Lecture 21 - Epithelia and cell junctions Flashcards
What are epithelia
avascular tissues composed of cells, usually organised into sheets or tubules, attached to an underlying ECM basement membrane
What does Epithelium mean in latin
Epi - Upon
Thelium - To Cover
Where do epithelial cells cover
cover both the internal and external surfaces of the body
What are some common modified forms of epithelia
glandular structures (exocrine glands)
What are the types of epithelia
Simple, Stratified, columnar, cuboidal, squamous
What is an example of simple cuboidal cells
Kidney tubules
What is an example of simple columnar epithelial cells
Small intestine
What is an example of Squamous epithelial cells
Lung alveolus
What is an example of stratified epithelia
Oesophagus
What are the functions of epithelia
Mechanical protection (e.g. skin)
Permeability barrier (e.g. small intestine)
Absorption (e.g. small intestine)
Filtration (e.g. epithelium of renal corpuscle)
Secretion (e.g. sweat glands)
Diffusion of gases or fluids (e.g. lung alveoli)
Sensory (e.g. retina)
What are the two sides of an epithelia
Apical and Basal
What are epithelial held together by
Cell junctions
What are cell junctions
A specialised site on a cell at which it is attached to another cell or the extracellular matrix
What are the classifications of cell junctions
Anchoring
Occluding
Channel-forming
singal-relaying
What do anchoring junctions do
Linking cells together or to the extracellular matrix
What do occluding auctions do
Seal gaps between cells
What do channel-forming junctions do
create passageways linking the cytoplasm of adjacent cells
What do single-relaying junctions do
allow signals to be communicated from cell to cell
What are some examples of anchoring/strengthening junctions
Adheren junctions
Desmosome
Hemidesmosome
Focal Adhesion
What do adherents do and what are they composed of
Bridge between epithelial cells
Actin filaments
cadherin
Alpha-catenin
Beta-catenin
(slide 15)
What do focal adhesions do and what are they composed of
Attach epithelial cell to basal lamina
Actin filaments
integrin
Focal adhesion kinase
(Slide 15)
What do hemidesmosomes do and what are they composed of
Attach epithelial cell to basal lamina
intermediate filaments
integrin/collagen
Dystonin
(Slide 15)
What do desmosomes do and what are they composed of
Strengthen gaps between cells
Intermediate filaments
Cadherin (desmoglein)
Plakoglobin
Desmoplakin
(Slide 15)
What do cadherins do
Mediate cell-cell attachment
(slide 16)
What do Adherens do
Link cadherins to the actin filaments of the cytoskeleton
(slide 17)
What features of epithelial sheets make them ideal for an organ such as the small intestine
1 cell thick
Can bend to form a tube or a vesicle
(slide 18+19)
What do desmosomes do
link cadherins to intermediate filaments of the cytoskeleton
(slide 20)
What do integrins do
Mediate cell-matrix contacts
(slide 21)
What is an example of a disease with defective desmosomes
Pemphigus Vulgaris
autoimmune destruction of desmosomal protein
severe blistering
dehydration and infection
death
(slide 22)
What are occluding junctions specialised for
Seal gaps between epithelial cells, typically found in the lumen of the gut
(slide 23)
What do some occluding and tight junctions help do
Maintain cell polarity
What diseases are associated with a loss of function of tight junctions
Barrier function:
Crohn’s disease - Inflammation of the bowels, Permeability disorder
Fence function:
Cancer – Loss of cell polarity and cell contacts (epithelial-mesenchymal transition - EMT), increase in motility and eventual metastasis
(slide 26)
What do channel-forming junctions allow
ions and small molecules to pass directly from cell to cell
What is an example of channel-forming junctions
Example : cardiac muscle
Gap junctions allow the passage of ions this permits changes in membrane potential to pass from cell to cell = rhythmic contraction of the heartbeat
(slide 28)
What are some inherited disorders from abnormal gap junctions
Cataracts (connexin 50 affected)
Vohwinkel Syndrome (connexin 26 affected)
(slide 29)
What are channel-forming junctions in plants called
Plasmodesmata
structure of signal-relaying junctions
SLIDE 32!!!!!
What is a disease associated with a loss of signal-relaying junctions
Myasthenia Gravis
autoimmune destruction of neuromuscular junction
first indication of disease is a droopy eye
severe muscle weakness
(slide 33)
How are epithelial tubes formed
Invagination of epithelial cell sheet caused by an organised tightening along adhesion belts in selected regions of cell sheet
Adhesion belt with associated actin filaments
Epithelial tube pinches off from overlying sheet of cells
