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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
structure of a specific cadherin junction
F-actin fibres are linked by alpha and beta catenins, vinculin and alpha actinin to E-cadherin - Ca2+
26
focal contact structure and function
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
27
desmosomes function
connect intermediate filament networks of adjacent cells
28
hemidesmosomes function
connect intermediate filament network of cells to extracellular matrix
29
where are adherent junctions most common?
towards apex of adjacent columnar and cuboidal epithelial cells
30
adhesion belt
linked submembranous actin bundles | prominent in small intestine - zone visible as eosinophilic band (terminal bar)
31
adherent junctions in embryogenesis
transmit motile forces generated by actin filaments across cell sheets. mediate folding of epithelial sheets to form organs in the embryo
32
desmosome structure - intracellular plaque, filaments inserted into plaque, cell adhesion mediation, transmembrane proteins
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)
33
hemidesmosome structure - intracellular plaque, tonofilaments, transmembrane proteins
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
34
tonofilaments
cytokeratin intermediate filaments
35
junctional complex
close association of several types of junction between adjacent epithelial cells - maintains structural and functional integrity
36
bullous pemphigoid
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
communication junctions - functions, proportions and site of location
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
communication junctions pores
several hundred/junction | formed by 6 protein subunits traversing cell membrane - connexon
39
basement membrane - function, structure
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
protein making up collagen + its synthesis
type IV collagen | synthesised by epithelial cells
41
examples of how epithelia adapt to perform functions
increased SA - microvilli, basolateral folds, membrane plaques moving substances over their surface - cilia
42
microvilli - what they are, where they're found
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
maintaining the shape of microvilli
actin filaments linked to cell membrane by spectrin, to eachother by actin binding proteins - fimbrin and fascin lateral anchoring protein - myosin
44
actin links to cell membrane
spectrin
45
actin binding proteins
fimbrin and fascin
46
lateral anchoring protein
myosin
47
actin core in small bowel epithelium
actin core linked to actin network of adherent junctions between adjacent cells
48
cell membrane covering microvilli
contains cell surface glycoproteins and enzymes involved in absorptive process
49
detection of specific cell surface specialisations on microvilli
immunohistochemistry/enzyme histochemistry used to detect specific proteins, e.g. lactase and alkaline phosphatase
50
stereocilia
extremely long forms of microvilli - found on epithelial cells lining epididymis sensors of cochlear hair cells
51
basolateral folds
deep invaginations of basal or lateral surface of cells
52
basolateral folds location and function
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
membrane plaques function and location
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
cilia - what they are, function
highly specialised extension of the cytoskeleton | move fluid over cell or confers cell motility
55
cilia core structure
``` 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
where are cilia evident in?
epithelium lining respiratory tract - move mucus | epithelium lining fallobian tube - convey released ova to uterine cavity
57
axonemal structure
similar one to cilia is found in flagellum of spermatozoa
58
glycocalyx
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
properties of protein secreting epithelial cells
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
mucins
mixture of glycoproteins and proteoglycans lubricant in mouth barrier in stomach
61
characteristics of cells that produce and secrete mucin
well developed basal rough ER - faint blue basal cytoplasm well developed supranuclear Golgi - protein glycosylation large secretory vesicles - unstained, vacuolated apical cell cytoplasm
62
aggregation of mucin secreting cells
aggregated into specialised glands in genital, respiratory and intestinal tract
63
steroid secreting glands location and characteristics
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
ion-pumping epithelial cells location, function and characteristics
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
substances secreted by: cells in kidney tubules and ducts of secretory glands, stomach cells
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
mediation of ion transport
membrane ion pumps | use ATP for energy
67
4 mechanisms of secretion of cell product
merocrine, apocrine, holocrine and endocrine
68
merocrine
exocytosis from cell apex into a lumen
69
apocrine
pinching off of apical cell cytoplasm containing cell product
70
holocrine
shedding of whole cell containing cell product
71
endocrine
endocytosis from cell base into bloodstream
72
gland
organised collection of secretory epithelial cells
73
what happens when more secretions are required?
SA increased by invagination of the surface to form straight tubular glands or more complex coiled or branched glands
74
single secretory cells
secretory cells in-between surface epithelium
75
straight tubular gland
surface epithelium | secretory cells
76
coiled tubular gland
surface epithelium ion-pumping cells single central lumen secretory cells in distal part of gland
77
branched gland
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
acini
secretory islands | prevents escape of secretions
79
supply of glands
rich vascular supply to provide metabolites
80
control of gland secretions
hormonal and innervatory control
81
barrier function specialisations
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
sphingolipids
consitutes urothelial transitional epithelium form membrane plaques resist fluid and electrolyte movements out of cells in response to osmotic effect of concentrated urine
83
keratinisation
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
lamellar bodies
membrane-bound granules containing phospholipids - secreted by exocytosis into extracellular space, form lamellar sheet between cells in upper epithelium
85
production of keratin
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
keratohyaline granules
small granules containing specialised proteins
87
protein associating w/ and thickening cell membrane
involucrin
88
keratin properties
non-living proteinacous material attached to underlying cells by existing anchoring junctions mechanically strong, flexible, inert, physical barrier
89
intercellular phospholipid
makes epithelium impermeable to water

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