Epithelial Tissue
August 26, 2010
Dr. Crissman
1. Identify the two major subdivisions of epithelium (epithelium and glands) and their
embryological origins.
a. Ectoderm: epidermis
b. Mesoderm: lining of internal cavities
i. Mesothelium: pericardium, pleura, peritoneum
ii. Endothelium: Lining of blood/lymph vessels
c. Endoderm: Lining of GI, respiratory tract
2. Be able to define tissue epithelium, list its functions and common structural
characteristics
a. Epithelium: Layer of cells that cover the body’s surfaces
b. Functions of Epithelium:
i. Physical barrier
ii. Protection from chemical/mechanical damage and dehydration
iii. Secretion (glands are epithelial tissue)
iv. Absorption (GI)
v. Transport (endothelium, lungs)
vi. Sensory surfaces
vii. Regeneration and repair
c. Structural characteristics of epithelium:
i. Predominantly cellular
ii. Numerous intercellular junctions
iii. Polar cell (Apical vs. Basolateral portions)
iv. Free surface
v. Sits on basement membrane of connective tissue
vi. Avascular
3. Be able to describe and classify types of epithelium by cell shape and number of layers
a. Two parts to epithelium naming, according to STRUCTURE
i. Number of layers
1. Unilaminar = Simple (single layer)
2. Multilaminar = Stratified (more than 1 layer)
ii. Shape of cell
1. Squamous – thin and flat
2. Cuboidal – cube-like
3. Columnar – Tall & Narrow
b. Types of Epithelial Tissues (based on shape of surface cells!)
i. Simple Squamous: Lining of blood/lymph vessels
ii. Simple Cuboidal: Ducts of glands, ovary covering
iii. Simple Columnar: GI tract, lower respiratory tract
iv. Pseudostratifed: Most of respiratory tract, nasal cavity
v. Keratinized Stratified Squamous:
1. NO nucleus. Cell dies as it migrates up
2. Epidermis
vi. Non-keratinized Stratified Squamous (mucosa):
1. Nucleus present
2. Wet inner surfaces (vagina, mouth, eye, esophagus)
vii. Stratified Cuboidal: Ducts of sweat glands, pancreas
viii. Transitional (Uroepithelium)
Epithelial Tissue
August 26, 2010
Dr. Crissman
1. Most of urinary tract
2. Non-distended Uroepithelium: Surface = Cuboidal
3. Distended Uroepithelial: Surface = Squamous
ix. Sensory
1. Gustatory: Tongue, taste buds
2. Olfactory: Nasal passage
3. Stato-acustic: ears (proprioception)
x. Germinal: seminiferous tubules
4. Be able to describe the polarity of the epithelial membrane and how its specializations
contribute to its polarity and function. Be able to relate structure to function
a. Epithelial cells are morphologically divided into Apical and Basolateral
domains, each with its own structural/functional characteristics
b. Apical Domains
i. Free surface (luminal) side of cell
ii. Contains: Carrier proteins, Glycoproteins, Glycocalyx, Hydrolytic
enzymes, Aquaporins
iii. Performs Endocytosis, Exocytosis, and Transcytosis
1. Endocytosis: Coated pit with clathrin pinched off, forms
coated vesicle which becomes endosome by shedding
clathrin
2. Exocytosis: At apical surface (mucous, saliva) or
basolateral surface (endocrine glands)
3. Transcytosis: One side to another in any direction
iv. Specializations of Apical Surface
1. Microvilli: small, non-motile finger-like projections
a. Form striated, brush-border
b. Actin filaments joined at top of microvilli
(Villin), connected to each other (Fimbrin),
embedded at base (into Terminal web), and
supported by linkages to membrane at regular
intervals (myosin-1, calmodulin)
c. GI tract, Proximal tubule of kidney
2. Sterocilia: longer version of microvilli, non-motile,
epididymis
3. Cilia
a. Motile, used to propel mucous across surface
b. Axoneme: core of cilia
c. Consist of microtubules attached to basal body
at bottom
d. 2 singlets surrounded by 9 doublets (made of
Subunit A of 13 protofilaments, and Subunit B of
10 protofilaments): 9+2 Arrangement
e. Sheath surrounds singlet’s and is connected to
Subunit A by radial spoke to prevent buckling
f. Nexin connects neighboring doublets
g. Dynein is microtuble-associated protein with 2
arms which project from Subunit A to B.
Epithelial Tissue
August 26, 2010
Dr. Crissman
Dynein ATPase causes dynein to
transiently attach to Subunit B and slide
toward tip and cilium. Nexin translates this
to bending. Dynein releases Subunit B,
causing cilia to return upright
h. Beat of cilia has Effector Stroke and Recovery
stroke
i. Primary Ciliary Dyskinesia or Immotile Cilia
Syndrome or Kartagener’s Syndrome: lacking
dynein or radial spokes, leading to malfunction cilia
(infertility, lung infections)
4. Flagella
a. Structurally similar to cilia, but longer and axoneme
is surrounded by mitochondria
c. Basolateral Domain
i. Lateral and base of epithelial cell
ii. Characterized by junctional complex, aka terminal bars, which
is where cells come in contact near apical surface and runs all
around the cell’s circumference
iii. 4 Different Structural/Functional Junctions of Lateral Domain
1. Zonula Occludens aka Tight Junction
a. Most superficial to apical surface
b. Quilt-like barrier which functions to make epithelial
sheet impermeable to substances. Tight vs. Leaky
c. Division of apical/basolateral membranes, and keeps
membrane proteins from each domain separate
d. Fusion of claudin and occludin, arranged as
anastomosing strands, and reinforced by
Cadherins
2. Zonula Adherens aka Adhesion Belt
a. Mechanical adhesion between neighboring cells
b. Cadherins are transmembrane linker proteins, and
are bound to Actin filaments of cytoskeleton by
Talin, Vinculin, and -Actin.
3. Macula Adherens aka Desmosome
a. Act as a “spot-weld” mechanical attachment
b. Attachment Plaques (made of desmoplakin &
plakoglobin) formed on cytoplasmic side of
membrane
c. Desmoglein & Desmocolin (both Cadherins) span
membrane/gap to connect plaques
d. Intermediate filaments anchor plaques into
membrane
e. Phemphigus vulgaris: antibodies attack self
cadherins (desmoglein). Causes severe blistering
due to high [desmosome] in epidermis
Epithelial Tissue
August 26, 2010
Dr. Crissman
4. Gap Junctions
a. Only in lateral domain, scattered throughout
b. Cell-cell communication
c. Disc of numerous connexons (total of 6 connexin
subunits) form aqueous pores in cell membrane
which connect cytoplasm of adjacent cells
d. Passable ONLY to ions, small amino-acids, c-AMP,
nucleotides and polysaccharides (i.e. no
macromolecules)
e. Can pass along electrical impulse to create
peristaltic wave
iv. 3 Specializations of Basal Domain:
1. Basal Lamina: Dense layer which holds cell to connective
tissue; located in ECM, subadjacent to basal
membrane
2. Plasma Membrane Enfoldings: highly folded basal
membrane which increases surface area for fluid
passage (tessellated).
3. Hemidesmosomes: Appears as half of a desmosome and
has ½ plaque on cytoplamsic side into which
Intermediate Filaments embed. Unlike Desmosomes,
transmembrane protein is Integrin, which holds cell
membrane to basement membrane i.e. connective
tissue.
5. Describe/differentiate between exocrine and endocrine glands
a. Endocrine Gland: No duct. Secretes directly into connective tissue
where it is transferred into blood
b. Exocrine Gland: Uses duct to deliver secretion to surface of epithelium
6. Be able to describe common components of an exocrine gland and classify glands by
morphology, mode of secretion, and type of secretion
a. Morphological/Structural Classification
i. Unicellular gland: single cell embedded in epithelial layer (ex.
Goblet cell)
ii. Multicellular Gland: consists of duct and secretory portions
and is named according to 1.) Branching of duct portion and 2.)
Shape of secretory portion
1. Duct Portion: branching-based
a. Simple exocrine gland: single duct
b. Compound exocrine gland: branched duct system
2. Secretory Portion: shape-based
a. Tubular: Secretory portion forms long tube
b. Acinar/Alveolar: Secretory portion is grape-shaped,
may have myoepithelial cells surrounding
secretory portion, contractile to help secretion
3. Multicellular glands are surrounded by Connective Tissue
Capsule
4. Larger versions may be subdivided by septa
Epithelial Tissue
August 26, 2010
Dr. Crissman
iii. Examples of structural nomenclature:
1. Simple tubular: Gastric glands
2. Simple alveolar: Sebaceous glands
3. Simple branched alveolar: Sebaceous glands
4. Simple coiled tubular: Sweat glands
5. Compound tubuloaveolar: Salivary, pancreas
b. Mode of Secretion
i. Merocrine secretion
1. Most common
2. Exocytosis of secretory vesicles, no cytoplasm loss
3. Sweat, saliva, pancreas, goblet cells
ii. Apocrine secretion
1. Secretion is pinched off of cell with partial cytoplasm and
membrane loss
2. Lipid portion of milk of mammary gland
iii. Holocrine secretion
1. Cell fills with secretion and dies, degeneration cell forms
secretion
2. Sebaceous gland of skin
iv. Cytocrine secretion
1. Whole living cell is secreted
2. Ovary, testis
c. Type of Secretion
i. Mucous
1. Thick, viscous, and rich in mucinogens
2. Appears as light-staining with foamy cytoplasm
3. Ex. Goblet cells, sublingual salivary
ii. Serous
1. Watery and rich in enzymes and ions
2. Cells appear acidophilic (darker)
3. Ex. pancreas, parotid, sweat glands
iii. Mixed
1. Both mucous and serous secretions
2. Demilunes: crescent shapes on outside of mucous alveolus
3. Ex: salivary gland
iv. Sebum
1. Oily, rich in lipid
2. Ex. Sebaceous glands of skin, eyelid
v. Ceruminous
1. Thick, waxy, protective secreation
2. Ex. Glands of auditory canal
7. Be able to define and describe the different levels of organization in the body
a. Cells: Basic unit of all animals
b. Tissues: groups of cells performing a specific function
c. Organs: groups of tissues performing specific function
d. Organ Systems: Groups of organs performing specific function
8. Be able to list and describe the 4 tissue types in the body.
Epithelial Tissue
August 26, 2010
Dr. Crissman
a. Tissue types are based on function of said tissue
b. Epithelium: layer of cells that covers the body’s surfaces
c. Muscle: groups of cells that change shape, specialized for contraction
and responsible for locomotion, constriction, pumping, and
peristalsis
d. Nerve: groups of cells characterized by excitability; receive stimuli and
transform stimuli into impulse
e. Connective Tissue: group of cells that connects other tissues together
in the body; relatively few cells, large amounts of ECM