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human epithelial biology > structure and organisation of epithelium > Flashcards

structure and organisation of epithelium Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

what is epithelia

A

tissue which interfaces with the external environment

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2
Q

examples of epithelial tissue

A

gut, ear, skin, nasal

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3
Q

how are cells in epithelia organised

A

packed into sheets

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4
Q

what domains do epithelial cells form

A

apical and basolateral domains which are polarised (orientated) the same way throughout the epithelial sheet

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5
Q

how do epithelial cells sit

A

next to each other

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6
Q

what are epithelial cells attached to

A

a thin, fibrous basement membrane

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7
Q

what does epithelia line

A

the surfaces of cavities and structures throughout the body

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8
Q

what can epithelia form

A

glands

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9
Q

what do epithelial sheets lack

A

blood vessels (but they can still interact with nearby vessels)

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10
Q

what do epithelial nerves allow neural contribution to

A

sensation, absorption, protection and secretion

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11
Q

what do epithelial cells do within development

A

act in conjunction with mesenchyme to form nearly every organ in the body

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12
Q

what does epithelia contribute to

A

embryonic development and to the maintenence and function of the body throughout its life

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13
Q

what is epithelium classified by

A

its morphology

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14
Q

what are the cell types of epithelia

A

cuboidal, columnar, squamous

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15
Q

how can epithelial cells be organised

A

simple epithelium (single layer), stratified epithelium (several layers), or pseudo-stratified epithelium (one layer, cells of varying heights)

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16
Q

what are the specialised forms of epithelium

A

ciliated (primary cilia, motile cilia), neural connections (neuroepithelial cells) and mucus secreting (goblet cells)

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17
Q

what are the epithelias main functions

A

fluid secretion, mucus secretion, motile cilia and pathogen defence

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18
Q

what do alveolar type-1 cells (squamous) do

A

surface area for gas exchange

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19
Q

what do capillary endothelium cells do (squamous)

A

capillary wall and surface area for gas exchange

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20
Q

what do type-2 alveolar cells (cuboidal) do

A

fluid secretion (airway surface liquid), surfactant secretion (mechanical support) and stem cell for AT-I cells

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21
Q

innervated epithelium functions

A

(lung neuroepithelial bodies)
functions: chemosensing and regulation of breathing

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22
Q

cuboidal secretory epithelium functions

A

(kidney nephron and collecting duct)
functions: ion transport, fluid homeostasis, hormone secretion (renin; erythropoietin) and acid/base balance

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23
Q

simple columnar epithelium with goblet cells functions

A

(gut mucosa)
functions: ion transport, fluid homeostasis, mucus and digestive enzyme secretion and nutrient absorption

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24
Q

endothelial interaction with astrocytes functions

A

(BBB)
functions: ion transport, fluid homeostasis and selective hormone signalling

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25
Q

ciliated neuroepithelual “hair” cells functions

A

(innervated sensory epithelium of the ear)
functions: mechanosensing and neurotransduction

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26
Q

neuroepithelium with highly modified cilium

A

(retinal photoreceptors of the eye)
functions: photoreception and neurotransduction

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27
Q

what is polarity crucial for

A

function

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28
Q

what is polarities main functions

A

gives direction to the transport of ions and nutrients (vectored transport)
specialisation of function at one end of the cell or the other (retinal/hair cells)
supports formation of complex architectural shapes (branching morphogenesis)

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29
Q

what is loss of polarity key for

A

disease

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30
Q

how does respiratory failure occur

A

influenza virus infection, disorganised ion transport, oedema of the lung

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31
Q

how does cancer occur

A

cell detachment and movement (metastasis), re-organisation as a tumour

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32
Q

what is the organisation of epithelial cell junctions in an organised sheet

A

hemidesmosome junction - gap junction - desmosome junction - adherens junction - tight junction - microvilli

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33
Q

what is the function of microvilli

A

increase surface area for interactions with the environment

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34
Q

what do the adherens junctions do

A

establish apical-basolateral polarity

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35
Q

what is cell-to-cell recognition

A

primitive contacts made through homophilic epithelial (E) cadherin interaction
F-actin bundles are diffuse
the adherens junction (zona adherens) binds the cells together

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36
Q

where do E-Cadherins extend from

A

external surface of the cell

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37
Q

what does the homophilic binding domain within the adherens junction mean

A

it recognises and binds to itself

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38
Q

what are cadherins

A

cell adhesion proteins

39
Q

what holds the cells in contact

A

Ca2+ dependant homodimerisation between extracellular domains

40
Q

what is the anchor for p120, a, b and g Catenin

A

Carboxy-terminus

41
Q

what is p120

A

a prototypical catenin isoform

42
Q

what does p120 do

A

it stabilises adherens junction and initiates formation of other junction complexes

43
Q

what does a-Catenin form

A

a homodimer that anchors actin filaments to the membrane

44
Q

where is b-Catenin released from and what does it do

A

E-cadherin by proteolysis
acts as a nuclear signal to stimulate loss of polarity and cell growth

45
Q

what does g-Catenin (plakogolin) do

A

alters types of junction complex and is common to desmosomes

46
Q

what do adherens junctions do

A

anchor F-Actin (which forms supporting belt sturcture around inner cell membrane)
supports transition to cuboidal structure and recruits other cytoskeletal elements (eg tubulin)

47
Q

where is b-Catenin anchored to

A

the cytoskeleton

48
Q

what is the dual role of b-Catenin

A

sequestered at adherens junction - cell growth neutralised; polarisation can begin - when its ‘free’ it acts as a transcription factor

49
Q

what happens if adherens junction is disrupted

A

b-Catenin moves to the nucleus and promotes cell growth and loss of polarity - this is a metastasis cue

50
Q

main mode of action of junctions!!!

A

junction complexes stabilise cell structure and inhibit cell cycle passage by sequestering key transcription factors

51
Q

where do tight junctions form

A

on the apical side of the adherens junction

52
Q

what do tight junctions do

A

create an impermeable barrier that blocks paracellular movement of molecules between cells which acts as a fence to separate the apical and basolateral membranes (barrier and fence function)

53
Q

what is the basic unit of tight junctions

A

occludin

54
Q

what does homodimerisation of occludin extra-cellular domains do

A

forms an impermeable seal between cells

55
Q

what do transmembrane occludin domains do

A

seperate apical and basolateral membranes - prevents movement of proteins between these membranes

56
Q

how do tight junction complexes work

A

they run as a belt around cells, sealing apical and basolateral membrane domains and the join between cells

57
Q

what proteins anchor cytoskeletal proteins (actin / tubulin) to the tight junction complex

A

zona occludens (ZO-1,2&3)

58
Q

what do tight junctions anchor the cytoskeleton for

A

apical membrane structures (microvilli, cilia)

59
Q

what are microvilli supported by

A

actin anchored to actin ring

60
Q

tight junctions activate what type of uptake

A

paracellular

61
Q

what regulates phosphoinositide (Ptdlns) content of the apical and basolateral membranes

A

phosphoinositide-3-kinase (PI3K) and its inhibitor (PTEN)

62
Q

what acts as a recognition signature for protein transport to either membrane

A

Ptdlns

63
Q

what recruits PTEN to tight junctions

A

Par3

64
Q

what does PTEN enrich

A

PIP2 in apical membrane

65
Q

what does PI3K localise to

A

adherens junction

66
Q

what does PI3K enrich

A

PIP3 in basolateral membrane

67
Q

what do desmosomes form

A

loose junctions between cells

68
Q

what do desmosomes enable

A

cell shape to distort without tearing during mechanical strain

69
Q

where are desmosomes most common

A

in cells exposed to stretch (lower airway of lung) and shear (vascular tissue; kidney glomerulus)

70
Q

what are desmosomal junctions composed of

A

cadherin-family proetins known as desmoglein, desmocollin which are anchored in the membrane by plakoglobin and plakophilin heterodimers

71
Q

what does desmoplakin bind desmin (a cytoskeletal protein) to

A

the desmosome junction complex

72
Q

what do gap junctions do

A

connect epithelial cells as a syncitium

73
Q

what are gap junctions formed from

A

hexamers of connexin proteins

74
Q

what do gap junctions function as

A

channels that connect the cytoplasm of one cell to another

75
Q

what do gap junctions establish

A

lateral or planar cell polarity (PCP)

76
Q

how many connexins form a hemi channel

A

6

77
Q

what links hemi channels between neighbouring cells

A

extracellular connexin loops

78
Q

what do channel pores facilitate

A

electric and metabolic coupling between cells

79
Q

what is the bystander effect

A

death of one cell spreads as a signal to neighbours
limits spread of infection by creating zone of cell death

80
Q

what is another name for the basement membrane

A

the hemidesmosome

81
Q

what is the hemidesmosome

A

an extracellular matrix underlying all epithelia connecting cells to connective tissue and providing structural support

82
Q

what does the hemidesmosome do

A

link basolateral cells to collagen/fibronectin below - if unlinked, they become motile , and so cancerous

83
Q

what is effected by basement membrane composition

A

cell metabolism, survival, proliferation and migration

84
Q

what are the major components of the basolateral membrane

A

laminin, integrins, collagens & fibronectin and nidogen & perlecan

85
Q

what does laminin do

A

primary organiser of BM proteins - forms lamina densa

86
Q

what does integrins do

A

expressed on basolateral side of cell and from lamina lucida - bind to laminin

87
Q

what does collagens and fibronectin do

A

chicken-wire-like meshwork that gives BM tensile strength

88
Q

what does nidogen and perlecan do

A

link laminin to collagen and fibronectin

89
Q

how does cell attachment between basolateral and basement membranes occur

A

through integrins

90
Q

what occurs when a laminin mutates

A

brutal detachment

91
Q

what are the common diseases that are caused by loss of epithelial structure

A

cancer, gluten intolerance, chron’s disease and hypermotility syndrome (EDS)

92
Q

how does cancer occur

A

factors that cause loss of cell polarity disrupt cell junctions and promote cell growth and migration - loss of the tight junction fence

93
Q

how does gluten intolerance and chron’s disease occur

A

activation of an auto-immune response which disrupts tight junction barrier function enhancing pathological paracellular transport
(basically allows allergens to cross barriers)

human epithelial biology (5 decks)

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