SSN Session
Epithelial Tissue
Jennifer Chang (jtc2109)
Bram Welch-Horan (tbw5)
October 11, 2005
Epithelium
What is epithelium?
• Covers exterior surfaces
• Lines internal closed
cavities and body tubes
• Forms secretory
portions of ducts and
glands
• Avascular tissue
• High regeneration
capacity
Polarized Cells
Apical:
• faces the lumen or outside world
• separated from the basolateral side
by tight junctions
Lumen
Apical
Basolateral:
• Lateral:
• side that faces neighboring cell
• forms functional continuum with
basal side
• Basal:
• adheres to extracellular
connective tissue – basement
membrane
Lateral
Basal
The Apical Region
Epithelial Specializations:
Microvilli
small intestines
Stereocilia
epididymis
Cilia
fallopian tube
Microvilli
• Cytoplasmic processes that
extend from cell surfaces
• Made of actin skeleton above
intermediate filaments
• Increase area for absorption as
in small intestine
• Insert into terminal web
microvillus border
terminal web
Small intestines
Stereocilia
• Long microvilli (NOT CILIA!)
• Non-motile
Epididymis
Cilia
• Motile processes of
microtubules that
move
synchronously
• Insert into basal
bodies (1 cilium per
1 body)
• 9+2 microtubule
arrangement
cilia
Basal bodies
Fallopian tube
Trachea
The Lateral Region
Junctional Complex (aka Terminal Bar)
: site of specialized attachment of adjoining epithelial cells
microvillus border
terminal bar
terminal bar
terminal web
Bodian silver stain
The Junctional Complex
3 Components (apical -> basal):
1. Zonula Occludens=Tight Junction
•most apical
•located around entire perimeter
•diffusion barrier
2. Zonula Adherens
•around entire perimeter
•add to integrity of epithelial surface
3. Macula Adherens=Desmosome
•occur at small discrete sites
Gap junctions
•at small discrete sites
•metabolic and electrical coupling
Electron micrographs of the
junctional complex
The Basal Region
Basement membrane
1. Basal Lamina
• Secreted by epithelial cells
• Barrier between epithelium and connective tissue
• Collagen type IV, proteogylcans & glycoproteins (PAS +)
2. Reticular Lamina
• Connective tissue below epithelium
• Collagen type III
Hemidesmosomes
Junctions that anchors epithelial cells to basal lamina
PAS stain
basal lamina
Question 1.
This structure is typically found in the
a)
b)
c)
d)
trachea
kidney
epididymis
small intestines
Question 2.
Which of the following is FALSE regarding the structure at the pointer?
a)
b)
c)
d)
its permeability determines whether the epithelia is “tight or “leaky”
it occurs at small discrete sites
it separates the apical surface from the basolateral surface
it is a component of the junctional complex
Question 3
What type of collagen is found in the tissue at the pointer?
a)
b)
c)
d)
type II
type III
type IV
type VII
Types of Epithelial Cells
Epithelial Cell Types - Nomenclature
• Simple – 1 cell layer thick
• Stratified – 2 or more cell layers thick
• Squamous – cell width > height (i.e., flat)
• Cuboidal – width/depth/height ~same
• Columnar – cell height >> width
Simple Squamous Epithelium
•
•
•
•
•
1 cell layer thick
function: exchange
absorption, secretion, diffusion
e.g. – blood vessels
barrier function in CNS
Simple Cuboidal
•
•
•
•
cuboidal shape (or pyramidal)
round, central nucleus
absorption / secretion, conduit
e.g. – small ducts of exocrine glands
(pancreas), kidney tubules
Simple Columnar
• elongated cells w/
elongated nuclei
• height > width
• absorptive
(e.g. small intestine)
or secretory
(e.g. gastric glands)
• other examples:
-lining of colon,
stomach, gall bladder
Stratified Epithelium
• 2 or more layers thick
• classified based on
surface cells
(can be squamous,
cuboidal, or columnar)
• functions include:
protection, barrier,
resist abrasion
What type of stratified epithelium
is seen above?
• Examples: epidermis,
esophagus, larger
exocrine ducts
Stratified Epithelium
• 2 or more layers thick
• classified based on
surface cells
(can be squamous,
cuboidal, or columnar)
• functions include:
protection, barrier,
resist abrasion
What type of stratified epithelium
is seen above?
Stratified Squamous Epithelium
• Examples: epidermis,
esophagus, larger
exocrine ducts
Pseudostratified Epithelium
All cells rest on basement membrane,
but not all reach apical surface
-function: secretion, absorption, conduit
-e.g., trachea, epididymis
Transitional Epithelium
Transitional Epithelium – “Urothelium"
• special stratified epithelium
• apical surface may appear “domed”
(empty) and flattened full)
• function: distensibility
• lines lower urinary tract
• i.e., ureters, bladder, proximal urethra
Question 4
What kind of epithelium
lines the secretory
alveoli of this
exocrine gland?
a.
b.
c.
d.
Simple Columnar
Simple Cuboidal
Squamous
Transitional
Questions 5, 6
Figure A
Lab 3, Slide 35
Figure B
Lab 3, Slide 25
• 5. Select the one correct statement regarding the surface
epithelium.
• 6. The tissue or tissues that are specialized to provide a barrier to
luminal absorption are shown in:
Question 7
This epithelial cell type is
found in:
a. Bladder
b. Kidney tubules
c. Intestinal epithelium
d. Epidermis
Question 8
What type of epithelium is this?
a. Pseudostratified
b. Stratified Columnar
c. Stratified Squamous
d. Stratified Cuboidal