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Microanatomy and Embryology > Epithelia and Connective tissue > Flashcards

Epithelia and Connective tissue Flashcards

1
Q

Four basic tissue types that compose all organs

A

Epithelial, Connective, Muscular, Neural

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2
Q

The polarity of epithelial cells

A

Basal Pole

apical pole

lateral domains

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3
Q

The basal surface of the epithelium is in contact with what other tissue type?

A

Connective tissue

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4
Q

How do you classify epithelial cells

A

1- Shape of the most superficial cell layer when sectioned perpendicular to exposed surface

  • Squamous (flat/thin cells)
  • Cuboidal (cells as thick as they are wide)
  • Columnar (cells taller than they are wide)

2- Number of layers

  • * Simple epithelium (single layer)
    • Pseudostratified - Simple epithelium that appears stratified – all cells touch basal lamina, all do not reach exposed surface
  • Stratified epithelium (two or more layers)
    • Urothelium – special features allow distension

3- Apical surface specializations

  • Cilia, Keratinization
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5
Q

Function of eptithelial cells

A

…

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6
Q

Types of stratified squamous epithelium

A

keratinized

nonkeratinized

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7
Q

Merocrine

A

vesicle contents released via exocytosis

  • acinar glands of pancreas
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8
Q

Apocrine

A

vesicle contents released along with some plasma membrane

  • mammary glands
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9
Q

Holocrine

A

entire cell fills, dies (apoptosis) and releases contents

  • sebaceous glands of hair follicles
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10
Q

Endocrine Cells realease into..

A

the blood stream via exocytosis

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11
Q

Paracrine release onto…

A

neighboring cells via exocytosis

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12
Q

What are microvilli

A

fingerlike projection that increases the surface area of the cell.

Absorptive role

present in intestinal tract, kidney

When dense on apical surface, forms ‘brush border’

visible by light microscopy

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13
Q

What is the composition of microvilli?

A
  • Composed of bundles of actin filaments (microfilaments)
  • Barbed end of actin filament anchored to villin at tip of microvillus
  • At base (apical cytoplasm of cell) actin filaments of microvillus extend into terminal web
  • Actin filaments in microvillus are crosslinked by actin-bundling proteins (fascin, espin, fimbrin)
  • Myosin I connects actin filaments to plasma membrane
  • Myosin II provide contractile ability to terminal web
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14
Q

What is the composition of cilia?

A

Axoneme = inner core of microtubules

* Central pair of microtubules surrounded by nine peripheral pairs of microtubules (9+2 pattern)

* Extends from basal body (recall MTOC; 9 triplets)

Movement of cilia due to movement of microtubule doublet

Dynein bridges (between each microtubule of the doublet) use ATP to slide along doublet

Basal bodies (feet) coordinate cilia movement

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15
Q

3 basic categories of cilia

A

Motile cilia

Primary cilia (monocilia)

Nodal cilia

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16
Q

Motile cilia

A

typical 9+2 microtubules

move fluid – trachea, bronchi

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17
Q

Primary cilia

A

9+0 arrangement of microtubules

no active movement (immotile) but passively bend to fluid flow,

lack associated motor proteins

chemosensors, osmosensors, mechanosensors

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18
Q

Nodal cilia

A

9+0 arrangement of microtubules

motile cilia (active rotational movement)

bilaminar embryonic disc at primitive node (L-R asymmetry)

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19
Q

Stereocilia

A

Long processes (significantly longer than microvilli)

Not very motile (immotile)

Ultrastructure like that of microvilli

Bundles of actin filaments crosslinked by fimbrin, but villinabsent

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20
Q

where is stereocilia found?

A
  • Absorptive function in epididymis & ductus deferens
  • Mechanoreceptor function in hair cells of inner ear
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21
Q

Basolateral Epithelial cell specializations

A

Essential for barrier function

Important for cell-cell communication

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22
Q

Tight junctions (zonulae occludens)

A

The most apical of the cell-cell junctions in epithelia

Junctions form network of bands that completely encircle the cell

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23
Q

Extent of zonulae occludens determine strength of…

A
  • barrier to flow of materials into space between epithelial cells
  • barrier to apical and basal lateral diffusion of membrane proteins
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24
Q

Membrane seal between epithelia cells is due to…

A

transmembrane proteins (occludin, claudin, JAM)

intracellular proteins (zonula occludens – ZO-1, ZO-2, ZO-3)

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25
Q

Adherent Junctions (Zonula adherens)

A

Located basal to (i.e. “below”) zonulae occludens, encircles cell

Adhesion mediated by transmembrane cell adhesion molecules (CAMs)

Cadherin-cadherin binding (homophilic)

Intracellular domain of cadherin binds catenin, catenin bind vinculin & α-actinin, and then actin cytoskeleton

Ca2+ dependent adhesion

26
Q

Desosome (Macula Adherens)

A

Disc shaped structure at a localized site (i.e. a “spot-weld”), does not form a band that encircles the cell

Transmembrane cadherins (desmogleins, desmocollins)

– homotypic binding

Intracellular domain of desmogleins & desmocollins bind anchoring proteins, plakophilin, plakoglobin, desmoplakin, that bind intermediate filaments (not actin)

27
Q

Gap Junctions (communicating junctions)

A

Found between cells in almost all mammalian tissues

Circular patches of aggregated protein complexes

Gap junctions are formed by connexin proteins. Connexins form a hexameric complex (connexon). Each connexon has a hydrophilic core about 1.5nm in diameter that aligns with a connexon on the adjacent cell.

Permit bidirectional exchange of small molecules (<1.5nm) such as cAMP, cGMP, and ions

28
Q

Hemidesmosomes

A

Adhesive structure found on basal surface of epithelial cells; between epithelial cells and the basal lamina

Resembles a half desmosome

Transmembrane integrins bind to the basal lamina

Cytoplasmic domain of integrins binds to plaque proteins (desmoplakin, plectin, BP230, erbin) which bind to intermediate filaments

29
Q

Focal adhesions

A

Small cell attachments that anchor actin filaments to the basal lamina

Integrins bind to extracellular matrix proteins (e.g. fibronectin) and intracellularly to the actin cytoskeleton

30
Q

What do integrins bind to?

A

Bind primarily ECM components

Binding promiscuity (i.e. multiple ligands can bind receptor heterodimer, multiple heterodimers can bind same ligand)

also binds RGD (arginine-glycine-aspartic acid) sequences

Generally low affinity binding to extracellular ligand

31
Q

function of integrins

A

Mediate cell-cell and cell-matrix adhesive interactions

Recall focal adhesion sites, hemidesmosomes

Intracellular signaling – linked to actin cytoskeleton

“Inside out” activation – cytoplasmic tails change conformation of extracellular ligand binding site

Binds to many molecules

32
Q

Cadherin function

A

Regulates calcium

Recall adherens junctions, desmosomes

Do not interact with ECM

Homophilic binding:

Like-like cadherin interactions greater

than like-nonlike cadherin interactions

Bidirectional signaling

Linked to cytoskeleton (actin, intermediate filaments)

Cadherin-catenin signaling – misregulated if adenomatous polyposis coli (APC) mutated = tumor

“Contact inhibition” – loss of E-cadherin in tumor progression

33
Q

Immunoflobulin function

A

Homotypic and heterotypic interactions

Trans- and Cis-interactions

Trans-interactions can result in bidirectional signaling

Activate intracellular signaling cascades

34
Q

Selectin function

A

Ca2+ dependent lectin domain – binds oligosaccarides

Binds mucin-like glycoproteins

high tensile strength (a few binding interactions sufficient to tether)

low binding affinity (hence leukocyte rolling)

Importance in leukocytes and platelet function

35
Q

3 classes of connective tissue

A

cells

fibers

ground substance

36
Q

What is the major component of connective tissue?

A

the extracellular matrix

37
Q

Function of connective tissue

A

Encompass the major structural constituents of the body

Connects and binds tissues and cells in organs

Mechanical / Structural role

Medium for diffusion of nutrients and waste

38
Q

Cells in connective tissue

A

Fibroblasts

Adipocytes

Macrophages

Mast cells

Plasma cells

Lymphocytes

39
Q

Fibroblasts

A

Predominant cell type found in connective tissue

Synthesize collagen, elastin, glycosaminoglycans, proteoglycans, glycoproteins (i.e. produce fibers and ground substance)

40
Q

Adipocytes

A

specialized for storage of neutral fats

41
Q

Macrophages

A

phagocytic cells

42
Q

Mast cells

A

promote local inflammatory response

43
Q

Plasma cells

A

produce antibodies

44
Q

lymphocytes

A

immune function

45
Q

How do you characterize adult connective tissue

A

1- Loose (areolar): flexible, not resistant to stress

2- Dense

  • Regular- collagen bundles, definite organization
  • Irregular – collagen bundles, 3D network

3- Specialized

  • Reticular: 3D mesh
  • Adipose- 3D network reticular fibers
46
Q

how do you characterize embryonic connective tissue?

A

mucous

mesenchyme

47
Q

3 types of connective tissue fibers

A

Three types of connective tissue fibers:

Collagen fibers (collagen)

Reticular fibers (collagen)

Elastic fibers (elastin and fibrillin)

48
Q

Composition of Fibers in connective tissue

A

Fibers in connective tissue are proteins that polymerize into elongated structures

49
Q

collagen

A

Most abundant protein in human body (30% dry weight)

Type IV collagen is 50% of all basal lamina protein, part of basal lamina, form long fibrils, forms anchoring fibrils, form networks

50
Q

Assembly of Collagen into triple helix

A

Repeating amino acid sequence of Glycine-X-Y

Most often X=proline, Y=hydroxyproline

Glycine is small, allowing tight association of the chains

51
Q

Reticular fibers

A

Extensive network of extremely thin fibers (‘threadlike’)

Around parenchyma of various organs

Abundant in hematopoietic organs (spleen, lymph nodes, bone marrow)

Type III collagen

52
Q

Elastic fibers

A

Thinner than collagen fiber; branching pattern

Sparse networks intersperse with collagen in tissues/organs that are subject to bending or stretching (i.e. arteries)

Composed of fibrillin and elastin

different proportions of fibrillin and elastin provide different resiliency to connective tissue

53
Q

Extracellular matrix of connective tissue

A

Fibers (e.g. collagen, reticular), Proteoglycans,Glycosaminoglycans (GAGs)

54
Q

Ground Substance

A

Part of Extracellular Matrix (ECM)

Highly hydrated and transparent (i.e. “gel-like”)

Fills the space between fibers and cells in Connective tissue

55
Q

3 molecule classes of ground substance

A

Glycosaminoglycans (GAGs)

keratin sulfate, dermatan sulfate, etc…

* Proteoglycans

aggrecan, syndecan, etc….

* Glycoproteins (multiadhesive proteins)

fibronectin, laminin, tenascin, osteopontin, etc…..

56
Q

Glycosaminoglycans (GAGs)

A

Repeating disaccharide of hexosamine (glucosamine or galactosamine) and uronic acid (glucuronic or iduronic) Forms linear polysaccharide

Highly hydrophilic

Highly viscous

57
Q

All GAGs, except hyaluronic acid, are…

A

*covalently attached to proteins (to form proteoglycan)

*synthesized in Golgi

*rich in sulfate

*10-40kDa

58
Q

Glycosaminoglycans: Hyaluronic acid (Hyaluronan

A

largest (100+ to 1000+kDa)

most ubiquitous GAG

synthesized into ECM by enzyme (hyaluronatesynthase)

located in plasma membrane

59
Q

4 primary Components of basal lamina

A

Collagens

Laminins

Entactin/nidogen

Proteoglycans

60
Q

Laminins

A

Cross-shaped glycoprotein composed of three polypeptide chains (α, β, γ)

Bind to integrins (receptors) on cell

Bind to nidogen/entactin to link to collagen

Bind to collagen IV

61
Q

Entactin/Nidogen

A

Glycoprotein that contains three globular domains

Binds to laminin, collagen IV, fibronectin, fibrinogen

Links laminin and type IV collagen

Binds Ca2+

Microanatomy and Embryology (8 decks)

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