Epithelia I, II, III Flashcards
7 general functions of Epithelia
- Barrier
- Selective absorption and transport of molecules
- Selective secretion
- Movement of particles and mucous
- Biochemical modification
- Communication to/from tissues/organs
- Reception of sensory stimuli
How does the naming convention of epithelia occur?
Epithelia classified on:
- # layers
- cell shape relative to apical basal sides
- 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))
Describe structural arrangement/polarity of epithelia
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
What does the polarity of epithelia allow for?
transcytosis: The endocytosis of substances from one membrane region, followed by trans-cellular transport of the vesicles and their exocytosis from another membrane
Describe pseudostratified epithelium
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
general structural relationships (orientation) to other structures
- 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
Are epithelial cells highly vascular or have no vascular supply?
No inbuilt vascular supply.
-Blood needs to diffuse through the connective tissue to reach the epithelia.
Describe epithelial-to-mesenchymal transition
-why is this important in cancer studies?
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
List the different types of cell junctions
- Tight junctions (zonula occludens)
- Adherence junctions ( zonula adherens)
- Desmosomes (macula adherens)
- Gap junctions
Tight junctions
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.
Adherence junctions
zonula adherens
-made of cadherins that link to actin filaments
- promote attachment and polarity of membrane
Desmosomes
macula adherens
-made of cadherins (diff from that of adherence junctions) that link to intermediate filaments
cadherins
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
gap junctions
small “tunnel” or channel between 2 adjacent cells.
promotes rapid communication between epithelial cells through diffusion of ions/small molecules (signaling molecules)
types and functions of different cell surface modifications on epithelial cells
- microvilli: cell surface protrusions containing actin meant to increase surface area (more efficient membrane transport/secretion)
- cilia: protrusions containing microtubules powered by dynein. Moves substances by rhythmic motion.
stereocilia
unusual type of microvillus found in epididymus and sensory cells in ear.
- extremly long, actin filled microvilli
- NOT related to cilia
3 kinds of cilia
- primary cilium: promote signal transduction
- non motile - motile cilia: cilia wave like boat oar to move shit
- sensory cilia: sensory reception
- non motile
basal laminae structure
thin sheet of extracellular material formed by special fibrous protein, collagen, interwoven with glycoproteins.
7 functions of basal laminae
- mediate attachment of epi to underlying CT
- selective filtration of substances diffusing to/from epithelia
- necessary for establishment/maintenance of epithelial cell polarity
- serve as “highways” for migration of cells through CT
- barrier to invading microbes/cancer
- control gene expression
- controls development, morphogenesis, organization, repair by providing scaffold
How do epithelial cells directly connect to basal laminae?
by attachment to hemidesmosomes and focal adhesions on basal surface via integrins
Integrins of hemidesmosomes and focal adhesions connect to ______
- integrins of hemidesmosomes connect to intermediate filament
- integrins of focal adhesions connect to actin
How did exocrine glands develop?
- How do they secrete material?
(What membrane do they HAVE to cross to get ‘outside’ of epithelial cells?)
Simple invaginations of epithelium (still in contact with epi)
- Secrete molecules onto epithelial surface
via Apical membrane using secretory units
(unidirectional)
types of exocrine secretions
- mucus secretions
2. serous secretions (watery, sweat, saliva)
How did endocrine glands develop?
How do they secrete material?
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
Secretions from both exocrine and endocrine glands are generally regulated by what?
Autonomic nervous system
How are epithelial tissues maintained and regulated?
- Most epithelia have self-renewing potential via stem cells at the base of crypts
- new cells push up old cells and old cells migrate towards apical direction
- Regulation via signaling pathways:
- ie: Wnt proteins (which can stimulate/inhibit differentiation depending on location)
What protein inhibits Wnt pathway? What happens to epithelial cell regulation if the protein is knocked out.
APC.
if it is knocked out, cell proliferation can occur
Key principles of signaling pathways
- each pathway is used by multiple, distinct stem cell systems in different organs/tissues
- single signaling pathway often triggers different developmental outcomes in different stem cell lineages
Term for all cancer of epithelial origin
-how are they used in diagnosis
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
Term for cancers derived from glandular epithelia
adenocarcinoma
What are carcinomas believed to be a result of?
Carcinomas result from defect in regulatory pathways that control epithelial stem cells or their progeny during tissue development and maintenance.
how are tissue sections made?
- tissue sample is cut (very thinly)
- put in saline buffer
- fix to slides
In histology stains, anything that doesn’t bind will appear how?
it will not show up dark
-no stain
Describe staining with antibodies (immunohistology).
- after fixing and staining, apply “primary antibody” (antibody that sticks to the protein you want to look at).
- 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).
- Then you wash off the unbound secondary enzyme, and look at either the fluorescence or the color against the background of the cells.
Common tissue layer framework?
- Mucosa - carries outer epithelium and a underlying CT layer (lamina propria). Immune function
- Submucosa - deeper, denser, CT with embedded tissues. supportive role.
