Epithelial Tissue Flashcards
Key Functions of Epithelial tissues
Selective Barriers (limit or aid transfer)
Secretory (onto a free surface)
Protective (especially from abrasion)
Epithelial tissue
covers body surface
lines hollow organs, cavities and ducts
forms the glands of the body
The cells of an epithelium are arranged…
1) in continuous sheets as single or multiple layers
The cells of an epithelium are held together by cell junctions such as..
Tight junctions
Adherens junctions
Gap junctions
Desmosomes
Hemidesmosomes
What are the 3 bases of epithelial cells
Apical (free surface), Lateral & Basal (Attached) surface
Lateral surface junctions?
Tight Junctions
Adherens junctions
Gap junctions
desmosomes
Basal surface junction?
Hemidesmosomes
Cytoskeleton
Microfilaments
Intermediate filaments
Microfilaments
(brown) – e.g. ACTIN
-bundles beneath cell membrane and
cytoplasm;
-strength, alter cell shape; link cytoplasm to membrane; tie cells together; muscle
contraction
Intermediate filaments
(purple)
e.g. KERATIN
-Strength
Tight junctions are found in
Stomach, intestines & bladder
Tight junctions are made up of
Individual sealing strands- the more strands, the tighter the junction.
- transmembrane
Join the cytoskeletons of adjacent
cells e.g. via ZO-1 to actin
* Keep cell polarity by preventing
migration of proteins between apical
and basal surfaces
Two key proteins involved in Tight junctions
Claudins & Occludins
Adherens junction
“Belt desmosome” or “adhesion belts (zonula adherens) in some epithelial cells
Others cells are less continuous and are called “adhesion plaques”
* More basal located than tight junctions
Adherens junctions prevent cell separation from tension forces like in contractions
Adherens junction proteins
Have a plaque layer of proteins on the inside of the cell to join actin to cadherins
– Cadherins (span the gap)
– Catenins link the Cadherins to Actin (microfilament in cell cytoplasm
Desmosomes junction
Lateral wall
* Have “plaque” just like adherens junctions
* Resist shearing forces
Cadherin spans the gap and binds to Desmoplakin
* Links cell surface to Keratin (a cytoskeletal intermediate filament)
* Keratin spans from one desmosome to another on other side of the cell – structural integrity
* Example: they bind muscle cells; most common in skin epithelium and cardiac cells of the
heart to prevent pulling apart.
Gap junctions
Direct connection between cells
* 6 connexIn protein molecules form
connexOn or hemichannel
* 2 hemichannels make up gap junction
* Allows up to ~1kDa small molecules
through
Anchoring proteins
Actin filaments (in adherens)
Keratin filaments (desmosomes)
Linking proteins
cadherin (adherens and desmosomes)
Complex protein
eg. occludin
Hemidesmosomes
Connect epithelia to basement
membrane
* Links cellular basal intermediate
filament (Keratin) to basement
membrane
* Hemidesmosome
– INTEGRIN linker protein (instead
of cadherin)
– binds to LAMININ in the BM and,
– to Keratin intermediate filament in
cytoplasm
Tight junctions are..
Electrically tight (Na + etc.)
e.g. of content: Occludin
Adeherns junctions are..
e.g. transmembrane Cadherin links to
microfilament Actin – cytoplasmic contractile
protein)
Gap junctions
eg. connexin
Desmosome junctions
transmembrane glycoprotein cadherin links to
intermediate filament called Keratin
Hemidesmosome
e.g. Integrin instead of cadherin
binds to Laminin in the BM and Keratin
intermediate filament in cytoplasm
The combination of: tight junction, adherens junction
and desmosome is called a…
Junctional complex
All epithelia overlay a basement
membrane composed of two
parts:
BASAL LAMINA (secreted by the
epithelial cells) containing collagen,
laminin, other proteoglycans,
glycoproteins, etc
RETICULAR LAMINA (produced by
cells of the underlying connective
tissue known as fibroblasts)
containing fibrous proteins such as
fibronectin, collagen etc
The basement membrane is found between the..
epithelium and connective tissue.
Epithelia contain
nerves but do not
contain …
Blood vessels (avascular)
The exchange of
nutrients and wastes
takes place by…
Diffusion from
vessels in the
connective tissue.
functions of the Basement Membrane?
-Supports the overlying epithelium
-Provides a surface along which epithelial cells migrate during
growth and wound healing
-Acts as a physical barrier
-Participates in the filtration of substances in the kidney.
The basement membrane can act as a barrier to invasion by..
malignant melanoma.
Once the barrier has been penetrated, the chances of metastasis
(spread) occurring increase.
The ABCD of melanoma warning signs:
A for asymmetry: one half of a mole doesn’t match the other;
* B for border irregularity: edges are ragged, notched or blurred;
* C for colour: mix of brown, black, red, white, or blue;
* D for diameter greater than 6 mm
What are the TWO types of Epithelial tissue?
1) Covering and Lining Epithelia
– Outer Covering e.g. skin and some internal organs.
– Inner Lining e.g. example blood vessels
2) Glandular Epithelia
– Constitute the secretory portion of glands.
Covering and Lining Epithelia
Classified according to…
a. the ARRANGEMENT of cells
b. the SHAPES of the cells.
Arrangement; simple??
single layer (secretion; absorption; filtration)
Arrangement; Stratified?
two or more layers (protective)
Arrangement; Pseudostratified??
appears to have multiple layers as judged by positions of nuclei.
Not all cells reach the apical surface.
* All cells are in contact with the
basement membrane i.e. actually a
simple epithelium (secretion).
Shape; Squamous?
flat and thin (helps allow passage by diffusion)
Shape; Cuboidal?
about as tall as they are wide (secretion; absorption)
Shape; Columnar?
more tall than wide (secretion; absorption)
Shape; Transitional?
a stratified epithelium
in which the cells can change shape
from cuboidal to flat shape depending
on organ shape (allow stretch e.g.
urinary bladder)
Different simple (single) layer epithelium types;
Simple squamous*
Simple cuboidal*
Simple columnar* (ciliated and non-ciliated)
Pseudostratified (actually a single layer)
Pseudostratified columnar* (ciliated and non-ciliated)
Different stratified layer epithelium types;
Stratified squamous* (keratinized and non-keratinized)
Stratified cuboidal
Stratified columnar
Transitional
Glandular Epithelia
Glands consist of a single cell or a group of cells that secrete
substances into ducts, onto a surface or into blood.
They are classified according to where they secrete their
substances.
The function of all glandular epithelia is secretion.
Endocrine
gland
Secrete directly into
blood via traversing
interstitial fluid
eg. Pituitary, pineal,
thyroid, parathyroid
Generally distant
strong effects
Exocrine gland
Secrete into ducts that
empty onto the surface
of a covering or lining
epithelium.
eg. Sweat and salivary
glands; oil glands; wax
glands; pancreas;
Generally local effects
Some glandular organs are mixed secreting into ducts and into
the blood such as..
Pancreas
EXOCRINE GLANDULAR
EPITHELIA- single cell gland
eg. goblet cells- Goblet cells are type of mucous single cell exocrine gland
(Not all mucous cells are goblet shaped)
3 characteristics used to describe structure of multicellular glands
i. Structure of duct
ii. Structure of secretory area
iii. Relationship between the two
Sometimes all called “flask-like”
Simple Squamous Epithleium Features
Most delicate epithelium
Where there is filtration (kidney); diffusion (lung); secretion where slippery surface needed (e.g. outer layer of serous membranes)
Simple Squamous Epithleium Appearance
Thin flat and somewhat irregular like jigsaw
* Cells are “like fried eggs” or paving stones
Simple Squamous Epithleium Specialised Subtypes
Mesothelium lines pericardial, pleural, peritoneal
cavities
Endothelium lines inside of heart and the blood and
lymphatic vessels
Simple Squamous Epithleium Specialised Subtypes info
A serous membrane (serosa)
lining the body cavity and
viscera (mesothelium +
connective tissue
Mesothelium: a layer of
squamous epithelial cells
covering the serous
membranes (peritoneum,
pericardium, pleura) of the
adult
Locations of Simple Squamous Epithleium
In Bowman’s capsule of kidney, lines cardiovascular
and lymphatic systems, inside eye, alveoli of lungs, visceral cavity linings, inside
blood vessels and inside heart
Simple Cuboidal Epithelium features
Where there is SECRETION and ABSORPTION
Simple Cuboidal Epithelium appearance
Cuboidal or hexagonal boxes.
* The distance between adjacent nuclei is approx. the height of epithelium
Simple Cuboidal Epithelium Specialised Subtypes
nil
Simple Cuboidal Epithelium locations
Pancreas ducts; parts of kidney tubules, smaller ducts of many glands;
secretory chambers of thyroid; anterior surface of lens; pigmented
epithelium at posterior of retina; secretory part of some glands like thyroid
Membrane modifications
Microvilli (brush boarder)
Cillia (moves stuff around- like seaweed)
Simple Columnar Epithelium features
More cytoplasm so more organelles
Often more metabolically active than squamous cells
Simple Columnar Epithelium appearance
Rectangular
* Often hexagonal but taller and more
slender than cuboidal
* Nuclei often elongated and near the
base of the cell
* Height of cell is several times the
distance between adjacent nuclei
Simple Columnar Epithelium - 2 subtypes
Non-ciliated simple columnar epithelium
Ciliated simple columnar epithelium
Simple Columnar Epithelium Specialised Subtypes
Simple columnar epithelium can have: cilia or microvilli
Non-Ciliated Simple Columnar Epithelium features
Single layer
* Microvilli on apical surface
* Have goblet cells interspersed
Can have Microvilli (e.g. small intestine)
Non-motile cytoplasmic projections.
Increase surface area for absorption.
“Brush boarder”
Location examples of non-ciliated columnar epithelium
Examples: lines gut mucosa from stomach to anus; ducts of many glands; gall bladder.
Function: secretion and lubrication (mucus goblet cells) ; absorption;
Features
* Single layer
* Microvilli on apical surface
* Have goblet cells interspersed
Ciliated Simple Columnar Epithelium (move materials) features
Single layer
* Have goblet cells as well
Ciliated Simple Columnar Epithelium (move materials locations
Examples: some bronchioles, uterine fallopian tubes, sinuses; central canal of
spinal cord, ventricles of brain
Function: synchronous movement assists motility of mucus and foreign objects
or oocytes
Features
* Single layer
* Have goblet cells as well
Stratified Squamous Epithelium features
Located where mechanical or chemical stresses are severe
* All forms protect against microbes
* Apical cells are packed with keratin in places where mechanical stress
and dehydration are a major issue– makes the surface tough and
waterproof
Stratified Squamous Epithelium appearance
Cells form layers like plywood or pancakes in upper layers
* Lower layers maybe cuboidal or columnar
* Cells furthest from nutrition are thinner, and less active.
Stratified Squamous Epithelium Specialised Subtypes
Keratinised
* Non-keratinised
Stratified Squamous Epithelium
Location examples:
Keratinised: skin
* Non-keratinised: mouth, throat, tongue, esophagus, anus, and vagina
stratified Squamous Epithelium (non-keratinized
Examples: mouth, throat, tongue, esophagus, anus, and vagina
Function: protection from abrasion, defence from microbes, require
secretions from glands
This gives the name
Psuedo-stratified Columnar Epithelium appearance
Nuclei at all different levels
* Appears to have several layers but it is not actually the case
Psuedo-stratified Columnar Epithelium features
All cells contact BM but not all reach the
apical surface of the tissue
* Actually a simple epithelium
Psuedo-stratified Columnar Epithelium Specialised Subtypes
Pseudostratified ciliated columnar epithelium
i) Cilia on some cells
ii) Secrete mucus (from goblet cells)
Pseudostratified non-ciliated columnar epithelium
i) No cilia
ii) Lack goblet cells
Appearance
* Nuclei at all different levels
* Appears to have several layers but it is not actually the case
Pseudostratified Columnar Epithelium (con’t)
Ciliated has goblet cells
(Non-ciliated have no goblet cells)
Examples:
Ciliated: most of upper airways
Non-ciliated: larger ducts of glands, epididymis, part of male urethra.
Function:
Ciliated: – secrete mucus, and move it
Non-ciliated: absorption and protection
Ciliated has goblet cells
(Non-ciliated have no goblet cells)
simple tubular
one teardrop shaped
simple branched tubular
many branched teardrops
simple coiled tubular
one coiled
simple acinar (alveolar)
one angled teardrop
simple branched acinar (alveolar)
many branched angled teardrops
compound tubular
many extending long leaf tear drops
compound acinar (alveolar)
many extending rounder leaf shaped
compound tubuloalveolar
both extending types combined
what are plaques
collection of proteins into a larger structure on the cell membrane
made up of lots of diff proteins
what tissue is responsible for making the basal lamina
epithelial
what tissue is responsible for making the reticular lamina
connective tissue- fibroblasts
stratified columnar epithelium features
unccomon type of epithelium
protection & secretion
startified columnar epithelium appearance
basal layers shortned irregular cells
only apical layers has columnar cells
sratified epithelia does it have cilia?
NO
locations of startfied columnar epithelia
part of urethra ; large excertory ducts of some glands eg oesophagus, pancreas, saliovary glands, areas of anas mucosa , part of conjuctiva of eye
stratified cuboidal epithelia features
unccom type of epithelium
protection
limited secretion and absoption
stratified cuboidal epithelia appearance
appears to have sevral layers
only apical layers has cuboidal cells
stratified cuboidal epithelia locations
ducts of sweat glands
; oesphgal glands
lubrication and protection of oeophagus from stomach acids; part of male uretha
endothelium found where
in vessels/cornea- internal pathways
mesothelium found where
in cavity- major body cavities eg. peritoneum (abdomen cavity) secreetes lubricant film called srous fluid
