(01) Epithelial Tissue Flashcards
name the main locations of epithelial tissue
covers body surfaces
lines hollow organs / cavities / ducts
forms the GLANDS
name three key functions of epithelial tissue
protective
selective barrier
secretory (glands)
name the three different surfaces of epithelial cells
apical (or free surface)
lateral
basal (attached to basement membrane)
Name the four lateral junctions
Tight
Adherens
Gap
Desmosome
what is a cytoskeleton
a structure that helps cells maintain their shape and internal organisation
(a network of protein filaments)
Important components of the cytoskeleton and the main protein each is made of
Microfilaments - ACTIN
Intermediate filaments - KERATIN
Describe microfilaments and their role
ACTIN
the thinnest elements of the cytoskeleton, bundles beneath cell membrane and cytoplasm
generate movement (eg. muscle contraction)
provide mechanical support (basic strength / structure of cells)
links cytoplasm to membrane + ties cells together
describe intermediate filaments and their role
KERATIN
thicker than microfilaments
Much stronger and less flexible
Adds strength
Moves materials through cytoplasm - pathways
describe the cellular and general locations of tight junctions
on lateral surfaces, near the apical end
lots in stomach / intestines / bladder
describe the structure of tight junctions
strands of pearl-like trans-membrane proteins, CLAUDINS and OCCLUDINS, seal adjacent plasma membranes together, leaving pockets of paracellular space
more strands = tighter junction
describe the function of tight junctions
joins the cytoskeletons of adjacent cells (eg. via ZO-1 to actin)
ELECTRICALLY tight - separates environments, keeps cell polarity
prevents the migration of proteins between apical and basal surfaces
describe the physical form and location (on cell) of adherents junctions
“belt desmosome” - often forms extensive zones = adhesion belt
forms a PLAQUE, with transmembrane glycoprotein
found just below tight junctions
define plaque
a dense layer of proteins on the inside of plasma membrane that attaches to membrane proteins and microfilaments of the cytoskeleton
explain how proteins form adherens junctions
CADHERIN crosses intercellular gap, joins to cadherins from adjacent cell
CATENINS link cadherins to ACTIN (microfilament)
function of adherens juncstions
prevent cell separation from tension forces (eg. in contractions)
describe the structure of desmosomes (incl proteins)
lateral wall
plaque, button-like
CADHERIN spans the gap, links to KERATIN in intermediate filament via desmoplakin
the intermediate filaments extend from desmosomes on one wall to the other
function of desmosomes
structural arrangement of connected intermediate filaments provides stability + structural integrity to the cell
resist shearing forces
prevents cells from pulling apart under tension
common locations of desmosomes
skin epithelium
cardiac cells of the heart (prevents pulling apart of muscle cells during contraction)
how do desmosomes appear in images (vs adherens)?
appears darker because of connection to thicker filaments
describe hemidesmosomes + function
looks like half a desmosome, links cellular basal intermediate filament (keratin) to basement membrane rather than adjacent walls
connects epithelia to basement membrane
proteins involves in hemidesmosomes
not cadherin but INTEGRIN
binds to LAMININ in the basement membrane and keratin in the cytoplasm
what is the purpose of gap junctions
communication
allows small molecules to pass
useful in coordinated movement (eg. in the heart - electrical impulses)
describe the structure of gap junctions
6 connexin proteins (monomer, like pizza slices) form a connexion / hemichannel
move around in membrane
2 hemichannels make up a gap junction (hydrophilic channel)
aggregation of gap junctions = plaque
define anchoring protein
actin / keratin filaments
in microfilament / intermediate filament of cytoskeleton
give an example of a linking protein
cadherin - transmembrane
what is a junctional complex?
a combination of a tight junction, adherens junction and desmosome
name the two layers of the basement membrane
Basal lamina
Reticular lamina
what is the basal lamina made up of
secreted by epithelial cells
COLLAGEN
LAMININ
other proteoglycans / glycoproteins
what is the reticular laminar made up of
produced by fibroblasts (cells of underlying connective tissue)
contains fibrous proteins: fibronectin, collagen etc
the basement membrane is found between the __ and ___
found between the EPITHELIUM and CONNECTIVE TISSUE
how does the exchange of nutrients / waste take place in the epithelia and why?
by diffusion from vessels in the connective tissue
because epithelia is AVASCULAR (but it contains nerves)
name four functions of the basement membrane
SUPPORTS overlying epithelium
Physical barrier
Growth and wound healing - provides a surface along which epithelia cells migrate to
participates in the filtration of substances in the kidneys
basement membrane and melanoma
BM can act as a barrier to invasion by malignant melanoma
once BM penetrated, chance of METASTASIS (spread) increases
tumor depth >4mm, 5year survival rate 50%
name the two types of epithelial tissue
- Covering / Lining epithelia
- Glandular epithelia
where is covering / lining epithelia found
Outer covering of the skin / internal organs
inner lining of blood vessels, ducts, cavities
interior of the respiratory, digestive, urinary and reproductive systems
where are glandular epithelia generally found + what are the two types
the secretory portion of glands
Exocrine: secretes onto external surfaces and into passages (ducts)
Endocrine: hormones / precursors into interstitial fluid
covering and lining epithelia is classified by __ and __
arrangement (of cells)
shapes
name and describe the three types of epithelia covering cell arrangement
simple = single layer
stratified = multiple layers
PSEUDOSTRATIFIED = looks like it’s layered but just a single layer (technically single) - all cells are in contact with basement membrane
name and describe the four shapes of covering epithelia
squamous = flat (generally for diffusion)
cuboidal
columnar
TRANSITIONAL - can be cuboidal / flat, changes
name one organ where transitional covering eplitheium cells are located
the urinary bladder
allows stretch
where is simple squamous epithelium located
where there is filtration (kidney), diffusion (lung), secretion for slippery surfaces (outer layer of serous membranes)
name the two specialised subtypes of simple squamous epithelium
MESOTHELIUM
ENDOTHELIUM
name some locations of simple squamous epithelium
lines cardiovascular / lymphatic systems
inside blood vessels, inside heart
alveoli of lungs
Bowman’s capsule of kidney
where is mesothelium found?
covers SEROUS membranes, lines big cavities
pericardial (around heart), pleural (lungs), peritoneal
(reminder: this is a type of simple squamous epithelium)
where is endothelium found?
lines inside of heart / blood+lymphatic vessels
(reminder: a type of simple squamous epithelium)
name the two functions of simple cuboidal epithelium
for SECRETION and ABSORPTION
locations of simple cuboidal
pancreas ducts and smaller ducts of many glands
secretory chambers of thyroid + other glands
parts of kidney tubules
describe microvilli
a membrane modification that increases surface area of membrane on the apical surface with fingerlike projections
NONMOTILE
(abundant in places of absorption)
describe cilia
MOTILE - controlled sweeps
moves fluids along a cell’s surface
feature of simple columnar epithelium
more cytoplasm, so more organelles
so more metabolically active
name the two major subtypes of simple columnar epithelium
Non-ciliated (can have microvilli)
ciliated
(may have cilia and / or microvilli)
appearance of simple columnar epithelium
rectangular when cut from the side
generally the nuclei (often elongated) is near the base of the cell
may contain goblet cells (for both ciliated and non-ciliated subtypes)
what is a goblet cell and what is its purpose?
a modified columnar cell
contains and secretes mucus at the apical surface, lubricates
locations of non-ciliated simple columnar epithelium
lines gastrointestinal tract (has microvilli for absorption)
ducts of glands
gallbladder
locations of ciliated simple columnar epithelium
uterine fallopian tubes
some bronchioles
sinuses
central canal of spinal cord, ventricles of brain (cerebral spinal fluid)
think: moving fluid / mucous etc
function of ciliated simple columnar epithelium
synchronous movement assists motility of mucus / objects / oocytes
describe the appearance of stratified squamous epithelium
cells for layers in upper layers (which it is named after)
lower layers may be cuboidal or columnar
cells furthest from nutrition are thinner + less active
What can stratified squamous epithelium generally withstand?
Severe mechanical / chemical stresses
function of stratified squamous epithelium
protect against microbes
makes surfaces tough / waterproof
name the two specialised subtypes of stratified squamous epithelium
keratinised
non-keratinised
describe the function and locations of non-keratinised stratified squamous epithelium
protects from abrasion
defence from microbes
mouth / throat / tongue / oesophagus
anus / vagina
describe the appearance and location of keratinised epithelium
has keratinised (dead) surface cells
skin
describe the appearance of pseudo-stratified columnar epithelium
nuclei at different levels
appears to have several layers but actually all cells contact BM (not al reach the apical surface)
name the two subtypes of pseudostratified columnar epithelium
ciliated
non-ciliated
everything columnar is either ciliated or non-ciliated!
describe pseudo stratified ciliated columnar epithelium (+location)
cilia on some cells
secrete mucus (from goblet cells) - this is a main function
most upper airways
describe pseudostratified non-ciliated columnar epithelium (+location)
HAS NO GOBLET CELLS!!!
and no cilia (obv)
functions to absorb + protect
larger ducts of glands
epididymus + male urethra
where is stratified transitional epithelium located?
the BLADDER
as well as some parts of ureter and urethra
what is a gland?
consists of a single cell / group of cells that SECRETE SUBSTANCES into ducts, onto surface or into blood
how are glandular epithelia classified?
according to where they secrete their substances
name the two classifications of glands
endocrine
exocrine
define endocrine gland
secretes directly into blood
usually via interstitial fluid
hormones diffuse to adjacent blood supply, no duct
generally distant strong effects
examples of endocrine glands
pituitary, pineal, thyroid, parathyroid
define exocrine glands
secretes into DUCTS that empty onto the surface of a covering / lining epithelium
generally LOCAL effects
examples of exocrine glands
sweat + salivary
oil / wax glands
pancreas (NOTE - this is mixed, does both)
describe the endo and exocrine functions of the pancreas
Endo - yellow cells hormones –> blood
exo - “pizza” cells, different roots via pancreatic ducts –> digestive juices
name the two broad types of exocrine glandular epithelia
single cell gland
multicellular
what are mucous cells
individual secretory cells in epithelia with independent, scattered gland cells
main parts of a mucous cell / single cell gland
apical cytoplasm is filled with large secretory vesicles - mucin? looks clear / foamy in light micrograph
what three characteristics are used to categorise multicellular exocrine glands?
structure of the duct
structure of the secretory area
relationship between the two
define “simple gland”
it has a single duct that does not divide on its way to the gland cells
define “compound duct”
the duct divides one or more times on its way to the gland cells
two main shapes of the secretory area
tubular - glandular cells form tubes
alveolar / acinar - glandular cells form sac-like pockets
name the five types of simple glands + examples
simple tubular (intestinal glands)
simple coiled tubular (merocrine sweat glands)
simple branched tubular (gastric, mucous glands)
simple alveolar
simple branched alveolar (sebaceous glands)
name the three types of compound glands and examples
compound tubular (mucous glands in mouth, in male urethra / testes)
Compound alveolar (mammary glands)
Compound tubuloalveolar (salivary glands, respiratory passages, pancreas)
