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Histology first semester 23-24 > block II (epithelium) > Flashcards

block II (epithelium) Flashcards

1
Q

From which germ layers does epithelium derive, embryologically?

A

Ectoderm, mesoderm and endoderm

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2
Q

Does epithelium have large amounts of extracellular matrix?

A

No, small amount

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3
Q

By what is epithelium composed?

A

Sheets of contiguous cells bound together by lateral junctional complexes

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4
Q

What is the purpose of the basement membrane in epithelium?

A

separate epithelium from adjacent connective tissue by a non-cellular layer (basement membrane

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5
Q

are cells in epithelium polarized?

A

Yes, polarized both functionally and morphologically (Apical, lateral, basal surfaces with different properties)

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6
Q

Does epithelium have a free border?

A

Yes

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7
Q

What is epithelioid?

A

A structure of a tissue similar to epithelium but that doe snot contain a free border. (not epithelium)

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8
Q

Describe the vascularity of epithelium

A

Avascular, if there is blood present, it comes from the connective tissue.

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9
Q

Identify type of epithelium

A

Small intestine epithelium

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10
Q

Identify type of epithelium

A

Tracheal epithelium and we can see the basement membrane

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11
Q

mention the function of epithelia

A
  1. Cover and line surfaces to provide protection/barrier
  2. Secretion
  3. Absorption
  4. Transport along epithelial surface
  5. Selectively permeable barrier
  6. Transcellular transport
  7. Sensory reception
  8. Contractility
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12
Q

Provide examples of the function of epithelia that Cover and line surfaces to provide protection / barrier

A

Skin is an example of an epithelium that provides protection to prevent water loss, to provide protection against abrasion, and protects the body against UV irradiation.

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13
Q

Provide examples of the function of epithelia that serves for Secretion

A

(both ducts and parenchyma): (e.g. glands- sweat, mucus, enzymes, hormones, stomach, small intestine).
Goblet cells play a key role secreting mucus into the epithelium

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14
Q

Provide examples of the function of epithelia that serves for absorption

A

small intestine: absorption in lumen.
kidney tubules: protourine to transform into final urine

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15
Q

Provide examples of the function of epithelia that serves for selectively permeable barrier

A

endothelium provides selectivity by selecting which components can enter or exit

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16
Q

Provide examples of the function of epithelia that serves for transcellular transport

A

intestinal lining - IgA, endothelium of blood vessel - pinocytosis) In IgA- is transported by vesicles into the lumen for immonulogic factors.
in pinocytocis it move cells by vesicular transport.

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17
Q

Provide examples of the function of epithelia that serves for sensory reception

A

neuroepithelium - taste buds, retina, inner ear) for sensory stimuli

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18
Q

Provide examples of the function of epithelia that serves for contractility

A

myoepithelial cells - glands; like sweat glans move secretion by contraction

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19
Q

Provide examples of the function of epithelia that serves for transport along epithelial surface

A

via cilia - oviduct, trachea) In the trachea for moving mucus along the surface

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20
Q

Identify the tissue and the function

A

Section through the epidermis of skin; provide protection/barrier

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21
Q

Identify the tissue and the function

A

Small epithelial cells; goblet cells for secreting mucus into epithelium and absoprtion in lumen and protourine.

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22
Q

Identify the tissue and the function

A

Tracheal epithelium; move mucus along the surface

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23
Q

Identify the tissue and the function

A

Micrograph of venule;
selective permeable barrier and transcellular transport

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24
Q

Identify the tissue and the function

A

Diagram and photomicrograph of a taste bud
and its component cell types ; sensory reception

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25
Q

Identify the tissue and the function

A

Secretory Portion of eccrine sweat Gland with myoepithelial cells (dark pink); contractility

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26
Q

Epithelia are broadly classified as:

A

Surface epithelia
Glandular epithelia
specialized epithelia

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27
Q

What are surface epithelia?

A

Those epithelia which line the general body
surfaces and lumens of organs

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28
Q

What is glandular epithelia?

A

Those epithelia forming the secretory portion of exocrine and endocrine
glands

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29
Q

What is specialized epithelia?

A

Epithelial cells specialized as sensory receptors or transducers such as in olfactory and optic systems

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30
Q

identify structure and classification

A

Specialized epithelia; epithelium lining pancreatic duct

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31
Q

identify structure and classification

A

Glandular epithelia; pancreatic acinar cells

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32
Q

identify structure and classification

A

Specialized epithelia; olfactory epithelium

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33
Q

What are goblet cells?

A

unicellular mucus secreting cells

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34
Q

hOW IS EPITHELIA CLASSIFIED ANATOMICALLY?

A
  1. the number of cell layers
  2. The shape of the surface cells
  3. Specializations of the apical cell surface
  4. presence of goblet cells
  5. Degree of keratinization
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35
Q

How is th eclassification of layers?

A

simple epithelium if single layer or stratified epithelium if more than one layer

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36
Q

How is the classification of the shape of surface cells?

A

squamous, cuboidal or columnar

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37
Q

How is the classification of the specializations of the apical cell surface?

A

microvilli, cilia, stereocilia

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38
Q

How is the classification of the presence of certain cells??

A

presence of goblet cells - are unicellular mucous
secreting cells

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39
Q

How is the classification of degree of keratinization?

A

Amount of keratin in stratified squamous epithelial

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40
Q

Identify the classification

A

simple squamous epithelium

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41
Q

Identify the classification

A

Simple cuboidal epithelium

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42
Q

identify the classification

A

Simple columnar epithelium

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43
Q

identify the classification

A

Stratified squamous epithelium

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44
Q

identify the classification

A

Stratified cuboidal epithelium

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45
Q

identify the classification

A

Stratified columnar epithelium

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46
Q

identify the classification

A

Simple pseudostratified epithelium

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47
Q

identify the classification

A

Stratified transitional epithelium

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48
Q

What are the functions of simple epithelia?

A

squamous, simple cuboidal, and simple columnar epithelia are typically involved in absorption and secretion, and translocation of molecules to and from the apical and basal surfaces. The single layer
facilitates increased permeability of the epithelium.

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49
Q

identify

A

Simple squamous epithelium (blood vessel venule). Allows molecules within the lumen of the cell to pass across thin cells into the connective tissue.

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50
Q

Identify

A

Simple cuboidal epithelium lining of pancreatic duct, plays a role in modification of product in the lumen of the duct and role in passage

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51
Q

Identify

A

Simple columnar gall bladder; sort prodcut stored in the bladder as well

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52
Q

What is pseduostratified epithelium?

A

a variation of simple epithelia in which all the cells touch the basement membrane and thus is considered a single layer of cells. However, the cells vary in height so that some of the cells do not touch the apical surface of the epithelium and nuclei
may be at several levels thus making it look stratified.

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53
Q

Identify by classification

A

tracheal epithelium pseudostratofied.

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54
Q

Name the structure (be specific)

A

Pseudostratified columnar epithelium with stereocilia

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55
Q

Where can goblet cells be found?

A

glands present in some simple and pseudostratified epithelia. If present they may be included as part of the classification

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56
Q

identify

A

(blood vessel) Simple squamous epithelium lining a venule b

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57
Q

Identify

A

Simple cuboidal epithelium lining a kidney tubule

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58
Q

Identify

A

Simple columnar epithelium lining a kidney tubule

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59
Q
A

Simple Columnar Epithelium with Microvilli and Goblet Cells (small intestine)

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60
Q
A

Simple Columnar Epithelium with Cilia (epithelium of oviduct)

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61
Q
A

Pseudostratified Columnar Epithelium with Cila and Goblet Cells (Tracheal epithelium)

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62
Q
A

Pseudostratified Columnar Epithelium with
Stereocilia (Epithelium of epididymus)

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63
Q

Describe stratified epithelia

A

are not as permeable as simple epithelia, and are less well suited to absorption, secretion or translocation of molecules from one side of the epithelium to the other

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64
Q

Describe function of stratified epithalia

A

function for protection against abrasion and water loss

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65
Q

Which stratified epithelia are the most common?

A

Stratified squamous epithelia and stratified cuboidal epithelia are the most common.

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66
Q

Which stratified epithelia is less common?

A

Stratified columnar is relatively uncommon except for male reproductive system

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67
Q

What is transitional epithelium?

A

a special stratified epithelium limited to the
urinary system found in the epithelia of the epididymus and vas deferens.

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68
Q

identify

A

Section through the epidermis of skin (stratified squamous)

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69
Q

Identify

A

Stratified cuboidal epithelium lining eccrine
sweat gland duct

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70
Q

Which epithelium is also classified by degree of keratinization and what are these classifications?

A

Stratified squamous epithelia;

Keratinized
Parakeratinized
Non-keratinized

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71
Q

Describe keratinized epithelium and provide example

A

the epithelial cells near the surface of the epithelium are completely filled with the protein keratin. The squamous cells on the surface of the epithelium are dead and lack nuclei (e.g. Epidermis of skin)

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72
Q

Describe parakeratinized epithelium and provide example

A

the epithelial cells near the surface of the epithelium are heavily filled with keratin, but still alive and retain their nuclei (e.g. epithelium of hard plate)

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73
Q

Describe non-keratinized epithelium and provide example

A

the epithelia cells near the surface are minimally filled with keratin, are still alive, and retain their nuclei (e.g. epithelium of esophagus)

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73
Q

With what does the degree of keratinization correlate to?

A

correlates with the ability of the epithelium to resist abrasion; keratinized epithelium resists abrasion more significantly than parakeratinized epithelium and non-keratinized

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74
Q

Identify keratinization

A

Keratinized

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75
Q

Identify keratinization

A

Parakeratinized (hard palate)

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76
Q

Identify keratinization

A

Non-keratinized (Esophagus)

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77
Q

Identify

A

Stratified Squamous Epithelium - Non-keratinized (esophagus)

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78
Q

Identify

A

Stratified Squamous Epithelium - keratinized (epidermis)

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79
Q

Identify

A

Stratified Squamous Epithelium- Para-keratinized (hard palate)

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80
Q

Which is sometimes referred to as minimally keratinized?

A

the non-keratinized epithelium because it does have keratin but very minimal

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81
Q

What is transitional epithelium?
Where is it found and by what is characterized for?

A

specialized stratified epithelium found only in the urinary system.

It is characterized by its ability to change the shape of the cells and the change the number of cell layers to increase the luminal surface area of the epithelium to accommodate the expansion and enlargement of the ureter and bladder when the
volume of urine increases.

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82
Q

Identify

A

Micrograph of transitional epithelium in bladder relaxed; numbreal shape? (apical)

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83
Q

Identify

A

Micrograph of transitional epithelium in bladder distended

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84
Q

How are the surfaces of epithelial cells divided?

A

-Apical domain (free surface)
-Lateral domain (adjacent to other cells)
-Basal domain (attaches to basal lamina)

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85
Q

Identify

A

small intestine cells

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86
Q

Where is polarization present?

A

In simple and stratified epithelia

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87
Q

Why is polarization important?

A

This polarization in the morphology of the epithelial cell and its cell surfaces is extremely important in allowing a separation of many of the epithelial cell’s functions to specific plasma membrane surfaces and domains

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88
Q

mention functions of microvilli and stereocilia in epithelium

A

May function to increase the surface area of the epithelium for absorption such as in the small intestine (microvilli) and epididymis
(stereocilia)

Stereocilia in the inner ear may also serve a sensory function in the perception of sound waves

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89
Q

mention functions of cilia in epithelium

A

Motile cilia may function to move substances such as mucus along the epithelia surface such as in the larger passageways of the respiratory tract (trachea, bronchi, bronchioles) and in the oviduct to facilitate passage of the oovte

In the form of primary cilia (monocilia) they also may serve as sensory organelles on many cells in the body and in the case of nodal cilia may be important for determination of left-right symmetry in the developing embryo

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90
Q

identify

A

Stereocilia male epididymis

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91
Q

identify

A

tracheal epithelium cilia

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92
Q

identify

A

Small instestine Microvilli

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93
Q

identify

A

intestinal Microvilli

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94
Q

identify

A

Stereocilia

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95
Q

identify

A

Cilia in trachea

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96
Q

What are the 2 types of specializations in lateral domains?

A

Junctional complexes
interdigitation (infoldings)

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97
Q

What are the functions of junctional complexes?

A

to isolate the lumenal contents from the lateral and basal domains and to attach cells together; acts as a seal to prevent things from passing to the cell.

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98
Q

What are the functions of lateral interdigitations (infoldings)?

A

To increase surface area and they are prevalent in cells involved in electrolyte and ion transport

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99
Q

What are infoldings site of?

A

Site of most ion and water transfer across epithelia from the lumen to underlying connective tissue; for example water, will enter the membrane and pas through the interdigitations pass the extracellular space into the connective tissue and also the concentration of substances that can be removed by capillaries

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100
Q

Identify the domain

A

Cell 1
cell 2
lumen
lateral domain of the apical portion of
two adjoining gastric mucosal cells
showing the apical junctional complex

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101
Q

Identify the domain

A

Lumen, cell 1, cell 2, interdigitation

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102
Q

What are the types of intercellular junctions?

A

occluding junctions
anchoring junctions
communicating junctions

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103
Q

What are the function of occluding junctions?

A

occlude the intercellular space (block off)

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104
Q

What are the functions of anchoring functions?

A

anchor or adhere cells together

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105
Q

What are the functions of communicating junctions?

A

provide electrical and metabolic communication between adjacent cells

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106
Q

What are the groups of proteins that link cells in the junctions called?

A

cell adhesion molecules (CAMs)

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107
Q

What do CAMs do?

A

act to bind cells together or to bind the cells to the extracellular matrix

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108
Q

What are the specific types of intercellular junctions?

A
  1. Zonula occludens = tight junctions
  2. Zonula adherens
  3. Maculae adherens = desmosome
  4. Gap junction = nexus
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109
Q

Which intercellular junctions form the apical junctional complex?

A

The zonula occludens, zonula adherens, and macula adherens

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110
Q

Identify

A

apical junction complex

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111
Q

Which junctions have clues to the spacial extent?

A

Zonula – “belt-like”, extending all the way around the cell
*Macula – “spot-like”, limited extent like a spot weld
*Fascia – “sheet-like”, just along one side or end of cell

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112
Q

Which junctions hive clues to the function?

A

Occludens – to “occlude” or block the intercellular space
* Adherens – involved in mechanical adhesion

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113
Q

What do zonula occludens serves as?

A

functions to “occlude” the extracellular space

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114
Q

Identify the gap junctions

A

Nexus (thin section)

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115
Q

Identify the tight junction

A

Nexus (freexe fracture)

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116
Q

What are the functions of apical occluding junctions?

A

provide a tight permeability seal between the cells which blocks passage of proteins and other large molecules from the lumen to the intercellular space between the cells (paracellular pathway)

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117
Q

wHAT IS TH EMAJOR OCCLUDING TYPE JUNCTION IN VERTEBRATES?

A

zonula occludens

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118
Q

Identify

A

Zonula occlundens thin section

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119
Q

Identify

A

Pentalaminar appearance of zonula occludens

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120
Q

What is the most apical of the junctions in the epithelial junctional complex?

A

zonula occludens

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121
Q

How is the strcuture of zonula occludens in thin sections, different from trilaminar plasma membranes?

A

In thin-sections it appears as a region in which the plasma membranes are fused together giving a pentalaminar appearance with no remaining extracellular space. (dark region at the center)

122
Q

How does zonula occludens appear in freeze fracture?

A

it appears as a series of anastomosing strands of particles on the protoplasmic fracture face (P-Face) and corresponding grooves on the extracellular fracture face (E-Face

123
Q

Identify

A

Freeze-fracture EM image of the P-face of
zonula occludens showing the anastomosing network of protein strands

124
Q

Identify

A

A freeze-fracture replica showing the P-face and E-face appearance of a zonula occludens

125
Q

Which transmembrane proteins are present in the zonula occludens?

A

occludins and claudins that form strands of particles in each of the adjacent junctional membranes.

126
Q

What do occludis and claudins do/

A

The extracellular domains of the proteins in each junctional membrane interact in the intercellular space to form strands of protein that seal the intercellular space (provide a permeability barrier) between the adjacent cells

127
Q

WHat other group is present in zonula occludens?

A

tricellulins, form strands at the corners between the epithelial cells

128
Q

What is the major protein that maintains the permeability barrier?

A

occludin

129
Q

What other proteins maintains the permeability barrier but differs in forming what?

A

claudin; differs in forming an extracellular aqueous channel allowing water between junctional membranes

130
Q

What other transmembrane junctional protein is present in zonula occludens? and function.

A

JAM (Junctional Adherence Molecule). It does not form strands but acts as an attachment site for white blood cells and facilitates their movement through the junction. allowing th eopening of zonula occludens and movement of vesicles

131
Q

What doe Tricellulin do?

A

forms vertical strands of protein (green particles in diagram) which seal the corners between cells in a similar way to those formed by occluding and claudin. prevents molecules to pass between corners of cells

132
Q
A

tricellulin

133
Q

What is the finction of zonula occludens?

A

Functions as a permeability barrier. The strands of the proteins occludin, claudin, and tricellulin seal the extracellular space (paracellular pathway) so that molecules and ions are restricted in moving between the cells by the paracellular route (between cells). Since claudin is also an aqueous channel, water may pass through the junctional seal to at least some extent.

134
Q

what does the junction of zonula occludens serve to blocK?

A

The paracellular pathway

135
Q

Identify structures

A

zonula occuldens, endothelial cells lining the capillary.

136
Q

WHy are JAMz important?

A

the junction may also act as a preferential pathway for movements of white blood cells from the lumen of blood vessels between the simple squamous epithelial cells into the connective tissue and vice-versa.

137
Q

WHta is the PDZ-domain proteins?

A

unique amino acid sequence of occludins, claudins and JAMz, that attracts regulatory and signaling proteins

138
Q

What are the fucntions of JAMz?

A

These proteins act to bind complexes of other receptor, regulatory, and cytoskeletal proteins to the junction and may be important for its formation and maintenance

139
Q

Zonula occludens associated PDZ-proteins include:

A

ZO-1 - binds actin and is tumor suppressor
ZO-2 - role in epidermal growth factor-receptor signaling
ZO-3 - interacts with ZO-1 & occludin to bind actin

(they can act as a function of opening the junction by binding to actin as necessary)

140
Q

Clinical conditions resulting from failure of the permeability-barrier maintained by the zonula occludens

A

Some microbes and toxins can bind to the junctional proteins and destroy the permeability barrier (Review Folder 5.3).
*
For example, the cholera bacterium, some types of E. Coli, some types of salmonella, helicobacter, and the clostridium bacteria have all been shown to destroy the permeability barrier at the zonula occludens. This can result in massive loss of water from the body into the lumen of the intestine or other GI organs resulting in dangerous diarrhea.

Failure of the junction to function properly as a permeability barrier has also been linked to some autoimmune conditions such as celiac disease (gluten may be capable of passing inbetween the zonula occludens to get into the lateral space of the cells into the connective tissue and initiate immune response attacking a protein present in intestinal epithelium, atigenic epitome resulting in destroying of intestinal epithelia)

141
Q

Clinical Considerations: Zonula occludens as a binding site for viruses

A

Some viruses can bind to the junctional proteins to disrupt it or use the junction as an entry point into the cell and body.

Examples of viruses which either bind to zonula occludins proteins or require its disruption for entry include:
Hepatitus C virus
Coxsackie B virus
Rotavirus
West Nile virus
Dengue virus

142
Q

WHat are the apical anchoring junctions?

A

These junctions provide tight mechanical adhesion between cells

143
Q

Where is the zonula adherens present?

A

just basal to the zonula occludens in the epithelial junctional complex.

144
Q

how does the zonula adherens appears in thin-sections?

A

region in which the plasma membranes of the epithelial cells are uniformly separated by a 15 - 20 nm intercellular space. A diffuse plaque of density called the “fuzzy” plaque is present on the cytoplasmic surfaces of the membranes. This corresponds to bound actin microfilaments

145
Q

Identify

A

EM of zonula adherens with fuzzy plaque

146
Q

Identify

A

Zonula adherens high magnification

147
Q

How many types of zonula adherens are and on what do they differ?

A

There are 2 different forms of the zonula adherens junction that differ slightly in the type of major cell adhesion molecule (CAM) linking the junctional membranes and the cytoplasmic proteins that link to adjacent actin microfilaments

148
Q

Which are the proteins in the zonula adherens?

A

E-cadherins (most comon) and Nectin (less common form)

149
Q

What is E-cadherin and how does it bind in the extracellular domain?

A

E-cadherin is the major transmembrane cell adhesion molecule present in the most common form of the zonula adherens junction.. The extracellular domain region of the E-cadherin molecules from adjacent cells bind to each other in the extracellular space. Ca+2 is required for this binding of the E-cadherins

150
Q

How does E-cadherin bind in the cytoplasmic domain?

A

On the cytoplasmic side of the membranes, the cytoplasmic domain of E-cadherin binds to the proteins b -catenin and a -catenin, which in turn bind to vinculin and a-actinin which link to the actin cytoskeleton.

151
Q

Explain Nectin?

A

In some zonula adherens, another family of proteins called nectins are found. These junctions do not require calcium and bind to a protein called afadin on the cytoplasmic domain.

152
Q

WHat is Afanin?

A

prtotein found on the cytoplasmic domain of zonula adheerens alternative class. Afadin (rather than b-catenin and a-catenin) binds to the actin microfilament network. These junctions are weaker than the E-cadherin junctions and are found in regions of frequent tissue turnover

153
Q

Main functions of zonula adherens

A

Provides mechanical adhesion between adjacent cells
*
Binds the actin cytoskeleton in adjacent cells together thus providing mechanical strength to the cells

154
Q

How does fascia adherens differentiate?

A

fascia adherens junction which links cardiac muscle cells together has a similar structure except that it is a sheet-like junction between the ends of the cardiac cells [key role in contraction of cardiac muscle]

155
Q

identify

A

Fascia adherens

156
Q

Zonula adherens as a binding site for measles virus

A

In contrast to many other viruses which use binding to or disruption of the zonula occludens junction for entry into the cells, measles virus has been found to use the nectin-afadin protein complex of the zonula adherens for entry into the cell and spreads from epithelial cell to epithelial cell by formation of pores between the cells in the lateral domain. The virus initially in the circulation, enters at the basal-lateral aspect of the cells, and passes between the cells until it reaches the zonula adherens where it binds to the nectin

157
Q

What is the macula adherens?

A

Or desmosome; typically present just basal to the zonula adherens in the epithelial junctional complex. It is not always seen since it is spot-like in shape

158
Q

Why cant macula dherens be seen always in EM?

A

Due to spot-like it can be missed

159
Q

How deos macula adherens appear in thin sections?

A

In thin-sections it appears as a region in which the plasma membranes are uniformly separated by a 30 nm intercellular space. A distinct dense line (intermediate line) is present between the junctional membranes.
*
A very dense, well defined plaque of density (the desmosomal attachment plaque) is present on the cytoplasmic surfaces of the membranes. Intermediate filaments bind to the dense cytoplasmic attachment plaque

160
Q

Identify

A

EM of macula adherens showing the dense
Intracellular desmosomal attachment plaque with
intermediate filaments

161
Q

which are the major transmembrane cell adhesion molecules (CAM’s) present in the macula adherens?

A

Desmogleins and desmocollins (members of the cadherin family of proteins)

162
Q

explain the location of desmogleins and desmocollins in the membrane

A

The extracellular domains of the desmogleins and desmocollins overlap in the intercellular space to form the intermediate line and their cytoplasmic domains attach to the dense demosomal attachment plaques on the cytoplasmic side of the junctional membranes

163
Q

WHat is the attachment plaque composed of?

A

Desmoplakins and plakoglobulins are the major proteins of the desmosomal attachment plaque which is a binding site for the intermediate filaments of the adjacent cells. The plakoglobulins share amino acid sequence similarities to the catenins (attachement point for intermediate filaments).

164
Q

main fucntion of macula adherens and fascia adherens

A

The major function of the macula adherens is to provide very strong adhesion between the adjacent cells and to provide strong mechanical strength to the cells and adjacent epithelial cells by linking the intermediate filament cytoskeletons of the cells at the junction.

165
Q

key point of the macula adherens

A

It is important to stress that this junction unlike either the zonula occludens or the zonula adherens serves as an attachment point for the intermediate filament cytoskeleton

166
Q

what are other junctions?

A

COMMUNICATING JUNCTIONS

167
Q

Functions of communicating junctions

A

These junctions function to provide both ionic and metabolic coupling between cells. They allow passage of both ions and small molecules directly between cells

168
Q

Major type of communicating junctions in vertebrates?

A

gap junction (Nexus)

169
Q

Describe nexus

A

The gap junction is a plaque-like junction (spot-like) that can occur anywhere between the cells of epithelia and other tissues

170
Q

How does gap junctions(NEXUS) appear in thin sections?

A

appears as a region in which the plasma membranes of 2 adjacent cells come together and lie parallel with a uniform very narrow 2 nm intercellular gap

171
Q

How does gap junctions(NEXUS) appear in freeze fracture?

A

characterized by a plaque of IMP’s of uniform diameter and shape on the PF-fracture face and a similar array of pits on the EF-fracture face

172
Q

Identify

A

thin section gap junction nexus

173
Q

identify

A

thin section gap junction nexus

174
Q

identify

A

thin section gap junction nexus

175
Q

Identify

A

freeze fracture gap junction

176
Q

Identify

A

freeze fracture gap junction

177
Q

is THERE distinct density or attachment of filaments on the cytoplasmic surface of the junction?

A

No, although actin attaches in some cases

178
Q

What is the major protein in gap junctions?

A

cONNEXINS

179
Q

Explain the molecular structure of gap junction?

A

6 integral transmembrane proteins called connexins form a cylindrical structure called a connexon which has a central aqueous pore 1.5 - 2 nm in diameter

The connexons from the adjacent cells bind in the extracellular space to form an aqueous channel connecting the cytoplasm of the adjacent cells
*
The connexons may be able to open and close

180
Q

Identify

A

Atomic force microscope image showing connexons
gap junction in open

181
Q

identify

A

Atomic force microscope image showing connexons
gap junction in closed

182
Q

What are the functions of gap junctions?

A

Gap junctions function to allow electrical coupling and metabolic coupling of cells by allowing ions and small molecules such as sugars, amino acids, nucleotides, small regulatory molecules to pass from cell to cell THROUGH AQUEOUS CHANNELS

183
Q

How many connexins have been identified?

A

21-27

184
Q

Explain the connexon pathway in terms of passage

A

When the connexons from adjacent membranes are composed of the same connexin (homotypic interaction), passage through the aqueous pore is similar in both directions, biridectional. If the connexons contain different connexins (heterotypic interaction), passage in one direction may predominate unidirectional.

185
Q

Clinical Considerations: Diseases Related to Mutations in Connexins

A

Mutations in members of the connexin family of genes are major pathological factors in several diseases. Currently mutations in 10 of the connexins are responsible or associated with at least 26 different pathologies. Mutations in connexin-26, connexin-32, and connexin-43 are the most common

186
Q

WHat are the examples of pathologies in mutations of connexins

A

Mutations in connexin-26 (Cx26) are associated with non-syndromic congenital deafness. Gap junctions containing connexin-26 are found in the inner ear and are involved in recirculation of K+ in the cochlear sensory epithelium. Mutations in connexin-30 and connexin-31 are also associated with deafness

Mutations in connexins-46 and connexin-50 have been associated with inherited cataracts. These connexins are found in gap junctions between the lens cells and lens fibers that are involved in delivering nutrients and metabolites to the cells in the avascular environment of the lens

187
Q

By what does the basal domain attach to?

A

basal lamina

188
Q

describe basal domain

A

Site of attachment of epithelial cell to underlying basement membrane & connective tissue
*
May have hemidesmosomes and focal adhesion plaques
*
May have basal infoldings and associated mitochondria for ion pumping
*
May be a site of secretion in some epithelial cells (for example endocrine or paracrine secreting cells)

189
Q

basemrnt membrane =

A

basal lamina + lamina reticularis

190
Q

what is the basal lamina?

A

extracellular matrix secreted by epithelium

191
Q

What is the lamina reticularis?

A

extracellular matrix secreted by underlying connective tissue (CT)

192
Q

identify

A

Section of colonic glands stained with periodic acid
Schiff reagent (stains carbohydrates) to show basement membrane

193
Q

Identify

A

Tracheal epithelium showing very thick basement
membrane below the epithelial cells (cilia)

194
Q

What is the function of the basement memebrane?

A

*Separates the epithelium & connective tissue (each organ =unique molecularly)
*Anchors and stabilizes epithelial cells to CT
*Influences cell polarity
*Functions in filtration of molecules to & from epithelium & CT
*Influences epithelial cell proliferation
*Guides cell migration and regeneration

195
Q

What are the regions of the basal lamina?

A

Lamina lucida and lamina densa

196
Q

identify

A

EM of two adjoining epithelial cells with their basal laminas

197
Q

identify

A

lamina lucida and lamina densa components

198
Q

What is the lamina lucida?

A

(adjacent to plasma membrane)-Light staining region in EM.
Contains the extracellular domain of the integrins (transmembrane proteins – laminin and fibronectin receptor proteins) + laminin

199
Q

What is the lamina densa?

A

(adjacent to underlying CT)-dark staining region of basal lamina in EM.
The major protein is collagen type IV. In addition it contains extracellular glycoproteins (laminin, fibronectin & nidogen/entactin), sulfated proteoglycans (perlecan)

200
Q

WHat do laminin and type IV collagen do?

A

can polymerize into sheet like macromolecular structures that comprise the basal lamina

201
Q

How does laminin polymerize?

A

polymerizes in a calcium-dependent process at the basal plasma membrane in association with laminin receptor proteins (Integrins of the CAM family) which bind the laminin polymer sheet to the plasma membrane

202
Q

How does collagen type IV polymerize?

A

polymerizes into a sheet-like collagen suprastructure below the laminin polymer sheet and is crosslinked to it by nidogen/entactin (sulfated glycoprotein) and perlecan (proteoglycan)

203
Q

Identify

A

showing the attachment of the basal lamina to the
underlying lamina reticularis collagen fibers by type VII collagen anchoring
fibrils and fibrillin microfibrils

204
Q

what other multiadhesive glycoproteins are present in the basal lamina?

A

fibronectin and other sulfated proteoglycans are present in the lamina densa.

205
Q

What is the lamina reticularis? and what proteins act in its attachment to the lamina densa

A

The lamina densa attaches to the lamina reticularis (an underlying network of reticular fibers and elastic fibers) by type VII collagen anchoring fibrils and fibrillin microfibrils

206
Q

WHat are the two types of specialized junctions that can attch the cell to the underlying connective tissue and what is the reason?

A

Focal adhesions and hemidesmosomes; providing additional strength to the cell binding to the connective tissue

207
Q

WHat are focal adhesions?

A

specialized membrane contacts that connect the actin cytoskeleton to the basal lamina & underlying CT

208
Q

WHat are the functions of focal adhesions?

A

Play an important role in dynamic changes in cell shape and movement;

Formation & dismantling of adhesions is important for control of cell migration (wound healing, embryogenesis)

Important for detection of contractile forces or mechanical changes in the extracellular matrix (ECM )and conversion of these to biochemical signals = mechanosensitivity role

209
Q

What are hemidesmosomes?

A

specialized membrane contacts that connect the intermediate filament cytoskeleton to the basal lamina & underlying CT

210
Q

What are the functions of hemidesmosomes?

A

Provide a very strong attachment of epithelial cell to the CT and resist shear or abrasive forces to the epithelial cell

211
Q

Explain the cytoplasmic molecular structure of focal adhesions

A

The cytoplasmic domains of the transmembrane integrins bind to the cytoplasmic proteins talin, paxilli, vinculin, and a-actinin which bind to actin cytoskeleton
*
The extracellular domains of the integrins bind to fibronectin in the lamina densa of the basal lamina and thus to the underlying CT

212
Q

identify

A

Fluorescent micrograph showing labeled focal
adhesion junctions (orange) and attaching actin stress fibers inserting at focal adhesions
(green)

213
Q

WHat happens if there is a change in the attachment of the focal adhesion?

A

Changes in this attachment of the actin cytoskeleton to the underlying CT may be related to changes in the cell occurring during transformation and cancer

214
Q

identify

A

hemidesmosomal junctions (arrows) at the basal plasma membrane of an epithelial cells. Note the intermediate filaments binding to the hemidesmosomes

215
Q

explain the cytoplasmic structure of hemidesmosomes and its proteins

A

The cytoplasmic attachment plaque contains the proteins plectin, BP230, and erbin which mediate attachment of the intermediate filaments to the cytoplasmic domains of the transmembrane proteins α6β4 integrin (yellow) and collagen type XVII (brown) [extracellular proteins]

216
Q

explain the extracellular structure of hemidesmosomes and its proteins

A

The extracellular domains of the α6β4 integrin transmembrane proteins interact with the basal lamina proteins laminin-332 (green) or perlecan (on collagen IV) providing a connection of the junctional plasma membrane and cell to the extracellular matrix

217
Q

Clinical Consideration of hemidesmosomes

A

Bulbous Pemphigoid;
group of skin blistering diseases (such as bulbous pemhigoid) which result from autoimmune reactions against the proteins of the hemidesmosome such as collagen XVII. This results in the autoimmune destruction of the hemidesmosome allowing separation of the basal layer of the epidermis from the underlying connective tissue of the dermis thus allowing for the formation of massive blistering of the skin.

218
Q

What are basal infoldings?

A

specialization of epithelium found in basal domain

219
Q

What are basal infoldings?

A

*
Increase the basal surface area
*
Are often associated with elongated mitochondria that provide energy
Function: active ion transport
[active pumping of Na+, and water follows passively]

This can operate as a mechanism by which the epithelial cell can concentrate or modify the contents of the fluid compartment found at the apical or luminal surface of the epithelial cell

220
Q

identify

A

Basal infoldings with associated mitochondria
to provide energy for ion pumping

221
Q

What is the turnover rate of epithelial cells?

A

Epithelia cells are among the most actively dividing cells in the body. The turnover rate of epithelia for replacement of the cells by new cells by cell division of stem cells is generally high ranging from approximately 4 -6 days in epithelia of the GI tract to longer than 40 days or more in skin and some other organs

222
Q

What is metaplasia?

A

Metaplasia is the conversion of one type epithelium to another type which occurs under some conditions of stress to the epithelium such as excess abrasion or chronic infections

223
Q

What is the most common metaplasia?

A

columnar to squamous metaplasia in which columnar epithelia are converted to a squamous epithelium as frequently seen in the respiratory epithelium of smokers or in the lining epithelium of the cervix in women with chronic infections

224
Q

What can occur in Barrett esophagus?

A

Squamous to columnar metaplasia where gastric reflux causes the stratified squamous epithelium of the esophagus to change to a simple columnar epithelium with goblet cells in response to the acid

225
Q

identify

A

Micrograph showing squamous metaplasia of the epithelium of the uterine
cervix

226
Q

Is metaplasia reversible?

A

Metaplasia is reversible and considered to be within the normal range of differentiation of a tissue and thus is not cancer. However, note that this plasticity and changes in the epithelium may be a prelude to cancerous changes.

227
Q

what is carcinoma? (epithelial cancer)

A

Carcinoma refers to a malignant neoplasm of epithelial origin or cancer of the internal or external lining of the body

228
Q

what are adenocarcinomas?

A

adenomas) are a subtype of the carcinomas which occur in glandular tissue of organs like the colon, prostate, and breast

229
Q

Carcinomas, malignancies of epithelial tissue, account for how much % and what are some examples?

A

80-90% of cancer cases in adults

Ovarian epithelial carcinoma- cancer of the ovary
Acinar adenocarcinoma- a major type of cancer of the prostate and lungs
Basal cellcarcinoma- a form ofskin cancer
Squamous cell carcinoma- a form of skin cancer
Gastric adenocarcinoma- stomach cancer
Renal cell carcinoma- kidney cancer

230
Q

Clinical Considerations: The Epithelial-Mesenchymal Transition (EMT)

A

During embryological movement epithelial cells undergo a process called the epithelial-mesenchymal transition in which the epithelial cells undergo a change to a more mesenchymal-like cell morphology. A key feature of this process is that the intermediate filament composition changes from cytokeratin-containing intermediate filaments to vimentin-containing intermediate filaments and the breakdown of desmosomal and hemidesmosomal junctions. The cells then assume a more mesenchymal – fibroblast-like morphology, express new cell adhesion molecules, new focal adhesion junctions and become motile.
The clinical significance of this is the finding that epithelial cells becoming cancerous typically recapitulate this epithelial-mesenchymal transition to become motile and metastatic. Evidence has been shown for example that vimentin expression is required for the invasive behavior and metastasis of both prostate and breast cancer cells

231
Q

What are glands?

A

Single epithelia cells or multicellular aggregates of epithelial cells (and their CT) specialized for the synthesis and release of a product needed by the body

232
Q

WHat are the origins of glands?

A

Multicellular glands originate as surface epithelial cells which penetrate into underlying CT and specialize for the secretion of the product as well as forming ducts

233
Q

larger glands can be divided into?

A

Parenchyma: secretory units & ducts = functional units
[epithelial origin]
-
Stroma: supporting CT (may form capsule & septa)
[connective tissue origin]

234
Q

what happens with the product of glands in a unicelular or multicellular gland?

A

manufactured intracellularly then secreted either to the duct (for exocrine glands) or into CT or blood vessels (for endocrine glands)

235
Q

identify

A

Light micrograph of parotid salivary gland showing serous secreting acini, intralobular ducts and the connective tissue stroma between the secretory acini and ducts

236
Q

Multicellular glands based upon presence or absence of a duct can be divided into:

A

Exocrine glands and endocrine glands

237
Q

Describe exocrine glands

A

These glands have a duct or duct system to convey the released product out of the gland. For example salivary glands, liver, pancreas.

238
Q

Describe endocrine glands

A

These glands are ductless and release their product into the CT. For example: adrenal gland, thyroid gland, parathyroid gland and pituitary gland

239
Q

identify

A

Micrograph of exocrine pancreas and diagram of the compound nature of the gland

240
Q

identify

A

Low magnification image of endocrine adrenal gland

241
Q

Exocrine glands are classified according to:

A
  1. cell number
  2. duct arrangement
  3. shape of secretory units
  4. type of secretion
  5. secretory mechanism (mode of secretion)
242
Q

by cell number how can exocrine glands be classified?

A

Unicellular (goblet cells)
*
Multicellular: e.g. sweat glands,gastric glands, salivary glands, colonic glands, pancreas, liver

243
Q

identify

A

Goblet Cells in Intestinal Epithelium –Unicellular gland (exocrine)

244
Q

identify

A

Exocrine Pancreas – Multicellular gland secretory acini

245
Q

Duct arrangement and secretory unit shape of exocrine glands?

A

Simple – single unbranched duct

Compound- branched duct system

246
Q

Name the simple classification?

A
  • Simple tubular
  • Simple alveolar (acinar)
  • Simple tubuloalveolar
  • Simple branched tubular or alveolar (multiple secretory units with single duct)
247
Q

Name the compound classification

A
  • Compound tubular
  • Compound alveolar
    (acinar)
  • Compound tubuloalveolar
248
Q

identify

A

Simple tubular

249
Q

identify

A

simple coiled tubular

250
Q

identify

A

simple branched tubular

251
Q

identify

A

Simple acinar

252
Q

identify

A

branched acinar

253
Q

identify

A

compound tubular

254
Q

identify

A

compound acinar

255
Q

identify

A

compound tubuloalveolar/acinar

256
Q

identify

A

simple tubular of mucosal glands of colon

257
Q

identify

A

Simple Branched Acinar (cardiac stomach

258
Q

identify

A

Simple Coiled Tubular (Sweat gland)

259
Q

where are large exocrine glands found?

A

salivary glands, liver, and pancreas are classified as compound glands which are characterized by a branched duct system.

260
Q

how are secretory acini typically arranged in exocrine secreting compound glands?

A

arranged into larger anatomical structures called lobules which are separated by septa of connective tissue.

261
Q

How are lobules drained in exocrine compound glands?

A

drained by a branched system of intralobular ducts of different sizes

262
Q

Identify

A

Low magnification light micrograph of parotid salivary
Gland showing secretory acini (inset) their arrangement and their
arrangement into lobules separated by connective tissue septa
and ducts

263
Q

What is the interlobular duct?

A

Groups of lobules are drained by still larger ducts called interlobular ducts which are present in the connective tissue septa between the lobules

264
Q

what are lobes?

A

The lobules in turn may be grouped to form even larger anatomical arrangements known as lobes which are drained by still larger ducts known as lobar ducts or excretory ducts

265
Q

Which cells are in the intercalated duct?

A

simple cuboidal epithelium

266
Q

where does the secretory acinus typically drains?

A

two types of intralobular ducts: 1) intercalated ducts and 2) striated ducts or intralobular collecting ducts)

267
Q

What is the extralobular duct?

A

(interlobular ducts and lobar ducts) which join to form the main excretory duct

268
Q

identify

A

compound acinar (pancreas)

269
Q

which duts are considered to be examples of interlobular ducts present within the lobule itself?

A

intercalated duct and intralobular duct

270
Q

identify

A

Compound Acinar (parotid salivary gland. striated ducts and in intercalated ducts [branched ducts bc there are two duct systems]

271
Q

identify

A

Compound Tubuloacinar (submandibular salivary gland) [serous and mocus secreting]

272
Q

what are the main types of secretions in exocrine glands?

A

serous
mucous
mixed

273
Q

describe serous secretion

A

an aqueous ionic or protein secretion. The cells may stain light or dark and are typically pyramidal in shape with centrally-located nuclei

274
Q

describe mucous secretion

A

A glycoprotein rich solution that is typically very viscous. Cells are typically very pale staining with nuclei flattened along base of cell

275
Q

describe mixed secretion

A

The secretion is a mixture of serous and mucous secretions

276
Q

identify

A

Micrograph of parotid gland showing serous secreting acini

277
Q

identify

A

Hard palate showing mucuous secreting
glands

278
Q

identify

A

Submandibular gland showing mixed serous secreting And mucous secreting secretory units

279
Q

identify

A

light micrograph showing both serous and mucous glands in tongue

280
Q

What are the modes of secretion of exocrine glands?

A

merocrine
apocrine
holocrine

281
Q

Describe merocrine

A

(most common mode) only product released. e.g. eccrine sweat gland

282
Q

Describe apocrine

A

thin layer plasma membrane also secreted
(e.g. lactating mammary, ciliary & ceruminous glands)

283
Q

Describe holocrine

A

whole cell secreted (dead or live) (e.g. sebaceous gland)

284
Q

identify

A

merocrine

285
Q

identify

A

apocrine

286
Q

identify

A

holocrine

287
Q

What are myoepithelial cells?

A

many glands such as eccrine sweat glands, the salivary glands and some sero-mucous glands of the respiratory tract are surrounded by epithelial cells specialized to have contractile properties.

288
Q

what is the fucntion of myoepithelial cells?

A

can contract forcing the secretion out of the gland and along the duct.

289
Q

identify

A

Eccrine sweat gland in skin
Eccrine sweat gland in skin showing myoepithelial cells (dark pink) surrounding the secretory unit

290
Q

Identify

A

EM of eccrine sweat gland showing myoepithelial cells`

291
Q

describe endocrine cells

A

Endocrine glands are ductless. The secretion is released at the base of cell into the CT. The secretion may enter the blood vessels or diffuse to nearby cells

292
Q

whata re the action of the secretion of endocrine glands?

A

endocrine
paracrine
autocrine

293
Q

What is endocrine secretion?

A

if the secretion is transported by the blood and effects a distant target

294
Q

What is paracrine secretion?

A

if the secretion acts on nearby cells by diffusion through the CT (local effect)

295
Q

What is autocrine secretion?

A

if the secretion acts on the cell itself or other cells of that type (feedback mechanism)

296
Q

identify

A

endocrine

297
Q

identify

A

paracrine

298
Q

identify

A

autocrine

299
Q

identify

A

Thyroid – Follicular Arrangement of Cells [thyroglobulin]

300
Q

identify

A

Adrenal Gland – Strands of Cells

301
Q

What is the diffuse neuroendocrine system? (DNES)

A

Single endocrine cells interspersed in epithelium. DNES cells are of different origin (neural crest) than epithelium

302
Q

IDENTIFY

A

Stomach Gastric Glands neuroendocrine cells. SOMETIMES REFERRED AS AMINOPRECURSOR CELLS, secrete acid and pepcin

Histology first semester 23-24 (22 decks)

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