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Peer teaching > Epithelial cells > Flashcards

Epithelial cells Flashcards

1
Q

Specialised functions of epithelial cells + examples

A

form a covering for body surfaces e.g. skin, gut and ducts
secretory glands e.g. salivary tissue and liver
absorption

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2
Q

joining of epithelial cells

A

joined by adhesion specialisations

anchor cytoskeleton to neighbours and underlying/surrounding extracellular materials

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3
Q

types of cell shape

A 
squamous - flat, plate like
cuboidal - height and width similar
columnar - height 2-5x greater than width
rounded
polygonal
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4
Q

simple epithelium

A

single layer where all cells are in contact w/ basement membrane

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5
Q

stratified epithelium

A

several layers where only bottom layer of cells contact basement membrane

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6
Q

pseudostratified epithelium

A

epithelial cells appear to be arranged in layers, but are all in contact w/ basement membrane

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7
Q

transitional epithelium

A

special type of stratified epithelium
restricted to lining of urinary tract
varies between cuboidal and squamous, depending on degree of stretching

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8
Q

simple squamous epithelium

A

single layer of flat, plate like cells

nuclei are flattened, cytoplasm distinct

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9
Q

types of simple squamous epithelium

A

endothelium - lines blood vessels

mesothelium - lines abdominal and pleural cavities

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10
Q

simple cuboidal epithelium

A

single layer of cells w/ similar height, width and depth

centrally placed nucleus

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11
Q

simple columnar epithelium

A

single layer of cells with height 2-5x their width

basal nuclei arranged in ordered layer

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12
Q

stratified squamous epithelium

A

several layers of cells, lower layer contacts basement membrane
superficial part has squamous cells
middle and basal layers have pyramidal or polygonal cells

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13
Q

how is structural integrity of epithelium maintained, and how is it mediated?

A

adhesion of constituent cells to each other and structural extracellular matrix
cell membrane proteins act as specialised cell adhesion molecules
specialised areas of cell membrane are incorporated into cell junctions

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14
Q

three types of cell membrane and their functions

A

occluding junctions - link cells together to form an impermeable barrier
anchoring junctions - link cells to provide mechanical strength
communicating junctions - allow movement of molecules between cells

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15
Q

main functions of occluding junctions

A

prevent diffusion of molecules between adjacent cells
prevent lateral migration of specialised cell membrane proteins - delineating and maintaining specialised cell membrane domains

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16
Q

what is the occluding function performed by?

A

intramembranous proteins - mediate adhesion of adjacent cells

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17
Q

where are occluding junctions well developed?

A

small bowel:
prevent digested macromolecules from passing between cells
confine specialised cell membrane areas involved in absorption/secretion to luminal side of cell

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18
Q

where else are occluding junctions important?

A

in cells actively transporting a substance, e.g. active transport of an ion against a concentration gradient
prevent back-diffusion of substance

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19
Q

how are intramembranous proteins arranged?

A

serpiginous intertwining lines (sealing strands)

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20
Q

examples of intramembranous proteins

A

occludin and claudin

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21
Q

what protein is mainly responsible for diffusion barrier?

A

claudin

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22
Q

function of anchoring junctions

A

provide mechanical stability - allow groups of epithelial cells to function as a cohesive unit

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23
Q

structure of anchoring junction

A

intracellular link proteins attach cytoskeletal filaments of adjacent cells to transmembrane proteins
extracellular interaction is mediated by additional extracellular proteins or ions, e.g. Ca2+

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24
Q

example of a transmembrane protein

A

cadherin - uses Ca2+

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25
Q

structure of a specific cadherin junction

A

F-actin fibres are linked by alpha and beta catenins, vinculin and alpha actinin to E-cadherin - Ca2+

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26
Q

focal contact structure and function

A

link actin filament network of a cell to extracellular matrix
bundles of actin filaments interact w/ alpha actinin, vinculin and talin (actin-binding proteins) to link w/ integrin

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27
Q

desmosomes function

A

connect intermediate filament networks of adjacent cells

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28
Q

hemidesmosomes function

A

connect intermediate filament network of cells to extracellular matrix

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29
Q

where are adherent junctions most common?

A

towards apex of adjacent columnar and cuboidal epithelial cells

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30
Q

adhesion belt

A

linked submembranous actin bundles

prominent in small intestine - zone visible as eosinophilic band (terminal bar)

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31
Q

adherent junctions in embryogenesis

A

transmit motile forces generated by actin filaments across cell sheets. mediate folding of epithelial sheets to form organs in the embryo

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32
Q

desmosome structure - intracellular plaque, filaments inserted into plaque, cell adhesion mediation, transmembrane proteins

A

intracellular plaque consisting of desmoplakin, associated w/ plakoglobin and plakophilin. tonofilaments (cytokeratin intermediate filaments) are inserted into plaque
cell adhesion mediated by transmembrane proteins desmoglein and desmocollin (cadherins)

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33
Q

hemidesmosome structure - intracellular plaque, tonofilaments, transmembrane proteins

A

interacts w/ extracellular matrix
tonofilaments usually terminate end-on, don’t loop through
intracellular plaque contains proteins plectin and BPAG1e
transmembrane anchoring proteins are beta4 integrin, alpha6 integrin and BPAG2

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34
Q

tonofilaments

A

cytokeratin intermediate filaments

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35
Q

junctional complex

A

close association of several types of junction between adjacent epithelial cells - maintains structural and functional integrity

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36
Q

bullous pemphigoid

A

blistering disease
antibodies form and are directed against proteins in hemidesmosomes - bullous pemphigoid antigens 1 and 2
leads to inflammation and separation of epithelium from basal lamina, causing blistering

37
Q

communication junctions - functions, proportions and site of location

A

allow selective diffusion of molecules between adjacent cells and direct cell-cell communication
low density in most adult epithelia
large amounts in embryogenesis - spacial organisation of developing cells
cardiac and smooth muscle cells - contraction signals

38
Q

communication junctions pores

A

several hundred/junction

formed by 6 protein subunits traversing cell membrane - connexon

39
Q

basement membrane - function, structure

A

attaches epithelial cells to support tissues at hemidesmosomes and focal contacts
specialised layer of extracellular matrix materials
type IV collagen - synthesised by epithelial cells

40
Q

protein making up collagen + its synthesis

A

type IV collagen

synthesised by epithelial cells

41
Q

examples of how epithelia adapt to perform functions

A

increased SA - microvilli, basolateral folds, membrane plaques
moving substances over their surface - cilia

42
Q

microvilli - what they are, where they’re found

A

finger-like projections of apical cell surface
small ones found on most epithelial surfaces
most developed in absorptive cells, e.g. kidney tubule cells and small bowel epithelium

43
Q

maintaining the shape of microvilli

A

actin filaments linked to cell membrane by spectrin, to eachother by actin binding proteins - fimbrin and fascin
lateral anchoring protein - myosin

44
Q

actin links to cell membrane

A

spectrin

45
Q

actin binding proteins

A

fimbrin and fascin

46
Q

lateral anchoring protein

A

myosin

47
Q

actin core in small bowel epithelium

A

actin core linked to actin network of adherent junctions between adjacent cells

48
Q

cell membrane covering microvilli

A

contains cell surface glycoproteins and enzymes involved in absorptive process

49
Q

detection of specific cell surface specialisations on microvilli

A

immunohistochemistry/enzyme histochemistry used to detect specific proteins, e.g. lactase and alkaline phosphatase

50
Q

stereocilia

A

extremely long forms of microvilli - found on epithelial cells lining epididymis
sensors of cochlear hair cells

51
Q

basolateral folds

A

deep invaginations of basal or lateral surface of cells

52
Q

basolateral folds location and function

A

in cells involved in fluid or ion transport
associated w/ high concs of mitochondria
striped appearance to basal cytoplasm
renal tubular cells and ducts of secretory glands

53
Q

membrane plaques function and location

A

rigid areas of apical cell membrane
only in epithelium lining urinary tract
fold down into cell when bladder is empty
unfolds to increase luminal area of cell when bladder is full

54
Q

cilia - what they are, function

A

highly specialised extension of the cytoskeleton

move fluid over cell or confers cell motility

55
Q

cilia core structure

A 
orgnaised core of parallel microtubules (axoneme)
bound together w/ other proteins to produce beating
nexin linking protein every 86nm 
dynein arms every 24nm
radial spoke every 29nm
outer doublet tubulin microtubule
central pair of microtubule
central sheath projections every 14nm
56
Q

where are cilia evident in?

A

epithelium lining respiratory tract - move mucus

epithelium lining fallobian tube - convey released ova to uterine cavity

57
Q

axonemal structure

A

similar one to cilia is found in flagellum of spermatozoa

58
Q

glycocalyx

A

layer of protein, glycoprotein and sugar residues
resolved ultrastructurally as amorphus fuzzy coating
stainable by PAS
surface proteins used in cell recognition and adherence mechanisms - immunity

59
Q

properties of protein secreting epithelial cells

A

well developed RER - purple cytoplasm in H+E
polarity w/ basal RER
supranuclear Golgi
apical zone containing granules w/ protein for secretion by exocytosis

60
Q

mucins

A

mixture of glycoproteins and proteoglycans
lubricant in mouth
barrier in stomach

61
Q

characteristics of cells that produce and secrete mucin

A

well developed basal rough ER - faint blue basal cytoplasm
well developed supranuclear Golgi - protein glycosylation
large secretory vesicles - unstained, vacuolated apical cell cytoplasm

62
Q

aggregation of mucin secreting cells

A

aggregated into specialised glands in genital, respiratory and intestinal tract

63
Q

steroid secreting glands location and characteristics

A

adrenal gland, ovary and testes
well developed smooth ER - granular pink appearance of cytoplasm
free lipid in vacuoles in cell cytoplasm
prominent mitochondria w/ tubular (not flattened) cristae - biosynthesis of steroids from lipid

64
Q

ion-pumping epithelial cells location, function and characteristics

A

kidney tubules and ducts of some secretory glands -
transport ions and water
acid producing stomach cells transport H+ ions
ion transport mediated by membrane ion pumps - use ATP
folded cell membrane - increase SA
mitochondria closely apposed to membrane folds, to provide ATP
tight junctions

65
Q

substances secreted by: cells in kidney tubules and ducts of secretory glands, stomach cells

A

transport ions and water (sodium and water from apical surface for absorption)
move ions and fluid out of apex of cell - watery fluid secretion
transport H+ ions

66
Q

mediation of ion transport

A

membrane ion pumps

use ATP for energy

67
Q

4 mechanisms of secretion of cell product

A

merocrine, apocrine, holocrine and endocrine

68
Q

merocrine

A

exocytosis from cell apex into a lumen

69
Q

apocrine

A

pinching off of apical cell cytoplasm containing cell product

70
Q

holocrine

A

shedding of whole cell containing cell product

71
Q

endocrine

A

endocytosis from cell base into bloodstream

72
Q

gland

A

organised collection of secretory epithelial cells

73
Q

what happens when more secretions are required?

A

SA increased by invagination of the surface to form straight tubular glands or more complex coiled or branched glands

74
Q

single secretory cells

A

secretory cells in-between surface epithelium

75
Q

straight tubular gland

A

surface epithelium

secretory cells

76
Q

coiled tubular gland

A

surface epithelium
ion-pumping cells
single central lumen
secretory cells in distal part of gland

77
Q

branched gland

A

main excretory duct lined by columnar epithelial cells
minor ducts lined by ion-pumping cells + fluid + electrolytes
secretory epithelial cells around small central lumen - acinus
myoepithelial cells expel secretions

78
Q

acini

A

secretory islands

prevents escape of secretions

79
Q

supply of glands

A

rich vascular supply to provide metabolites

80
Q

control of gland secretions

A

hormonal and innervatory control

81
Q

barrier function specialisations

A

occluding junctions prevent diffusion of molecules between cells
apical cell membrane of urothelial transitional epithelium has many sphingolipids
desmosomes and hemidesmosomes provide tight linkage to resist shear and provide mechanical stability/barrier
stratified squamous epithelium - keratinisation - cytoskeleton of superficial cells becomes condensed w/ other specialised proteins into a resilient mass - cell death and tough impervious, protective layer from remaining cell membrane and cytoplasmic contents

82
Q

sphingolipids

A

consitutes urothelial transitional epithelium
form membrane plaques
resist fluid and electrolyte movements out of cells in response to osmotic effect of concentrated urine

83
Q

keratinisation

A

basal cells anchored to basement membrane and adjacent cells by hemidesmosomes and desmosomes and contain tonofibrils
cells differentiate and move up stratified epithelium
cytokeratin proteins change to higher molecular weight forms - cells develop lamellar bodies

84
Q

lamellar bodies

A

membrane-bound granules containing phospholipids - secreted by exocytosis into extracellular space, form lamellar sheet between cells in upper epithelium

85
Q

production of keratin

A

cells in upper epithelium express genes coding for specialised proteins interacting w/ tonofilaments and cell membrane to produce resilient and mechanically robust compact mass (keratin)

86
Q

keratohyaline granules

A

small granules containing specialised proteins

87
Q

protein associating w/ and thickening cell membrane

A

involucrin

88
Q

keratin properties

A

non-living proteinacous material attached to underlying cells by existing anchoring junctions
mechanically strong, flexible, inert, physical barrier

89
Q

intercellular phospholipid

A

makes epithelium impermeable to water

Peer teaching (10 decks)

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