epithelium

1. GOOD MORNING….

2. EPITHELIUM
NAVEEN PARVATHAREDDY
I MDS, NARAYANA DENTAL COLLEGE

3. CONTENTS
 Introduction
 Origin of the epithelium
 Characteristics of epithelium
 Functions of epithelium
 Classification of epithelium
 Specialized epithelium
 Cell surfaces and their specializations
 Intercellular junctions
 References

4. INTRODUCTION
 One of the primary tissues of the body.
 Epithelium is a Greek word where Epi-upon and thelium-nipple
 Composed of continuous closely packed sheets of polyhedral cells
always supported by connective tissue.
 Two broad subdivisions
1.Covering Epithelia
Cover exterior of the body
Line internal closed cavities and tubes
Line body tubes communicate with exterior
2.Glandular Epithelia
Cellular sheets invaginate into connective tissue and
differentiate into secretory / duct cells.

5. ORIGIN
 ECTODERM MESODERM ENDODERM
epidermis & peritoneal cavities, lining of GIT,
glands of skin, CVS , lymphatics, Respiratory tract,
cornea , lens, kidneys and liver,
oral and reproductive pancreas,
nasal mucosa, organs thyroid,
mammary glands parathyroid,
thymus

6.  Avascular
 Free Surface
 Close cell apposition with little ECF
 Intercellular junctions
 Basement Membrane
 Regenerate & repair quickly
CHARACTERISTICS OF EPITHELIUM

7. FUNCTIONS OF EPITHELIUM
 Protection
 Absorption
 Filtration
 Secretion
 Transport
 Sensory reception
 Contractility & immunologic function

8. CLASSIFICATION OF COVERING EPITHELIUM:
 Based on number of cell layers
1.Simple
2.Stratified
o Based on cell shape
1. squamous
2. cuboidal
3. columnar

9. ACCORDING TO THE PRESENCE OF SURFACE
SPECIALIZATIONS
 Keratinizing  Ciliated

11. SIMPLE EPITHELIA

12. SIMPLE SQUAMOUS
 Structure - single layer of flattened cells
 Location function
alveoli - exchange of gases
bowmans capsule - filtration
endothelium - passive transport
mesothelium - lubrication , diffusion

13. SIMPLE CUBOIDAL
 Structure: Single layer of cube shaped cells
 Location: tubules in glands & kidney, covers ovaries,
respiratory passages
 Function: Secretion ,filtration, absorption

14.  Structure
 Elongated layer of cells with nuclei at same level
 Special Features
 Goblet cells
 Microvilli, cilia
 Location
 Linings of entire digestive tract, respiratory tract
 Function
 Absorption, Protection & Secretion
SIMPLE COLUMNAR EPITHELIUM

16. STRATIFIED EPITHELIUM

17. • Degree of stratification related to the kind of
physical stress, to which the surface is exposed
• Function mainly protection
• Poorly suited for absorption
STRATIFIED EPITHELIA

18. STRATIFIED SQUAMOUS EPITHELIUM
 Basal layer- cuboidal / columnar
 Intermedite – polyhedral towards surface they flatten
 Superficial - squamous cells

19.  Basal layer cells divide continuously & push the cells
towards the surface
 During this process the cells undergo first maturation &
then degeneration
 They also undergo keratinazation. Based on this
stratified squamous epithelium is divided into 2 types
Stratified squamous non keratinized
epithelium
Stratified squamous keratinized
epithelium

20. STRATIFIED SQUAMOUS NONKERATINIZED EPITHELIUM :
 Location:- common on wet
surfaces subjected to wear
& tear
 oral cavity , oesophagus ,
pharynx , vagina
 Functions :-Well adopted
to withstand abrasion
 protection

21. STRATIFIED SQUAMOUS KERATINIZED EPITHELIUM
 Keratinization:-During
maturation, epithelial cells
accumulate cross linked
Cytoskeletal proteins
resulting in the formation of
a tough ,non-living surface
layer
 Location: Skin, Attached
gingiva,Hard palate,
 Functions:-
 Protection , prevents
dehydration
 Adapted to with stand
abrasion & desiccation

22.  Thin stratified epithelium consisting of 2-3 layers of
cuboidal or low columnar cells.
 Location - large ducts of exocrine glands
 Function – conduction , barrier
STRATIFIED CUBOIDAL EPITHELIUM

23.  Location :-
 largest excretory ducts of glands, male urethra,
conjunctiva of eye & parts of pharynx , epiglottis
 Ciliated type - nasal surface of soft palate, larynx, fetal
esophagus
 Function :- conduction, barrier
STRATIFIED COLUMNAR EPITHELIUM

24. TRANSITIONAL EPITHELIUM
 Location :- urinary bladder, ureter, lower urinary tract
(urothelium)
 Structure :- changes in thickness & appearance
 Empty - relaxed
 Full – Stretched
 Function :- distention , barrier , protection

25.  Structure
 Appear as stratified, but aren’t.
 All cells reach basement membrane
 Location
 Respiratory Linings & Reproductive tract
 Function
 Absorption and Secretion
 Goblet cells produce mucus
 Cilia (larger than microvilli) sweep mucus
PSEUDOSTRATIFIED EPITHELIUM

27. GLANDULAR EPITHELIUM
oConsists of specialized secretory cells
oSecretions – enzymes , hormones , mucus
ounicellular - goblet cells , paracrine glands
omulticellullar - Exocrine & Endocrine

28.  Endocrine glands
 duct less
 Groups of secretory cells arranged around wide
capillaries
 Often hormones
 Thyroid, adrenal and pituitary glands
 Exocrine glands
 Contain ducts
 Sweat, sebaceous glands, Salivary glands, Mammary
glands
 Classified on various basis

29. CLASSIFICATION
BASED ON MODE OF RELEASE OF THEIR PRODUCTS

30.  Based on nature of secretion exocrine glands are
1.mucous glands
2.serous glands
3.mixed glands
 Based on branching
1.Simple
2.compound
o Based on shape
1.tubular
2.alveolar
3.tubuloalveolar

31. SPECIALIZED EPITHELIUM
 Neuro epithelium
 Myo epithelium

32.  Specialized epithelium
 Neuro epithelial cells
 Approximately 10,000 taste buds present within the epithelium
 Location of taste buds
NEURO-EPITHELIUM

33.  limited distribution (formerly
basket cells)
 Cells lie between basal plasma
membrane of the epithelial cells
& basal lamina of epithelium
 highly branched, stellate shaped
contain
 Found in mammary glands,
salivary and sweat glands (intra-
lobular ducts )
MYOEPITHELIUM

34. EPITHELIAL CELL POLARITY
FUNCTIONAL AS WELL AS MORPHOLOGIC POLARITY
 The 3 distinct morphological surfaces / domains are :-
• Apical / free surface/ luminal surface
• Lateral surface/intercellular surface
• Basal surface

35.  Lateral membranes of epithelial cells often exhibit
several types of membrane modifications
 On the molecular level, inter cellular junctions
consists of 3 components
1.Cytoskeletal filaments
2.Cell adhesion molecules
3.Cytoplasmic adapter
Lateral surface:

36. • CYTOSKELETAL STRUCTURE: cell possess a
cytoskeleton that provides a structural
framework for the cell, facilitates intracellular
transport, supports cell junctions and permits
motility.

37. CELL ADHESION MOLECULES
 Cadherins homophil
 Selectins heterophil
 Integrins heterophil
 Adh. mol. with
Immunoglobulin domain homophil

38. INTERCELLULAR JUNCTIONS

39. CLASSIFICATION:
 Occluding junctions- (zona occludens or tight junction)
 Adhesive junctions
a) cell-to-cell
1. zonula adherens
2. macula adherens (desmosomes)
b) Cell-to-matrix
1. focal adhesions
2. hemidesmosomes
 Communicating or gap junctions

40. TIGHT JUNCTION(OCCLUDING
JUNCTION)
 Zona occludens
 Most apical
 Formed by
 function
 Transmembrane proteins
 Fascia occludens

41. ZONULA ADHERENS
 Adhesion belt
 Deep to the
 Provide structural
reinforcement to the
occluding junction
 Has an intercellular space
of about 20-25 nm
 CAMs

42.  This material consists of
two proteins
 Α-actin
Vinculin
 In addition myosin &
tropomyosin also have
been present
 Plays imp role in support
and helps in producing
some minor changes in
apical cell shape
 Both ZO, ZA

43. MACULA ADHERENS (DESMOSOMES)

44.  Complex disk shaped structure
 Cell membranes in this region
 Numerous number of desmosomes
 Intermediate cytokeratin filaments, cadherin
proteins, anchor proteins

45. FUNCTIONS :
 Provides mechanical stability
 Creates and maintains the structural unity of epithelium
 Plays an important role in cell to cell recognition,
morphogenesis & differentiation.
CLINICAL IMPLICATIONS:
 Pemphigus vulgaris and pemphigus foliaceous,
blistering diseases of oral mucosa and skin are
caused by autoantibodies to desmoglein-3 and
desmoglein-1.

46. GAP OR COMMUNICATION JUNCTION
 Occur anywhere
 Each gap junction is
formed
 Each connexon
 Gap junctions permit
 Both desmosomes and
gap junctions are spot like
plaques

47. • Earlier electron
microscopy studies
suggested that gap
junctions are opened
and closed by twisting
of connexin subunits.
• Recent atomic force
microscopy(AFM)
studies provide a
dynamic view of the
conformational change
that takes place in
connexons.

48. FUNCTIONS:
•Maintains organ homeostasis
•Allow electrical and metabolic signals to pass from one
cell to another.
CLINICAL IMPLICATIONS:
•Mutation in connexin-26 congenital deafness.
•Mutations in Cx-46 & Cx-50 inherited cataracts.

49. FOCAL ADHESIONS:
• Form a structural link
• Transmembrane proteins-
• On the cytoplasmic phase,
integrins interact with
• On the extracellular side,
integrins bind to
extracellular matrix
glycoproteins, laminin and
fibronectin.

50. FUNCTIONS:
• Play a prominent role during dynamic changes
that occur in epithelial cell. Eg: migration of
epithelial cells in wound repair
• These are important sites of signal detection
and transduction.

51. HEMIDESMOSOMES
Present
Morphologically appears
Play a role in binding
epithelial cells to the
underlying basement
membrane & connective
tissue

52.  Exhibits intra cellular attachment
plaque.
 The three major proteins identified
in plaque are:
i) plectin
ii) BP230
iii) erbin
 Contains transmembrane
glycoprotein integrin
 These include
i) α6 β4 integrin
ii) type XVII collagen
iii) CD 151
 Integrins attach to intermediate
filaments and the protein laminin
present in the basement membrane
 An attachment plaque and
extensive tonofilaments are
characteristics of the
hemidesmosomes

53. LUMINAL SURFACE AND ITS SPECIALIZATIONS
• CILIA
• MICROVILLI
• STEREOCILIA
 Epithelioid tissue – lack free surface
typical of endocrine glands
Ex:- Islets of Langerhans ,
Interstitial cells of Leydig in testis ,
Lutein cells of ovary.

54. CILIA
 Short, fine, hair like, motile
structure that emanate from
free surface.
 0.25µm in diameter, 2 to 10 µm
in length
 Single cell may have upto 300
cilia, in orderly rows.

55.  Cilium- plasma
membrane &
axoneme
 Basal body – 9 short
triplet microtubules
in a ring
 9+2 pattern - 9
longitudinal
doublets & 2 central
microtubules
 Central doublets are
enclosed
by a central sheath

56. FUNCTIONS
o Ciliary action moves :-
-Secretions in the respiratory tract
-Ova through the uterine tube.
-Spermatozoa through the male genital tract
-Cells in embryogenesis
o Abnomalities in cilia can lead to primary ciliary
dyskinesia(PCD) or immotile cilia syndrome.

57.  Microvilli are finger like cytoplasmic projections
 Increases the surface area for absorption of materials
 0.5 – 1.0 µm in length
 Striated border – intestine, Brush border - kidney
MICROVILLI

58.  Core - actin
filaments(myosin I)
 Tip -Villin
 Cross links(10nm) –
fascin & fimbrin
 TERMINAL WEB –
horizontal network of
actin filaments just
below base.
 Spectrin – stabilizes,
anchors
 Myosin II
 Tropomyosin
contra
ctile

59. STEREOCILIA / STEREOVILLI
 Unusually long, immotile microvilli
 Epididymus, proximal part of vas deferens
( absorption)
& sensory hair cells of ear

60. MOLECULAR STRUCTURE
 Thick stem portions
 cytoplasmic bridges
 Ezrin, Fimbrin
 α-actin filaments
 Absent in sensory
epithelium

61. BASAL DOMAIN
 Characterized by
 Basal lamina or Basement membrane
 Hemidesmosomes
 Basal cell membrane infoldings

62. BASAL LAMINA
 Sheet of extra cellular material
 EM
 Main components
 Influences cell polarity , cell metabolism
 Reticular lamina

63. BASEMENT MEMBRANE
 Formed by
 LM – amorphous, dense layer of variable thickness
 PAS stain - Well defined magenta layer
 In electron microscope BM consists of 3 layer
 Lamina Lucida
 Lamina Densa
 Lamina fibro-reticularis

64.  Main constituents of BM are
 The glycosaminoglycan, heparin sulphate
 Fibrous protein –collagen type-IV , VII
 Structural glycoproteins – fibronectin , laminin & enactin

65. Functions :-
- structural attachment
- compartmentalization
- selective barrier
- regulation & signaling
 In some cases the BM fenestrated & facilities movement of
cells & materials across them

66.  Basal membrane Infoldings –
 increase surface area ,
 cells show active transport
 More mitochondria and their vertical orientation
within the folds results in striated appearance
 Ex:- proximal and distal tubules of kidney
certain ducts of salivary glands (striated ducts)

67. REFERENCES
 Ham’s histology -9th edition
 Histology (a text and atlas)-Micheal h. ross,
wojcieh pawlina - 5th edition,
 Atlas of histology – Difiore’s -9th edition
 Oral anatomy, histology & embryology – Berkovitz -3rdedition
 Text book of basic histology – Wheater’s - 5th edition
 Text book of human histology – Inderbir singh- 5th edition
 Basic histology, text & atlas- Junqueira-11th edition

69. ORAL EPITHELIUM:
 The tissue that forms the surface of the oral mucosa
 Constitute as a primary barrier between the oral
environment & deeper tissues
 It is of stratified squamous type
 Maintain structural integrity by continuous cell removal

70.  The cells keratinocytes consists of 2 functional population
Progenitor population – performing epithelial proliferation
Maturing population – performing epithelial maturation
 Non-keratinocytes are of following types
 Melanocytes
Langerhans cells
Merkel cells
Inflammatory cells

71.  Keratins (previously also called cytokeratins) are
filament forming proteins of epithelial cells and are
essential for normal tissue structure and function
 Forms the cytoskeleton of all the epithelial cells,
along with microfilaments & microtubules.
 Provide mechanical linkage & distribute force over
wide area

72.  Based on distribution
o Soft keratin
o Hard keratin
 Based on X-ray diffraction pattern
o Alpha
o Beta
o Feather keratins
o Amorphous keratins

73.  Based on amino acid sequence and charge
o Type I: Acidic proteins
: Keratins 9-20
: 40-56 kDa
o Type II: Basic or neutral proteins
: Keratins 1-8
: 52-67kDa
 Based on molecular weight
o Low molecular weight keratins: 40kDa
o High molecular weight keratins: 57kDa

74.  Known as intermediate filament associated proteins
 These include
o Filaggrin
o Trichohyalin
o Desmosomal proteins
o Proteins of cornified cell envelope

75.  They together makes up 10% of cell population in the
oral epithelium
 In light microscope – appear as clear cells
 No tonofilaments
 No maturation

76.  Different non- keratinocytes in oral epithelium are
Melanocytes
Langerhans cells
Merkel cells
Inflammatory cells

77.  Endogenous pigmentation most commonly
contributing to the colour of the oral mucosa are
melanin & hemoglobin
 Melanin produced by melanocytes
 They are present in the basal layer of the oral
epithelium

78.  Melanocytes arise embryonically from neural crest
ectoderm
 They enter the epithelium at about 11 weeks of
gestation
 Lack desmosomes & tonofilaments
 Posses long dentric process that extend between
keratinocytes ,often passing through several layers
 Melanin synthesied with in the melanocytes as small
structures called melanosomes

79.  In heavily pigmented persons melanin may be seen in con
tissues,which is taken up by macrophages and called as
melanophages
 Skin colour,directly proportional to melanin deposition
 Melanocytes involved in pigmented lesions of oral mucosa
are
◦ Oral melanotic macule
◦ Nevus
◦ Melanoma

80. Melanocytes
H& E EM

81.  Seen in the suprabasal layer
 Lacks desmosomal attachments
 Characterized by the presence of a small rod or flask
shaped granules called Birbeck granules
 Capable of limited division with in the epithelium
 Can move in and out of the epithelium

82. Langerhans Cells
H & E EM

83.  Situated in the basal layer
 Not a dentritic cell
 Posses tonofilaments & occasional desmosomes ,
hence not always resemble clear cells in histologic
sections

84.  Characteristic feature is presence of small membrane
bound vesicles in the cytoplasm sometimes situated
adjacent to a nerve fiber associated with the cell
 Granules release neurotransmitter between the nerve
and thus trigger an impulse
 Sensory & respond to touch
 May arise from division of a keratinocyte

85. Merkel Cells

86.  Mostly lymphocytes
 Some times PMN & mast cells
 Lymphocytes often associated with Langerhans cells
 Few inflammatory cells – normal component in non
keratinocyte population

88.  Progenitor cells present in the basal layer
 Dividing cells tend to occur on clusters
 Progenitor compartment consists of 2 functional sub
population of cells
◦ Small stem cells which produce basal cells and retain the
proliferate potential of the tissue
◦ Large amplifying cells-increase the number of the cells for
subsequent maturation (cannot be distinguished by appearance)

91.  Turnover time of the epithelium is the time it takes for a
cell to divide and pass through the entire epithelium
 Turnover time
Skin – 52 – 75 days
Gut – 4 – 14 days
Gingiva – 41 – 57 days
Cheek – 25 days
(In non keratinized epithelium turnover faster than keratinized
epithelium )

92.  Proliferation is controlled by biologically active
substances called cytokines
Epidermal growth factor
Keratinocyte growth factor
Interleukin – 1
Transforming growth factor α and β

93.  Maturation follows 2 main patterns
Keratinization
Non– keratinization

94. St. Basale St. Basale
St. Spinosum
St. Granulosum St. Intermedium
St. Corneum St. Superficiale

95. Keratinization
Occurs in masticatory mucosa which is tough &
resistant to abrasion
Histologically , shows a number of distinct layers
or strata

97. Stratum basale
Basal layer adjacent to basement membrane
Formed of cuboidal or columnar cells
The cells in the basal layer capable of division and so
called as stratum germinivatum

98. Stratum spinosum
Above basal layer
Occur as rows of large elliptical or spherical cells
Contacts only at points known as intercellular bridges or
desmosomes

99. Microscopically looks spine like(prickle layer)
Tono filaments insert into attachment plaque of
desmosomes
Basal & spinous layer together contribute to 2/3rd the
thickness of the epithelium
Increased thickness – acanthosis
Separation caused by loss of intercellular bridges –
acantholysis

100. Stratum granulosm
Next to spinous layer
Consists of large flattened cells
Cells contain small granules that stain immensely with
hematoxylin
The granules are called as keratohyalin granules

101. Stratum corneaum
Surface layer
Composed of very flat cells
Eosinophilic do not contain any nuclei
This pattern of maturation is called orthokeratinization
Some times in some mucosa,retain the shrunken nuclei
,called as parakeratinisation

102. Para keratinization
There is incomplete removal of organelles from the cells
of the granular layer
The nuclei remains as shrunken, pyknotic structures
Sometimes outermost squames of keratinized epithelium
do not look like the rest of the epithelium
(incomplete keratinization – due to rehydration)
No pathologic significance

103. Non keratinization
◦ Usually the lining mucosa
◦ Basal & prickle layers resemble that of keratinized
except the prickle cells of non- keratinized epithelium
are slightly larger and intercellular bridges are less
conspisious

104. Above the prickle layer, divided into 2 zones
Stratum intermedium
Stratum superficiale
# No granular layer
# Superficial layer contain plump nucleus
# Not stain intensely with eosin

105. Prickle cell layer
In prickle cell layer, increase in size is more than
that of keratinized epithelium
Tonofilaments remain dispersed
Contain membrane bound granules
They are circular in shape, with an amorphous coat

106. Stratum superficiale
The cells of the superficial layer,
Are more flattened
Contain dispersed tonofilaments and nuclei
Number of cell organelles are diminished
Not dehydrated

107.  Depends on the
Thickness of the epithelium
Pattern of maturation
Thinnest epithelium allow better penetration
Permeability barrier is due to the lipids derived
from the membrane coating granules

108.  Boundary between epithelium & connective tissue
 “They are extra cellular deposits at the base of epithelial
sheets that are co-operatively produced by both epithelial
cells and the underlying connective tissue cells”
 Basal lamina is a portion of the BM produced by epithelial
cells
 BL is a continuous meshwork of specialized ECM
 40-120 nm thick

110.  Electron lucent layer that extend from the lamina
densa to cell membrene
 EM preparations show that this layer is traversed by
delicate cords, these cords are believed to be the
anastomosing cords that make up lamina densa
 Made up of type IV collagen

111.  Thickest layer seen in electron microscope due to
more delicate cords extending from lamina lucida
 20-200nm thickness
 Made of type IV collagen

112. Connects the basal lamina to the underlying
connective tissue
Produced by fibroblasts
Contain mainly type-III collagen
Plays an important role in attaching lamina
densa to reticular fibers of reticular lamina

113. Laminin
 Large complex consisting of 3 very long polypeptides
which forms another polymer network of BM
 Has a cross shaped structure
 High concentration in lamina lucida
 Binds to Type-IV collagen
 Aids in binding the basement membrane to the cell by
interacting with a laminin receptor in the epithelial cell

114. EnactinNidogen
 Sulfated glycoproteins
 Bind to collagen and laminin
HSPG(Heparin sulfate proteoglycan)
 Located principally in lamina lucida
 Binds to both laminin & type-IV collagen
 Important for its charge dependent molecular sieve
properties

115. Fibronectin
 Widely distributed, high MW, adhesive type of
glycoproteins
 Extra cellular Y shaped molecule consisting of 2 similar
polypeptide chains joined by 2 disulphide bonds
 Attaches fibronectin receptors in the basal plasma
membrane to the ECM (each fibronectin molecule has
binding sites for heparin & collagen

116. Functional role
 Compartmentalize tissues
 Anchor cell sheets
 Play major role in control of cell migration
 Act as an stimulus for cell differentiation during development
 BM in nephrons play a important role as a selective
filtration barrier or molecular filter
 Serve as a barrier,so that fibroblast cannot touch the epithelial
cells

117. EPITHELIAL DISORDERS:
Epithelial atrophy Epithelial hyperplasia

119. HYPERKERATOSIS ULCERATED EPITHELIUM

120. ACANTHOLYSISACANTHOSIS

121.  Anatomy, histology & embryology –
Berkovitz – 3rd edition
 Atlas of histology – difiore’s – 9th edition
 Text book of basic histology – wheater’s
 Text book of human histology – inderbir
sing – 5th edition
 Ham’s histology -9th edition
 www.google.com