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MSK Week 4 > ICL 1.0: Epithelium > Flashcards

ICL 1.0: Epithelium Flashcards

1
Q

what are the characteristics of epithelial cells?

A
  1. functionally diverse – they do different things based on which organ system you get them from
  2. contain intercellular junctions
  3. they form sheets which are polarized = they have an apical and basal face
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2
Q

what is the function of intercellular junctions?

A
  1. mechanical stability

2. a barrier to permeability across the epithelial sheet so not just anything can enter

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3
Q

what is the function of villi?

A

they increase surface area!

like in the bladder when it gets filled the villi allow the tissue to expand and accommodate the increasing volume

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4
Q

what is located at the core of villi?

A

lamina propria

it’s lymphatics, arteries, veins, WBCs and so much other stuff that make up the villi

so like in the GI tract, when nutrients are absorbed through the villi, they go to the lamina proper and get to the circulatory system to they can be spread through the body

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5
Q

what are the components of a basement membrane? what does it do?

A

the basement membrane separates epithelial sheets from the subjacent connective tissue

basement membrane = basal lamina + lamina reticularis

the basal lamina is synthesized by epithelial cells

the lamina reticularis is synthesized by fibroblasts and is composed of type III collagen

on light microscopy the basal lamina and lamina reticularis cannot be distinguished. and together they are called the basement membrane

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6
Q

when do you use the term basement membrane vs. basal lamina?

A

light microscope = basement membrane

EM = basal lamina

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7
Q

what are the components of a membrane?

A

membrane = epithelium + connective tissue

the term membrane is applied to a tissue which has an epithelium and a subjacent connective tissue

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8
Q

what are the 3 types of membranes?

A
  1. mucous membranes
  2. serous membranes
  3. cutaneous membranes
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9
Q

what are mucous membranes?

A

they line cavities which communicate with the external environment

so they separate the inside of the body from the outside of the body

ex. urinary tract, respiratory tract

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10
Q

what are serous membranes?

A

they line internal surfaces of body cavities (parietal) and external surfaces of organs (visceral)

ex. peritoneum, pleura, pericardium

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11
Q

what are cutaneous membranes?

A

aka the skin

the cutaneous membrane includes stratified squamous epithelium (epidermis) and underlying dense irregular connective tissue (dermis

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12
Q

what is the function al epithelial cell sheets?

A

epithelium functions in transport by regulating what passes between body compartments and what passes between the “outside” of the body and the “inside” of the body

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13
Q

you classify epithelium based on what?

A
  1. number of cell layers

1 cell layer = simple

2+ cell layers = stratified

  1. the shape of the cell

if stratified, base it on the shape of cells in apical layer

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14
Q

what is the function of simple squamous epithelium?

A

high rate of transport without significant processing of transported material

so this type of epithelium is really common for mucous membranes or serous membranes

ex. in the lungs, the epithelium will be simple squamous so that oxygen can travel into the lungs easily

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15
Q

what is simple squamous epithelium?

A

single cell layer composed of flat, plate-like cells with flattened nuclei

every cell sits on the basal lamina

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16
Q

what is simple cuboidal epithelium?

A

it is composed of cube shaped cells with centrally located, spherical nuclei

ex. very common in renal tubules!

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17
Q

what is the function of simple cuboidal epithelium?

A

epithelial tissue which is involved in secretory or absorptive functions is usually simple cuboidal or simple columnar because more organelles allow for more processionals g of transported material

simple cuboidal cells look eosinophilic because of all the mitochondria in the cytoplasm that they use for active transport!

ex. renal tubules!!

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18
Q

what is simple columnar epithelium?

A

simple columnar epithelium is composed of cells that are taller than they are wide, with nuclei usually located in the basal compartment of the cell

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19
Q

what is the function of simple columnar epithelium?

A

it performs a variety of secretory and/or absorptive tasks, such as absorption of the end products of digestion in the intestine and concentration of bile in the gallbladder

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20
Q

what is the function of goblet cells?

A

they make mucous to protect the epithelial cells

without them you’d end up with ulcerations

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21
Q

what is pseudo stratified columnar epithelium?

A

it is actually a simple epithelium, since all its cells are in contact with the basement membrane!

however, the apical surfaces of some of these cells do not reach the apical surface of the epithelial sheet

the taller cells in this type of epithelium will have different placement of their nuclei within the epithelial sheet as a whole than will the shorter cells, which have their nuclei near the basement membrane – this variable placement of nuclei gives the false (“pseudo-”) impression that this epithelium is stratified

the shorter cells in pseudostratified columnar epithelium are stem cells – these stem cells give rise to the other cell types in this epithelium.

22
Q

what is the function of psuedostratified columnar epithelium?

A

pseudostratified columnar epithelium is found in segments of the respiratory tract not involved in gas exchange, and in some regions of the male reproductive tract

23
Q

what is stratified epithelia?

A
  1. two or more cell layers
  2. named for most apical cell type
  3. less permeable than simple epithelia
  4. provide protection and structural support for protection for subjacent tissues

in stratified epithelium, cells in the upper layers are continuously lost and replaced by cells migrating apically from lower layers

stem cells are located in the basal layer, which is in contact with the basal lamina

24
Q

what are the types of stratified squamous epithelium?

A
  1. stratified squamous non-keratinized
  2. stratified squamous keratinized
  3. stratified cuboidal
  4. stratified columnar
25
Q

what is stratified squamous non-keratinized epithelium?

A

in this type of epithelium, the apical cells are squamous, but do not undergo keratinization

this epithelium forms a relatively tough, impermeable barrier

it is seen in the esophagus and the vagina

26
Q

what is stratified squamous keratinized epithelium?

A

in keratinized epithelium, cells undergo a process of differentiation as they migrate to more apical layers –> in the course of this differentiation process, cells acquire more cytoskeletal elements, create more intercellular links, and extrude a material which creates a water impermeable barrier

by the time these cells reach the most apical layers, they have lost all of their organelles, including their nuclei

this process is called keratinization or cornification!

in the epithelial component of skin, the epidermis, stratified squamous, keratinized epithelium acts as an effective barrier against water loss, and protects against the abrasive external environment

27
Q

where are stratified cuboidal and stratified columnar epithelium found?

A

they are both not very permeable

they are found lining some ducts, which act as conduits rather than modifying a secretory product

such ducts are found in sweat glands and in mammary glands

28
Q

what is transitional epithelium?

A

it looks like fluffy pillows

it’s only seen in excretory passages of the urinary tract

it protects underlying tissues from the components of urine and accommodates for rapid volume changes

29
Q

what causes metaplasia?

A

changing environmental conditions may change the signals that are sent to epithelial stem cells – this causes the stem cells to produce a different type of epithelial cell

the process of metaplasia, therefore, does not result from transformation of one mature cell type into another mature cell type; instead, it occurs at the point where cells are produced by a given stem cell

an example of metaplasia is seen in respiratory tract epithelium subjected to chronic irritation, such as results from smoking – under these conditions, the lining epithelium may change from pseudostratified ciliated columnar epithelium to the tougher stratified squamous, non-keratinized epithelium

although in this process the respiratory tract gains the protective effects of stratified squamous epithelium, because the metaplastic epithelial cells have no cilia, and because goblet cells have been lost, the respiratory tract loses the benefits of the mucociliary escalator

30
Q

what are the types of epithelial junctions?

A
  1. occluding junction
  2. anchoring junction
  3. communication junction
31
Q

what are the components of a generic intercellular junction?

A
  1. transmembrane proteins
  2. cytoplasmic proteins
  3. cytoskeletal attachment
  4. size of intercellular space
32
Q

what is an occluding junction?

A

aka tight junction

these junctions are the MOST apical junction between two cells and regulate what gets through the cell junction

the transmembrane proteins form strands, which fuse at discreet points (“kisses”), occluding the intercellular space at those points

the zonula occludens is formed by the fusion of two different classes of transmembrane proteins: claudins and occludins

the claudins and occluding are then linked to a variety of cytoplasmic proteins which in turn are linked to actin cytoskeletal protein

33
Q

what is the function of an occluding junction?

A

the tight junction establishes an apical and basal compartment

it limits the mobility of membrane proteins like transport proteins or receptors so that they are restricted to the apical or basal region of the cell

this creates functional differences between the apical and basal regions of the cell, and of the tissue as a whole

ex. epithelial cells may have specialized proteins for transporting glucose across the apical membrane, and have other proteins for the transport of ions on the basal membrane

they also act like a gate a regulate the passage of lateral between cells establishing a permeability barrier across the epithelial sheet –> large molecules can’t get through the small pores created by strands of claudins ut small ones probably can get through

34
Q

what are the 2 transmembrane proteins involved in a tight junction?

A
  1. claudins

2. occludins

35
Q

what are the 2 types of anchoring junctions?

A
  1. cell to cell = they link the cytoskeleton of one cell to the cytoskeleton of adjacent cells

zonula adherent and macula adherens

  1. cell to basal lamina = link the cytoskeleton of a cell to the underlying basal lamina

hemidesmosome and focal adhesion

36
Q

what is the function of anchoring junctions?

A

they provide structural support and strength

they act as points of mechanical attachment between adjacent epithelial cells and between epithelial cells and the underlying tissue

they are more prominent in epithelium which is subjected to relatively large shear forces, such as the epidermis of the skin

37
Q

what is the zonula adherens?

A

the zonula adherens is ALWAYS just basal to the zonula occludens

it’s a band that provides a lot of structural support and anchor two cells together

a zonula adherens is required for the formation of an occluding junction

E-cadherins are the transmembrane proteins that bind to the cytoplasmic proteins and form an intracellular plaque composed of vinculin and actinin

these cytoplasmic proteins are bound to actin filaments in the apical region of the epithelial cell –> the resulting band of actin is called the terminal web

38
Q

what are the transmembrane proteins in a zonula adherens? cytoplasmic proteins?

A

E-cadherin

these are glycoproteins that are Ca dependent members of the cadherin family

they bind to catherine of an adjacent cell and form a strong mechanical link –> the resulting intercellular space includes regions for Ca binding

the cytoplasmic proteins are the vinculin and actinin

39
Q

what is a macula adherens?

A

aka desmosome!

it’s a spot of strong cell-cell adhesion but it’s not a band so it won’t always be seen in section

they look like multiple little spot welds that extend all the way down the two cells

however, you don’t see the terminal web like you do with zonula adherens

40
Q

what are the transmembrane proteins of the macula adherens?

A

cadherin

41
Q

what is a junctional complex?

A

a grouping of intercellular junctions common to all epithelial sheets

this grouping includes:
1. occluding junctions

  1. zonula adherens
  2. macula adherens

ZO-ZA-MA

42
Q

what are hemidesmosomes?

A

they link an epithelial cell to its underlying basal lamina

transmembrane proteins = integrins which interact with the laminin and type IV collagen of the basal lamina

cytoplasmic proteins form a plaque and are linked to intermediate filaments of the cytoskeleton

43
Q

what are communicating junctions?

A

aka gap junctions

transmembrane proteins, called “connexins”, of one cell align and bind to transmembrane proteins of the adjacent cell to form a pore, called the “connexon”

small, water-soluble molecules (ions, some cytokines) can pass from one cell to another through these communicating junctions

44
Q

what are the apical specialization of epithelial cells?

A
  1. microvilli

2. cilia

45
Q

what are the basal specialization of epithelial cells?

A
  1. lateral infoldings

2. basal inholdings

46
Q

what are microvilli?

A

finger-like projections which extend from the apical surface of the cell

individual microvilli cannot be resolved in light microscopy, but can be seen in EM

used to increase surface area or move material over the apical cell surface

47
Q

what are the components of a microvilli?

A
  1. glycocalyx
  2. actin
  3. terminal web

microvilli have an actin core which goes down and interacts with the terminal web

they also have a glycocalyx which is rich in enzymes and helps break stuff down or speed up reactions which is important in the GI tract for example

48
Q

can microvilli move?

A

yes

contraction of the terminal web which is connected to the actin core of the microvilli can cause the microvilli to move!

49
Q

what are stereocilia?

A

very large microvilli

as with other microvilli, stereocilia increase the apical cell membrane surface area, allowing for increased absorption

stereocilia are found in the cochlea of the ear and the epididymis* of the male reproductive tract

50
Q

what are cilia?

A

motile structure on the apical side of epithelial cells that help move material across an epithelial surface like through the lumen of an airway

51
Q

what is the function of lateral and basal infoldings?

A

they increase surface area

basal infoldings are really common in epithelial cells which are engaged in ion transport across the basal cell membrane, such as in renal tubule cells

MSK Week 4 (11 decks)

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