Lecture 3A: Epithelial Border Mods

Epithelia are allowed to perform specific functions due to

border modifications

Epithelial junctions can be classified according to their

function

most cell junctions are part of the

junctional complex

where is the junctional complex located?

on the lateral border of epithelial cells

Epithelial junctions are typically how big in size

20-90 nm

What is another name for tight junctions

zona occludens

tight junctions begin just beneath the

luminal surface

what do tight junctions do?

they seal neighboring cells

Tight junctions cause the outer membrane of neighboring cells to

fuse

the fuse between cells in the tight junction form a

circumferential belt

the circumferential belt of the tight junction seals the

intercellular space from the lumen

What are the 3 types of cytoskeletal linked junctions?

adherent

desmosomes

hemidesmosome

what is another name for adherent junctions

zona adherens

Adherent junctions form a continuous adhesion belt around each interacting epithelial cell near the apical surface just beneath the

tight junction

membranes of the adherent junction are fused as well - T or F

F - they are not fused but separated by a narrow space

plasma membranes found in the narrow space of adherent junction

cadherins

what is occurring in the narrow space of the adherent junction?

cadherins interact with one another

proteins are anchored by adjacent ________ _______ containing numerous _____ filaments

cytoplasmic condensations, actin

What forms the terminal bar

tight junction and adherent junction

Desmosomes are also called

macula adherens

How are desmosomes similar to adherent junction?

membrane apposition and protein interactions

how do desmosomes differ from adherent junctions?

they do not have to be located near the lateral luminal surface

desmosomes do not ______ the cell and occur more often as _____ _____

encircle, spot welds

Unlike adherent junctions, desmosomes also have extracellular filaments that space the _________ ______ and further -

extracellular space

anchor the membranes together

what are hemidesmosomes?

half a desmosome used to anchor cell to basal lamina

what is a gap junction?

broad area of closely opposed plasma membranes that are NOT fused.

The gap junction is spanned by assemblies of

hexagonal connexon proteins with central pore

the proteins and pore of the gap junction allows for a

low resistance channel of electrochemical communication between cells

what are the two types of apical border modifications

microvilli and cilia

Microvilli in comparison to cilia are

smaller but more numerous

microvilli have finger like projections about ____ microns long and usually have _____/cell

1-2 microns

3000/cell

Microvilli have an internal network of

actin filaments

microvilli act to

increase surface area in absorptive epithelia

Microvilli are referred to as ______ _______ in the gut, and ______ ______ in the renal tubules

striated border - gut

brush border - renal tubules

What are stereocilia

branched microvilli (uncommon)

where are stereocilia found

epididymis of male reproductive tract

Cilia are hair like projections about _____ microns long and have about ____/cell

5-10 microns

300/cell

cilia contain a core of

bundled microtubules

microtubules have _____ _____ that use ATP to cause the tubules to move ______ to one another

dynein motors

longitudinal

cilia occur in

parallel rows that beat together

Cilia rows beat together to move

fluid over the surface

cilia are most common in

respiratory and reproductive tracts

(from lecture) tight junctions and adherent junctions both

loop around the cell

(from lecture) epithelial cells do not have to have all types of junctions - T or F

T

(from lecture) Gap junctions have ___ channels of how many proteins

2 channels of 6 proteins

(from lecture) microvilli provide _____ and have _____ on the top/surface

structure, glycoproteins

(from lecture) the central microtubule of cilia has how many motors

9

(from lecture) what are the three types that make up the junction complex

tight, adherent, desmosome

gap is not part of it

What is A?

tight junction

what is B?

Adherent junction

What is C?

desmosome

What is D?

Gap junction