LEC 6: Epithelial Cell Specialization - 08.19.2014 Flashcards
1
Q
Where are epithelial cell specializations found
A
- Intercellular surfaces (between cells)
- Luminal surfaces
- Basal surfaces
2
Q
What epithelial cell specializations are found on/near intercellular surfaces and what is their purpose
A
- occluding, adhering, and communicating junctions
- permit epithelia to form a continuous, cohesive layer so that all cells can communicate
3
Q
What epithelial cell specializations are found on luminal surfaces
A
cilia, microvilli, stereocilia
4
Q
What epithelial cell specializations are found on basal surfaces
A
basement membrane and hemidesmosomes
5
Q
Occluding (Tight) Junctions
A
- seal intercellular spaces so that luminal contents can’t get between cells
- located directly below luminal surface of simple columnar epithelium
- e.g. intestinal lining
6
Q
What proteins make up occluding (tight) junctions
A
Claudin and Occludin
7
Q
zonula occludens
A
- each tight junction forms a continuous circumferential band or zonule around cell
- “occludens zone”
8
Q
Adhering Junctions: 2 types
A
- bind epithelial cells together
- act as anchorage site for cytoskeleton of each cell
- two types:
- zonula adherens - below luminal surface, deep to zonula occludens
- desmosomes - deep to zonula adherens, as well as widely scattered elsewhere in epithelial intercellular surfaces
9
Q
zonula adherens
A
- form strong bond between adjacent cells
- transcellular network
- located deep to zonula occludens
- Purpose/location (protein):
- transmembrane (cadherins)
- cystoplasmic face (actin filaments)
- attachment proteins (catenins, vinculin, alpha-actinin)
10
Q
Desmosomes (macula adherens)
A
- provide structural integrity
- large number in stratified squamous
- located deep to adhering junctions, scattered
- Purpose/location (protein):
- intercellular (desmocollins)
- transmembrane (desmogleins)
- plaque (desmoplakin, keratin)
11
Q
macula
A
Latin, “spot”
12
Q
Junctional Complex
A
- combination of zonula occludens (ZO), zonula adherens (ZA), and desmosomes
- divides plasma membrane of cell into apical and basolateral surfaces
- desmosomes widely scattered in epithelial tissues
13
Q
location of junctions beyond epithelial cells
A
adhering junctions (ZA, desmosomes) and communicating (gap) junctions are not exclusive to epithelia and are also present in cardiac, visceral muscle
14
Q
What proteins are associated with tight junctions
A
- occludin
- claudin
- cingulin
- ZO proteins
15
Q
What proteins are associated with adhering junctions (zonula adherens)
A
- actin filaments
- cadherins
- vinculin
- catenins
- alpha-actinin
16
Q
What proteins are associated with macula adherens (desomosomes)
A
- intermediate filaments
- tonofilaments
- cytokeratins
- desmoplakins
- desmoscollins
- desmogleins
17
Q
What does this slide depict
A
Simple columnar epithelial cells and the junctional complex (terminal bar)
18
Q
Terminal Bar
A
Zonula Occludens, Zonula Adherens, Macula Adherens (Desmosomes)
19
Q
Gap Junctions
also called: Communicating Junctions, Nexus Junctions
A
- communication between cells
- numerous in embryonic tissues
- located below junctional complex (ZO, ZA, macula adherens)
- regulate: Ca++, pH, cAMP
- Purpose/Location (protein):
- composition (connexon-6)
- transmembrane proteins (connexin, 24 genes known)
20
Q
What affects the permeability of gap junctions
A
- pH
- Calcium (will close if too high)
- ion concentration
- cAMP
- selectively permeable to (<1500 MW):
- positively charged ions
- amino acids
- sugar
- vitamins
- hormones
21
Q
What are the two (2) epithelial cell specializations at the basal surface
A
- hemidesmosomes
- basement membrane
22
Q
Hemidesmosomes
A
- anchor cytoskeleton at base of the cell to the basement membrane
- located at basal plasma membrane
- Purpose/location (protein):
- composition (integrins, laminin)
23
Q
Basement membrane
A
- physical support
- cell attachment
- selective barrier
- growth and differentiation
- special functions:
- ultrafiltration in kidney
- blood-air barrier (lung)
- tumor metastasis
24
Q
What color is the basement membrane in Azan stain
A
blue
25
Composition of the basement membrane
* **Type IV collagen** (Exclusive to BM)
* **Laminin** (binds collagen to BM)
* **Proteoglycans**
* **Entactin** (binds laminin to Type IV collagen)
* **Fibronectin** (binds integrins of plasma membrane, produced by fibroblasts of the connective tissue)
* **Type VII collagen** (binds basal lamina to subjacent collagen)
26
Basal Lamina
* **Type IV collagen** (Exclusive to BM)
* **Laminin** (binds collagen to BM)
* **Proteoglycans**
* **Entactin** (binds laminin to Type IV collagen)
* **Fibronectin** (binds integrins of plasma membrane, produced by fibroblasts of the connective tissue)
* **Type VII collagen** (binds basal lamina to subjacent collagen)
NB: actually 3 layers of basal lamina seen in electron micrograph, but all represents the 1 layers seen in light microscope
27
Cilia
* simple cuboidal and simple columnar cells
* up to 300/cell at apical surface for movement
* functions include cleaning airways, transporting ovum
28
Label the parts of the cilia
A. Plasma membrane
B. Peripheral microtubule doublet (9 pairs)
C. Central microtubule pair
D. Basal body
E. Plasma membrane
F. Microtubule triplet (9 pairs)
29
What protein makes up the microtubules found in cilia
Tubulin
30
What protein makes up the thin filaments found in microvilli
Actin
31
Differences between cilia and microvilli
* microvilli MUCH shorter than cilia
* microvilli does not have active motion (no ATP)
32
What type of cells are these and what are their distinguishing characteristics (hint: trachea slide)
* Pseudostratified ciliated columnar
* purpose of cilia at apical surface is to move along mucus and entrapped particles
33
What type of cells are these and what are their distinguishing characteristics (hint: oviduct slide)
* ciliated columnar epithelial cells
* cannot be pseudostratified ciliated columnar because this isn't the trachea
34
Microvilli
* about 1mm (micrometer) in length
* composed of 20-30 actin filaments
* covering of microvilli is glycoprotein, glycocalyx
* contract and elongate to prevent clogging, no ATPase
35
Terminal Web
* found at apical surface in cells with microvilli
* actin filaments stabilized by spectrin
* anchors terminal web to apical cell membrane
* when contracted, terminal web causes decrease in diameter of apex of the cell
* microvilli spread apart, aiding in absorption
36
Striated border
* also known as brush border
* microvilli covered surface of simple cuboidal and simple columnar epithelium cells
* brush border found mainly in
* small intestine tract
* kidney
* appears as fuzzy line/fringe in light microscope (individual microvilli too small to be resolved with LM)
37
What kind of cells are shown in this slide and what distinguishes them
* Simple columnar epithelium
* striated border (individual microvilli cannot be resolved with LM)
38
What do the red arrows point to
* Striated border
* found in simple columnar cells (these) or simple cuboidal cells
39
What do the red arrows point to
* Striated border (microvilli)
* Kidney tubule, so cells are simple cuboidal
* move liquid
40
Stereocilia
* found in male reproductive tract -- epididymus
* composed of actin
* incapable of active movement - moves sperm
* much longer than cilia
* believed to facilitate absorption
41
What is shown in this slide
* sperm in epididymis being passively moved by stereocilia
42
epidermolysis bullosa
* skin blisteres resulting from mutations in keratin 5 and 14 genes
43
bullous pemphigoid
autoantibodies against hemidesmosomes (blisters)
44
immotile cilia syndrome
defect in dynein arms that affect ability of cilia to move
45
epithelial cell tumors
if normal mechanisms for regulating epithelial turnover fail, tumors can develop
46
carcinomas
malignant tumors that arise from membranous epithelia
47
adenocarcinomas
malignant tumors that arise from glandular epithelium
