ANAT241 Lecture 8 - Epithelial Tissue and Cell Membrane Specialisations Flashcards
what are tissues?
tissues are specialised, similar cells embedded in an extracellular matrix (ECM)
what are the 4 tissue types?
epithelial tissue
connective (support) tissue
muscle tissue
nervous tissue
what are cells composed of?
an internal cytoskeleton network
what is the function of the internal cytoskeleton network?
for shape, support and movement
what do cells secrete?
extracellular matrix (ECM)
why do cells secrete extracellular matrix?
for support, structure, regulation of cell communication and behaviour
where does epithelial tissue line?
lines organs and cavities within the body and covers the external body as the epidermis
what is epithelial tissue?
a protective barrier with absorptive and secretory adaptations that has polarity with an apical and basal surface and a basement membrane that acts as a scaffold to underlying connective (support) tissue
how does epithelial tissue acquire nutrients?
epithelial tissue is avascular and therefore acquires nutrients via diffusion
what allows the regeneration of epithelial tissue layers?
stem cells
what 3 criteria is epithelia classified based on?
classified based on cell shape
the number of cell layers
cell surface specialisations
what are the 3 types of epithelial cell shape?
squamous
cuboidal
columnar
what are the 4 types of epithelial cell layers?
simple
stratified
pseudo-stratified
transitional
what are the 2 epithelial cell surface specialisations?
microvilli and cilia
what are microvilli?
finger-like projections of the plasma membrane
what is the size of microvilli?
they are short between 0.5um and 1um
what is the function of microvilli?
increase the surface area for absorption in the intestine and kidney
what are microvilli composed of?
composed of a core of parallel actin bundles
what do microvilli appear as under light microscopy?
appear as a brush border
what do microvilli appear as electron microscopy?
appear as individual microvilli
what is the shape of microvilli maintained by?
maintained by actin filaments
what are cilia composed of?
a cytoskeleton with a core of microtubules
what is the size of cilia?
they are half of the cell length as they are upto 10um long
what is the function of non-motile cilia?
to provide sensory information
what is the function of motile cilia?
to beat in rhythm to move substances across the surface of epithelium
what is an example of motile cilia?
cilia in the respiratory tract or sperm flagellum
what are modified cillium?
sperm flagellum
what are epithelial cells connected together by?
connected via cellular junctions
what are the 3 types of cell junctions?
occluding junctions
anchoring junctions
communication junctions
what are the 2 types of occluding junctions
tight junctions
zonula occludens
what are tight junctions?
tightly bound junctions at the apical region of a cell
what do tight junctions control?
control the paracellular pathway through the transmembrane proteins of occludens and claudins
what is the function of claudins?
different provide different permeabilities in different tissues
what is the function of claudin-1?
claudin-1 is responsible for the waterproof qualities of the skin
what is claudin-16 responsible for?
responsible for permeability to Mg2+ ions in specific regions of the kidney
what does a mutation in the claudin-16 gene result in?
results in an abnormal claudin-16 causing the tight junction to be impermeable to the Mg2+ ion
what is the effect of low Mg2+ reabsorption?
low Mg2+ reabsorption back into the blood results in a deficiency causing kidney damage/renal failure
what are the 3 types of anchoring junctions?
zonula adherens
desmosomes
hemidesmosomes
what is the function of zonula adherens?
to strengthen the attachment to neighbouring cells at the apical region by linking the cytoskeleton of adjacent cells through the main transmembrane protein of E-cadherins attached to actin microfilaments via anchoring proteins
why are cadherins important?
the loss of E-cadherins has been linked to the metastasis of cancer cells
what is the relationship between malignant cancer cells and E-cadherins?
cancer cells have lower levels of E-cadherin expression
what is another name for desmosomes?
macula adherens
what is the function of desmosomes?
to firmly anchor neighbouring cells together by linking the cytoskeletons of adjacent cells by connecting to the intermediate filaments of cytokeratin
what is the main transmembrane protein in desmosomes?
cadherins such as desmoglien
what are hemidesmosomes?
modified desmosomes on the basal surface of cells
what is the function of hemidesmosomes?
to anchor cells to the basement membrane by binding to cytokeratin
what is the main transmembrane protein of hemidesmosomes?
integrins
what is a type of communication junction?
gap junctions
what is the function of gap junctions?
communication between neighbouring cells
what is the main transmembrane protein of gap junctions?
connexins
what is the function of connexins?
connexins form channels called connexons that can open/close to allow the passage of ions and small molecules
what are connexons?
connexin channels that open/close to allow the passage of ions and small molecules
how is epithelial tissue linked?
linked as sheets through lateral junctions and linked to the basement membrane via junctions
what is the function of the basement membrane?
the basement membrane binds epithelial cells to connective tissue and form a barrier that allows nutrients to pass to epithelia to regulate permeability controlling growth and differentiation
what is the basement membrane?
sheet-like arrangement of ECM proteins that if formed and maintained by both epithelia and connective tissue
what is the relationship between the basement membrane and the light microscope?
under light microscope the basement membrane is not easily distinguished with H&E staining but immunocytochemistry can be used to stain specific components
e.g collagen
what are the 3 layers of the basement membrane?
lamina lucida
lamina densa (basal lamina)
lamina fibroreticularis
what can be seen under the electron microscope in terms of basement membrane?
the 3 layers of lamina lucida, lamina densa (basal lamina) and the lamina fibroreticularis
where are basal foldings present?
present on the basal surface
what is the function of basal foldings?
to increase the surface area on the basal surface of a cell
what are the structures that act as a protective barrier in epithelium?
the basement membrane and junctional complexes that hold epithelium as a sheet
what is the dual function of microvilli, basal foldings and the basement membrane?
structures that absorb substances from the apical surface and pass it onto to the underlying tissues