5. Basement membrane composition
• Basal Lamina – glycoproteins to which
membrane proteins of the epithelial cells
are anchored in the basal lamina.
The 2 major glycoproteins - LAMININ and Type
IV COLLAGEN
FXN: acts as a selective, permeable filter
between epithelium and connective tissue
(CT).
• Reticular Lamina - Reticular fibers
embedded in ground substance that
connect the basal lamina with the
underlying CT. It is synthesized by cells of
the CT.
6. Functions of Epithelia
• Absorption - intestines
• Secretion - glands
• Sensation - gustative and olfactory
neuroepithelium
• Contractility - myoepithelial cells – breast
• Regenerates quickly when subjected to
trauma & destruction.
• Epithelial exposure to different matters:
– Gases-integumentary & respiratory;
– Liquids-circulatory & urinary;
– Semisolids-GI tract
7. 2 Types of Epithelia
1. Cover or line all body surfaces,
cavities and tubes
- SURFACE EPITHELIA
2. Epithelium that is primarily involved
in secretion is often arranged into
structures called glands.
- GLANDULAR EPITHELIA
8. Surface Epithelia are recognized based
on 3 morphological characteristics:
1. Number of cell layers
2. Shape of the component cells
3. Presence of surface specializations
- keratin
- cilia
- microvilli or brushborders / stereocilia
9. Modifications on the Apical
surface of epithelial cells
• Microvilli
• Cilia
• Stereocilia
10. Microvilli
• Fingerlike process that protrude from
the cells apical surface -EM.
• Striated border or brush border in LM
(fine vertical lines on cell surface)
• To increase surface area of
absorption.
• Particularly numerous in the intestinal
mucosa.
• Core : consist of actin filament
12. Cilia (Kinocilia)
• Fingerlike extensions
• Present in cells specialized for
transport of fluid or mucus over
the surface of the epithelium.
• Cilia are motile – beat
sequentially or synchronously in
one direction.
• Core : microtubules that comprise
the axoneme.
13.
14. Stereocilia
• Essentially only microvilli that
are as long as cilia.
• Non-motile
• In epith.cells of ductus
epididymis and “hair cells” of
the inner ear.
18. Simple squamous
• lining surfaces involved in passive
transport (diffusion)
– gases (as in the lungs)
– fluids (as in the walls of blood capillaries).
• forms the delicate lining of the
pleural, pericardial and peritoneal
cavities
– allows passage of tissue fluid into and
out of these cavities.
25. Simple Cuboidal
• lines small ducts and tubules
that may have excretory,
secretory or absorptive
functions.
–Ex. collecting tubules of the
kidney and the small excretory
ducts of the salivary glands and
pancreas.
27. Simple Columnar
• cells are taller and appear columnar
• nuclei are elongated; basal, central, or
apical
• most often found on absorptive
surfaces such as in the small intestine.
• it may constitute the lining of
secretory surfaces such as that of the
stomach.
28.
29. Simple columnar epithelium
Modifications:
• Non-ciliated type - 1 Layer of rectangular
cells, often containing goblet cells;
(+)microvilli
Organ: GI tract (stomach to anus), ducts of
glands and gallbladder
Fxn: Secretion and Absorption
• Ciliated type – (+)cilia
Organ: parts of upper resp. tract, uterine
tubes, uterus, central canal of spinal cord
Fxn: Moves fluids / particles along
passageways
32. Simple Columnar
ciliated
•Found mainly in female
reproductive tract
•Fallopian tube / uterine
tube
•Ciliary action facilitates
transport of the ovum / egg
from the ovary to the
uterus.
33. Pseudostratified
• A variant of simple columnar
epithelium.
• The appearance in section conveys the
erroneous impression that there is more
than one layer of cells.
• All the cells rest on the basement
membrane.
• Almost exclusively confined to the
larger airways of the respiratory system.
34. Mucociliary escalator
•Mucus secreted by goblet
cells are converyed on the
surface.
•Mucus traps foreign
material
•The cilia propel mucus
with entrapped particles
towards the pharynx.
35. • Kartagener’s syndrome –
inherited abnormality in cilia,
compromising respiratory
functions, with ineffective
clearance of mucus.
36. Stratified Epithelia
• epithelia consisting of two or more
layers of cells.
• function mainly for protection.
• the degree and nature of the
stratification are related to the kinds
of physical stresses to which the
surface is exposed
NOTE: A stratified epithelium is classified on
the basis of the shape of the cells in the TOP
LAYER ONLY
46. Transitional epithelium
• Variable appearance – cuboid
to squamous
• Organs: exclusively in
excretory urinary passages
(renal calyces and pelvis,
ureter, urinary bladder, and
part of the urethra).
• Fxn: Permits distension
47.
48. Urinary bladder - Highly specialised to accommodate a great
degree of stretch and to withstand the toxicity of urine.
‘Relaxed‘
(contracted)
‘Distended’
(stretched or uncontracted)
Transitional Epithelium
49. Modifications on the lateral
surfaces of epithelial cells.
• Cell Junctions / Intercellular jxns. /
Junctional complexes
• bind epithelial cells to adjacent cells
• to provide physical strength and
mediate exchange of information and
metabolites.
The intimate contact between epitheiial cells ensures that
materials passing through the epithelium have to pass
through the cells, rather than between them.
51. Tight junction
or Occluding junction
• “occlude” – to block / hinder
• Most apically situated of the
junctional complexes
• a continuous belt-like junction
– zonula = latin for belt ; “zonula occludens”
• Proteins in the membrane of adjacent cells
called occludin interact with each other to
produce this tight seal.
• to seal the intercellular spaces so that
luminal contents cannot penetrate between
the lining cells.
52. Tight / Occluding / zonula occludens
• Common in
transport epithelia.
Example:
• beneath the luminal surface
of simple columnar
epithelium
53. Adherens jxn./ Zonula adherens
• Also called “belt desmosome”
• Located just below tight/occluding jxn.
• Forms a band that completely
encircles each epith. cells.
• Cell membranes of adjoining cells are
very close but neither adhere nor fuse.
– Separated by an intercellular space (15-
20 nm wide)
Particularly present in epithelia with microvilli or cilia
55. Spot Desmosome
• Usually situated just below zonula
adherens.
• They do not form a band around the
epithelial cells
• (instead) button-like or rivet-like
adhesions that are arranged in a line
• At the desmosome jxn, the cells are
separated by a relatively wide
intercellular space (about 30 nm)
57. Gap Junction
• Also called “communicating” junction.
• Gap – broad areas
• Intecellular space is only 3 nm wide
• Apposed plasma membranes are
perforated by tiny tubes –
“connexons”
• Connexon allow exchange of ions and
small molecules bet. adjacent cells
58. Gap Junctions
Gap or nexus junction
• provide a conduit for passage of
small molecules between
adjacent cells.
• (ex:epithelium, cardiac &
smooth muscles)
59. Hemidesmosomes
• Modification on the basal
surfaces of epithelial cells.
• Half of a desmosome!
• Helps anchor the epithelial
cells to the underlying basal
lamina (basement
membrane)
60. References:
• Young B. 2009. WHEATER’S FUNCTIONAL
HISTOLOGY. 5TH
Edition. UK: Churchill
Livingstone. Distributor: Phils: C & E
Publishing, Inc.
• Gonzales E. 2009. ESTEBAN and GONZALES’
TEXTBOOK OF HISTOLOGY. 4TH
Edition. PHILS: C
& E Publishing, Inc.
it seems to be formed by many cell layers. The most basal cells have a cuboidal or columnar shape. Followed by several layers of polyhedral cells, and, finally, a layer of superficial cells, which have convex, Dome-shaped surface (Umbrella or dome-shaped cells).
