supportive role.