Ch 4: Epithelium & Connective Tissues Flashcards
Papillae
Small evaginations that serve as irregularities between the epithelium and connective tissue.
They serve where tissue is subject to friction.
Do epitheail cells show Polarity?
Yes
What does the lamina propria do?
The connective tissue that underlies the
epithelia lining of the organs of the digestive, respiratory, and
urinary systems.
the opposite end, usually facing a space,
is the….
Apical Pole
Regions of cuboidal or columnar cells
that adjoin the neighboring cells are called
The Lateral Surfaces.
cell membranes here often have numerous infoldings to increase
the area of that surface, increasing its functional capacity.
All epithelial cells in contact with subjacent connective tissue
have at their basal surfaces a specialized, feltlike sheet of extracellularmaterial referred to as….
basement membrane
Nearest the epithelial basal poles is an electron-dense layer,
20-100 nm thick, consisting of a network of fine fibrils that
comprise
The Basal Lamina:
This lamina is made up of fine fibrils near the epithelial basal pole
reticular lamina
Lies Beneath the Basal lamina and is a more diffuse and fibrous.
The 3 parts that make up the Basal Lamina are?
Laminin: These are large glycoproteins that self-assemble
as a lacelike network immediately below the cells’ basal
poles where they are held in place by the transmembrane
integrins.
■■ Type IV collagen: Monomers of type IV collagen contain
three polypeptide chains and self-assemble further
to form a feltlike layer.
■■ The laminin and type IV collagen networks are held
together by the adhesive glycoprotein entactin/
nidogen, and by perlecan, a proteoglycan.
lateral surfaces of epithelial cells exhibit several specialized
intercellular junctions, which serve different functions
The 3 are:
Tight or occluding junctions form a seal between
adjacent cells.
■■ Adherent or anchoring junctions are sites of string cell
adhesion.
■■ Gap junctions are channels for communication
between adjacent cells.
The seal between the membranes is due to
interactions between the transmembrane proteins known as?
claudin
and occludin of each cell.
Review the joint complexes of epithelial cells:
Most cuboidal or columnar epithelial cells have four major
types of intercellular junctional complexes. At the apical end,
You have tight junctions (zonulae
occludens) and adherent junctions (zonulae adherens) are
typically close together and each forms a continuous ribbon
around the cell. Multiple ridges of the tight junction prevent
passive flow of material between the cells but are not very
strong
Gap junctions,
each a patch of many __________in the adjacent cell membranes,
have little strength but serve as intercellular channels
for flow of molecules.
connexons
Desmosomes (macula adherens)
Surface structure that helps with matching adjacent cells
What bind epithelial cells to the underlying basal lamina?
Hemidesmosomes
Adherent of anchoring junctions (Zonula Adherens) is done with?
Cell adhesion is mediated by cadherins in the presence of Ca2+.
After Tight Junctions, you have a second kind of junction, known as Zonula Adherens, what do they do?
encircles the epithelial cell,
usually immediately below the zonula occludens. This is an
adherent junction, firmly anchoring a cell to its neighbors.
What do Cadherins do?
They mediate cell adhesion and transmembrane
glycoproteins of each cell that interact in the presence
of Ca2+. At their cytoplasmic ends, cadherins bind catenin
that is linked via actin-binding proteins to actin filaments
What are Maculae adherens or desmosomes?
are discshaped
structures at the surface of one cell that are matched
with identical structures at an adjacent cell surface
Desmosomes (macula adherens) also contain:
larger members of the
cadherin family called desmoglein and desmocollin. On the
cytoplasmic side of each cell membrane, these proteins insert
into a dense attachment plaque of anchoring proteins (plakoglobin and desmoplakin) that bind intermediate filaments
rather than actin filaments.
The gap junction proteins, called connexins do what?
form hexameric
complexes called connexons, each of which has a central
hydrophilic pore about 1.5 nm in diameter.
When two
cells attach, connexins in the adjacent cell membranes move
laterally and align to form connexons between the two cells
(Figure 4–4), with each junction having dozens or hundreds
of aligned connexon pairs.
If you have Abnormal desmosome function, it causes
Blisters
What are Hemidesmosomes?
These adhesive structures
resemble a half-desmosome ultrastructurally, but, unlike
desmosomes, they contain abundant integrins rather than
cadherins. The transmembrane integrin proteins bind the
extracellular macromolecules laminin and collagen type IV.
