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Lecture 53- Epithelium Histology, NAMING -layers (1st) + shape (2nd),…
Lecture 53- Epithelium Histology
Recap:
4 Tissue Types
Epithelial
Connective
Muscle
Nervous
composed= cells + ECM
cells --> tissues --> organs
Parenchyma=
organ cells**
Stroma
= Supporting cells!
Epithelia
:star:
Covering epithelia:
lines all surfaces
FUNCTIONS
Covering, lining, & protection
Absorption
Secretion
Specialized: sensory
CHARACTERISTICS
Tightly packed cells
Very little ECM
Avascular
Assoc. w/ C.T.
Highly regenerative
Innervated
Polarity
Apical Side
Apical side specializations
Microbilli (brush border)
Cillia (hair-like)
Lumen
(empty space) inside endothelial lining
Basolateral
side (
facing mesoderm
)
CLASSIFICATION
SHAPE
of cell :red_flag: :fire:
Layers:
simple
or
stratified
1. Squamous
:red_flag:
1A:
Simple Squamous Epithelia
:black_flag:
Passive diffusion & filtration
Serous membranes
Locations
Renal corpuscles
Alveoli
Heart lining
Vessels
Serosa
Special Types
Endothelium
(
inner
coverings)
slick lining of hollow organs
lines vascular system
Mesothelium
(
middle
coverings)
lines peritoneal, pleural, + pericardial cavities + covers visceral organs of these
ex: Uterine tube
1B:
Stratified Squamous Epithelium
:black_flag:
many layers of squamous
deeper layers= cuboidal
THICKEST
epithelial tissue! :fire:
Specific Types
Function
: protects underlying tissues from abrasion
Locations:
Keratinized
- forms epidermis
Non-keratinized
- lining of esophagus, mouth, vagina
2. Cuboidal
:red_flag:
2A: Simple Cuboidal Epithelium
Function:
-mostly secretion
-some aborptive
Locations:
-kidney tubules
-secretory portions-small glands
-ovaries
-thyroid follicles
3. Columnar
:red_flag:
3A:
Simple Columnar Epithelium
Function:
-absorption
-secretion (mucus)
-ciliated type propels mucus or reproductive cells
3B:
Pseudostratified Columnar Epithelium
ALL
cells originate at basement membrane!
only tall cells reach apical surface
may have goblet cells and/or cilia
Non-ciliated
: ducts of M reproductive tubes & large glands
Ciliated
trachea & most upper resp. tract
SPECIAL
2/3:
Stratified Cuboidal & Columnar Epithelia
:star:
rare!
stratified cuboidal
conjunctiva lining- eyelids, anorectal juncture
stratified columnar
excretory ducts of salivary & sweat glands
Glandular epithelia:
secretory
Exocrine
glands
ducts carry products to epithelial surface
OUTside
Examples
mucus-secreting glands
sweat & oil glands
salivary glands
enzymes (liver & pancreas)
mammary glands
Unicellular Exocrine glands
(goblet cell)
goblet cells make
mucin
mucin + H20 --> mucus
protects internal body surfaces
digestive + respiratory track
Multicellular Exocrine Glands
many shapes
often
tubular
or
acinar
simple, branch, or coiled
SECRETION
Merocrine secretion
:explode:
most common!
exocytosis
e.g., salivary glands
Serous
mostly H20, but also has some proteins (
non-glycosylated)
i.e., parotid glands, pancreas
Mucous
mucus (
heavily
glycosylated proteins-
mucins
)
i.e., sublingual glands, goblet cells
Mixed
(
seromucous glands)
serous & mucus combined
(
i.e., submandibular gland
)
Holocrine secretion
whole cell disintegrate (
i.e., sebaceous gland)
Apocrine secretion
apical portion lost (
i.e., mammary glands)
Endocrine
glands
Ductless
Hormones into tissue fluid
may occur single
or
in small groups
not all epithelia
Basement Membrane
(thin felt-like sheet of macromolecules)
FUNCTION
1) Structural support
2) Attach epithelia to C.T.
3) Filtration
4) Scaffold for regeneration/repair
5) Physical barrier against tumor cell invasion
BASAL LAMINA
thin, electron dense
sheet-like layer of fine fibrils
near epithelial cells
Type IV collagen
2D-network, evenly spaced subunits; resembles mesh of window screen
Laminin
attach to transmembrane integrin proteins in basal cell membrane
Nidogen & Perlecan
:<3:
proteoglycans
that
cross-link
laminins
type IV collagen
provide basal lamina's
3D structure
bind epithelium to that structure, and
determine
porosity/size
of mol able to filter through
RETICULAR LAMINA
diffuse & fibrous
Type III
collagen
INTRACELLULAR ADHESIONS & JUNCTIONS
:red_flag:
Epithelial cells adhere strongly to neighboring cells & basal lamina -> subject to friction + mechanical forces
1. TIGHT JUNCTIONS
:black_flag:
form
seal
b/w adjacent cells
most apical
location
prevent
paracellular transport
maintain
2 distinct membrane domains
Interaction b/w Transmembrane proteins:
Claudin & Occludin
C. perfringens
enterotoxin binds claudin!
2. ADHERENS JUNCTION
(zonula adherens)
:black_flag:
site of strong cell adhesion
Below
Tight junctions
Anchoring
junctions
(
mechanical
attachment)
allows cells to
move as 1 unit!
Cadherins
bind
catenins
that link to
actin
3. GAP JUNCTIONS
:black_flag:
communication b/w adjacent cells
channel*
b/w
*2 adj. cells
(1.5nm)
allow
small mol (cAMP)/ions
to move
cells connected by hollow cylinders of
connexins
4. DESOMOSOMES
(
macula adherens
) :star:
coupling b/w adjacent cells
Single
"spot-weld"
Stress & stretch resistance
Bullous Pemphigoid
60+ years old
; when desmosomes fall apart & weaken -> skin gets loose
5. HEMIDESMOSOMES
:black_flag:
anchor cell to basal lamina
NAMING
-layers (1st) + shape (2nd)
May include
accessory structures
Goblet cells
Cilia
Keratin
Special Epithelial Tissues
Pseuodostratified
Transitional Epithelium
:explode:
aka
urothelium
Description:
-basal cells= cuboidal or columnar
Function
:
-
stretches
+ permits distension of urinary bladder
Location:
URINARY system!
-lines ureters, urinary bladder, part of urethra
