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Block 1 Week 2 > Histology: Epithelium > Flashcards

Histology: Epithelium Flashcards

1
Q

What is epithelium?

A

the thin tissue forming the outer layer of a body’s surface and lining the alimentary canal (esphogous) and other hollow structures.

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2
Q

What does the epithelium do? (5)

A

1) keeps things in (tissue& organ boundary)
2) keeps things out (barrier from disease)
3) directs traffic (ducts/vessels)
4) enable transport across gradients
5) secrete stuff (glands)

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3
Q

components of epithelia?

A

surface, glandular, & special epithelia

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4
Q

components of connective tissue?

A
  • connective tissue proper
  • tissues and blood
  • cartilage & bone
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5
Q

components of muscular tissues?

A

-smooth, skeletal, & cardiac

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6
Q

components nervous tissues?

A
  • autonomic, motor, central
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7
Q

how are epithelial cells nourished?

A
  • by diffusion from capillaries in underlying connective tissue
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8
Q

Why are some epithelial cells more or less active than others?

A
  • cells closets to the source of nutrients (capillaries) get most nutrients, more active, divide more to give rise to the upper cell layer
  • activity decreases as move away from capillary, leading to differentiation in cell types and death if TOO far away
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9
Q

how are epithelia cells identified/ defined?

A

-sheet of cells sitting on a basement membrane

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10
Q

The basement membrane?

A

1) provides solid support & integrity so epithelia cells don’t shift relative to eachother
2) gives cells something to attach to
3) most components made by epithelial cells themself
4) help define polarity of epithelium ( top vs bottom)

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11
Q

Basement membrane vs apical membrane?

A
  • basement membrane= bottom of cell (leads to tissue/ organ)
  • apical membrane = top surface of epithelia (has microvilli, borders lumen)

-diff functions & specializations define them

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12
Q

How does epithelial sheet have polarity?

A

-because has an inside (basolateral) vs outside-lumenal (apical)

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13
Q

What does polarity provide/do?

A

1) provides barrier to hold things in/keep things out
2) surface to organize differentiated structures
3) ability for transport down tubes
4) boundary for directed movement (selective permeability) to ions, molecules etc

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14
Q

Apical boundary specializations?

A
  1. has microvilli that define apical/lumenal space, absorb nutrients from capillaries
  2. Junctional complexes between neighboring epithelial sites
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15
Q

Basal membrane specializations?

A

1) transport functions (selectively permeable. membrane & transport proteins)
2) functions as barrier

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16
Q

Two components of the basement membrane? Why is distinction important?

A
  1. the basal lamina
  2. reticular fibers

*distinction between basal lamina and membrane is important for function & structure of lungs & kidneys

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17
Q

What is the basal lateral lamina?

A
  • an ordered combo of type IV collagen, proteoglycans, & glycoproteins
  • acts as size & charge filter to regulate access to the epithelium
  • thickness & properties vary according to the tissue
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18
Q

What are reticular fibers?

A
  • type III collagen wrapped in glycoprotein coat
  • serve to anchor the basal lamina to the underlying general connective tissue
  • provide integrity to epithelial sheets
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19
Q

Anchorage of cells to the basal lamina?

A
  • done via hemidesmosomes
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20
Q

interactions between transmembrane protein of the cell & basal lamina provide?

A

1) Stimuli for polarization & differentiation of epithelial
2) regulation of epithelial proliferation

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21
Q

Simple epithelia?

A

when only one layer of cells sits on the basement membrane

  • what most tissue is composed of
    1) simple squamous
    2) simple cuboidal
    3) simple columnar
    4) Pseudostratifed columnar
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22
Q

Simple squamous epithelia?

A

-cells look like flat, fried eggs

Most common= lining blood vessels (endothelial cells)

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23
Q

Simple cuboidal epithelia?

A

-cells look like cubes
-nucleus in center
-if not squamous or columnar…are cuboidal
Most common= line ducts since help move secretions; not usually secretory cells

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24
Q

Simple cuboidal epithelia?

A

-cells look like cubes
-nucleus in center
-if not squamous or columnar…are cuboidal
Most common= line ducts since help move secretions; not usually secretory cells

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25
Q

Pseudostratified columnar?

A

-looks stratified, but all cells sit on the basement membrane so NOT stratified
-nucleus at diff levels
Most common: airway epithelium

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26
Q

stratified epithelia?

A
  • when have more than 1 layer of cells siting on basement membrane
  • epithelium is defined by shape of cells in TOP layer
  • occurs when epithelial membrane are actively diving, old cells move up as new cells are formed
  • so has active layer (on basement) and inactive layer (apical side)
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27
Q

transitional-stretched epithelia?

A

-stratified epithelia
-looks like stratified squamous, but cells are bi-nucleated and surface is very pink
-tissue able to handle stretch while maintaining barrier function & integrity
Most common: bladder

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28
Q

transitional un-stretched?

A

-looks like stratified columnar bit are gaps between the surface cells and basement membrane making basement membrane look wavy…which allows for stretch
Most common: bladder

29
Q

Simple squamous function?

A
  • lining of blood vessels

- if lost in endothelium of blood vessels

30
Q

Simple squamous structure-function?

A
  • lining of blood vessels
  • if lost in endothelium of blood vessels will result in blood clotting
  • is lost in mesothelium will cause adhesions

-passive diffusion

31
Q

simple cuboidal structure-function?

A
  • line ducts & help move secretions
  • increased structural rigidity for tubes compared to just simple squamous
  • increased activity of the cell (secretion/absorption)
32
Q

simple columnar structure-function?

A
  • further increased structural rigidity for tubes

- high cell activity, this form packs as many cells as possible into the epithelium

33
Q

pseudo stratified columnar structure-function?

A
  • same properties as columnar as well as:
  • regeneration from basal cells which are in area that is highly subject to damage, so needs very active cells to replace damaged one
34
Q

stratified cuboidal functions?

A
  • inactive surface cells, but only two cells thick so is a non-problem
  • strong wall for tubes
    ex: sweat glands
35
Q

stratified columnar function?

A
  • stronger walls (than cuboidal)

- are the walls of large tubes & ducts

36
Q

stratified squamous function?

A
  • best protection against outside world
  • but surface cells can’t absorb/secret
  • no dead keratinized layer in wet areas but have best protection when it is present
    • this layer also helps prevent dehydration
37
Q

transitional epithelia function?

A

protection and stretch of the epithelium itself

-ex: urinary bladder

38
Q

How ID sepithelia?

A

1) ID basement membrane, allows you to see polarization
2) the connective tissue below basement membrane
3) luminal side (where blood flows) on the apical side

39
Q

How ID simple cuboidal epithelium?

A
  • nucleus centered
  • seen in tubules/ ducts (salivary glands, kidneys)
  • not always clear where basmenet membrane is, so look for lumen (apical side) where material is flowing
  • ducts situated in complex tissue
40
Q

How ID transitional epithelium? (airway vs intestinal tract)

A

1) Basement membrane not as clear depending on looseness of connective tissue
2) apical tissue specialized w/ microvilli in intestines (is absent in airways, have cilia instead))
3) look jumbled when not stretched

41
Q

Cillia vs. micro villi with transitional epithelium?

A
  • cillia in the airways, have microtubules that help sweep things through the lumen
  • microvilli in intestines to help absorb nutrients, have actin filament but microvilli don’t move since all are crosslinked
42
Q

How ID pseudostratifed vs. stratified columnar epithelium

A

pseudo: in airway epithelium, has cilli not microvilli
stratified: when need extra layers to maintain integrity of barrier or in salivary glands where 2 cell layers are needed

43
Q

3 types of junctions in epithelial cells?

A

1) Adhesive junctions (provide seal between epithelial cells and basement membrane)
2) sealing junction (tight junction, between neighboring epithelial cells)
3) communicating junctions (gap junctions, between epithelial cells)

44
Q

Types of adhesive junctions (3)

A

1) hemidesmosomes: cell to basement membrane adhesion
2) desmosomes
3) adherens

45
Q

Desmosomes?

A

Mechanical boundary keeping cells stuck together

  • cadherins (glue made by transmembrane proteins) hold cells together via spot welds
  • keep epithelial cells from shifting relative to eachother; therefore keeps basement membrane barrier tight & intact
46
Q

Hemidesmosomes ?

A

-keep cells connected to basal lamina via connective tissue

47
Q

Hemidesmosomes & Desmosomes together?

A
  • desmosomes keep cells connected to eachother; Hemidesmosomes keep them connected to the basal membrane
  • together ensure that cells don’t shift or fall off basal membrane
48
Q

Adherens junctions?

A
  • epithelial cells in a sheet use these to control permeabiltiy across barrier
  • use cadherins as glue between the cells, keep them together and plug gaps
  • use actin filaments since spread pull through the cell
49
Q

Tight Junctions

A

zonula occludens

  • form selective seal to limit/ prevent fluids dissolved in substances passing between the space between epithelial cells (prevents passing from one side of epithelium to the other)
  • at apical end
  • some cells require extremely tight junctions, other can handle looser connections
50
Q

tight junction selectivity depends on?

A

the number of rows of protein complexes& the charge on the protein that make up the complexes.

  • proteins are made by both neighboring cells and are transmembrane
  • permeability is not static, can be regulated
51
Q

gap junctions

A
  • communication between cells
  • selectively allows molecules to go between epithelial cells via connexons channels (6 connexin combined)
  • allows spread of message via a single point & cells to respond to signals they may not have had receptor for
52
Q

more than 1 junction?

A
  • yes can form complexes
  • different junctions can work together to help maintain integrity and boundary of epithelia
  • diff tissues have diff combo of junctions
  • ex: junction to hold cells to eachother, the basal lamina, and prevent flow of molecules between them
53
Q

glands and 2 main types?

A
  • develop embryologically from surface of epithelia
    1) endocrine (lost polarity): when connection to surface is lost, secrets apically into blood.
    2) exocrine(have polarity): when connection to surface is maintained, secrets onto original surface
54
Q

complex exocrine glands?

A
  • have branched ducts, seen in pancreas/kidneys

- if have branching and get a blockage can have different pathology within the gland

55
Q

acinar?

A
  • collections of exocrine secreting gland cells (still epithelial w/ poalrity)
  • secreting into the gut/ organ they are on
56
Q

shapes of secretory glands?

A
  • secretory portions of glands have a variety of shapes,

- can occur on single or branched ducts

57
Q

Globlet cells look? what are they?

A
  • round and clear; near a stem going toward basement membrane
  • intestinal endothelial cells that secret mucuous into lumen
  • aren’t gland structure, single cells distributed in intestine
58
Q

types of exocrine secretions?

A

1) mucuous
2) serous
3) mumcoserous- mixed glands
4) 0ther- neither mucous or serous (ex= sweat glands)

59
Q

Modes of exocrine secretions? (2 main)

A

1) merocrine: exocytosis of product w/ H20 & ions, membrane= intact
2) apocrine: small number of cells secrete a part of the cell membrane w/ the product
- cuz lipid isn’t bound to membrane

60
Q

special modes of secretions?

A

1) microvesciles
2) exosomes
* both variations of apocrine*
- contain miRNA & mRNA
- can travel in circulation & fuse w/ other cells linking them physiologically & pathologically

61
Q

holocrine secretions:

A

glands that secrete whole cells

62
Q

development of epithelia to organs?

A
  • during embryonic development tissue/organs made from simple epithelia
  • glands,ducts, branch and become complex tissue (pancreas)
  • epithelia tissues form cords that separate from basement membrane & fold to become solid tissue
63
Q

blood vessels?

A
  • all vessels lined by endothelial cells on basement membrane of epithelium
  • endothelial cells have various purposes (barriers) & permeability (for nutrients in the blood)
64
Q

apical specialization?

A

epithelial cells apical surfaces can vary

1) AIRWAY epithelium: cillia
2) intestinal epithelium: microvilli
3) auditory epithelium

65
Q

cillia

A

made from tubulin filament (microtubules) that provide motor for cilia beating

  • use ATP, are mechanically active
  • in airway epithelium
66
Q

airway epithelium?

A

uses CILIA to transport luminal contents in mucus &help sweep mucus up the airway passages to help keep airways clear
-helps us swallow secretions from lung & esphogous

67
Q

intestinal apical epithelium?

A 
have Microvilli (actin) that are cross linked so they don't move
-provide extra surface area for absorption/secretions
68
Q

Microvilli in intestinal epithelium ?

A

-formed from arrangement of actin filaments that provide structure but DON’T actively beat since are cross linked at tips

69
Q

auditory apical epithelium?

A
  • have kinocilium (actin based)
  • opens K+ channels when associated stereocilia are displaced by movement or sound vibrations
  • how we sense sound

Block 1 Week 2 (9 decks)

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