3. INTRODUCTION
TISSUES ARE GROUP OF CELLS OR AGGREGATES TO
PERFORM ONE OR MORE FUNCTIONS.
EPITHELIUM (epi + thele + ium) is one of the four basic
types of animal tissue, along with
A-CONNECTIVE TISSUE
B-MUSCLE TISSUE
C-NEURAL TISSUE
4. The term EPITHELIUM is applied to the layer of cells
covering the body surfaces.
Epithelium is an avascular tissue comprised of cells that
line both the internal cavities and external surfaces.
5. DEFINITION
Epithelium is an avascular tissue composed of cells that
cover the exterior body surfaces and line internal closed
cavities (including the vascular system) and body tubes
that communicate with the exterior (the alimentary,
respiratory, and genitourinary tracts). Epithelium also
forms the secretory portion (parenchyma) of glands and
their ducts. In addition, specialized epithelial cells function
as receptors for the special senses (smell, taste, hearing,
and vision).
6. DEVELOPMENT
EPITHELIUM IS DERIVED FROM THREE GERM
LAYERS
ECTODERM
MESODERM
ENDODERM
ALTHOUGH MOST OF THE EPITHELIA ARE
DERIVED FROM ECTODERM AND ENDODEREM
7.
8. ECTODERM: Oral and nasal mucosa, cornea, epidermis
of the skin & glands of the skin & the mammary glands.
ENDODERM: The liver, the pancreas & the lining of the
respiratory and GIT.
9. MESODERM: Uriniferous tubules of the kidney, the lining
of the male and female reproductive systems,the endothelial
lining of the circulatory system and the mesothelium of the
body cavity.
10. FUNCTIONS OF EPITHELIUM
Selective Barriers
Protection
Secretory function
Sensory function
Characteristic of Epithelia
11. Predominantly Cellular
The Basal surface of an epithelium is in contact with
Basal Lamina.
Avascular
Can regenerate when injured
14. Epithelium can be grouped mainly into
Lining Epithelium
Glandular Epithelium
The lining epithelium is further classified into
A-Simple epithelium (unilaminar)
B-Stratified epithelium (multilaminar)
17. SIMPLE SQUAMOUS EPITHELIUM
Composed of flattened, irregularly shaped cells
forming a continuous surface which may be refered
to as pavemented epithelium.
Term ‘squamous’ derives from the comparison of the
cells to the scales of a fish.
Supported by an underlying delicate membrane.
Involved in passive transport of either gases or fluids.
18. PRESENT IN:
Lining- pulmonary alveoli, loop of Henle, parietal layer of
Bawman capsule, inner and middle ear, blood and lymphatic
vessels, pleural and peritoneal cavities.
FUNCTION:
Limiting membrane
Fluid transport
Gaseous exchange
Lubrication
Reducing friction
Lining membrane
22. Single layer of cube like cells with large , spherical
central nuclei.
Location- Kidney tubules , Ducts and secretory
portions of small glands , ovary surface , Intercalated
ducts of salivary glands.
FUNCTIONS- Secretion and absorption.
23. SIMPLE COLUMNAR EPITHELIUM
• Cells are taller and appear columnar in sections at right
angles to the basement membrane.
• Nuclei are elongated and may be located towards the
base, the centre or occasionally the apex of the
cytoplasm, this is known as polarity.
PRESENT IN:
• Small intestine & colon
• Stomach lining and gastric glands
• Gall bladder
25. SIMPLE COLUMNAR EPITHELIUM
Single layer of tall cells with round nuclei.
CILIATED – most of respiratory tract small bronchi ,
uterine tubes , and some regions 0f the uterus.
29. PSEUDO STRATIFIED EPITHELIUM
Simple columnar epithelium , nuclei at different levels in
a vertical section.
Migrating lymphocytes and mast cells give this
appearance.
Seen in ciliated lining of the respiratory tract and
sensory epithelium of the olfactory areas.
Excretory ducts of salivary glands.
Multi-laminar epithelium.
30. STRATIFIED SQUAMOUS
Stratified squamous epithelium
Basal cells are cuboidal or columnar
Surface cells squamous
Occur in sites exposed to constant damage
Two types keratinized and non- keratinized
Location : Non-keratinized forms the moist linings of
the esophagus , mouth, and vagina;
Keratinized variety forms the epidermis
32. STRATIFIED CUBOIDAL
STRATIFIED CUBOIDAL EPITHELIUM
Thin, stratified epithelium which usually consists of
only two or three layers of cuboidal or low columnar
cells.
Not involved in significant absorptive or secretory
activity
PRESENT IN:
Ducts of sweat glands
Large ducts of exocrine glands
Anorectal junction
37. Transitional Epithelium
Resembles both stratified squamous and stratified cuboidal ;
basal cells cuboidal or columnar surface cells dome shaped or
squamous like ,depending on degree of organ stretch.
Stretches readily and permits distension of urinary organ by contained
urine
Lines the ureters, urinary bladder and part of the urethra
Transitional epithelium of ureter
38. Transitional Epithelium
In the stretched state, it appears 2-3 cells thick (although
the actual number of layers remains constant) and the
intermediate and surface layers are extremely flattened.
PRESENT IN:
Urethra
Ureters
Bladders
Renal calyces
FUNCTION:
Protection
Distensible
39. Oral mucosa
Mucous membrane : moist lining of the gastrointestinal
tract, nasal passages ,Other body cavities that
communicate with the exterior.
In the oral cavity the lining is called as oral mucous
membrane or oral mucosa.
40. Functions of oral mucosa
Protection: Barrier for mechanical trauma and
microbiological insults
Sensation: Temperature (heat and cold) , touch ,pain,
taste buds, thirst; reflexes such as swallowing , etching,
gagging and salivating .
Secretion : Salivary secretion
41. Development and structure of oral epithelium
The epithelium of the oral cavity derived from the
embryonic ectoderm.
Most of the mucosal surface is lined by a non-
keratinized stratified squamous epithelium.
Except for Gingiva , hard palate and dorsal surface of
the tongue where the epithelium is keratinized.
42. FUNCTIONAL CHARACTERISTICS
As the cells migrate from the basal layer to the
surface layer, differentiation produces a surface layer
that is either
Non-keratinized
Ortho Keratinized
Para keratinized
43. Non-Keratinized Epithelium
The surface cells retain their nuclei and cytoplasm does not
contain keratin filaments.
Stratum spinosum and granulosum is absent.
Lining mucosa of the oral cavity.
Clinical considerations:
Prosthetic devices thin the epithelium
Linea alba
Angina pectoris- Nitroglycerine tablets are placed
sublingually and absorbed quickly through the thin non-
keratinized epithelium and into large veins of the ventral
surface of the tongue.
44. Ortho Keratinized epithelium
Stratum basale- tall columnar or cuboidal.
Stratum corneum elliptical / spherical.
In contact only by Desmosomes.
Stratum granulosum- flat cells with keratohyaline
granules.
Stratum spinosum- squamous cells with no nuclei.
Masticatory mucosa-Ortho keratinized.
45. ULTRA STRUCTURE OF THE EPITHELIAL CELL
Cells of the basal layer are least differentiated.
They contain organelles and typical filamentous strands
called tonofilaments.
Tonofilaments aggregate- tonofibrills.
Chemically they are cytokeratins.
Epithelial cells are named as keratinocyte
Keratins
Epithelial cells produce proteins- carbohydrate complex
which provide cohesion.
Desmosomes.
Hemi desmosomes.
46. APICAL CELL SPECIALISATION
Microvilli
Finger like cytoplasmic processes.
Number and shape correlates with absorptive capacity.
Contain actin filament.
Cilia:
Stereocilia
47. GLANDULAR EPITHELIUM
Classification of Glands
ENDOCRINE GLANDS:-
Hormones are secreted directly into blood.
No ducts.
Under the microscope , they look like any stratified
epithelial tissue with one big difference: THEY DO NOT
HAVE A FREE SURFACE AND SURROUNDED DIRECTLY BY
OTHER TISSUES.
48. EXOCRINE GLANDS
Release their products onto the free surface of the skin or of
the open cavities of the body such as the digestive ,
respiratory or reproductive tracts.
Their products are NOT released into the blood.
THESE ARE OF TWO TYPES:
UNICELLULAR:
They are scattered amongst other non-secretory epithelial
cells.
They have NO ducts, but they secrete their products directly
on the free surface.
The most common unicellular exocrine glands are the
Goblet cells(mucous secreting)
51. SECRETORY CELLS
SEROUS CELLS
Pyramidal cells with basal nuclei Microvilli on the
luminal surface.
Spherical nuclei basally.
Lateral surface have folds interdigitating with same
from adjacent cells.
Joined together by cell junctions.
52. MUCOUS CELLS
Tubular configuration with mucous cells surroundings
a central lumen.
Demi Lune- serous cells associated with them at the
end of the tubule.
Apical cytoplasm has accumulated mucous
53. Ducts – Intercalated ducts
Lined by simple cuboidal epithelium.
Centrally placed nuclei.
Small cytoplasm , few ER and a small Golgi complex.
Apically few secretory granules.
Few short microvilli
Unidentified in routine histology.
54. Striated duct cells
Cells are columnar , centrally placed nucleus and
acidophilic cytoplasm.
Striation appear in the basal cytoplasm, mitochondria
in cytoplasmic partition separated by highly folded cell
membrane.
55. Excretory ducts
Pseudo stratified epithelium with columnar cells.
Larger than striated ducts.
Scattered Goblet cells seen.
56. Clinical importance
Cystic fibrosis (CF) is a genetic disorder of certain
exocrine glands including the salivary glands, the sweat
glands, the pancreas and the mucous glands of the
respiratory tract.
A person with CF has clogged bronchial tubes, frequent
episodes of pneumonia and ultimately lungs that can
not carry out gas exchange.
CF –mutations in the gene that encodes the CF
transmembrane conductance regular
57. SPECIAL EPITHELIA
Epithelium of sense organs:olfactory, gustatory and
vestibulocochlear epithelium.
Myoepithelial cells/basket cells.
Seminiferous epithelium
61. Forms tight seals between cells such as the epithelial
cells that comprise the inner lining of the stomach,
intestine, and urinary bladder.
They prevent the passage of substances between cells
62. ADHERENCES JUNCTIONS
Strongly fasten cells to each other or to the extracellular
matrix.
They help epithelial surfaces resist separation.
Cardiac muscle
63. Desmosomes (cell to cell)
Desmoglein and Desmocollin interaction with adjacent
cells forms a dense middle line.
65. Gap junctions
Formed by minute, fluid filled tunnels that permit
passage of electrical signals or chemicals (i.e. ions and
small molecules) from one cell to a neighbouring cell,
located in some parts of the nervous system, in heart
muscle and in the gastrointestinal tract.
67. SUMMARY
Epithelial is an avascular tissue derived from all the
three germ layers.
They line the external surface of the body , occur as
membranes and as glands.
All epithelia lie upon a basal lamina.
68. Cells are connected to each other by cell junctions.
May possess cilia or microvilli.
They are protective , secretory , absorptive , sensory
depending on the location
69. BIBILOGRAPHY
Freshney, R.I. (2002). “Introduction “. In Freshney,
R .Ian; Freshney, Mary. Culture of epithelial
cells.ISBN 978-0-471-6.
Orban’s Oral Histology and Embryology-10th
Edition
Essential of Oral Histology and Embryology-
James K Avery, 2nd Edition
Oral Histology Development, Structures &
Fundamental – Ten Cate’s, 7th Edition
70. Histology Text and Atlas- Michael H Ross,Lynn J
Romrell, Gorden I Kaye, 3rd Edition
Gray’s Anatomy- The Anatomical Basis of Clinical
Practice ,40th Edition Susan Standing
Bloom & Fawcett’s Concise Histology- Don W
Essentials of Anatomy and Physiology ,5th Edition,
Valerie Scalon ,PhD.