Define tissue
 Describe the germ tissue layers, their location,
and what tissues they produce in eucoelomate
animals (humans).
 List the 4 major types of tissues of the human
body.
 Describe the characteristics, cell types,
function, and the location of epithelial tissues.
 Describe the characteristics, cell types,
functions, and the location of connective tissues.
 Describe the characteristics, cell types,
functions, and the location of muscle tissues.
 Describe the characteristics, cell types,
functions, and the location of nervous tissues.

 Histology
is defined as the study of the
microanatomy of animal and plant tissues

A tissue is a group of like cells of similar
specialized structure which carry out similar
specific functions.
 We
all start as a single cell called a zygote.
 This cell begins to divide, and gives rise to
germ cells or stem cells that eventually form
the developing embryo.
 Because humans are eucoelomate (true
body cavity) animals, like earthworms, we
have three germ tissue layers:
A.
B.
C.
Endoderm
Mesoderm
Ectoderm
The endoderm layer is the
innermost layer, which forms
the epithelial lining in our
digestive tract from mouth to
rectum.
 The endoderm also forms
many organs: the stomach, the
liver, the pancreas, the urinary
bladder, the epithelial parts of
trachea, the lungs, and the
intestines

 The
mesoderm layer is the
middle layer.
 It surrounds the endoderm
layer develops into our
large body cavities.
 The mesoderm also gives
rise to: muscle, bone,
connective tissue, adipose
tissue, the circulatory
system, the kidneys, the
dermis
 The
ectoderm layer
is the outermost
layer.
 It is the tissue layer
which gives rise to
our skin, hair, nails,
eyes and nervous
tissue (brain, spinal
chord, nerves).
A
tissue is a group of cells with similar
specialized structure which carry out
specific functions.
 Groups of tissues compose and work
together to form organs.
 All organs are composed of two or more
types of tissues.
 There are four major tissue types:
1. Epithelial
2. Connective
3. Muscle
4. Nervous
General
Locations
 Body coverings
 Body linings
 Glandular tissue
 Including:
 Skin, lining of trachea, esophagus,
urinary bladder, and digestive tract,
sweat glands, kidneys
General
a.
b.
c.
d.
Functions
Protection
Absorption
Filtration
Secretion
Functions
e.
f.
(continued):
These cells are rapidly dividing
because they are constantly being
sloughed away or rubbed off.
Therefore they must constantly be
replaced.
 General
Characteristics:
a. Cells fit closely together and often form
sheets
b. The apical (top) surface is the free surface
of the tissue
i.
They face the air (skin, lungs) or a fluidfilled organ cavity (the lumen of the gut).
ii. Apical ends may have cilia or be highly
folded to increase surface area
(microvilli).
Characteristics
d.
e.
i.
(cont’d):
The basal (lower layer) consists of
germ cells, which are constantly
dividing to produce new cells.
The basal surface of the epithelium
rests on a basement membrane.
Basement membrane: a layer of
extracellular matrix and proteins
(desmosomes) anchoring the epithelium
to the connective tissue underneath
Apical surface of simple
cuboidal epithelial with
Nucleus microvilli present.
Basement membrane where the cells
are attached to the non-living basal
lamina.
Microvilli
Characteristics
e.
f.
(cont’d):
Epithelial are avascular (no direct
blood supply)
Regenerate easily if well nourished (by
diffusion through other cells)
Apical surface
Basal
surface
Simple
Apical surface
Basal
surface
Stratified
(a) Classification based on number of cell layers
Figure 3.17a
 Epithelial
tissues
are classified in
two ways:
A. Number of cell
layers
B. Shape of cells
A. Number of cell Layers:
i. Simple epithelial tissues are only one
cell layer thick.
ii. Stratified epithelial tissues are several
layers thick.
iii. Pseudostratified epithelial tissues looks
like multiple layers, but on close
examination are actually only one cell
layer thick.

c. Pseudostratified
epithelial tissues
appear to be
composed of
multiple layers but
on close
examination are
actually only one
cell layer thick.
 Classification
shape – three
basic shapes:
a. Squamous
b. Cuboidal
c. Columnar
by
a. Squamous flattened cells,
fried egg shape
in appearance.
b. Cuboidal - square
or cubed shaped.
Cells are as wide as
they are tall.
c. Columnar - cells
are taller than they
are wide. Shaped
like columns or
rectangles.
Epithelial
tissues are named in the
following manner:
1.
2.
3.
First word: Number of layers
(simple, stratified, pseudostratified)
Second word: Shape of cell
(squamous, cuboidal, columnar)
Third word: Describes the apical
surface; if there are structures (cilia
or microvilli) or materials present
(keratin).
 You
can tell a lot about a tissue from
its name
For example: pseudostratified
columnar ciliated epithelium
What can you tell from the name
about the tissue?
1. It is one cell-layer thick
2. It is column shaped.
3. It has cilia on its apical surface
I.
II.
III.
IV.
Simple Squamous
Simple cuboidal
Simple Columnar
Stratified Squamous
Non-keratinized
II. Keratinized
I.
V.
VI.
VII.
Pseudostratified columnar
Stratified transitional
Glandular
Name: Simple squamous epithelium
 Single layer of flat cells
b. Location: usually forms membranes
 Lines body cavities
 Lines lungs and capillaries
c. Function: diffusion, filtration, or
secretion in membranes
a.
d.
Unique Facts:
 Found
lining blood vessels
and is called endothelium.
 Found in alveoli (or “air
sacks”) of the lungs.
 Allows the rapid exchange
of materials by diffusion
and osmosis from cell to
cell.
Air sacs of
lungs
Nucleus of
squamous
epithelial cell
Basement
membrane
(a) Diagram: Simple squamous
Nuclei of
squamous
epithelial
cells
Photomicrograph: Simple
squamous epithelium forming part
of the alveolar (air sac) walls (185×).
Figure 3.18a
Name: Simple cuboidal epithelium
 Single layer of cube-like cells
b. Locations:
 Common in glands and their ducts
 Form walls of kidney tubules
 Covers the ovaries
c. Functions: secretion and absorption;
ciliated types propel mucus or propel
reproductive cells
a.
d.
Unique Facts:
 Simple cuboidal cells are common in
secretory glands and ducts
 Found in the walls of kidney tubules
where they are involved with
reabsorption of materials as urine is
being produced
 Found on the surface of mammalian
ovaries, where their ciliated surfaces
move the ovum (egg cell) from the co
Simple
cuboidal
epithelial
cells
Nucleus of
simple
cuboidal
epithelial
cell
Basement
membrane
Basement
membrane
Connective
tissue
(b) Diagram: Simple cuboidal
Photomicrograph: Simple cuboidal
epithelium in kidney tubules (250×).
Figure 3.18b
Name: Simple columnar epithelium
 Single layer of tall cells
 Often includes mucus-producing
goblet cells
b. Location: lines digestive tract
c. Functions: in secretion and
absorption; ciliated types propel
mucus or reproductive cells;
microvillate types absorb nutrients
a.
d.
Unique Facts:
 Commonly
found in the lining of the
small and large intestine where it is
involved with absorption of
molecules from digested food and
re-absorption of water.
 Some are microvillate (have
microvilli on their apical surface)
 Microvillate
epithelium: In the small intestine
the apical surface of these cells have microvilli
present on their surface and specialized gland
cells called goblet cells
which
produce
and
microvilli on apical surface
secrete mucus.
microvilli on apical surface
 Stratified
cuboidal and columnar epithelia:
 Rare in human body
 Found mainly in ducts of large glands
 Stratified cuboidal — two layers of cuboidal
cells; functions in protection
 Stratified columnar — surface cells are
columnar, cells underneath vary in size and
shape; functions in protection
Name: Stratified squamous epithelium
 Cells at the apical surface are
flattened
b. Functions: as a protective covering
where friction is common
c. Locations: linings of the…
i. Skin
ii. Mouth
iii. Esophagus
a.
Nuclei
Stratified
squamous
epithelium
Stratified
squamous
epithelium
Basement
membrane
(e) Diagram: Stratified squamous
Photomicrograph: Stratified
squamous epithelium lining of
the esophagus (140×).
Basement
membrane
Connective
tissue
Figure 3.18e
d.
Unique Facts:
 Present in areas where there is
wear and tear on the tissue, where
cells are continually being sloughed
away, (or rubbed off) by abrasion.
 Two
types of stratified squamous
epithelial tissue: Keratinized and
Non-keratinized.
e.
Stratified squamous non-keratinized epithelium:
 Lines the oral cavity and the esophagus and the
vagina of the female reproductive system.
 The surface of these epithelia are moist and
protected by mucosa
Stratified squamous keratinized epithelium
f.
Keratin is a layer a waterproof protein
 Produced on the apical surface of these epithelia

Name: Pseudostratified columnar
 Single layer, but some cells are
shorter than others
 Often looks like a double layer of
cells but all cells rest on the
basement membrane
b. Location: respiratory tract, where it
is ciliated
c. Functions: in absorption or secretion
a.
d.
Unique Facts:
 Can

be ciliated:
The apical surface of
these cells have tiny,
hair-like projections
called cilia, which are
involved with the
movement across the
surface of the cells.
Cilia
Pseudostratified
epithelial
layer
Pseudostratified
epithelial
layer
Basement
membrane
(d) Diagram: Pseudostratified (ciliated)
columnar
Basement
membrane
Connective
tissue
Photomicrograph: Pseudostratified
ciliated columnar epithelium lining
the human trachea (430×).
Figure 3.18d
Name: Transitional epithelium
 Composed of modified stratified
squamous epithelium
 Shape of cells depends upon the amount
of stretching
b. Location: lines organs of the urinary
system
c. Functions: stretching and the ability to
return to normal shape
a.
d.
Unique Facts:
 This epithelium is unique to the urinary
bladder and a small portion of the
ureters.
 It has the unique property of expansion
and contraction.
 This allows the tissue to adjust to the
urinary bladder’s expansion and
contraction when it is full or empty.
Basement
membrane
Transitional
epithelium
Basement
membrane
Transitional
epithelium
Connective
tissue
(f) Diagram: Transitional
Photomicrograph: Transitional epithelium lining of
the bladder, relaxed state (215×); surface rounded
cells flatten and elongate when the bladder fills
with urine.
Figure 3.18f
Glands
 One
or more cells responsible for
secreting a particular product
 Secretions contain protein
molecules in an aqueous (waterbased) fluid
Two
major gland types:
1. Endocrine gland
 Ductless since secretions diffuse into
blood vessels
 All secretions are hormones
2. Exocrine gland
 Secretions empty through ducts to the
epithelial surface
 Include sweat and oil glands