Epithelial Tissues

Question 1

What is epithelia ?

Answer 1

cells that line or cover internal and external body surfaces. Form secretory gland or ducts.

Question 2

Function of epithelia

Answer 2

Protection- epidermis
Absorption- intestinal lining
Secretion- salivary gland

Question 3

Lamina propria

Answer 3

CT underneath epithelium

Question 4

How does epithelial cells derive nutrition?

Answer 4

Epithelial cells are avascular (lack blood vessels).
Derive nutritions and O2 from vessels in the lamina propria (connective tissue)

Question 5

Epithelium is classified by ?

Answer 5

Shape and arrangement.

Question 6

What are the shapes of epithelial cells?

Answer 6

Squamous- flat cells, wider than they are tall.
Cuboidal- equal in height and width
Columnar- taller than they are wide.

Question 7

What are the arrangements of epithelial cells?

Answer 7

Simple- single layer of cells
Stratified- multiple layers of cells.
Specialized- pseudostratified and transitional epithelium.

Question 8

Simple Squamous

Answer 8

-Single layer of flattened cells
tends to have scanty cytoplasm and flatter nuclei.
- cells specialized for easy diffusion across their cytoplasm.

Don’t need to know location
appear in air sacs of lungs, lining of blood vessels (endothelium), and structures in kidney

Question 9

Simple cuboidal

Answer 9

appear square. round nuclei.

line collecting tubules of kidneys that participates in water reabsorption.

Question 10

Simple columnar and location

Answer 10

Taller than they are wide.
rounded nuclei.
found in bronchial tubes of the lungs, uterine tubes, and lining of stomach and intestinal tract.

Question 11

Stratified epithelium?

How is it classified?

Answer 11

-epithelia composed of more that one layer of cells.
-only bottom layer touches the basement membrane.
-nuclei in each layer are basically aligned with each other.

classified based on shape of the TOP layer into:
stratified squamous, stratified cuboidal, and stratified columnar.

Question 12

What are the rare types of stratified epithelium found in larger gland and male urethra?

Answer 12

Stratified cuboidal and stratified columnar epithelium.

Stratified cuboidal line ducts of sweat gland.

Stratified columnar in the male urethra protect tissue from urine by secreting mucus.

Question 13

Stratified Squamous

Answer 13

-Piles of flattened cells with many layers.
- most common type of stratified epithelium.
- in places that undergo friction.
- can undergo keratinization; cells synthesize keratin filament to enhance cell toughness.
- Found in the vocal folds, esophagus, epidermis of the skin, vagina.

Question 14

What is the most common type of stratified epithelium ?

Answer 14

Stratified squamous cells

Question 15

Keratinized stratified squamous cells

Answer 15

Cells synthesized keratin filament to enhance cell toughness.
found in high friction area.
Cells in the upper layers may eject cellular organelles including nucleic. In histological section , cells closest to the lumen lack nuclei.

Question 16

Pseudostratified epithelium

Answer 16

Cells of different shapes and sizes.
May appear as if cells are in layers, however all cells touch the basement membrane.

Eg. epithelium of respiratory system contains columnar cells, basal cells, and globules.

Cilia often associated with pseudo stratified but not always.

Question 16

Non keratinized stratified squamous

Answer 16

in esophagus and vagina.

Question 17

Apical Domain

Answer 17

Facing the lumen.
Contains specialized structures that add functionality such as receptors.
three important apical specializations:
- microvilli
-cilia
-stereocilia

Question 18

Microvili
what are they?
what side of the cell?
where are they present ?
how do they appear in TEM?

what are they made off ?

Answer 18

-Short, finger-like projections of UNIFORM length. Enclosed by plasma membrane
- on the apical surface.
- appear as individual structures in a TEM
Increases surface area.
- compromised of actin microfilaments that inserted into network cytoskeletal protein referred to as the terminal web
- bc it can’t be seen clearly in LM, it’s referred to as brush border

Question 19

Cilia

what is the protein?
can it bee seen in LM ?

Answer 19

-Longer, hair-like apical specializations
-Not uniformed in length
-individual strands can be seen in light microscope.
-Microtubules in 9+2 arrangement.
- Motility; attached to outer microtubules are dyne motor proteins
In respiratory tract; cilia beats to move fluid and harmful surfaces.

Question 20

Primary Cilia Dyskinesia

why does this happen?

Answer 20

Recessive genetic disorder where ciliary microtubules lack dyne arms and are therefore nonmotile.

In respiratory system, cilia can’t clear mucus resting in chronic sinusitis and bronchitis.

All cilia in the body is affected since this is a genetic disorder.

Question 21

Stereocilia

what kind of filaments?
Motility ?
length? branching ?

Answer 21

Related to microvilli
Core of actin filament that attache to terminal web
Longer, can branch.

Rare; found in the epididymis(male parts) and inner ear.

Not motile.

Question 22

Basal domain

Answer 22

faces the basement membrane.
Includes important structures:
- Basement membrane
- hemidesmosomes: junctions that attach the cell to BM
- basal infolding (striations): plasma membrane of the cell folds around the cell.

Question 23

Basement membrane

Cellular/aceelular?
function?
mutation cause what?

Answer 23

Acellular sheet of macromolecules that function as:
- structural support of epithelium and attachment site to lamina propria
- semipermeable filter; mutation in BM results in kidney disease where filtration is compromised

divides into basal lamina and reticular lamina.

Question 24

Important macromolecules of BM ?

Answer 24

Colagen fibers
laminas,
integrin proteins

Question 25

BM appearance

Answer 25

H&E- acellular pink area

EM- resolves into two layers:
– Basal lamina: dense line. base of epithelial is attached here , contains molecules that act as permeability barrier
– Reticular lamina: fibrous mesh that provides structure and attaches basal lamina to lamina propria

Question 26

Hemidesmosome

Answer 26

Junction that attach the basal domain of the cell to the basal lamina.
- distribute force through the epithelium, increasing structure integrity.

Consist of proteins that anchor to structures in the following ways:
inside cell- intracellular plaques binds to keratin intermediate filament.
outside cell- extracellular domains of integrals and laminin within the hemidesmosome bind to molecules in the basal lamina.

Question 27

Lateral Domains

Answer 27

site of attachment to other cells in epithelia cells.
house junctions.

avenue of paracellular transport

Question 28

Tight junction

Answer 28

AKA Zonula Occludens.

Important to cellular polarity .
Selective permeability

Form seals that prevent proteins from migrating to other domains.

Limit transcellular transport.

Found in lateral domain adjacent to the apical surface.

Formed by Claudin and Occluding.

Claudin and occluding attach to actin filaments of the terminal web inside the cell

Outside the cell they bind to each other.

Question 29

Zonula Adherens (ZA)

Answer 29

Attach cells together and stabilize the sheets.

Form continuous belt (Zonula) around the lateral surface of the cell.
Directly apposed in adjacent cells- plasma membrane is held together by cadherins.

outside the cell- cadherins bind to one another.
inside the cell - cadherins connect to actin filaments .

Found below tight junction.

Question 30

Desmosomes

Answer 30

Aka Macula adherens

Forms a series of attachment points (spot welds) that stabilized epithelium.
important in skin .

Below tight junction and zone adherent.

Hold adjacent plasma membrane together by desmocollin and desmoglein

outside cell they bind to each other
inside cell thick they attache to thick protein plaques that connects them to intermediate filaments.

disruption causes Pemphigus blisters.: individual make antibodies that disrupt desmosomes resulting in severe blistering of skin.

Question 31

Pemphigus blisters

Answer 31

Antibodies bind and disrupt desmosomes resulting in sever blistering of the skin.

Question 32

Gap junction

Answer 32

Electrochemical communication bt cells.

below desmosomes

Consists of transmembrane connexin proteins that form channels between cells called connexions.

six connexin makes up one connexon

two connexons make up one gap junctions

Question 33

What type of filament does each of the junctions associate with?

Answer 33

Tight junction- actin filament
Zonula Adherens- actin filament
Hemidesmosome- intermediate filament
macula adherens / desmosome- intermediate filaments.