Epithelial Tissue Morphology Flashcards
epithelia functions
trans-epithelial transport,
secretion and synthesis and absorption,
protection,
generation of movement over apical surface (thanks to cilia)
how are epithelia classified?
dependent on their shape and number of layers
different types of shape
cuboidal, flat and columnar
transitional- capacity to change shape
different types of layers
simple epithelia- one layer
stratified epithelia- many layers
pseudostratified- appear as if many layers however only one
another name for transitional epithelium
uroepithelium
how else can epithelia be classified and give the classes?
dependent on function
absorptive, mechanical and secretory
two different types of surface specialisations + functions
cilia- movement of particles
microvilli- increase surface area for absorption
simple squamous location
blood vessels, loops of Henle
simple cuboidal location
kidney
simple columnar location
alimentary tract (nucleus is at the base of all cells)
stratified squamous location
skin
stratified squamous structure + function
many flat layers, that begin more cuboidal and become more squamous nearer the surface
differentiator cell found at the top
protect against abrasion and infection
rarest epithelia + location
stratified cuboidal
sweat glands and ducts
pseudostratified columnar cells location + structure
respiratory epithelium
nucleus appears in different places, cillia on surface
location of transitional epithelium + function
urinary tract (bladder)
capacity to alter their width, able to distend or contract the bladder
cilia structure + function
microtubulin core
move back and forwards to repel mucus out of the respiratory tract, dyenin
microvilli structure + function
microfilament actin core
increase SA of small intestine for absorption, forming a brush border
what separates epithelia from connective tissue?
basement membrane
what is the basement membrane?
a thin, fibrous, non cellular matrix that separates the lining of an internal or external body surface from the underlying connective tissue
structure of basement lamina
composed of three layers
lamina lucida- layer closest to the epithelia (not electron dense)
lamina densa (electron dense)- contains perlecan (heparan rich GAG)
lamina reticularis- also associated with reticular fibres of the underlying connective tissue
contains collagen VII anchoring fibrils and fibrillin microfibrils
basement membrane function
anchors the epithelium down to loose connective tissue (dermis/lamina propria)
acts as a mechanical barrier, preventing the infiltration of malignant cells
cell differentiation
differentiates between apical and basolateral domains
key feature of epithelia
polarity of cells
two different domains
apical- external surface
basolateral- internal surface
what does the basolateral domain consist of?
cell unctions
5 main types of cell junctions
tight- occluding junctions
adhesive
gap
desmosomes and hemidesmosomes
gap junctions structure + function
formed of connexins
allow chemical and electrical signals to diffuse through cells rapidly, forming syncytiums
tight-occludng junctions structure + function
zona occludens, a band formed near the apical region of the cell
formed of occludins and other adhesion molecules
prevent intercellular transport
explain adhesive junctions
bind cells together, forming the zonula adherens
cadherin proteins linked to actin cytoskeleton
desmosome location
localised spot like adjesions on the lateral sides of plasma membranes
desmosome structure
desmosome intermediate filament complexes
a network of cadherin proteins, linker proteins and keratin intermediate filaments
desmogleins and desmocollins
desmosome function
strong cell to cell adhesions that are found in tissues that experience intense mechanical stress, such as cardiac muscle, bladder tissue
hemidesmosome location + function
attach basal epithelial cells to lamina lucida (basement membrane)
hemidesmosome structure
integrin and plectin membrane spanning components
no cadherin
bind to keratin intermediate filaments in the cytoskeleton
two types of movement through epithelia defined
transcellular - through the cells
paracellular- between the cells
what determines which transport will be favoured?
type and number of junctional complexes
two types of epithelia
leaky, tight
disorder of the junctional complexes
pemphigus
explain pemphigus
antibodies produced against adherens and desmogleins in the skin
no desmosomes
cells become unglued from each other, resulting in blisters and sores
