MTM AP02 - epithelia Flashcards
What are the functions of epithelia?
barriers
selective diffusion
absorption/secretion in simple epithelia
physical protection in stratified epithelia
When might simple epithelia look stratified?
When their nuclei are at varying levels
Which layer in stratified epithelium is significant for classification?
The uppermost one
What might be present on epithelia surfaces?
Cilia or Keratin
What are transitional epithelia
Stratified epithelia found in the urinary tract, resisting the toxicity of urine
What might an epithelial cell’s size suggest about its’ activity?
A larger cell is typically more active, as it may contain more organelles
What is the function of cilia?
help trap dirt and bacteria in mucus
What is the structure of cilia?
Has an annexone centre, with 9 peripheral microtubule doublets around 2 microtubules.
kinesin and dynein move along the peripheral microtubules
What is the structure of microvilli?
Have actin microfilaments, connected by Fimbrin and villin.
The structure is connected to the membrane by myosin
The filaments are capped by formin
What cells line the bladder epithelium?
Umbrella cells, with membranes specialised to survive hypertonic urine
What is the structure of the basement membrane?
split into the finer basal lamina and the diffuse fibrous reticular lamina.
The macromolecules of the basal lamina are secreted from the basal ends of the epithelia
It separtes cellls and surrounds some cells (such as blood vessel endothelium
What is the difference between euchromatic and heterochromatic nuclei?
Euchromatic nuclei are actively transcribing, and tend to be stained much lighter
What are adhering junctions?
bind adjacent cells tightly together and act as anchorage sites for cytoskeletal components
What are the two types of adhering junctions?
Adherins - form a continuous band deep to the tight junctions
Desmosomes - small discrete attachments deep to the adherins juncitons (‘rivets’)
What are adhrerin junctions made of?
Cadherin proteins
What are hemidesmosomes?
desomosomes at the basal surface of the cell adjacent to the basement membrane
What are Gap junctions?
formed of 6 connexins in 1 connexon between adjacent cells
What are the functions of tight junctions?
seal cells together at the apical end (to maintain conc. gradients)
They control the passage of molecules between cells.
separate apical and basolateral membrane domains
What is neoplasia?
develops from abnormal growth of epithelial cells, continuing even when the stimulus is removed
What is metaplasia?
when epithelial tissue undergoes irreversible transformations.
What is the structure of a desmosome?
an adhering plaque holds the cadherin proteins in the junction, and join the keratin intermediate filaments
What to hemidesmosomes connect to at the basal end?
Integrin, NOT cadherin
What do gap junctions allow?
a concentration gradient between tissues to be regulated
Where are stratified cuboidal epithelia found?
usually only found in the salivary duct
What are the functions of the basement membrane?
filter
structural support
What are the sub-divisions of the basal lamina?
The lamina lucid
The lamina densa
