Epithelial tissue and cell membrane specialisations Flashcards
what is a tissue?
specialized cells embedded in an extracellular matrix, organised functionally and form organs and organ systems
What are the 4 key types of tissue?
- Epithelial tissue
- Connective (support) tissue
- Muscle tissue
- Nervous tissue
what types of cells form a tissue?
multiple cells can for a tissue
or
one type of cell can for a tissue
what are adhesion molecules?
hold cells together and to surfaces
where do cells sit in the body?
cells are embedded within an extracellular matrix
what is a cellular internal cytoskeleton?
network of filaments for shape, support, and movement
what is the function of the extracellular matrix?
provides structural support to cells and allows them to remain in a differentiated state
what secretes the ECM?
cells
why do cells secrete ECM?
for support and structure, and regulation of cell communication and behaviour
what is an example of when the ECM helps to maintain a differentiated state of the cell?
mouse mammary gland epithelium cultured without ECM are flat and don’t produce milk
what is an example of how ECM maintains normal development?
inactivating genes for ECM proteins results in defective skeletal development
what is a big differentiator between different types of tissue?
the ratio of cells to ECM
where is epithelial tissue found?
lines the organs and cavities within the body
covers the external body
what is the function of epithelial tissue?
protective barrier
Absorptive and secretory adaptations
how many cells form a secretory gland?
either individually or as a group
how is epithelial tissue classified?
based on layers, shapes, surface specialisations and function
what is the polarity of epithelial tissue?
has polarity, has the apical and basal surfaces
what is the purpose of the epithelial cells basement membrane?
a scaffold and anchor to underlye connective tissue (support tissue)
are epithelial tissues avascular?
yes
how do epithelial tissues get nutrients?
via diffusion
are epithelial tissues regenerative?
yes, they have stems cells that allow regeneration
what are the different epithelial cell shapes?
squamous
cuboidal
columnar
what are the different number of cell layers?
simple
stratified
pseudostratified
transitional
what is pseudostratified?
look columnar but nuclei are not in an even plain, still only one layer of cells
what are the surface classifications?
microvilli and cilia
what are the different forms of glandular epithelium?
can be single cells or grouped into glands to allow focused production of a secreted product
what are occluding junctions?
tight junctions (zonula occludens)
what are the anchoring junctions?
zonula adherens
desmosomes
hemidesmosomes
what are the communicating junctions?
gap junctions
where are junctions located?
tightly bound junction at apical region
where are zonula adherens located?
strengthens attachment to neighbouring cells as apical region
where are the gap junctions?t
communication between neighbouring cells
what are the desmosomes?
firmly anchors neighboring cells together
what are hemidesmosomes?
anchors cell to basement membrane
what is a junctional complex?
made up from a tight junction, zondula adheren, and desmosome
epithelial cells have a junctional complex
what is the function of tight junctions?
controls paracellular pathway
tight junctions are selectively permeable, evolved to allow certain molecules to pass through
what are the transmembrane proteins of a tight junction?
occludin
claudins
what is the function of claudins?
allow different molecules to pass between epithelial cells.
Different claudins for different permeabilities in different tissues
what is the function of claudin-16?
only certain regions of the kidney are permeable to Mg2+ ions
what are the effects of low Mg2+ into the blood?
magnesium deficiency
Kidney damage/renal failure
what is the functions of zonula adherens?
links cytoskeletons of adjacent cells
what is the main transmembrane protein in zonula adherens?
E-cadherins
what is the structure of zondula adherens?
they have actin microfilaments that run across the apical region of the cell
what happens if the zondula adherens dont have cedherins?
Loss of E-cadherins linked to metastesis of cancer cells
what is the function of desmosomes?
link cytoskeletons of adjacent cells. Connect to cytokeratin (intermediate filaments)
what is cytokeratin?
protein found within epithelial cells
what are desmosomes main transmembrane protein?
cadherins such as desmoglein
what is pemphigus vulgaris?
Autoimmune disease.
Antobodies attack desmoglein 3 which keeps cells bound together.
what is the phenotype of pemphigus vulgaris?
cells fall apart, skin sloughs off
what is the function of cadherins?
cadherins are important for maintaining structural integrity of epithelium
what is the function of hemidesmosomes?
modified desmosomes
on the basal surface of the cell
anchor the cell to the basement membrane
they bind to cytokeratin
what is the main transmembrane protein of hemidesmosomes?
integrins
what are gap junctions?
communicating junctions
what are the main transmembrane proteins of gap junctions?
connexins
what is the function of connexins?
form channels called connexons that have open/close
allow passage of ions and small molecules
what is the structure of polarised epithelial tissue?
epithelial cells have an apical and basal surface
linked as sheets through lateral junctions
linked to basement membrane via junctions
Different specialisations linked to polarity of cell-provide hints as to function
what are microvilli?
fingerlike projections of plasma membrane
what is the function of microvilli?
increased surface area
what is the length of microvilli?
very short- 0.5-1 micro meter
what is the structure of microvilli?
core of parallel actin bundles
what do microvilli look like under light microscopy?
brush border
what is the function of cilia?
Motile- beat in rhythm to move substances across the surface of epithelium
Non-motile- sensory information
is the length of cilia?
~10 micrometers
what is the structure of cilia?
has a cytoskeleton composed of a core of microtubules
what is the function of the basal membrane?
binds epithelial cells to the connective tissue
Forms a barrier but allows nutrients to pass to epithelia. Regulates permeability
Controls growth and differentiation
what forms the basal membrane?
formed and maintained by both epithelia and connective tissue
What is the structure of the basal membrane?
sheet-like arrangement of ECM proteins
what does the basal membrane look like under a light microscope?
not easily distinguished with H&E staining
Immunocytochemistry can be used to stain specific components
what does the basal membrane look like under an electron microscope?
the 3 layers of the basal membrane are visible
What are the 3 layers of the basal membrane?
Lamina lucida
Lamina densa (aka basal lamina)
Lamina fibroreticularis
what are epithelial basal foldings?
folding of the basement membrane to increase surface area for exchange
what are the general properties of stem cells (no matter where they come from)?
- capable of dividing and renewing themselves for long periods
-Unspecialised
-can give rise to specialised cell types