Epithelial Tissue Flashcards
what does epithelia do? (3)
covers body surfaces
lines body cavities
forms glands
epithelial cells are characterized by the production of — intermediate filaments
keratin
do all epithelia produce the same type of keratin?
no, different epithelia produce different keratin
keratin can be useful in
tumor ID
what is keratin derived from? (3)
ecto, endo, mesoderm
what is derived from the ectoderm? (5)
epidermis cornea/lens epithelial of eye enamel organ and enamel of teeth anterior pituitary inner ear
what is derived from the neuroectoderm? (2)
neural tube (CNS) neural crest (PNS)
neural tube (CNS) (5)
pineal body posterior pituitary sensory epithelium of eye ear nose
neural crest (PNS) (6)
ganglia nerves glial cells adrenal medulla melanocytes neuroendocrine cells
what is derived from mesoderm? (4)
epithelium of kidneys and gonads
mesothelium
endothelium
adrenal cortex
what is derived from endoderm? (5)
respiratory epithelium
alimentary epithelium (except oral and anal cavity)
liver, pancreas, gallbladder, thyroid, parathyroid, thymus
epithelial lining of tympanic cavity and Eustachian tubes
transitional epithelium of bladder
what are the epithelium functions? (6)
barrier SPM secretion absorption transport sensation
do epithelia have blood vessels?
no they are avascular, they are never penetrated by blood vessels
what separates the epithelium from underlying connective tissue and blood vessels?
the basement membrane
cells rely on — of O2 and nutrients from underlying tissue
diffusion
mucous membrane (mucosa)
epithelium that lines cavities that connect with outside world
(ex. alimentary, respiratory, or urogenital tracts)
the mucous membrane contains (4)
surface epithelium of ectoderm (or endoderm)
basement membrane
supporting connective tissue (lamina proprietary)
smooth muscle (muscular mucosae)
serous membrane (serosa)
epithelium that lines closed body cavities
ex. peritoneal, pleural, pericardial cavities
serosa consists of (4)
epithelial lining
mesothelium (mesodermal derived)
basement membrane
supporting connective tissue
what does serosa lack?
muscularis mucosae
endothelium
epithelium that lines blood and lymph vessels (mesodermally derived)
endothelium are associated with variable numbers of (2)
smooth muscle and connective tissue layers, or tunics
most epithelial cells have a — lifespan
finite
what is the basal surface of epithelial cells attached to>
underlying basement membrane and extracellular matrix proteins (external lamina)
functions of the basement membrane (5)
structural support scaffolding for growth differentiation migration of cells during embryonic growth regeneration
function of the non-cellular, protein and polysaccharide-rich layer
acts as a filter between epithelium and underlying connective tissue
how is negative charge maintained?
SPM for nutrients and metabolites to and from epithelium
function of the glomerular basement membrane in the kidneys
acts as a highly selective filter for urine formation
what are the major components of the basement membrane? (4)
GAGs
type 4 collagen
structural glycoproteins
large polypeptides with branched, polysaccaride side chains
structural glycoproteins (3)
laminin
fibronectin
enactin
what are the three layers of the basement membrane seen with electron microscopy?
lamina lucida (electron Lucent) lamina densa (electron dense) lamina reticularis (electron Lucent)
lamina lucida
in contract with the basal cell membrane
10-50 nm
lamina reticularis
merges with surrounding tissue
20-30nm
lamina densa
anchored to underlying connective tissue by microfibrils of type 4 collagen (anchoring filaments)
how do epithelial cells adhere to one another?
cell junctions
intercellular epithelial attachment sites
cell junctions allow for
communication between cells
what are the three types of cell junctions?
occluding
adhering
communicating
occluding junctions are also known as
tight junctions
where are occluding junctions located?
beneath the luminal surface of simple columnar epithelia
occluding junctions act as
gaskets
zonula occludent
opposing cell membranes that fuse together
fascia occludens is present between
endothelial cells in the wall of blood vessels
adhering junctions are also known as
anchoring junctions
adhering junctions function to
bind cells together, act as anchoring points for cell cytoskeleton
zonula adherent
a continuous band characterized by transmembrane glycoproteins called cadherins
cadherins
class of cell adhesion molecules, or interns
in adhering junctions, are the adjacent cell membranes fused?
no
macula adherens/desmosomes
small, circular patches
most common type of cell junction
macula adherens/desmosomes
macula adherent/desmosomes are located on
the lateral surface of the cell
macula adherent/desmosomes are associated with attachment of plaques containing attachment proteins including (3)
desmoplakins
desmoglzins
tonofilaments
hemidesmosomes
half desmosomes
hemidesmosomes are found on the
basal surface of the cell
anchoring it to the BM via integrins
hemidesmosomes are associated with high
mechanical abrasion/shearing forces
ex. skin
junctional complex is also known as
terminal bar
junctional complex
specialized, circumferential intercellular connection
junctional complex is a hybrid between
adhering and occluding junctions
junctional complex forms a
diffusion barrier between cells
threes zones of junctional complexes
zonula occludens (tight junction) zonula adherens (adherent junction) macula adherens (desmosomes)
communicating junctions are also known as
gap junctions or nexus junctions
what are gap junctions?
focal, or regional adherent zones located on lateral border of cell
what are hap junctions formed by?
hundreds of connexions formed by ring of 6 integral proteins called connexions surrounding 2 nm diameter pores
what do gap junctions allow for?
passage of small molecules between adjacent cells, allow transport of info and metabolites between cells
microvilli
finger-like cytoplasmic projections, extend from the cell surface
microvilli contain — filaments
actin
microvilli work to increase
surface area for absorption or secretion
=striated border in intestine
=brush border in renal tubules
microvilli are supported by the
terminal web
terminal web
network of actin microfilaments at the base of microvilli which provide support
stereocillia
long microvilli, not Cilia
where are setereocilia found? (2)
epidermis of males
sensory cells of the inner ear
are stereocilia motile?
no
stereoilia contain — filaments
actin
cilia
long, motile cytoplasmic extensions
cilia posses an
axoneme
axoneme
9+2 arrangement of microtiniles
each cilium arises from individual
basal body
basal body develops from
centrioles
cilia beat in what kind of rhythm?
synchronous, metachronal rhythm
cilia strokes
effective vs recovery
rapid, rigid, effective stroke
slower, flexible recovery stroke
what do cilia contain?
microtubule doublets with dynein arms
what happens if microtubules lack dynein arms?
ciliary mobility is impaired or absent
kartageners syndrome
causes sterility in males due to non functional flagella on sperm
dextrocardia (or sinus inversus)
due to absence of ciliary activity during embryonic Development
hydrocephalus
due to non functional cilia on ependymal cells unable to circulate CSF
what are the 3 criteria for epithelial classification?
# of cell layers shape of cells (at epithelial surface) surface specializations (cilia, keratin, etc)
of layers (3)
simple
stratified
pseudostratified
simple
1 cell layer thick
stratified
two or more cell layers
pseudostratified
looks stratified, but isn’t
all cells rest on the basement membrane, but not all cells extend t the epithelial surface
shape of cells (3)
squamous
cuboidal
columnar
squamous
flattened
width>height
cuboidal
width~=depth~=height
columnar
hight>width
transitional epithelia (3)
lines most of the urinary tract (except parts of the urethra)
stratified epithelium, modified for distensibility
varies from squamous to cuboidal
endothelium
epithelial lining blood vessels and lymphatics; simple squamous
mesothelium
epithelium lining closed body cavities
(ex. thoracic, pericardial, and abdominal cavities)
simple squamous
glands are composed of epithelial cells, specialized for (2)
synthesis and secretion
glands can be classified through (3)
morphology
type of secretory product
mode of discharge of secretory product
duct morphology (2)
simple gland
compound grand
simple gland
unbranched cuts (straight or coiled)
compound gland
branched ducts
shape of gland (3)
tubular
acinar
tubuloacinar
tubular
tube-like (straight or coiled)
acing/alveolar
sac-like or flat shaped, individual sac called acinus
tubuloacinar
intermediate, tube with dilated end
type of secretory product (5)
serous mucous mixed sebaceous ceruminois
serous
water; basophilic acini
ex. parotid
mucous
thick, viscid secretion (mucus); clear on H&E
ex. palatal
mixed (seromucous)
contain both cuboid and serous acini, often include serous demilunes
(ex. submandibular)
sebaceous gland of the skin
secrete lipids in the form of sebum
ceruminous glands of external ear canal
secrete cerumen (ear wax)
two main functional groups
endocrine glands
exocrine glands
endocrine glands
lack ducts secrete products (hormones) directly into the bloodstream
exocrine glands
secrete product onto epithelial surface via ducts
exocrine glands containspecialized contractile cells, called
myoepithelial cells
li between secretory cells and the BM, assist in secretion
goblet cells
specialized, unicellular exocrine glands, located in epithelium, secrete mucous
mode of discharge (3)
merocrine
apocrine
holocirine
merocrine (eccrine)
only secretory product is released, generally proteins
most common mode of discharge
merocrine, involves simple exocytosis
apocrine
secrete membrane bound vesicles, product accompanied by some cytoplasm
usually lipid precuts (ex. sweat and mammary glands)
holocrine
entire cell secreted (ruptures, released contents)
ex. sebaceous glands
