Polarity & specializations of epithelial tissue College of Medicine Al Nahrain University

1. Polarity &
specializations of
epithelial tissue
College of Medicine Al Nahrain University

2. Dr. Russul Hassan01
Dr. Huda Kareem02
Dr. May Majid03
Moderators

3. Welcome!!

4. Our Team
‫ﻣﮭدي‬ ‫ﺻﺎﻟﺢ‬ ‫ﺳﻌد‬01 ‫ﻓﻼح‬ ‫اﻟﻌﺎﺑدﯾن‬ ‫زﯾن‬02 ‫ﻧوري‬ ‫رﺑﺎح‬ ‫ﺣﯾدر‬03
‫ﻋﻧﯾد‬ ‫ﺟﺎﺳم‬ ‫ﺣﯾدر‬04 ‫ﺟوﺣﻲ‬ ‫ﻋﻠﻲ‬ ‫ﺣﺳن‬05 ‫ﻣﻛﻲ‬ ‫ﺳﺟﺎد‬06

5. Our Team
‫ﺳﻌد‬ ‫ﺧﺿﯾر‬ ‫ﻣؤﻣل‬07 ‫ﻣؤﻣل‬‫ﺷﺣﯾل‬ ‫ﻋﻠﻲ‬08 ‫رﺣﻣﺎن‬ ‫ﺣﺳﯾن‬09
‫ﻣرﺿﻲ‬ ‫اﺣﻣد‬10 ‫اﻟدﯾن‬ ‫ﻧور‬11 ‫ﻣﺣﻣد‬ ‫اﻟﺻﺎدق‬ ‫ﺟﻌﻔر‬12

6. Our Team
‫راﺿﻲ‬ ‫ﺣﯾدر‬13 ‫ﻣﺣﻲ‬ ‫ﻟﻘﺎء‬ ‫اﻣﯾر‬14 ‫ﻋﻣر‬ ‫ﻣﺣﻣد‬ ‫ﺣﻣﺎد‬15
16 ‫اﺗﮭﺎم‬ ‫ﺧﺎﻟد‬

7. Our Team

8. INTRODUCATION
Epithelium
There are two basic types of epithelial tissues:
covering and lining epithelia and glandular epit
helia.
form a continuous layer over all the free surfaces of the body:
 The outer layer of the skin.
 The inner surface of the digestive and respiratory cavities.
 The inner surface of the heart and blood vessels.
 The walls and the organs of the closed ventral body caviti
es.
 The ducts of the exocrine glands.
Lining epithelial cells
make up most of the glands in
the body
Glandular epithelia

9. General Features of epithelia
 With the exception of endocrine glands,
a. All epithelia have one free surface, called
the apical surface, which is exposed at the
body surface or at the lumen (space) of the
body cavity, duct, tube or vessel.
b. The basal surface of epithelium rests on a
basement membrane: a non-living adhesive
material secreted by the epithelium and the
underlying connective tissue.
c. These cells are often characterized by
frequent cell division because they are
exposed to wear and tear and injury,
necessitating replacement.

10. General Features of epithelia
 Maximum cell-to-cell contact.
 Minimum extracellular material.
 Cell junctions: Several types of junctional
specializations unite adjacent epithelial cells (tight
junctions, desmosomes and gap junctions).
 Supported by basement membrane (basal
lamella).
 Avascular: There are no blood vessels within
the epithelial layer.
 Derived from all embryonic germ layers,
including endoderm, mesoderm and ectoderm

11. Introduction
Surface specialization
Polarity (structural and functional asymmetry) is
characteristic of most epithelial cells. It is best seen in
simple epithelia, where each cell has 3 surfaces: an
apical (Free) surface, lateral surfaces, and a basal
surface attached to the basal lamina
 Cilia
 Flagella
 Microvilli
 Stereocilia
It is specialized to carry out functions that occur at these
interfaces, including secretion, absorption, and movement of
luminal contents.
Apical (Surface or luminal) modifications

12. Cilia
Overview
 Are membrane-covered extensions of the entire apical
surface.
 They beat in waves, often moving a surface coat of
mucus and trapped materials.
 Ciliated epithelia include ciliated pseudostratified
columnar (respiratory) epithelium and the ciliated
simple columnar epithelium of the oviducts.
 Primary cilia (The non-motile). sensory
organelles
 Motile cilia
 Nodal cilia
Types
Definition :cilium (from Latin, meaning 'eyelash’
the plural is cilia) is an organelle found on
eukaryotic cells in the shape of a slender
protuberance that projects from the much larger
cell body.

13. Cilia
Primary cilia
 The cilium is a hair-like structure composed of the ciliary membrane, cilioplasm, axoneme, and
basal body.
 This sensory organelle is membrane-bound and contains multiple microtubules running along
its length.
 The ciliary membrane and axoneme make up the upper part of the cilium. The axoneme has
nine peripheral microtubule doublets.
 The axoneme may have two central microtubules (9+2 vs. 9+0 axoneme). The 9+2 cilia usually
have dynein arms and radial spokes that link the microtubule doublets and are motile,
whereas most 9+0 cilia lack dynein arms, radial spoke, and central sheath and are nonmotile
(primary cilia). Some 9+0 cilia only lack the central microtubule and are motile (nodal cilia).
 The axoneme is enclosed in the ciliary membrane, which is distinct from the cell membrane.
Between the cilia and the cell membrane, there is a hypothetical transition membrane
surrounding the transition fibers. The transition fibers at the junction of the basal body act as
a filter for molecules that can pass into or out of the primary cilium.
Structure

14. Cilia
Primary cilia
as "sensory cellular antennae
that coordinate many cellular
signaling pathways,
sometimes coupling the
signaling to ciliary motility or
alternatively to cell division
and differentiation.
Function
in human sensory organs
such as the eye and the
nose
found

15. Cilia
Primary cilia
 Vesicles carrying molecules for the cilia dock at the
transition fibers. The transition fibers form a transition
zone where entry and exit of molecules is regulated to and
from the cilia.
 Molecules can move to the tip of the cilia with the aid of
anterograde IFT particles and the kinesin-2 motor.
 Molecules can also use retrograde IFT particles and the
cytoskeletal dynein motor to move toward the basal body.
 Some of the signaling with these cilia occur through ligand
binding such as Hedgehog signaling.
 Other forms of signaling include G-coupled receptors
including the somatostatin receptor 3 in neuronal cells.
Mechanism

16. Cilia
Primary cilia

17. Motile cilia
Structure
9+2 pattern refers to the nine doublet microtubules
surrounding the two microtubules that are centrally located.
The ring of microtubule scaffolding, in this case, is known as
the axoneme.
In addition to the microtubules, which are the main
components of the structure, motile cilia are also composed of
dynein arms and radial spokes that contribute to the overall
motility of the structure.
At its base (where it attaches to the cell), the axoneme is
attached to cylindrical structures known as basal bodies. The
basal bodies measure about 0.4um in length and 0.2um in
width and are made up of the A tubule (nine (9) triplet
microtubules consisting of protofilament microtubules), an
incomplete B tubule as well as an incomplete C tubule. Apart
from anchoring cilia in the cytoplasm, basal bodies also play an
important role in the assembly of these structures.
1 2

18. Motile cilia
Found & function
 respiratory system
 fallopian tube
Found
 they are either involved in the clearance of or
moving of substances.
 In the respiratory system, cilia trap and
remove dirt (as well as mucous) from the
lungs and other parts of this system.
 In the fallopian tube, on the other hand, cilia
serve to move the ovum to the uterus.
 On the cell surface, motile cilia are present in
large numbers where they beat in a
coordinated wavelike manner to perform their
functions effectively.
Function

19. Motile cilia
Beating Mechanism of Cilia
As is the case with muscle contraction, the
beating/working mechanism of cilia
(axoneme in particular) has been shown to
be the result of sliding protein filaments.
Although the mechanism, in its entirety, is
yet to be fully understood, studies have
shown dyneins, which act as the molecular
motors, to play an important role in
powering the ciliary beat.
One of the models that have been used to describe the bending and
thus the functioning of motile cilia is the switch model hypothesis.
According to the switching model, each side of a curved cilia consists
of dyneins in a given state of force generation cycle which
contributes to the asymmetry and change with alterations in
curvature.
Here, according to studies, dyneins on one microtubule (in the force
generation cycle state) slide past each other while those on the
other side do not.
This results in the bending of the
axoneme while the switching of this
system causes the structure to bend to
the other side.
Ultimately,the repeat of this
mechanism causes motile cilia to beat
and thus perform their function.
* The attachment and release of dynein
arms to adjacent doublet is caused by
binding or hydrolysis of ATP.

20. Defective cilia
disease syndromes
01
02
is a rare, ciliopathic, autosomal recessive genetic disorder that
causes defects in the action of cilia lining the respiratory tract
(lower and upper, sinuses, Eustachian tube, middle ear),
fallopian tube, and flagellum of sperm cells
Primary cilia dyskinesia
is a rare condition that affects many body systems. ... Alström
syndrome is characterized by a progressive loss of vision and
hearing, a form of heart disease that enlarges and weakens
the heart muscle (dilated cardiomyopathy), obesity, type 2
diabetes (the most common form of diabetes), and short
stature
Alström syndrome
03 is the loss of the ability to detect one or more smells
Anosmia

21. Defective cilia
disease syndromes
04
05
06
is a rare and lethal autosomal recessive disorder
characterized by occipital encephalocele, postaxial polydactyly
and bilateral dysplastic cystic kidneys. ... We describe a
female baby who had the typical triad of Meckel-Gruber
syndrome and died shortly after birth
Meckel-Gruber syndrome
is a genetic disorder of the kidneys which affects children. It is
classified as a medullary cystic kidney disease. The disorder
is inherited in an autosomal recessive fashion and, although
rare, is the most common genetic cause of childhood kidney
failure. It is a form of ciliopathy
Nephronophthisis
is an inherited genetic disorder that results in progressive
renal cyst formation with ultimate loss of renal function and
other systemic disorders
polycystic kidney disease

22. Flagella
Overview
A flagellum (plural: Flagella) may be described as a filamentous organelle that is primarily used
for locomotion. Like cilia (found in eukaryotic cells), flagella also protrude from the body of the
cell which allows them to perform their functions effectively. However, they are longer in
length, measuring between 5 and 20um.
Cells that possess this structure are referred to as flagellates and include both eukaryotic and
prokaryotic cells. For instance, apart from a majority of bacteria that use flagella for locomotion,
the structure can also be found on such single-celled organisms as euglena and protozoa species
like Trypanosoma evansi. On the other hand, flagella can be found on gametes of various
organisms including slime molds, fungi, and animals.
 Type :
 Bacterial
 Archaeal
 Eukaryotic

23. Flagella
Structure
 The structures and pattern of movement of
prokaryotic and eukaryotic flagella are
different. Eukaryotes have one to many
flagella, which move in a characteristic
whiplike manner. The flagella closely resemble
the cilium in structure.
 The core is a bundle of nine pairs of
microtubules surrounding two central pairs of
microtubules (the so-called nine-plus-two
arrangement); each microtubule is composed
of the protein tubulin. The coordinated sliding
of these microtubules confers movement. The
base of the flagellum is anchored to the cell
by a basal body.

24. Flagella
Found & function
 The only human cells that have flagella are
gametes – that is, sperm cells. ... These cilia also
play important roles in the middle ear and the
female reproductive tract, where they help move
sperm cells toward the egg cell
 The primary function of a flagellum is that of
locomotion, but it also often functions as a sensory
organelle, being sensitive to chemicals and
temperatures outside the cell.

25. Microvilli
Overview & structure
 Though these are cellular extensions from the plasma
membrane surface.
 Microvilli are covered in plasma membrane, there are little or
no cellular organelles present .
 Microvilli are covered in plasma membrane, which encloses
cytoplasm and microfilaments. Though these are cellular
extensions, there are little or no cellular organelles present in the
microvilli. Each microvillus has a dense bundle of cross-linked actin
filaments, which serves as its structural core

26. Microvilli
Location
apical surface of some
epithelial cells, such as
the small intestines.
Location of microvilli
Microvilli are observed
on the plasma surface
of eggs, aiding in the
anchoring of sperm
cells that have
penetrated the
extracellular coat of
egg cells.
On the cell surface
of white blood cells,
as they aid in the
migration of white
blood cells.
*microvilli on T-cell
surface.

27. Microvilli
Relationship to cell:
 Actin filaments, present in the cytosol, are most
abundant near the cell surface.
 These filaments are thought to determine the
shape and movement of the plasma membrane.
 The nucleation of actin fibers occurs as a response
to external stimuli, allowing a cell to alter its shape
to suit a particular situation.
 This nucleation process occurs from the minus end,
allowing rapid growth from the plus end.
 Though the length and composition of microvilli is
consistent within a certain group of homogenous
cells, it can differ slightly in a different part of the
same organism.

28. Microvilli
Function of microvilli
1-nutrient absorption in the
gastrointestinal tract.
2-the microvillar membrane
is packed with enzymes that
aid in the breakdown of
complex nutrients into
simpler compounds that are
more easily absorbed.
Function of
microvilli
** For example, enzymes that
digest carbohydrates called
glycosidases are present at high
concentrations on the surface
of enterocyte microvilli.
3-they also increase the number
of digestive enzymes that can be
present on the cell surface.
 The microvilli are covered
with glycocalyx, consisting of
peripheral glycoproteins that
can attach themselves to a
plasma membrane via
transmembrane proteins.
 This layer may be used to aid
binding of substances needed
for uptake, to adhere
nutrients or as protection
against harmful elements.

29. Microvilli
Destruction of microvilli
 The destruction of microvilli can occur in certain diseases
because of the rearrangement of cytoskeleton in host cells.
 This can lead to malabsorption of nutrients and persistent
osmotic diarrhea, often accompanied by fever.
 This is seen in infections caused by EPEC subgroup Escherichia
coli, in celiac disease, and microvillus inclusion disease (an
inherited disease characterized by defective microvilli and
presence of cytoplasmic inclusions of the cell membrane other
than the apical surface).
 The destruction of microvilli can actually be beneficial
sometimes, as in the case of elimination of microvilli on white
blood cells which can be used to combat auto immune diseases.
 Congenital lack of microvilli in the intestinal tract causes
microvillous atrophy, a rare, usually fatal condition found in
new-born babies.
 Celiac disease, also called gluten-sensitive
enteropathy or sprue, is a disorder of the small
intestine in which one of the first pathologic
changes is loss of the microvilli brush border of
the absorptive cells. This is caused by an immune
reaction against the wheat protein gluten during
its digestion, which produces diffuse enteritis
(intestinal inflammation), changes to the
epithelial cells leading to malabsorption, and
eventu- ally to pathologic changes in the
intestinal wall. The mal- absorption problems and
structural changes are reversible when gluten is
removed from the diet.

30. Stereocilia
Overview
 Stereocilia definition
are a much less common type of apical process, best seen on
the absorptive epithelial cells lining the male reproductive
system such as epididymis. Like microvilli, stereocilia
increase the cells’ surface area, facilitating absorption.
 More specialized stereocilia with a motion-detecting
function are important components of inner ear sensory
cells.
 Stereocilia resemble microvilli in containing arrays of
microfilaments and actin-binding proteins, with similar
diam- eters, and with similar connections to the cell’s
terminal web.
 However, stereocilia are typically much longer and less
motile than microvilli, and may show branching distally.

31. stereocilia
 Site of stereocilia :
1-ductus deferents
2-epididymis
3-sensory hair cell of inner ear (cochlea)
 Physiology of stereocilia in inner ear
It locates within the spiral organ of corti on the thin basilar
membrane in the cochlea of inner ear that protrude from the
apical surface of the cell into the fluid -filled cochlear duct it of 2
anatomical and functional distinct type
-inner hair cell transform the sound vibration in the fluid of the
cochlea into electrical signals that are then relayed via the
auditory nerve to the auditory brain stem and to the auditory
cortex
-Outer hair cell mechanically amplify low -level sound that enters
the cochlea .

32. stereocilia
Pathology
Damage to these hair cells result in decreased hearing sensitivity ,and because the inner
ear hair cell can not regenerate so this damage is permanent .

33. Zonula occludens (tight junctions, occluding junctions):
Lateral
specializations
cells attach tightly to one
another by specialized
intercellular junctions. Several
types of junctions can be seen,
such as:
Zonula occludens
Zonula adherens
Macula adherens
Junctional complex
Communicating junctions
junctions and folding
are located near the cell apex and seal off the intercellular space,
allowing the epithelium to isolate certain body compartments (they
help keep intestinal bacteria and toxins out of the bloodstream).
Their structure, best seen in freeze-fracture preparations, results
from the fusion of 2 trilaminar plasma membranes of adjacent cells
to form a pentalaminar structure; this fusion may require specific
"tight-junction proteins." In some tissues, tight junctions can be
disrupted by removing calcium ions or treating with protease.

34. Lateral specializations
Zonula adherens
 (sometimes called belt desmosomes): are usually
just basal to the tight junctions. The membranes of
the adhering cells are typically 20-90 nm apart at a
zonula adherens. An electron-dense plaque
containing myosin, tropomyosin, alpha actinin, and
vinculin is found on the cytoplasmic surface of each
of the membranes participating in the junction. Actin
containing microfilaments arising from each cell's
terminal web insert into the plaques and appear to
stabilize the junction
 Adherens junctions are composed of the following proteins:
 cadherins. The cadherins are a family of transmembrane proteins that form homodimers in a
calcium-dependent manner with other cadherin molecules on adjacent cells.
 p120 (sometimes called delta catenin) binds the juxtamembrane region of the cadherin.
 γ-catenin or gamma-catenin (plakoglobin) binds the catenin-binding region of the cadherin.
 α-catenin or alpha-catenin binds the cadherin indirectly via β-catenin or plakoglobin and links the
actin cytoskeleton with cadherin.

35. Lateral specializations
Zonula adherens
Principal interactions of structural proteins at cadherin-based
adherens junction. Actin filaments are associated with
adherens junctions in addition to several other actin-binding
proteins such as vinculin. The head domain of vinculin
associates to E-cadherin via α-, β - and γ -catenins. The tail
domain of vinculin binds to membrane lipids and to actin
filaments.
The accepted model has been that adherens junctions serve as
a bridge connecting the actin cytoskeleton of neighboring cells
through direct interaction. However, scientists have not been
able to isolate the quaternary complex of cadherin-βcatenin-
αcatenin-actin in vitro. Recent data (2005) demonstrate that
membrane- associated actin is several fold less stable
compared to components of the adherens junctional complex

36. Lateral specializations
Macula adherens
 Macula adherens or desmosome, consists of 2 dense,
granular attachment plaques composed of several
proteins and borne on the cytoplasmic surfaces of the
opposing cell membranes.
 Desmosomes, distributed in patches along the lateral
membranes of most epithelial cells.
 Transverse thin EM sections show dense arrays of
tonofilaments (cytokeratin intermediate filaments) that
insert into the plaques or make hairpin turns and return
to the cytoplasm.
 The gap between the attached membranes is often over
30 nm.
 Sometimes fibrillar or granular material (probably
glycoprotein) is seen as a dense central line in the
intercellular space

37. Lateral specializations
Junctional complex
attachment structure.
It is usually found
around the apical
membrane of an
epithelial or endothelial
cell. It limits the passive
movement of fluids
across the membrane
by diffusion.
combination of
zonula occludens,
zonula adherens
and desmosomes.

38. Lateral specializations
Communicating junctions
 Communicating junctions (gap or nexus
junctions): is a disk- or patch-shaped structure,
best appreciated by viewing both freeze-fracture
and transverse thin EM sections. The intercellular
gap is 2 nm, and the membrane on each side
contains a circular patch of connexons, the
connexons in one membrane link with those in
the other to form continuous pores that bridge
the intercellular gap, allowing passage of ions and
small molecules (<800 daltons). As sites of
electrotonic coupling (reduced resistance to ion
flow), gap junctions are important in intercellular
communication and coordination; they are found
in most tissues.

39. Lateral specializations
Communicating junctions structure
Gap Junction Structure
In vertebrate cells, gap junctions are made up of connexin proteins. ... Groups of six connexins form a
connexon, and two connexons are put together to form a channel that molecules can pass through. Other
channels in gap junctions are made up of pannexin proteins

40. Basal specialization
The last part

41. 1. A basal lamina
3. Sodium-potassium ATPase
2. Hemidesmosomes
4- Intracellular Polarity
Basal specialization
Overview
 The basal surface contacts
the basal lamina. Because it
is the surface closest to the
underlying blood supply, it
often contains receptors for
blood borne factors such as
hormones.

42. Basal specialization
Basal lamina
1. A basal lamina underlies all true epithelial tissues. The basal lamina is a sheet-like structure,
usually composed of type IV collagen, proteoglycan, and laminin, a glycoprotein that aids in binding
cells to the basal lamina. The basal lamina exhibits electron-lucent and electron-dense layers termed
the lamina lucida (lamina rara) and the lamina dense, respectively. Basal lamina components are
contributed by the epithelial cells, the underlying connective tissue cells, and (in some locations)
muscle, adipose, and Schwann cells. In some sites, a layer of type III collagen fibers (reticular fibers),
produced by the connective tissue cells and termed the reticular lamina, underlies the basal lamina.
Basal laminae accompanied by reticular laminae are often thick enough to be seen with the light
microscope as PAS- positive layers and are sometimes termed basement membranes. The basal
lamina forms a sieve-like barrier between the epithelium and connective tissue. It aids in tissue
organization and cell adhesion and (through trans membrane linkages with cytoskeletal components)
helps maintain cell shape. it has a role in maintaining specific cell functions, probably through its
effect on shape. Muscle basal laminae are critical in establishing neuromuscular junctions.

43. Basal specialization
Basal lamina

44. Hemidesmosomes
2. Hemidesmosomes: are located on the inner surface of basal
plasma membranes in contact with the basal lamina. They help to
attach epithelial cells to the basal lamina. The best examples are
found in the basal layers of stratified squamous epithelium.
Basal specialization

45. Basal specialization
Sodium-potassium ATPase
3. Sodium-potassium ATPase is a plasma membrane-bound
enzyme localized preferentially in the basal and basolateral
regions of epithelial cells. It transports sodium out of and
potassium into the cell.

46. Basal specialization
Intracellular Polarity
 4- Intracellular Polarity: The nucleus
and organelles are often found in
characteristic regions of epithelial
cells, a feature particularly important
to glandular cells.
 For example, in protein secreting
cells, the RER is preferentially located
in the basal cytoplasm, the nucleus in
the basal to middle region just above
the RER, and the Golgi complex just
above the nucleus.
 Mature secretory vesicles collect in
the apical cytoplasm.

47. Thank you

48. Reference & Sources
 Adler PN, Zhu C, Stone D. 2004. Inturned localizes to the proximal side of wing cells under the instruction of
upstream planar polarity proteins. Curr Biol 14: 2046–2051. [PubMed] [Google Scholar]
 Al Jord A, Lemaitre AI, Delgehyr N, Faucourt M, Spassky N, Meunier A. 2014. Centriole amplification by mother and
daughter centrioles differs in multiciliated cells. Nature 516: 104–107. [PubMed] [Google Scholar]
 Ameen N, Apodaca G. 2007. Defective CFTR apical endocytosis and enterocyte brush border in myosin VI-deficient
mice. Traffic 8: 998–1006. [PubMed] [Google Scholar]
 Anderson RA. 1977. Actin filaments in normal and migrating corneal epithelial cells. Invest Ophthalmol Vis Sci 16:
161–166. [PubMed] [Google Scholar]
 Andrews PM. 1976. Microplicae: Characteristic ridge-like folds of the plasmalemma. J Cell Biol 68: 420–429. [PMC
free article] [PubMed] [Google Scholar]
 Antic D, Stubbs JL, Suyama K, Kintner C, Scott MP, Axelrod JD. 2010. Planar cell polarity enables posterior localization
of nodal cilia and left–right axis determination during mouse and Xenopus embryogenesis. PLoS ONE 5: e8999. [PMC
free article] [PubMed] [Google Scholar]
 Apodaca G, Gallo LI. 2013. Epithelial polarity. In Colloquim series on building blocks of the cell: Cell structure and
function (ed. Nabi IR). Morgan & Claypool Life Sciences, Williston, VT. [Google Scholar]