Lecture 6: Epithelial Cell Specializations Flashcards Preview

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Flashcards in Lecture 6: Epithelial Cell Specializations Deck (22):

3 sites of epithelial cell specializations

1. intercellular surfaces: between cells, the occluding, adhering, and communicating junctions

2. luminal surfaces: facing lumen, with cilia, microvilli, and stereocilia

3. basal surfaces: basement membrane and hemidesmoses


components of junctional complexes

1. tight junction/occluding junction

2. adherens junction

3. desmasome

4. gap junction

5. hemidesmosome

6. basal lamina/basement membrane


purpose of epithelial intercellular surfaces

permit epithelia to form a continuous cohesive layer so cells can communicate


tight junction/occluding junction/zonula occludens characteristics

fxn: seals intercellular spaces so luminal contents can't penetrate between the cells (i.e. proteins)

location: directly below luminal surface

intracellular protein components: Z01, Z02, Z03, AF-6

intercellular protein components (like thread): occludin and claudin, seal 2 cells' membranes to each other


adhering junctions characteristics

fxn: bind epthelial cells together and act as anchorage site for cytoskeleton of each cell

2 types:
a. zonula adherens
b. desmosomes (macula adherens)


zonula adherens characteristics

location: deep to zonula occludens

fxn: form strong bond between adjacent cells

composition: cadherins (transmembrane proteins); actin filaments (cytoplasmic face); catenins, vinculin, alpha-actinin (attachment proteins)


desmoses (macula ("spot") adherens) characteristics

location: deep to adhering junctions; scattered or can be associated with zonula occludens or zonula adherens

fxn: provide structural integrity; **HAVE MANY in stratified squamous tissue; can connect plasma membranes of 2 adjacent epithelial cells

composition: desmocollins (intercellular); desmogleins (transmembrane); desmoplakin, keratin (plaque)


terminal bar

junctional complex including all 3 types of junctions: zonula occludens, zonula adherens, and desmosome/macula adherens


gap junction characteristics

location: below junctional complex

fxn: communication between cells; numerous in embryonic tissue; are gromet-like structures that extend from 1 cell membrane to another membrane, w/ open pores for ions, molecules; pores are regulated by pH, Ca++, cAMP

regulation: Ca++, pH, cAMP

composition: connexins (TM proteins); at least 24 known genes, but not all are alike in different tissues

particles of MW<1500 can flow through them

brings membranes very close together (2-4 nm) with connexion molecules


luminal (aka apical) surface specialization

simple cuboidal and simple columnar cell tissue

cilia (up to 300/cell) for movement

microvilli (up to 3000/cell) for increased surface area for absorption


cilia characteristics

example of luminal surface specialization

20 microtubule core axoneme, bound by plasma membrane; central pair surrounded by 9 doublets

have dynein arms that have ATPase activity for movement

inserts into a basal body composed of 9 triplets of microtubules

move by longitudinal movement of doublets relative to one another

fxns: clean airways; transport of ovum; line trachea, oviduct; help sperm flagella move

composed of: tubulin


microvilli characteristics

example of luminal surface specialization

1 micrometer in length

20-30 actin filaments (thin filaments)

covered in glocalyx, a glycoprotein

no ATP activity; contract & elongate to prevent clogging; no active motion

connect to terminal web of apical membrane at cell's cytoskeleton

can have as many as 3000 microvilli on cell



in epididymus of male reproductive tract

longer than cilia

composed of actin! (so are misnamed)

incapable of active movement

facilitate absorption & movement (i.e. sperm)


2 types of basal surface cell specialization

1. hemidesmosome
2. basement membrane



location: basal plasma membrane

fxn: anchor cytoskeleton at base of cell to basement membrane

composition: integrins a6B4, which stick thru basal membrane; laminin 5; cytokeratins


basement membrane

fxn: connects cell to underlying connective tissue; physical support; selective barrier, i.e. vs fibroblasts; growth, differentiation; regeneration of epithelial tissue; ultrafiltration of kidney, blood-air barrier for lung, prevent tumor metastasis by being impenetrable

composition: *** type IV collagen *** specific to basement membrane; laminin (binds collagen to bm); proteoglycans; entactin (binds laminin to type IV collagen); fibronectin (binds integrin of plasma membrane, produced by fibroblasts of connective tissue); type VII collagen (binds basal lamina to subjacent collagen)


clinical correlations of specializations of epithelial cells

1. epidemolysis bullosa
2. bullous pemphigoid
3. immotile cilia syndrome
4. epitheleal cell tumors


epidemolysis bullosa

skin blisters from mutations in keratin 5 & 14 genes


bullous pemphigoid

autoantibodies against hemidesmosomes that cause blisters


immotile cilia syndrome

defect in dynein arms that affect cilia's ability to move

can cause embryonic development issues

doesn't allow sperm to move, so no fertilization occurs


epithelial cell tumors

if mechanisms for regulating epithelial turnover fail, tumors can develop

carcinomas: malignant tumors that arise from membranous epithelia; no defined layers of skin

adenocarcinomas: malignant tumors that arise from glandular epithelium


Mohs procedure

method to examine skin for cancerous tissue; remove skin ring by ring progressively until noncancerous tissue is encountered

possible only because junctional complexes hold epithelial tissue together and allow cutting of skin and its reformation via binding to actin filaments and cytoskeleton with cohesive junctions so skin can reform