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Tissues
Part A
What is a tissue?
Found only in multicelled
organisms
Form “cell communities” that share
cytoplasm, etc. through gap
junctions
Held together by desmosomes and
tight junctions
Tight Junctions
• Found at the top sides of
four adjacent cells
• Weld cells together
• Create impermeable
barrier - stop movement
of substances from the
lumen down between
cells
• Why would this be
important in the stomach
or intestines?
Desmosomes
• Desmo – “bond or
adhesion”
• Regions where cells are
bonded together; spot like
adhesions
• Located between cells of
simple and stratified
squamous epithelial cells
(both exterior and interior)
• Also bind muscle cells to
each other
• Why are they helpful in
these types of cells?
Gap Junctions
• “Connexon” proteins that
form a “doorway”
between adjacent cells
• Permit movement of
cytoplasm, chemicals and
electrical currents
between adjacent cells
• Cell “sharing” of materials
within tissue
• Will close if cell is
damaged to prevent
problems for adjacent
cells
Histology
Is the study of tissues of the human
or animal body
Requires a Medical
Technology/Biology degree and
American Society of Clinical
Pathologist certification
4 Major Types of Tissues
•
•
•
•
Epithelial
Connective
Muscle
Nervous
Epithelium
• Covering and lining epithelium
• Glandular Epithelium
Covering or Lining Epithelium
• Include
– Simple Squamous
– Simple Cuboidal
– Simple Columnar
– Pseudostratified Columnar
– Stratified Squamous
– Stratified Cuboidal
– Stratified Columnar
– Transitional Epithelium
Characteristics of ALL Epithelial
Tissue
• Close-packed cells
• Fit close together with desmosomes or
tight junctions
• Apical surface exposed to body or organ
exterior, or to the lumen (opening) of an
organ
• Basal surface attached to basal lamina,
sheet of glycoproteins that selectively filter
diffusing chemicals from underlying
connective tissue
Epithelial cells
Terminology
• Apical, apex, apo – means “top”
• Basal – means bottom
• Lateral – means side
Characteristics Continued
• Avascular but innervated – means they
lack blood vessels, but contain nerve cells.
Epithelial cells receive nourishment from
the cells below them.
Characteristics Cont’d
• Regenerative ability – very high; cells
functions to protect – therefore need to
replace themselves as they are lost.
– Being located as surface coverings, they
receive a lot of “friction” as chemicals, cells or
other surfaces rub against them
Shapes of Epithelial Cells
•
•
•
•
Squamous – “flat”
Cuboidal – cube shaped
Columnar – column shaped
All have an apical (top) surface and a
basal (bottom) surface
Stratified vs. Pseudostratified vs.
Transitional
• Pseudo means “false”
• Cells are actually columnar
• Stratified means “layered”; can see the
layers of cells
• “Transitional” means cells change size or
shape – are ‘stretchy’
Pseudostratified
• Notice that the nuclei
are either above or
below each other
• Gives a false idea of
layers, rather than
columnar-shaped
cells
Transitional Epithelium
• When normal, appear
rounded
• When stretched by
function of organ,
appear flat!
• What organ or organs
is this tissue found in?
• Why does it need this
“stretchability”?
Simple Cuboidal
• Provide protection,
active or passive
movement of
chemicals across the
lumen
• Kidney glomerulus,
eyes, ovaries, thyroid
gland
Simple Columnar
• Longer than wide
• Line digestive tract
mostly
• Ciliated are found in
fallopian tubes and
trachea
Simple Vs. Stratified Squamous
• Simple
• Minimum resistance
to diffusion or
osmosis
• Linings/coverings
• Stratified
• Multiple Layers
• Usually outside areas,
like skin
• Resistant to friction,
chemicals
Muscle Cell Characteristics
• Well, what are they?
Smooth Muscle
• Found surrounding
arteries (two layers),
veins, digestive organs,
reproductive tracts of
both sexes, urinary
bladder, respiratory tract,
iris of eye
• Involuntary muscle;
controlled by nervous
system
• Cells are “spindleshaped”, wide in middle,
tapering to ends, nucleus
in center and non-striated
Cardiac Muscle
• Major tissue that makes up the heart structure;
involuntary, controlled by brain stem
• Branched striated cells with intercalated discs
between the cells
• At an intercalated disc, the cell
membranes of two adjacent
cardiac muscle cells are
extensively intertwined and
bound together by gap
junctions and desmosomes.
• Connections help stabilize the
relative positions of adjacent
cells and maintain the threedimensional structure of the
tissue.
• The gap junctions allow ions
and small molecules to move
from one cell to another.
– This arrangement creates
a direct electrical
connection between the
two muscle cells.
– An action potential can
travel across an
intercalated disc, moving
quickly from one cardiac
muscle cell to another.
Intercalated
discs
Skeletal Muscle
• Makes up the
muscles that move
the body proper;
voluntary movement
• Striated, nucleus
seen, long fibers
Nervous Cell Characteristics
• Well? Spit it out!
Nervous Tissue
• Makes up the brain, spine and
outer nerve cells
• Control voluntary and
involuntary movement,
reflexes and reactions,
conscious and subconscious
thought processes