Ctb009 - Cell Junctions And Epithelia

Front 1

What are the four basic types of tissue?

Back 1

connective tissue
nervous tissue
muscular tissue
epithelial tissue

Front 2

What germ layers does epithelial tissue arise from? How does it differ from connective tissue?

Back 2

All three germ layers.

ET = entirely cellular with the only connective tissue being the basement membrane

CT = very few cells, lots of extracellular matrix

Front 3

What are the functions of the epithelial tissue?

Back 3

1) protection
2) diffusion
3) absorption
4) secretion
5) excretion
6) sensation

Front 4

What are the characteristics of epithelial tissue?

Back 4

1) polarized: apical, basal, lateral surfaces
2) avascular
3) basement membrane: extracellular matrix where basal cell layer rests

Front 5

How is epithelial tissue classified?

Back 5

1) number of cell layers
2) shape of cells
3) presence of cell surface modifications

Front 6

What are ways to characterize the number of cellular layers in epithelial tissue?

Back 6

1) simple = single layer
2) stratified = 2+ layers, only basal layer contacts basement membrane
3) pseudostratified = all cells contact basement membrane, never ciliated

Front 7

Describe transitional epithelium.

Back 7

stratified epithelium

# of cell layers differs btn when the epithelium is relaxed or stretched

found only in urinary tract

Front 8

How is the shape of epithelial cells characterized?

Back 8

- squamous: flat, diffusion-friendly
- cuboid: cube-shaped
- columnar: rhomboid-shaped; high metabolic function-friendly

Front 9

How are stratified epithelia named?

Back 9

the shape of the cells in the most superficial layer dictate the name of the epithelium (eg, stratified squamous)

Front 10

What types of cell surface specializations are present in epithelium? What do they do?

Back 10

- keratinized/cornified epithelium: keratin-covered outermost surface provides tough, water-resistant, non-living surface
- glycocalyx: carbohydrate-rich complex; protects and recognizes

Front 11

Describe cilia.

Back 11

- motile structures propel extracellular material through a tube
- anchor = basal body/centriole (9 microtubule triplets beneath cell membrane)
- 2 central microtubules, 9 microtubule+dynein arms project outward (axoneme)

Front 12

Where are cilia found in the body?

Back 12

respiratory tract, oviduct

Front 13

What is a flagellum?

Back 13

highly elaborated cilia, used for cellular locomotion

Front 14

Describe microvilli.

Back 14

- small finger-like projections of plasma membrane
- increase surface area for absorption
- found mostly in intestinal tract
- contains actin cross-linked by villin

Front 15

What do lateral cell membrane specializations do?

Back 15

- maintain coherence
- provide communication
- distribute stress among cells of epithelium
- only seen with electron microscope

Front 16

Describe tight junctions/zonula occludens.

Back 16

- selectively permeable layer surrounding each cell
- only water and small solutes pass between cells
- important for transcellular transport
- dark-light-dark-light-dark light appearance under electron microscope

Front 17

Describe tight junction proteins.

Back 17

- occludin, claudin, junctional adhesion molecule (JAM)
- regulate passage of solute molecules
- interact with specialized proteins in sub-plasmalemmal plaque termed zonula occludens proteins (ZOs)
- tight junction transmembrane proteins interact with actin cytoskeleton via ZOs

Front 18

Describe the adherens junction/zonula adherens.

Back 18

- beneath tight junctions
- anchoring junction
- surrounds cell

Front 19

Describe the three components of the adherens junction.

Back 19

1) cadherin
- transmembrane linker protein
- Ca-2+ dependent
- cell adhesion molecule (CAM)

2) catenin-filled plaques
- catenin = <-actinin, vinculin, etc
- sub-plasmalemmal plaque proteins

3) actin microfilaments
- cytoskeletal filaments

Front 20

What are the prominent cadherins found in the human body?

Back 20

- E-cadherin (epithelium)
- N-cadherin (neurons, heart, sk mm, lens, fibroblasts)
- P-cadherin (placenta, epidermis, breast epithelium)
- VE-cadherin (endothelial cells)

Front 21

Describe the macula adherens/desmosome.

Back 21

- anchoring junction
- spots; do NOT surround cell
- transmembrane linker proteins = desmogleins & desmocollins
- plaque proteins = desmoplakin, plakoglobin, plakophilin
- keratin = intermediate filament

Front 22

Describe gap junctions.

Back 22

- communicating junctions
- 6 connexin proteins per connexon
- 2 connexons
- ~1.5nm = 1500 kDa molecules can pass
- important for cardiac, smooth mm myocytes
- NO plaque, cytoskeletal protein associated with connexons

Front 23

What type of junctions are basal membrane specializations? What types are there?

Back 23

- anchoring junctions
1) hemidesmosomes = 1/2 desmosomes;
- linker proteins = integrins → attach to laminin, collagen, fibronectin
2) adhesion plaques = contain <-actinin & vinculin → attach to actin;
- linker protein = integrin

Front 24

What is a junctional complex?

Back 24

group of cell membrane specializations along lateral surface of epithelial cells

Front 25

Describe epithelial cells.

Back 25

- self-replacing in adults
- turnover rate depends on location and function
(skin = 28 days, small intestine = 5 days)

Front 26

What is metaplasia?

Back 26

change in epithelial cells to a biochemically different cell type

Front 27

What are carcinomas?

Back 27

malignant tumors of epithelial cells

Front 28

What are adenocarcinomas?

Back 28

malignant tumors of epithelial glandular cells

Front 29

What percentage of cancers do carcinomas and adenocarcinomas comprise? Why?

Back 29

- 85% of all cancers
- mitotic activity; role as barrier

Front 30

How is the origin of the tumor determined?

Back 30

immunohistochemical staining to detect the type of intermediate filament proteins present in the tumor
e.g., epithelium tumors have keratin, glial tumors have glial fibrillary acidic protein, muscle tumors have desmin, CT tumors have vimentin