Lecture 2, Microstructure Of Epithelium

Question 1

Epithelia definition

Answer 1

Sheets of cells that cover or line internal and external body surface, form secretory glands and ducts

Question 2

Functions of epithelia

Answer 2

Protection - all substances entering or leaving an organ must cross this tissue (ex epidermis)
Absorption (ex intestinal lining)
Secretion ( ex salivary gland)

Question 3

Characteristics of epithelia

Answer 3

Cells tightly packed together
One free surface not in contact with other cells (faces cavity of the organ)
Attached to underlying connective tissue (CT) by an acellular basement membrane (BM)
Lack of blood vessels (derive nutrition and O2 from vessels in the lamina propria

Question 4

Basement membrane definition

Answer 4

Mesh work of carbohydrates and proteins

Question 5

Lamina propria

Answer 5

Connective tissue underneath an epithelium

Question 6

Types of epithelium

Answer 6

Described by both shape and arrangement
Shape : squamous, cuboidal, columnar
Arrangement: simple, stratified, specialized

Question 7

Squamous general definition

Answer 7

Flattened cells wider than they are tall

Question 8

Cuboidal general definition

Answer 8

Cells relatively equal in height and width

Question 9

Columnar general definition

Answer 9

Taller than they are wide

Question 10

Simple general definition

Answer 10

Single layer of cells

Question 11

Stratified general definition

Answer 11

Multiple layers of cells

Question 12

Specialized general definition

Answer 12

Pseudostratified and transitional epithelium (kinda lumped together looking)

Question 13

Simple squamous epithelium

Answer 13

Single layer of flattened cells (scanty cytoplasm and flatter nuclei)
Cells specialized for easy diffusion across their cytoplasm
**appear in air was of lung, lining of blood vessels, structures in kidney

Question 14

Simple cuboidal epithelium

Answer 14

Cells have about equal physical dimensions and appear square in histo section (nucleus appears round)
Function in protection, absorption, synthesis and secretion of substances needed for the function of the organs they line
***line the collecting tubules in kidneys to participate in the reabsorption of water

Question 15

Simple columnar epithelium

Answer 15

Taller than they are wide, rounded nuclei
Function in protection, transport of materials, absorption and secretion
Found in bronchial tubes of lungs, uterine tubes, lining of stomach and intestinal tract
***cells in lining of the stomach secrete mucus that serves as a protective barrier for nearby cells

Question 16

Stratified epithelium

Answer 16

Composed of more than one layer of cells - only bottom layer touches BM
Nuclei in each layer aligned with each other
Classified based on the shape of the TOP layer of cells

Question 17

Stratified cuboidal and columnar epithelium

Answer 17

Rarer type of stratified epithelium found in larger glands and male urethra
**cuboidal line ducts of sweat glands, recycle sodium and chloride ions in sweat
***columnar in male urethra protect tissue from urine by secreting mucus

Question 18

Stratified squamous epithelium

Answer 18

Piles of flattened cells with many layers
Not as easy to see lines of nuclei (aka rows)
*most common type of stratified
Found in vocal folds, esophagus, epidermis of the skin, vagina

Question 19

How is stratified squamous adapted for toughness?

Answer 19

**seen in areas that undergo friction
Can undergo keratinization
High turnover rate because of mito activity

Question 20

Keratinization meaning

Answer 20

Cells synthesize keratin filaments that enhance cell toughness
Cells in upper layers may eject cellular organelles (including nuclei) —— in a histological section, cells closest to lumen lack nuclei

Question 21

Specialized epithelium

Answer 21

Don’t fit into simple or stratified categories

Question 22

Pseudostratified epithelium

Answer 22

Has cells of different shapes and sizes
May appear as if cells are in layer, but all cells touch the BM

Question 23

Transitional epithelium

Answer 23

Urothelium
Found in bladder and ureter
Functions to maintain a urinary barrier to keep urine stored, even when the organ is distended

Question 24

Epithelial cell polarity domains

Answer 24

Apical - faces lumen
Lateral - attached to other cells
Basal - opposite apical domain, in simple epithelium it is the domain that touches the BM

Question 25

Apical domain

Answer 25

Surface facing the lumen
Contain specialized structures that add functionality
-proteins (receptors, transporters, channels) allow interactions with lumen
-other specializations increase surface area or help move substances along epithelial surface
Microvilli, cilia, stereo cilia

Question 26

Microvilli

Answer 26

Short, finger-like projections of uniform length on apical surface
-enclosed by plasma membrane
-significantly increases SA
Appear as individual structures in TEM
**present in cells specialized for absorption

Question 27

Microvilli in microscopy

Answer 27

In TEM - individual structures
-supported by actin filaments which insert into a network of cytoskeletal proteins (terminal web)
-glycocalyx seen as a fuzzy border
In light - look like bristles of a soft brush (brush border)

Question 28

Cilia

Answer 28

Longer, hair like apical specializations
-not as uniform in length
-individual strands can be seen in light micro.
**specialized for motility
Ex; resp tract have cilia that flex to move fluid along surface to transport particulate to places where it can be disposed of

Question 29

Structure of cilia

Answer 29

Internal array of microtubules arranged with one pair at the center and 9 pairs in a ring (9+2)
Dynein motor proteins attached to outer microtubule pairs

Question 30

Primary ciliary dyskinesia

Answer 30

Recessive genetic disorder where cilia lack dynein arms (=nonmotile)
In resp. System, cilia can’t clear mucus = chronic sinusitis and bronchitis
All cilia in body are affected

Question 31

Stereocilia

Answer 31

Specializations related to microvilli
Rarer - found in epididyis and inner ear
Not motile
Have core actin filaments that attach to terminal web
Longer, can branch

Question 32

Basal domain

Answer 32

Area opposite apical domain
Basement membrane (BM)
Hemidesmosomes
Basal unfolding (striations)

Question 33

Basement membrane

Answer 33

Acellular sheet of macromolecules
Functions :
Structural support for epithelium and attachment site to lamina propria
Semipermeable filter
Collagen fibers, laminins, and intergrin proteins

Question 34

BM appearance microscopy

Answer 34

H&E - acellular pink area in basal domain of bottom row of epithelium
EM - two layers
-basal lamina - dense line, base of epithelial cells is attached here, contains molecules that act as permeability barrier
-reticular lamina -fibrous mesh that provides structures and attaches basal lamina to lamina propria

Question 35

BM reticular lamina

Answer 35

fibrous mesh that provides structures and attaches basal lamina to lamina propria

Question 36

BM basal lamina

Answer 36

dense line, base of epithelial cells is attached here, contains molecules that act as permeability barrier

Question 37

Hemidesmosome

Answer 37

Junction that functions to:
Attach basal domain of cell to the basal lamina
Distribute force throughout epithelium = increases structural integrity
Consist of protein plaques that anchor to structures

Question 38

Hemidesmosome protein plaque inside cell

Answer 38

Binds to intermediate filaments (keratin) of cytoskeleton

Question 39

Hemidesmosome protein plaques outside cell

Answer 39

Extracellular domains of inegrins and laminins within HD bind to molecules in basal lamina

Question 40

Lateral domain

Answer 40

Site of attachment to other cells in sheet
Avenue of transport for materials (paracellular pathway)
**Proteins here form junctions that attach cells together and regulate transport

Question 41

Occluding junctions in lateral domain

Answer 41

Seals cells together, control transport of substances via paracellular pathway (tight junctions)

Question 42

Adhering junctions in lateral domain

Answer 42

Mechanically attaches cells together or to extracellular matrix
Zonula adherents, macula adherens (desmosome)

Question 43

Communicating junctions in lateral domain

Answer 43

Mediates passage of chemical or electrical signals from one cell to another
Gap junctions

Question 44

Tight junctions

Answer 44

Zonula occludens
Important to cellular polarity & ability to constrict fluids (selective permeability)
Found in lateral domain adjacent to apical surface
Formed by transmembrane proteins Claudin and occludin

Question 45

Tight junctions form seals that :

Answer 45

Prevent proteins from migrating to other domains
Limit transcellular transport

Question 46

Zonula adherens (ZA)

Answer 46

Junctions that attach cells together and stabilize sheet
Forms a continuous belt (Zonula) around cell on lateral surface
Directly apposed in adjacent cells - plasma membranes held together by cadherins
Found just below tight junctions

Question 47

Desmosomes (macula adherens)

Answer 47

Form a series of attachment points that stabilize
**important in skin
Generally below tight junctions and zona adherens
Hold adjacent plasma membranes together by desmocollin and desmoglein

Question 48

Gap junctions

Answer 48

Junctions that permit flow of ions and small molecules
Allow for electrochemical communication between cells
N lateral domain below tight junctions and ZA
Consist of transmembrane connexin proteins that form channels between cells (connexons)
2 connexons form a gap junction *****

Question 49

Order of junctions in lateral (from apical)

Answer 49

Tight, adherens, desmosome, gap
Hemidesmosome basal domain to basal lamina