lecture 14 - epithelia Flashcards
What are Epithelia?
- avascular tissues compose of cells, usually organised into sheets or tubules , attached to an underlying EC, basement membrane
- Cover both the internal and external surfaces of the body
How are some epithelia modified?
modified to form glandular structures
What are the 5 types of epithelia?
- simple
- stratified
- Columnar
- Cuboidal
- squamous
What type of epithelial cellar kidney tubules made of
cuboidal
What type of epithelial cells are the small intestine made of?
columnar
What type of epithelial cells are the lung alveoli made of?
squamous
What type of epithelial cells is the oesophagus made of?
stratified
What are the 7 functions of the epithelia?
- Mechanical protection
- permeability barrier
- absorption
- filtration
- secretion
- Diffusion
- Sensory
How are epithelia polarised?
- apical
- basal
How are the epithelia polarised?
- biochemically polarised
How is the physical integrity of the epithelium maintained?
Epithelia are 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 is an anchoring junction?
linking cells together or to the extracellular matrix, maintain physical integrity
What is an occluding junction?
seal the gaps between cells, prevent the leakage of water
What is an channel - forming junction?
create passageways linking the cytoplasm of adjacent cells,
What is an signal - relaying junction?
allows signals to be communicated from cell to cell of the nervous system
Where are adherens junctions situated?
At the apical part of the cell
What are the main components that adheren junctions are made up of?
- actin filaments
- cadherin
- a-catenin b-catenin
Where are desmosome junctions situated?
below the adherens junction
What are desmosome junctions made up of?
- intermediate filaments
- cadherin
- plakoglobin desmoplakin
Purpose of the adherens junction
Adherens contain plaque which attaches to both membrane proteins and microfilaments of the cytoskeleton. Adherens help epithelial surfaces resist separation during various contractile activities
purpose of desmosome junctions?
Link cadherins to intermediate filaments of the cytoskeleton
purpose of focal adhesion junctions
Link cadherins to the actin filaments of the cytoskeleton
What is the purpose of a hemidesmosome
Hemidesmosomes are multiprotein complexes that facilitate the stable adhesion of basal epithelial cells to the underlying basement membrane.
What are focal adhesions made up of?
- actin filaments
- integrin
- Focal adhesion kinase
What are hemidesmosomes made up of?
- intermediate filaments
- integrin/collagen
dystonin
What are the role of cadherins and where are they situated?
- mediate cell to cell attachment and hold them together
- They are found between cells in the plasma membrane
What is a use of the adhesion belt associated with actin filaments?
- Causes invagination of the epithelial sheet caused by the tightening of the adhesion belt .
- forms layers of cells and eventually an epithelial tube which can form many things such a neural tubes and even the brain
What are the role of integrin molecules within hemidesmosomes
Play a role in mediating cell - matrix contacts , anchor the epithelial cells to the basal lamina
What is keratin?
type of intermediate filament
What is Pemphigus vulgaris an example of?
- autoimmune destruction of the desmosomal protein
What does Pemphigus vulgarisms cause?
- severe blistering
- dehydration and infection
- potentially death
What can occluding junctions be called?
Can be called an tight junction
What do tight junctions/ occluding junctions do?
seal gaps between epithelial cells
What are tight junctions/ occluding junctions made up of?
- Claudin and occludin
- Zona occluding scaffold protein
What are the two functions of tight proteins?
- Barrier function (regulate passage of ions, water and macromolecules)
- Fence function (Maintains cell polarity)
How was it determined that occluding/ tight junctions help maintain cell polarity?
Take a fragment of epitheliem and placed in a aqeueos solution and then there is a tracer such as a salt
Process the sample and look for the tracer
Black area is the tracer , can only get so far to the tight junction
What happens when there is a loss of barrier function In tight junctions?
Crohns disease - inflammation of the bowels , permeability disorder
What happens when there is a loss of fence function in tight junctions?
Cancer - Loss of cell polarity and cell contacts (epithelial-mesenchymal transition - EMT), increase in motility and eventual metastasis
What do gap junctions do?
- allow ions and small molecules to pass directly from cell to cell
What are gap junctions made up of?
- 6 connexins form a connexon
- 1 connexon pairs up with a connexon in another cell
- They are organized as patches where you gave lots of connexons
- The connexons can open and close
What happens when there are abnormal gap junctions and what are the human inherited disorders?
- cataracts
- Vohwinkel syndrome
What are the names of channel forming junctions in plants called?
- plasmodesmata
What are the roles of neuralgia and neurexin in the synapse?
Neurexins and neuroligins are synaptic cell-adhesion molecules that connect pre- and postsynaptic neurons at synapses
What is the role of cadherin in the synapse?
Also helps to hold the cells together
What is Myasthenia Gravis?
- autoimmune destruction of the neuromuscular junction
- first indication is a droopy eye
What are epithelia?
Epithelia are avascular tissues composed of cells, usually organised into sheets or tubules, attached to an underlying ECM basement membrane
