BIOL 109 Lecture Notes - Lecture 10: Epithelium, Tight Junction, Cell Adhesion Molecule
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4.1
Tissues- collections of specialized cells and cell products that carry out a limited number
of function
Histology- study of tissues
Epithelial tissue- covers exposed surfaces, lines internal passageways and
chambers, and forms glands
Connective tissue- fills internal spaces, provides structural support for other
tissues, transports materials within the body, and stores energy
Muscle tissue- specialized for contraction and includes the skeletal muscles of
the body, the muscle of the heart, and muscular walls of hollow organs
Neural tissue- carries information from one part of the body to another in the
form of electrical impulses
4.2
Epithelial tissue has an exposed surface, which faces the exterior of the body or an
internal space, and a base which is attached to underlying tissues
Epithelial- layers of the cells that cover internal or external surfaces
Glands- structures that provide fluid secretions
They are either attached to or derived from epithelia
Characteristics of Epithelial tissue
●Cellularity
- made almost entirely of cells bound closely together by
interconnections known as cell junctions
● Polarity-
refers to the presence of structural and functional differences
between the exposed and attached surfaces
○ Apical surface- layer of cells that is exposed
○ Basal surface- attached layer of cells
● Attachment-
base of epithelium is bound to a thin noncellular basement
membrane (basal lamina)
● Avascularity-
avascular without blood vessels
○ Get nutrition from diffusion
● Regeneration-
cells are continuously replaced through stem cell division
○ Rates are higher in epithelia than other tissues
Functions of Epithelial tissue
● Provide physical protection-
protect exposed and internal surfaces from
abrasion, dehydration, and destruction by chemical or biological agents
● Control permeability-
any substance that enters or leaves the body must
cross an epithelial tissue
● Provide Sensation-
sensitive to stimulation because of the large sensory
nerve supply
○ Neuroepithelium- epithelium that is specialized to perform a
particular sensory function
● Produce specialized secretions-
produce secretions called gland cells
○ Glandular epithelium- most or all the epithelial cells produce
secretions
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■ Discharge their secretions onto the surface of the
epithelium (to provide physical protection or temperature
regulation) or release them into the surrounding interstitial
fluid and blood
Specializations of epithelial cells
● The movement of fluid over the epithelial surfaces providing protection
and lubrication
● The movement of fluid through the epithelium to control permeability
● The production of secretions that provide physical production or act as
chemical Messengers
Apostille surface- where the cells exposed to the internal or external
environment
Basolateral surfaces- include both the base where they sell attaches to the
underlying epithelial cells are deeper tissues and the sides where the cell
contacts its neighbor
Cilia epithelium- cilia are characterized by the surface is covered
Maintaining the integrity of Epithelia
Intercellular connections
●Cell adhesion molecules (CAM)- transmembrane proteins that
connect large areas of opposing plasma membrane
○ This binds to each other and to the extracellular materials
●Hyaluronan- membranes of adjacent cells may also be bonded
by thin layers of proteoglycans that contain polysaccharides
● Cell junctions- specialized area of plasma membrane that attach
a cell to another cell or extracellular material
○ Tight junctions-Liquid portion of 2 plasma membranes are
tightly bound together by interlocking membrane proteins
■ continuous adhesion belt forms a band that encircle
cells and binds them to their neighbors
● so tight that it largely prevents water and
solute from passing between the cells
■Lumen- tight junctions that line passageways like
intestinal tract
○ Gap Junctions- two cells are held together by interlocking
transmembrane proteins called connexon
■ Connexon- Composed of 6 connexin protein the
form a cylinder with a central core
○ Desmosomes-Very strong and can resist stretching and
twisting
■ spot desmosomes- Small disk connected to
intermediate filaments
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■ Hemidesmosomes- Resemble a spot desmosomes,
but rather attaching the to a cell, they attach
themselves to extracellular filaments
Attachments to the basement membrane
● The inner surface of each epithelial is attached to a two-part
basement membrane
● clear layer- the layer of the proteins and the network of fine
protein filaments
● Dense layer- the deeper proportion of the basement membrane
○ Gives membrane and strength
Epithelial Maintenance and Repair
● Only way the epithelium can maintain its structure over tie is by
the continual division of stem cells
● Germinative cells- located near the basement membrane in a
relatively protected location
4.3
Simple epithelium- one layer of cells covering the basement membrane
distance from the nucleus to the basement membrane does not change from one
cell to the next
line internal compartments and passageways such as the pleural
pericardial and peritoneal cavities
Stratified epithelium- several layers of the cells covering the basement membrane
exposed to areas of stress, like the lining of the mouth
Squamous- thin and flat
Simple squamous epithelium- body's most delicate type of epithelium; located
where absorption or diffusion take place
examples include alveoli of the lungs, the lining of the thoracic and
abdominopelvic body cavities, and the lining of the heart and blood
vessels
Mesothelium- simple squamous epithelium that lines body
cavities including the lungs, heart, and abdominal organs
Endothelium- Simple squamous epithelium lining the inner
surfaces of the heart and all the blood vessels
Stratified squamous epithelium- generally located where mechanical stresses
are severe
Keratinized- epithelial cells pass with filaments of the protein keratin
Nonkeratinized
stratified squamous epithelium will resist operation but
dried out unless kept moist
examples include oral cavity, pharynx, esophagus, anus, and
vagina
Cubital- little boxes
Simple cuboidal epithelium- provides limited protection and occurs where
secretion and absorption takes place
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