ILS6-epithelial tissue Flashcards
Functions of the Epithelial Tissue (7)
- Protection or barrier (epithelial cells of the
skin)(ILS-4 HDM) - Absorption (epithelium in liver, intestines, and
lungs) - Secretion (epithelial tissue in glands secrete
enzymes, hormones, and fluids) - Excretion and transport (epithelial tissue in the
kidney and sweat glands) - Filtration (epithelium in the kidney and
respiratory system) - Contractility (Myoepithelial cells)
- Sensory reception (Taste buds of the tongue,
what is the basement membrane (BM) of epithelial tissue compossed of?
basal lamina + reticular lamina
basal lamina contains____
a thin meshwork of type IV collagen (ILS-7) and laminin associated with proteoglycans and glycoproteins, secreted by epithelial
cells
reticular lamina contains ____
type III collagen and anchoring fibrils of type
VII collagen, secreted by fibroblasts
function of Basement membrane
- attach epithelia to connective tissue
- provide a guide or scaffold during tissue regeneration after injury
- compartmentalize epithelial cells from other tissues
- filter substances passing from connective tissue into epithelia
- Prevent tumor metastasis
below the Basement membrane you find the _____
Lamina propria is a thin, irregular connective tissue
special function of basement membrane in kidney
filter
Microvilli
short membrane projections with cores of actin filaments
* increase epithelial cells’ apical surface area for absorption (intestine)
- Stereocilia
- Long microvilli with specialized mechanosensory functions in cells of the
inner ear and for absorption in tissues of the male reproductive tract
Cilia
- larger projecting structures
- has a well-organized core of microtubules (in a 9 + 2 arrangement called
the axoneme) in which restricted, dynein-based sliding of microtubules
causes ciliary movement that propels material along an epithelial surface
The internal structure of microvilli
The internal structure of microvilli contains a core of
actin that is cross-linked by actin-bundling proteins
what are the Actin-bundling proteins:
Actin-bundling proteins: fascin, espin, and fimbrin FEF
what anchors the actin of microvilli to the membrane
tip of head is anchored by villin
Myosin I: binds the actin to the plasma membrane of the microvillus
* Myosin II and tropomyosin of the terminal web (TW)
explain its contractile ability
* The TW is composed of actin filaments stabilized
by spectrin, which also anchors the TW to the apical cellmembrane
stereocilia
immotile microvilli
where is stereocilia found ?
- Limited to the epididymis, the proximal part of
the ductus deferens of the male reproductive
system, and the sensory (hair) cells of the
inner ear - Stereocilia of the genital ducts are extremely
long processes that extend from the apical
surface of the cell and facilitate absorption - Stereocilia of the sensory epithelium of the
ear are sensitive to mechanical vibration and
serve as sensory mechanoreceptors - Stereocilia can be easily damaged by
overstimulation, so they have a molecular
mechanism to continuously renew their structure
stereocilia of epididymis are ______
long
stereocilia are anchored to the memebrane by
Ezrin (myosin 1 and 1 in microvilli)
no villin
cilia
different types of cilia
Cilia
* Hair-like extensions of the apical plasma membrane containing an axoneme
different types of cilia
- Motile cilia are on the apical side of
epithelial cells - Primary cilia (monocilia) are solitary
immotile projections on almost all
eukaryotic cells - Nodal cilia are in the embryo on the
bilaminar embryonic disc at the time of
gastrulation
Motile cilia
Motile cilia are on the apical side of
epithelial cells
- Primary cilia (monocilia)
are solitary
immotile projections on almost all
eukaryotic cells
-function as chemosensors, osmosensors,
and mechanic sensors
- mediate light sensation, odorant, and
sound perception
- Nodal cilia
_____are in the embryo on the
bilaminar embryonic disc at the time of gastrulation
- play an important role in early embryonic development
- perform clockwise rotational movement
what is the structure of Cilia?
Axoneme- microtubule based structure, extends from the basal body
a centriole-derived, microtubule-organizing center (MTOC) located in
the apical region of a ciliated cell
microvili and cilia look similar under microscope
- ciliary apparatus= basal bodies + basal body–associated structures
- Motile cilia and their counterparts, flagella, possess a typical 9 + 2
axonemal organization with microtubule-associated motor proteins
generating forces needed to induce motility
Epithelial intercellular junctions
* Lateral cell-to-cell junctions (3)
Tight or occluding junctions:
Adherent junctions or desmosomes
Gap or communicating junctions
Tight or occluding junctions:
interacting
transmembrane proteins (claudin and occludin)
prevents intracellular passage
Adherent junction or desmosomes
formed by the
cadherin, strong sttachement between epithelium
may form zonula adherens encircling epithelial cells just below
their tight junctions and attach indirectly to actin filaments or
scattered, spot-like attachment sites
called desmosomes or maculae adherens, which attach
to keratin* intermediate filaments
Gap or communicating junctions
points of cell contact
where both plasma membranes have hexameric complexes
of transmembrane connexons, each forming a channel
(pore) allowing passage of small molecules from one cell to
the other
epithelial Basal surface junction
Basal surface junction
* Hemidesmosomes composed of transmembrane integrins
attach cells to proteins of the basal lamina
Tight junctions (TJ) fuction
Allow epithelial cells to function as a barrier
* Form the primary paracellular diffusion
barrier between adjacent cells
* Limit the movement of ions, water, and other
macromolecules through the intercellular
space
* Act as fences to prevent the migration of
lipids and specialized membrane proteins
between the apical and lateral surfaces
* Maintain cell polarity and integrity of the
apical and lateral surfaces
* Recruit signaling molecules to the cell
surface and link them to the actin
filaments of the cell cytoskeleton
Helicobacter pylori damages
binds the extracellular domains of tight-junction proteins in cells
of the stomach and inserts a protein into these cells, which
targets (Zona Occludin-1) ZO-1 and disrupts signaling from the
junction
leads to gastric ulcers
Pemphigus vulgaris
autoimmune skin disorder where IgG
targeting desmoglein leads to dissolution of the desmosomes, fluid
accumulation, and epidermal cells detach
– Symptoms: painful blisters and sores in the mouth, skin blisters
– Treatment: corticosteroids, immune suppressants,
plasmapheresis or immunoglobulins
Bullous Pemphigoid:
rare autoimmune skin disorder where IgG
(antibody) targets hemidesmosomes, specifically type XVII collagen,
causing the epidermis to detach from the basement membrane,
causing blistering
gap junctions
consists of an accumulation of
transmembrane channels or pores
* present in epithelia, smooth and
cardiac muscle, and nerves
* permit the direct passage of
signaling molecules from one cell to
another
* important in tissues in which the
activity of adjacent cells must be
coordinated, such as epithelia
* engaged in fluid, electrolyte, small
metabolites transport, vascular and
intestinal smooth muscle, and heart
muscle
what microorganism damages the tight junction s
Clostridium perfringes
-its enterotoxin binds to claudin of tight junction and messes up its maintence
causes fliud loss
Helicobacter Pylori,
target the Zona occludin and disrupt the signaling from the junction, leads to gastric ulcers
