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30 Cards in this Set

  • Front
  • Back
What are the four basic types of tissue?
connective tissue
nervous tissue
muscular tissue
epithelial tissue
What germ layers does epithelial tissue arise from? How does it differ from connective tissue?
All three germ layers.

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

CT = very few cells, lots of extracellular matrix
What are the functions of the epithelial tissue?
1) protection
2) diffusion
3) absorption
4) secretion
5) excretion
6) sensation
What are the characteristics of epithelial tissue?
1) polarized: apical, basal, lateral surfaces
2) avascular
3) basement membrane: extracellular matrix where basal cell layer rests
How is epithelial tissue classified?
1) number of cell layers
2) shape of cells
3) presence of cell surface modifications
What are ways to characterize the number of cellular layers in epithelial tissue?
1) simple = single layer
2) stratified = 2+ layers, only basal layer contacts basement membrane
3) pseudostratified = all cells contact basement membrane, never ciliated
Describe transitional epithelium.
stratified epithelium

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

found only in urinary tract
How is the shape of epithelial cells characterized?
- squamous: flat, diffusion-friendly
- cuboid: cube-shaped
- columnar: rhomboid-shaped; high metabolic function-friendly
How are stratified epithelia named?
the shape of the cells in the most superficial layer dictate the name of the epithelium (eg, stratified squamous)
What types of cell surface specializations are present in epithelium? What do they do?
- keratinized/cornified epithelium: keratin-covered outermost surface provides tough, water-resistant, non-living surface
- glycocalyx: carbohydrate-rich complex; protects and recognizes
Describe cilia.
- 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)
Where are cilia found in the body?
respiratory tract, oviduct
What is a flagellum?
highly elaborated cilia, used for cellular locomotion
Describe microvilli.
- small finger-like projections of plasma membrane
- increase surface area for absorption
- found mostly in intestinal tract
- contains actin cross-linked by villin
What do lateral cell membrane specializations do?
- maintain coherence
- provide communication
- distribute stress among cells of epithelium
- only seen with electron microscope
Describe tight junctions/zonula occludens.
- 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
Describe tight junction proteins.
- 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
Describe the adherens junction/zonula adherens.
- beneath tight junctions
- anchoring junction
- surrounds cell
Describe the three components of the adherens junction.
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
What are the prominent cadherins found in the human body?
- E-cadherin (epithelium)
- N-cadherin (neurons, heart, sk mm, lens, fibroblasts)
- P-cadherin (placenta, epidermis, breast epithelium)
- VE-cadherin (endothelial cells)
Describe the macula adherens/desmosome.
- anchoring junction
- spots; do NOT surround cell
- transmembrane linker proteins = desmogleins & desmocollins
- plaque proteins = desmoplakin, plakoglobin, plakophilin
- keratin = intermediate filament
Describe gap junctions.
- 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
What type of junctions are basal membrane specializations? What types are there?
- 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
What is a junctional complex?
group of cell membrane specializations along lateral surface of epithelial cells
Describe epithelial cells.
- self-replacing in adults
- turnover rate depends on location and function
(skin = 28 days, small intestine = 5 days)
What is metaplasia?
change in epithelial cells to a biochemically different cell type
What are carcinomas?
malignant tumors of epithelial cells
What are adenocarcinomas?
malignant tumors of epithelial glandular cells
What percentage of cancers do carcinomas and adenocarcinomas comprise? Why?
- 85% of all cancers
- mitotic activity; role as barrier
How is the origin of the tumor determined?
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