a note on epithelial tissue histology

1. 1
Epithelial Tissues and
Glands
ANA 201 (Anatomy for Pharmacy Students I)

2. 2
Epithelial Tissues
ANA 201 (Anatomy for Pharmacy Students I)

3. Introduction
• A tissue = a mass of similar cells and cell products that forms a
discrete region of an organ and performs a specific function
• The four basic tissue types in the body:
the epithelial, connective, muscular, and nervous tissue
o all these tissues exist and function in close association with one
another.
• The four basic tissues differ from each other in the:
Types and functions of their cells
Characteristics of the matrix (extracellular material) that surrounds
the cells
Relative amount of space occupied by cells versus matrix 3

4. Introduction cont’d
• Epithelial tissue, or epithelium, consists of sheets of cells
that:
cover the external surfaces of the body
line the internal cavities
form various organs and glands, and line their ducts
• Characteristics of epithelial tissues
i. Continuous sheets of closely packed, tightly joined cells
ii. Cells are attached to basement membrane – 2 layers
Basal lamina - proteins and polysaccharides secreted by epithelial cells
Reticular lamina - protein fibres and glycoproteins secreted by
underlying connective tissue 4

5. Introduction cont’d
• Characteristics of epithelial tissues cont’d
iii. Has two surfaces: apical (free) and basal surface
iv. It is avascular - exchanges occur by diffusion from blood supply
of underlying connective tissue
v. Have nerve supply
vi. Have a high capacity for regeneration (lots of mitosis)
vii. Basic functions - protection, secretion, absorption
Function is dependent on the location
5

6. Classification of Epithelial
Tissues
•It is according to the:
Number of cell layers
oSimple – single layer
oStratified – more than single
Morphology or structure of the
surface cells
oSquamous = flat
oCuboidal = squarish or roundish
oColumnar = tall and narrow cells
6

7. Types of Epithelial tissues
Simple Epithelium
i. Simple squamous epithelium:
Are Single layer of thin cells, nucleus flattened in the
plane of the cell
Cytoplasm may be so thin it is hard to see in tissue
sections
In surface view, cells have angular contours and nuclei
appear round
Covers the external surfaces of the digestive organs,
lungs, and heart = mesothelium.
Covers the lumina of the heart chambers, blood
vessels, and lymphatic vessels = called endothelium
Functions: Allows rapid diffusion or transport of
substances through membranes; secretes lubricating
serous fluid
7

8. Types of Epithelial tissues cont’d
Simple Epithelium cont’d
ii. Simple cuboidal epithelium
Single layer of square or round cells
In glands, cells often pyramidal and arranged like
segments of an orange around a central space;
spherical, centrally placed nuclei
Often with a brush border of microvilli in some
kidney tubules; ciliated in bronchioles of lung
Representative locations: Liver; thyroid,
mammary, salivary, and other glands; most
kidney tubules; bronchioles
Functions: Absorption and secretion; production
and movement of respiratory mucus
8
Simple Cuboidal Epithelium in Kidney
Tubules (×400).

9. Types of Epithelial tissues cont’d
Simple Epithelium cont’d
iii. Simple columnar epithelium
Single layer of tall, narrow cells; oval or sausage-
shaped nuclei, vertically oriented, usually in basal
half of cell
Apical portion of cell often shows secretory vesicles
visible with the transmission electron microscope
(TEM)
Often shows a brush border of microvilli; ciliated in
some organs; may possess goblet cells
Representative locations: Inner lining of stomach,
intestines, gallbladder, uterus, and uterine tubes;
some kidney tubules
Functions: Absorption; secretion of mucus and
other products; movement of egg and embryo in
uterine tube
9
Simple Columnar Epithelium in the
Mucosa of the Small Intestine (×400).

10. Types of Epithelial tissues cont’d
Simple Epithelium cont’d
iv. Pseudostratified Columnar Epithelium
Microscopic appearance: Looks multi-
layered
some cells do not reach free surface but
all cells reach basemen membrane;
nuclei at several levels in deeper half of
epithelium;
often with goblet cells; often ciliated
Representative locations: Respiratory
tract from nasal cavity to bronchi;
portions of male urethra
Functions: Secretes and propels mucus
10
Ciliated Pseudostratified Columnar Epithelium
in the Mucosa of the Trachea (×400.

11. Types of Epithelial tissues cont’d
Stratified Epithelium cont’d
i. Stratified squamous epithelium
contains multiple cell layers.
The basal cells are cuboidal to columnar; these cells give rise to cells
that migrate toward the surface and become squamous.
There are two types of stratified squamous epithelia: non-
keratinized and keratinized.
11

12. Types of Epithelial tissues cont’d
Stratified Epithelium cont’d
Keratinized Stratified squamous
epithelium
Microscopic appearance: Multiple cell layers
with cells becoming increasingly flat and
scaly toward surface;
The surface covered with a layer of compact
dead cells without nuclei;
basal cells may be cuboidal to columnar
Representative locations: Epidermis; palms
and soles are especially heavily keratinized
Functions: Resists abrasion; retards water
loss through skin; resists penetration by
pathogenic organisms
12
Keratinized Stratified Squamous Epithelium of
the sole of the foot (×400).

13. Types of Epithelial tissues cont’d
Stratified Epithelium cont’d
Non-keratinized Stratified squamous
epithelium
Microscopic appearance: Same as
keratinized epithelium but without the
surface layer of dead cells
Representative locations: Tongue,
esophagus, anal canal, vagina
Functions: Resists abrasion and
penetration by pathogenic organisms
13
Nonkeratinized Stratified Squamous Epithelium
in the Mucosa of the Vagina (×400).

14. Types of Epithelial tissues cont’d
Stratified Epithelium cont’d
ii. Stratified cuboidal epithelium and
stratified columnar epithelium
have a limited distribution in the body.
Microscopic appearance of stratified
cuboidal epithelium:
Two or more layers of cells; surface cells roughly
square or round
Representative locations: Sweat gland ducts;
egg-producing vesicles (follicles) of ovaries;
sperm-producing ducts (seminiferous tubules) of
testes
Functions: Contributes to sweat secretion;
secretes ovarian hormones; produces sperm
14
Stratified Cuboidal Epithelium in the Duct of a
Sweat Gland (×400).

15. Types of Epithelial tissues cont’d
Stratified Epithelium cont’d
iii. Transitional Epithelium
Microscopic appearance: Somewhat resembles
stratified squamous epithelium, but surface cells
are rounded, not flattened, and often bulge above
surface;
typically five or six cells thick when relaxed
two or three cells thick when stretched;
cells may be flatter and thinner when epithelium
is stretched (as in a distended bladder);
Some cells have two nuclei
Representative locations: Urinary tract—part of
kidney, ureter, bladder, part of urethra; allantoic
duct and external surface of umbilical cord
Function: Stretches to allow filling of urinary tract
15
Transitional Epithelium in the Kidney (×400

16. Apical Cell and Baso-lateral surface Specialization of
Epithelium
Apical cell surface specializations
Microvilli - actin filaments
Cilia - microtubules (dyneins)
Intercellular junctions
i. Zonula occludens (tight junction) - ridges and grooves, seal intercellular spaces -
Selective permeability barrier
ii. Zonula adherens - actin filaments - cell to cell adhesion
iii. Macula adherens (desmosome) - intermediate filaments - attachment plaque (spot)
iv. Hemidesmosome - attaches epithelium to basal lamina
v. Nexus (gap junction) - connexons - cell to cell communication

17. Clinical Applications
Immotile cilia syndrome
(Kartegener’s syndrome):
• Disorder that causes infertility in
male and chronic respiratory tract
infection in both sexes.
• It is caused by immobility of cilia
and flagella induced by deficiency
of dynein.
• Dynein protein is responsible for
movements of cilia and flagella.
Metaplasia:
• It is the transformation of one type
of tissue to another in response to
injury. This condition is usually
reversible if the injury is removed.
• Example: pseudostratified ciliated
columnar epithelium of the
respiratory passages, e.g. trachea, of
heavy smokers may undergo
squamous metaplasia, transforming
into stratified squamous epithelium.

18. 18
Introduction to Histology of
Glands
ANA 201 (General Histology and Introduction to Body System)

19. 19
Introduction
• A gland is an organ that consists of specialized secretory cells.
• Secreted material is usually a liquid.
• Epithelial in origin
Glands are epithelial cells specialized to perform a secretory function
• Present in singly or in groups.
• Unicellular or Multicellular
• 2 types:
 Exocrine
 Endocrine

20. 20
Unicellular glands
• Unicellular glands are single cell interspersed amongst other (non-secretory)
epithelial cells.

21. 21
Multicellular glands
• Formed by invagination of
epithelial layer in deeper tissue to
form a diverticulum:
• Proximal part forms duct.
• Distal part forms secretory
element.

22. 22
Types of Glands
 Exocrine: pour their secretions
onto an epithelial surface, directly
or through ducts.
 Endocrine (ductless): pour
their secretions directly into
the blood.

23. 23
Classification of exocrine glands
• Based on shape & branching pattern of duct
• Based on mode of release of their product
• Based on the nature of their secretion

24. Classification based on shape & branching pattern of duct
• Two types on branching pattern of ducts:
Simple glands: secretions are discharge into one duct
Compound glands:
oSometimes there are a number of groups of secretory cells
oeach group discharging into its own duct.
oThese ducts unite to form larger ducts that ultimately drain on to an epithelial
surface
Simple Compound
24

25. Classification based on branching pattern of duct
• Based on shape of secretory units (tubular or alveolar) & branching pattern of
ducts.
• 2 types on branching pattern of ducts:
Simple glands: secretions are discharge into one duct
Compound glands:
o Sometimes there are a number of groups of secretory cells
o each group discharging into its own duct.
o These ducts unite to form larger ducts that ultimately drain on to an epithelial surface
Simple Compound
25

26. Classification based on shape of the Secretory Unit
• Both in simple and in compound glands the secretory cells may be arranged in
various ways:
i. ‰Tubular glands: Secretory unit are tubular in shape. The tube may be straight,
coiled or branched. e.g., gastric glands.
ii. Acinar glands
‰ : Secretory unit are round or oval in shape, e.g., salivary glands.
iii. ‰Alveolar glands: Secretory unit are flask-shaped.
Note that the terms acini and alveoli are often used as if they were synonymous.
iv. Saccular glands: The secretory elements are greatly distended are called.
26

27. Classification based on shape & branching pattern of duct
Cont’d…
Simple glands:
 Simple tubular
 Simple coiled tubular
Simple branched tubular
Simple alveolar
 Simple branched alveolar
27

28. 28
Classification based on shape & branching pattern of duct
Cont’d…
Compound glands:
Compound tubular
 Compound alveolar
 Compound tubulo- alveolar

29. 29
Compound glands

30. 30
Crypt of Lieberkuhn Sweat glands Fundic glands of stomach Meibomian glands
Brunner glands Submandibular gland Mammary gland

31. 31
Classification of Exocrine gland based on mode of secretion
 Merocrine:
• secretion is released by exocytosis
of secretory granules
• Examples: pancreas, parotid gland,
protein component of milk from
mammary gland.

32. 32
Classification of Exocrine gland based on
mode of secretion cont’d
•Apocrine: apical portion of cell
along with secretory product is
pinched off (lipid component of
milk from the mammary gland).
•Holocrine: entire cell is shed along
with secretory product (sebaceous
glands).

33. 33
Classification based on the nature of secretion
• Serous glands – lacrimal glands
• Mucous glands – sublingual salivary glands
• Mixed glands – submandibular salivary gland

34. 34
Serous glands
• Secretion: thin, watery, rich in
enzymes, protein in nature.
• Cytoplasm: granular (stain darkly
from pink to dark purple with H/E
stain) & rich in rER.
• Nuclei: rounded & basally placed.

35. 35
Mucous glands
• Secretion: contains
mucopolysaccharides which
collects in the apical part of cell.
Cytoplasm: stain very lightly with
H/E stain & therefore gives empty
look.
Nuclei: basally placed & flattened
(mucoid pushes the nuclei).

36. 36
Mixed glands
• Contain both serous & mucous
secretory units.
• Sometimes serous cells form
crescentic caps on mucous acini
called as serous demilunes.

37. 37
Structural Organization of Exocrine Glands
• It consists of three components:
i. Parenchyma
The secretory cells of a gland constitute its parenchyma
ii. Stroma
The stroma is the connective tissue in which the parenchyma lies
It forms septa that divides the glandular tissue into lobules
Aggregations of lobules may form distinct lobes.
The connective tissue covering the entire gland forms a capsule for it
iii. Duct system
Could be within a lobule as intra-lobular, between a lobule as interlobular or lies
between adjacent lobes as inter-lobar .
Intra-lobular has the least diameter while interlobar has the greatest diameter