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MLSCI 250 > LECTURE - Epithelial Tissue > Flashcards

LECTURE - Epithelial Tissue Flashcards

1
Q

Epithelia mediate a wide range of activities

A 
selective diffusion
absorption
secretion
physical protection
containment
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2
Q

all epithelia are supported by a ..

A

basement membrane

  • separate epithelia from underlying supporting tissues and are never penetrated by blood vessels
  • epithelia depend on diffusion of oxygen and metabolite from supporting tissues
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3
Q

classification of epithelia (3)

A
  1. number of cell layers
  2. shape of component cells
  3. presence of surface specializations
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4
Q

simple epithelia

A
  • selective diffusion, absorption, secretion

- not found on surfaces subject to stress bc little protection against mechanical forces

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4
Q

simple epithelia

A
  • selective diffusion, absorption, secretion

- not found on surfaces subject to stress bc little protection against mechanical forces

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5
Q

simple epithelia

A
  • selective diffusion, absorption, secretion

- not found on surfaces subject to stress bc little protection against mechanical forces

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6
Q

simple squamous epithelium

A
  • flattened, irregularly shaped cells forming a continuous surface = pavement epithelium
  • line surfaces involved in passive transport (diffusion) of gases or fluids
  • lining of of pleural (lung), pericardial (heart), and peritoneal (abdominal) cavities
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7
Q

simple cuboidal epithelium

A
  • in sections perpendicular to basement membrane = square
  • nucleus usually round; centre of cell
  • lines small duct and tubules which may have excretory, secretory, or absorptive functions
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8
Q

simple columnar epithelium

A
  • similar to cuboidal except cells are taller
  • nuclei elongated; may be located towards base, center, or apex of cytoplasm
  • found mostly on highly absorptive surfaces such as small intestine
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9
Q

simple columnar ciliated epithelium

A
  • presence of cilia makes it different from simple columnar epithelium
  • among ciliated cells are scattered non-ciliated cells which usually have a secretory function
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10
Q

pseudostratified columnar ciliated epithelium

A
  • appearance of more than one layer of cells; but because all cells rest on basement membrane, this is true simple epithelium
  • nuclei at different levels (illusion of stratification)
  • almost exclusive to larger airways of resp. tract = respiratory epithelium
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11
Q

how do we distinguish pseudostratified from true stratified epithelia

A
  • nuclei are mainly confined to basal two-thirds of epithelium
  • clia are never present on stratified epithelia
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12
Q

stratified epithelia

A
  • two or more layers of cells
  • mainly a protective function; poorly suited for secretion/absorption due to thickness
  • classification based on shape + structure of surface cells (basal cells usually cuboidal)
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13
Q

stratified squamous epithelium

A
  • cuboidal basal layer to a flattened surface layer
  • basal cell divide continuously to replenish surface cells that are lost
  • lines oral cavity, pharynx, esophagus, anal canal, uterine cervix, vagina
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14
Q

keratinized stratified squamous epithelium

A
  • specialized form of stratified squamous epithelium that contributes to epithelial surface of skin epidermis
  • maturation = epithelial cells accumulate cross-linked cytoskeletal proteins = keratinization
  • keratin allows epithelium to withstand the constant abrasion and dessication to which it is exposed
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15
Q

stratified cuboidal epithelium

A
  • thin, stratified epithelium = only two or three layers of cuboidal or low columnar cells
  • larger excretory ducts
16
Q

transitional epithelium

A
  • urinary tract
  • features of both stratified cuboidal and squamous = transitional
    relaxed (contracted) state = 4-5 cell layers thick ; stretched = 2-3 cells thick (intermediate and surface layers extremely flattened)
  • basal cells cuboidal for relaxed state, intermediate is polygonal, and surface cells are large and rounded and may contain two nuclei = binucleate cells; umbrella cells
  • urothelium
17
Q

intercellular surfaces

A

adjacent cells have cell junctions that permit the epithelia to form a continuous cohesive layer in which all of the cells ‘communicate’ and cooperate

18
Q

three functional types of cell junctions:

A
  • occluding junctions (tight)
  • adhering junctions
  • communicating junctions (gap or nexus junctions)
19
Q

occluding junctions

A
  • tight junctions
  • immediately beneath luminal surface of simple columnar epithelium where they seal intercellular spaces and may prevent migration of floating membrane proteins from their appropriate domains on the cell surface
  • each tight junction forms continuous circumferential band around the cell
20
Q

adhering junctions

A
  • tightly bind constituent cells of epithelium together
  • act as anchorage sites for cytoskeleton each cell so cytoskeleton of all cells are effectively linked into a single functional unit
    two types:
  • zonula adherens: deep to tight junctions of columnar epithelial cells, forms a continuous band around cell providing structural; reinforcement to occluding junction
  • desmosomes (macula adherens): small circular patches or pots that are circumferentially arranged around columnar cells deep to the continuous zonula adherens
20
Q

adhering junctions

A
  • tightly bind constituent cells of epithelium together
  • act as anchorage sites for cytoskeleton each cell so cytoskeleton of all cells are effectively linked into a single functional unit
    two types:
  • zonula adherens: deep to tight junctions of columnar epithelial cells, forms a continuous band around cell providing structural; reinforcement to occluding junction
  • desmosomes (macula adherens): small circular patches or pots that are circumferentially arranged around columnar cells deep to the continuous zonula adherens
21
Q

communicating junctions (gap/nexus)

A

circular intercellular contact areas containing hundreds of tiny pores which permit the passage of small molecules between adjacent cells

22
Q

junctional complex

A

tight junctions, zonula adherens, desmosomes

23
Q

the luminal surface may incorporate three main types of specialization:

A
  • cilia
  • microvilli
  • stereocilia
24
Q

cilia

A
  • relatively long
  • motile structures which project in parallel rows from certain epithelial surfaces (resp and female reproductive tract)
  • beat with a wave-like synchronous rhythm propelling surface films of mucus or fluid in a consistent direction over the epithelial surface
  • axoneme = central core; 20 microtubules arranged as a central pair surrounded by nin peripheral doublets; base = inserts into basal body
  • each axoneme doublet = one tubule which is c-shaped in cross-section
  • dynein extends towards incomplete tubule of adjacent doublet and towards central microtubule pair
25
Q

microvilli

A
  • minute finger-linked projections of luminal PM
  • can be seen as brush border on surface of cells
  • usually for absorption; can increase SA available for absorption by up to 30x
  • cytoplasmic core = fine actin filaments which insert into terminal web
  • terminal web anchored to zonula adherens at periphery of cell
26
Q

stereocilia

A
  • extremely long microvilli
  • found in small number in parts of male reproductive tract
  • filamentous skeleton inside
  • may facilitate absorption
27
Q

basal surface

A
  • hemidesmosomes are present on the inner aspect of basal plasma membrane adjacent to basement membrane and provides a means of anchorage of cell via cytoskeleton to basement membrane and underlying supporting tissues
28
Q

gland that discharge their secretory product via a duct onto an epithelial surface

A

exocrine gland

29
Q

exocrine glands classified according to two major characteristics

A

MORPHOLOGY

  • simple: single, unbranched duct; secretory portions of simple glands have two main forms = tubular or acinar (which may be coiled and/or branched)
  • compound: branched duct system and their secretory portions have similar morphological forms as simple glands

MEANS of discharge of secretory products from cells:

  • eccrine secretion: involves process of exocytosis; proteins are major secretory product
  • apocrine: discharge of free, unbroken membrane-bound vesicles containing secretory product; applies to lipid secretory products in beast and some sweat glands
  • holocrine: disintegration of secretory cell to release secretory product; sebaceous glands
30
Q

secretory products of some exocrine glands are embraced by contractile cells called

A

myoepithelial cells

31
Q

ductless glands

A

endocrine

- secretory products diffuse directly into bloodstream

32
Q

secretory products of endocrine glands

A

hormones

  • control activity of cell and tissues far removed from the site of secretion
  • most consist of groups or cords of secretory cells surrounded by a rich network of blood vessels; each group of cells surrounded by basement membrane reflecting its epithelial origin
  • release hormones into intercellular space and then diffuse rapidly into surrounding blood vessels
33
Q

epithelial cells are closely bound to one another by a variety of membrane specialization called …

A

cell junctions

  • provide physical strength and mediate exchange of ‘information’ and metabolites

MLSCI 250 (35 decks)

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