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Histology
Teamwork
• The human body contains about
100 trillion cells.
• However, no one cell can carry out all the
necessary bodily functions by itself. So, cells
aggregate and form TISSUES.
• Tissue  Collection of cells with a similar
structure and function.
• The study of tissues is known as histology
Tissues
•
There are 4 primary tissue types in the human
body:
1. Epithelial
(covering/lining)
2. Connective
(support)
3. Muscle
(movement)
4. Nervous
(control)
•
These tissues differ in the types and functions of
their cells, and the products of those cells and the
relative distribution of the two.
•
Which picture on this slide corresponds to which
tissue?
Epithelial Tissue
• Covers the surface of the body, lines
the body cavities, forms the external
and internal linings of most organs, and
constitutes the bulk of most glands.
• Functions include:
1. Protection
4. Absorption
2. Secretion
5. Filtration
3. Sensory reception
• It’s found all over the place!
Characteristics of Epithelia
• Composed almost entirely of sheets of close-packed
cells – very little extracellular material.
– Look at the cartoon below (it represents the epithelium that
lines much of your respiratory tract) . Do you see much space
between these cells? Now look at the actual slide and notice
the same thing.
• Epithelial cells are often strongly connected
to adjacent cells via tight junctions and desmosomes:
– Tight junctions are protein complexes that are found on the surfaces of
a cell and thus connect it to all its neighboring cells and makes it
impossible for anything to pass between them. Common in lining of the
stomach & intestines. (Why would they occur here?)
– Desmosomes – “spot weld” that holds cells together and enables a
tissue to resist mechanical stress. Common in the epidermis and cervix.
(Why these 2 areas?)
Characteristics of
Epithelia
• Polarity (surface)
– Different areas of epithelial cells have
different structures. (If they have
different structures, they can have
different functions).
– The area of an epithelial cell adjacent
to the exterior or to a body cavity is
the apical side and the opposite area
is the basal side.
• In the picture at the top right, what is
present in the basal portion of the cell
that’s not in the apical portion?
• The basal side is supported by a
layer of connective tissue.
– It’s known as the basement
membrane and is labeled by arrows
in the pictures at the right.
More Characteristics of Epithelia
• No blood vessels – it’s avascular.
– Can you pierce your skin with a
needle without bleeding?
• Has the capacity to regenerate.
– Why is this a good thing?
– Considering the locations of epithelial
tissue, is it likely to get damaged?
•
We classify epithelia based on the number of cell layers
present and the shape of the cells in the apical layer.
•
If there is only one layer of cells, the epithelium is simple. If
there is more than one layer, the epithelium is stratified.
•
There are 3 cell shapes:
1.
2.
3.
Squamous = flat, scale-like
Cuboidal = cube-shaped
Columnar = column-shaped
Epithelia Types
•
You can see that we’ve got at least 6:
1.
2.
3.
4.
5.
6.
•
Simple squamous
Simple cuboidal
Simple columnar
Stratified squamous
Stratified cuboidal
Stratified columnar
There are actually 2 other ones that are special –
transitional epithelium and pseudostratified
columnar epithelium.
Simple Squamous Epithelium
• Microscopic Appearance:
– Single layer of flattened
cells, shaped like fried eggs
with bulge where nucleus is
located.
– Nucleus is flattened in the
plane of the cell.
– Cytoplasm may be very thin
and tough to see.
– In surface view, cells have
angular contours and nuclei
appear round.
Above, the roundish structure is a ball of capillaries
found in the kidneys known as a glomerulus. The
blue arrow indicates the simple squamous
epithelium surrounding it.
Simple Squamous Epithelium
• Locations:
– Air sacs (alveoli) of lungs
– Glomerular capsules of
kidneys
– Some kidney tubules
– Lining of heart and all
blood vessels
• Here it’s called the
endothelium
– Serous membranes
– External lining of visceral
organs
– Here it’s called the
mesothelium
Endothelium
The blue arrow points
directly at the nucleus of
an endothelial cell. What
type of cell does the yellow
arrow indicate?
Simple Squamous
Epithelium
• Functions:
– Thinness allows material to
rapidly diffuse or be
transported through the
epithelial layer.
• Example  Gases diffuse
across the thin air sac
epithelium in the lungs.
• Blood traveling to the
lungs is high in CO2 and
low in O2. After gas
exchange in the lungs, the
blood leaving is high in O2
and low in CO2
• Why is thinness an asset in
this situation?
• In pneumonia, a build-up
of mucus can increase the
distance that the gases
must move. Does this
make it easier or harder
“to breathe?”
Simple Squamous Epithelium
• More Functions
– Blood is filtered through the epithelium of the kidney
capillaries.
• This begins the process of removing waste products from
the blood and modifying its ionic content.
– Secretion of a lubricating fluid by the epithelium
making up the serous membranes (we’ll talk about
them soon).
Simple Cuboidal Epithelium
• Microscopic Appearance:
– Single layer of square or
round cells.
– Centrally-placed spherical
nuclei.
– Apical layer often has
microvilli.
• Microvilli are small
extensions of the cell
membrane that increase
the surface area of the cell.
• You usually want a cell to
have more surface area
when it is involved with
secretion or absorption.
– WHY?
Above, we have a longitudinal section of
a kidney tubule. Notice the almost
square-shaped cells . One cell is
highlighted for you in red.
Simple Cuboidal Epithelium
• Locations:
– Liver
– Pancreas
– Thyroid, salivary, and
most other glands
– Most kidney tubules
– Bronchioles (small
tubes within the lungs)
Cross-Section of a kidney tubule
Simple Cuboidal Epithelium
• Functions:
– Absorption
• Kidney tubules
– Microvilli often present
to increase the available
surface area
• Liver
– Secretion
•
•
•
•
Kidney tubules
Liver
Pancreas
Thyroid, salivary, and
most other glands
Cross-section of the thyroid gland
Simple Columnar Epithelium
• Microscopic Appearance:
– Single layer of tall, narrow cells.
– Oval or sausage-shaped nuclei,
vertically-oriented, usually located
in the basal half of the cell.
– Secretory vesicles sometimes
visible in apical portion of the cell.
– Microvilli occasionally present.
– Cilia occasionally present.
• Cilia are hair-like extensions of
the cell membrane that can move
and sweep material across the cell
surface
– Goblet cells often interspersed.
• Secrete a lubricating mucus
Simple Columnar Epithelium
• Locations:
– Inner lining of
stomach, intestines,
and rectum.
– Inner lining of
gallbladder
– Inner lining of uterus
and uterine tubes
Simple columnar epithelium lining the lumen of the gallbladder.
Simple Columnar Epithelium
• Functions:
– Absorption and secretion
• Columnar cells in small
intestine have microvilli to
increase the available
surface area for the
absorption of nutrients.
– Movement of egg and
embryo in uterine tube.
• Hence the presence of
cilia.
– Secretion of mucus.
• Lots of goblet cells in the
large intestine so as to
lubricate it and ease the
passage of feces.
Stratified Squamous
Epithelium
• Microscopic Appearance:
– Multiple cell layers with
cells becoming flatter and
flatter toward surface.
– In keratinized stratified
squamous epithelium, the
apical layers are layers of
dead cells lacking nuclei
and packed with the tough
protein keratin.
– Nonkeratinized stratified
squamous epithelium lacks
the layers of dead cells at
the surface.
This is keratinized stratified squamous
epithelium from the sole of the foot. It
extends the length of the blue line on the left.
Notice the multiple layers of clear, dead,
enucleated cells.
Stratified Squamous Epithelium
• Location of
keratinized version:
– Epidermis. Palms
and soles of feet are
typically heavily
keratinized.
• Locations of nonkeratinized version:
– Lining of oral cavity
and surface of tongue
– Lining of esophagus
– Lining of vagina and
anal canal
Non-keratinized stratified squamous epithelium
What do the regions that contain the nonkeratinized version have in common?
Which of these is keratinized and which is nonkeratinized stratified squamous epithelium?
Stratified Squamous
Epithelium
• Functions:
– Protection!
– Keratinized version (a.k.a. dry
epithelium) protects against
mechanical abrasion, water
loss, and pathogen entry.
• Keratin is very strong,
waterproof, and is
bacteriostatic (prevents
bacteria from reproducing).
– Non-keratinized version (a.k.a.,
wet epithelium) also protects
from mechanical abrasion.
• Eating food, swallowing,
sexual intercourse, birth,
defecation.
Stratified Cuboidal Epithelium
• Microscopic Appearance:
– 2 or more layers of cells.
– Surface layers are square
or round (cuboidal).
• Locations:
– Some sweat gland ducts.
– Ovarian follicle
• Cells that surround the
developing egg
Stratified
Cuboidal
Epithelium
• Functions:
– Contributes to
sweat secretion.
– Secretion of
ovarian
hormones (e.g.,
estrogens)
To the left, we
have an oocyte
(egg cell)
surrounded by
stratified
cuboidal
epithelium. The
oocyte is circled
in blue
Stratified Columnar
Epithelium
• Microscopic Appearance:
– 2 or more layers of cells.
– Surface cells tall and narrow with
basally located nuclei.
• Locations:
– Rare.
– Small portions of anal canal, pharynx,
epiglottis, and male urethra.
– Sometimes seen in large ducts of
sweat and salivary glands.
• Functions:
– Often seen where 2 other tissue types
meet
– Structural integrity of gland ducts
Pseudostratified Columnar Epithelium
• Microscopic Appearance:
– Looks multi-layered, but
it’s NOT!
• All cells touch the
basement membrane.
• In stratified epithelia, only
the bottom cell layer
touches the basement
membrane.
– Cells are of varying heights
which gives the appearance
of stratification. Nuclei are
at several levels.
– Often has goblet cells
interspersed.
– Cells often have cilia.
Pseudostratified Columnar Epithelium
• Locations:
– Respiratory tract from nasal cavity to bronchi.
• Ciliated
• Goblet cells
– Portions of male reproductive tract
• Non-ciliated
Ciliated pseudostratified epithelium from the respiratory tract. Do you see how it
appears that there are multiple layers. Do you see the cilia (indicated by the arrow)?
Pseudostratified
Columnar Epithelium
• Functions:
– In the respiratory tract there
are lots of mucus-secreting
goblet cells.
– The mucus traps dust and
bacteria
– Cilia “sweep” the bacterialaden mucus up the
respiratory tract towards the
pharynx where it can be
swallowed.
– Smoking paralyzes cilia –
smokers have to cough
violently to expel their
mucus. Then they die!
Here, we have pathogens traveling down the pharynx
trying to attack the surface cells. How can they be
repelled???
The mucosal cells lining the trachea have released a flood of
mucus, trapping the pathogens! Now what???
The cilia successfully sweep the pathogens up and away!
Transitional Epithelium
• Microscopic Appearance:
– Somewhat resembles
stratified squamous
epithelium, but the surface
cells are rounded and often
bulge above surface (domeshaped).
– Typically 5-6 cell layers thick
when relaxed and 2-3 cell
layers thick when stretched.
– Cells may be flatter and
thinner when epithelium is
stretched.
– Some cells are binucleate,
i.e., they have 2 nuclei.
Transitional Epithelia
• Locations:
– Predominant epithelium lining
the urinary tract
– Found in part of the kidney, the
ureters (tubes that connect the
kidney to the urinary bladder),
the urinary bladder, and part of
the urethra.
• Functions:
– Stretches to allow filling of the
urinary tract.
– Originally called “transitional”
because it was thought to be an
intermediate between stratified
squamous and stratified
columnar epithelium. This isn’t
true but the name has persisted.
Easy Epithelium Review 
Glands
•
•
•
A gland is a cell or
an organ that
secretes substances
for use inside or
outside the body.
Glands are
composed
predominantly of
epithelial tissue.
Glands are broadly
classified as:
1. Endocrine
2. Exocrine
Thyroid Gland:
An endocrine
gland
An exocrine
gland
Stomach: Both
an exocrine and
an endocrine
gland
Exocrine Glands
• Typically secrete material into ducts
that lead to the body surface or to
one of the cavities that is continuous
with the body surface, i.e., digestive,
reproductive, respiratory tract.
• Exo = outside and crine = secrete. The parotid gland (a salivary gland)
• Can be multicellular or unicellular.
– Multicellular:
• Pancreas, stomach, sweat glands,
salivary glands, mammary glands,
sebaceous glands, etc.
– Unicellular:
• Goblet cells.
Goblet Cell
Endocrine Glands
• Endo = within.
• Do not secrete material
into ducts.
• Secrete chemical signals
called hormones into the
bloodstream where they
travel through the body
and affect other cells.
• Examples include:
– Thyroid, thymus, testes,
ovaries, pituitary, pineal,
adrenal, etc.
Exocrine Gland Structure
• Exocrine glands are either:
– Simple if their ducts do not
branch.
– Compound if their ducts do
branch.
• Exocrine glands are further
classified by the shape of their
secretory portion as:
– Tubular if the secretory portion is
the same diameter as the duct.
– Alveolar if the secretory portion
is like a round ball .
– Tubuloalveolar if it’s a
combination of the 2.
Simple
Compound
Connective
Tissue
• Most abundant, widely distributed, and histologically variable of the 4
primary tissue types.
• Consists of cells that are typically widely separated by lots of
extracellular material – referred to as the extracellular matrix.
– In the diagram above, compare the density of cells in the epithelial layers
and in the connective tissue layers. What’s the difference?
• Most cells are not in contact with each other but are distributed
throughout the extracellular matrix.
Functions of Connective Tissue
1.
2.
3.
4.
5.
6.
7.
8.
Binding of organs
Support
Physical protection
Immune protection
Movement
Storage
Heat production
Transport
What do you NOT see a lot of in this micrograph of
connective tissue?
Loose Connective Tissue
Categories of CT
1.
2.
3.
Blood
Fibrous connective
tissue (a.k.a. connective
tissue proper)
Supporting connective
tissue
Fluid connective tissue
Bone
Fibrous Connective Tissue
• Most diverse type of CT.
• Contain extremely conspicuous fibers – hence the name, fibrous
connective tissue.
• The illustration below shows a 3-D model of some typical CT fibers,
typically made of multiple strong filamentous proteins twisted about one
another.
• Fibrous CT consists of cells, fibers, and something called ground
substance.
• Of these 3, which you do suppose is typically NOT that abundant?
Cells of Fibrous CT:
1.
Fibroblasts
–
–
–
2.
Fibro = fat, blast = making
Large, flat cells with tapered ends;
produce fibers and ground substance.
Inactive ones are known as fibrocytes.
Macrophages
–
–
–
–
Macro = large, phage = eating
Large phagocytic cells that wander
through connective tissue, where they
engulf and destroy bacteria, other
foreign particles, and dead or dying cells
of our own body.
They activate the immune system when
they encounter foreign matter called
antigens.
Derived from white blood cells known
as monocytes.
Cells of Fibrous CT
3.
Leukocytes
–
–
4.
Leuko = white, cyte = cell
White blood cells that crawl out of the
bloodstream and spend the majority of
their time in the CT. Many are phagocytes
that wander in search of pathogens.
Plasma Cells
–
–
Certain white blood cells differentiate into
plasma cells when they detect foreign
agents.
Plasma cells produce and secrete
antibodies (proteins that bind to foreign
molecules (antigens), thus inactivating
them or marking them for future
destruction.
Cells of Fibrous CT
5.
Mast Cells
–
–
6.
Often found in CT adjacent to
blood vessels.
Secrete a chemical called
heparin which is an anticoagulant and a chemical
called histamine which is a
vasodilator.
Adipocytes
–
–
–
–
Adipo = fat
Appear in small clusters in
some fibroconnective tissues.
If they dominate an area, we
call that area adipose tissue.
Contain huge droplets of
lipids for storage.
Fibers in Fibrous Connective Tissue:
1. Collagenous Fibers
2. Reticular Fibers
3. Elastic Fibers
Collagen Fibers as seen with a
scanning electron microscope
Collagenous Fibers
Close-up of a
single fiber
• Interwoven strands of the protein
collagen.
– The most abundant protein in the
human body.
• Thick fibers with great tensile
strength – i.e., it’s tough to pull
them apart.
• In fresh tissue, they have a white
appearance, so they are sometimes
called white fibers.
• In stained slides, they are often pink
and they usually appear quite wavy.
• Tendons, ligaments, and the deep
layer of the skin (the dermis) are
made primarily of collagenous
fibers.
Multiple fibers
arranged in the
extracellular
matrix
Reticular Fibers
• A thinner collagen
fiber coated with
glycoproteins.
– Stained black in the
adjacent micrograph
of the liver.
• These fibers can
branch extensively
and form networks
or frameworks for
certain organs.
Elastic Fibers
• Made primarily of a
protein called elastin,
whose coiled structure
allows it to stretch and
snap back like a rubber
band.
• Account for the ability of
the lungs, arteries, and
skin to spring back after
they are stretched.
• Fresh elastic fibers are
yellowish and thus often
called yellow fibers.
In this slide, “A” is an elastic fiber
– what do you suppose “B” is?
Ground Substance
•
Gelatinous material that occupies the space between
the cells and the fibers in connective tissues.
Imagine some lime Jell-o
that a not-so-bright chef
decided to make with
carrots and grapes. The
carrots are like fibers, the
grapes like cells, and the
Jell-o itself is the ground
substance/
Types of Fibrous Connective Tissue
•
2 types based on the
relative abundance of
fibers.
–
Loose Connective Tissue
•
•
–
Lots of ground substance
and cells. Fewer fibers.
Leaves lots of empty
space in tissue sections.
Dense Connective Tissue
•
•
Fibers occupy the most
space. Much lower
number of cells and less
ground substance.
Appears closely packed in
tissue sections.
1
Types of Loose CT
1. Areolar CT
2. Reticular Tissue
3. Adipose Tissue
2
3
Areolar CT
Microscopic
Appearance:
• Loose arrangement of
collagenous and
elastic fibers. Some
reticular fibers. (All 3
fiber types.)
• Scattered Cells. All 6
types can be present.
• Abundant ground
substance.
• Numerous blood
vessels. (Highly
vascular.)
Areolar CT
• Locations:
– Underlying nearly all
epithelia.
– Surrounding blood vessels,
nerves, trachea, and
esophagus.
– Between muscles.
– Within mesenteries, and the
visceral layers of the
pericardium and the pleura.
• Functions:
– Loosely binds
epithelia to deeper
tissues.
– Allows passage of
nerves and blood
vessels through
other tissues.
– Provides an arena
for immune
defense.
– Blood vessels
provide nutrients
and waste removal
for overlying
epithelia.
Areolar CT
Reticular Tissue
• Microscopic Appearance:
–
Loose network of
reticular fibers and a type
of fibroblast known as the
reticular cell.
– Infiltrated with numerous
white blood cells.
– Often appears dark purple
or black.
• Locations:
– Lymph nodes, spleen,
thymus, and bone
marrow.
Reticular Tissue
• Functions:
– The branching network
of reticular fibers will
form a scaffold-like
framework for
lymphatic organs.
• Spleen, thymus, and
lymph nodes.
• Such a framework is
known as a stroma.
• The functional tissue of
these organs is known
as the parenchyma.
Adipose Tissue
• Microscopic Appearance:
– Dominated by adipocytes –
large, empty-looking cells
with thin margins.
– Nucleus usually pressed
against the cell membrane –
signet ring appearance.
– Often pale.
– Blood vessels often present.
Adipose Tissue
• Locations:
– Subcutaneous fat
beneath skin.
– Breast.
– Heart surface.
– Cushioning organs
• Kidneys
• Eyes
Adipose Tissue
• Functions:
– Energy storage.
– Thermal insulation.
– Shock absorption
– Protective
cushioning for
some organs.
Types of
Dense CT
1. Dense regular
2. Dense irregular
2
1
Dense Regular
CT
• Microscopic
Appearance:
– Densely packed,
parallel, often wavy
collagenous fibers.
– Slender fibroblast nuclei
compressed between
bundles of collagenous
fibers.
– Scanty open space (little
ground substance)
– Scarcity of blood
vessels.
Dense Regular Connective Tissue
• Locations:
– Tendons.
– Ligaments.
NOTE the waviness of the fibers. What function could this
structural aspect provide?
Dense Regular CT
• Functions:
– Ligaments bind bone
tightly to other bones.
Resist stress.
– Tendons attach skeletal
muscles to bone and
transfer muscular
tension to bones.
Dense Irregular CT
• Microscopic Appearance:
– Densely packed, collagenous
fibers running in random
directions. Compare this to
dense regular CT.
– Scanty open space (ground
substance).
– Few visible cells.
– Scarcity of blood vessels.
Dense Irregular CT
• Locations:
– Deeper portion of
dermis of skin.
– Capsules around
visceral organs
such as the liver,
spleen, and
kidneys.
– Fibrous sheaths
around cartilages
and bones.
Dense Irregular CT
• Functions:
– Provides a durable,
hard to tear structure
that can withstand
stresses placed in
unpredictable
directions.
– Why aren’t tendons
and ligaments made of
this stuff?
Supporting Connective Tissue
•
•
They provide the
majority of the
structural support of
the human body.
2 types:
–
–
1
Cartilage
Bone.
2
Cartilage
• Supportive CT with a
flexible, rubbery matrix.
• Cells called chondroblasts
secrete the matrix and
surround themselves in it
until they become trapped
in little cavities known as
lacunae (lacuna is Latin
for “lake”).
• Once enclosed in lacunae,
cells are called
chondrocytes.
Cartilage
• Cartilage is avascular and chondrocytes
depend on the diffusion of nutrients
through the stiff, viscous matrix.
– Thus their metabolism and rate of
division (a.k.a. mitosis) is low and
healing of torn cartilage is a long
process.
– It’s avascular b/c chondrocytes produce
a chemical called antiangiogenesis
factor that, like its name suggests,
prevents the growth of blood vessels.
• Based on this, why do you suppose
shark cartilage has been touted as a
possible aid in the fight against cancer?
• Cartilage matrix collagenous fibers that
range in thickness from invisibly fine
to conspicuously coarse.
3
Cartilage
•
3 types (classified based on fiber
differences):
1.
2.
3.
2
Hyaline Cartilage
Elastic Cartilage
Fibrocartilage.
1
Hyaline Cartilage
• Microscopic Appearance:
– Clear, glassy matrix, often
stained light blue or pink.
• Hyalos is Greek for glass.
– Fine, dispersed collagenous
fibers, not usually visible.
– Chondrocytes often in small
clusters of 3-4 cells within a
single lacuna (known as cell
nests or isogenous groups).
– Covered by a
perichondrium – a fibrous
sheath made of dense
irregular connective tissue.
Hyaline Cartilage
• Locations:
– Forms the majority of
the fetal skeleton.
– Forms boxlike
structure around larynx
and supportive rings
around trachea and
bronchi.
– Attaches ribs to the
sternum.
– Forms a thin articular
cartilage over the ends
of bones at moveable
joints.
Close-up of Hyaline Cartilage. Notice
the 2 cells in the single lacuna
Hyaline Cartilage
• Functions:
–
–
–
–
Eases joint movements.
Keeps airways patent.
Moves vocal cords.
Precursor of bone in
the fetal skeleton.
– Structural attachment.
Elastic
Cartilage
• Microscopic Appearance:
– Elastic fibers form web-like
mesh amid lacunae.
– Always covered by a
perichondrium.
• Locations:
– External ear.
– Epiglottis – flap of tissue
that covers the tracheas
when you swallow to
prevent food/liquid from
going down the “wrong
pipe.”
– Eustachian tube – connects
the ear to the nasopharynx.
Elastic Cartilage
• Functions:
– Provides flexible,
elastic support.
– What happens when
you bend and release
your ear?
A – Chondrocyte
B – Matrix w/ black
elastic fibers
C -Lacuna
Fibrocartilage
• Microscopic Appearance:
– Parallel collagenous fibers
similar to those of tendon.
– Rows of chondrocytes in
lacunae between
collagenous fibers.
• Chondrocytes are fewer and
smaller and are not in
isogenous groups.
– Never has a perichondrium.
• Locations:
– Pubic symphysis – the anterior
joint between the 2 halves of the
pelvic girdle.
– Intervertebral discs that separate
the bones of the spinal column.
– Menisci (shock-absorbing pads of
cartilage) in the knee joint.
– At points where tendons insert on
bones near articular hyaline
cartilage.
• Functions:
– Resists compression and absorbs
shock in some joints.
– Often a transitional structure
between dense connective tissue
and hyaline cartilage.
• For example, at some tendon-bone
junctions.
Fibrocartilage
More Connective Tissues
• Bone is the other supporting
connective tissue. It will be
discussed in detail later.
• Blood is a fluid connective
tissue that you’ll examine in
A&P II.
Muscle and Nervous Tissue
• Nervous tissue
– Consists of 2 cell types:
Neurons and glia.
– Detects stimuli, integrates
information, and transmits
signals.
• Muscular tissue
– 3 types: skeletal, cardiac,
and smooth.
– Specialized to contract and
exert forces on other
tissues.
– Major function is the
creation of movement.
Body Membranes
• The majority of the body’s structures are lined by
epithelial membranes.
– Such structures include: body cavities, tracts, external
surfaces of organs, and the external surface of the body
itself.
• An epithelial membrane is defined as:
– A continuous multicellular sheet composed of at least 2
primary tissue types: An epithelium bound to an
underlying layer of fibrous connective tissue.
Epithelial Membranes
Serosa covering
the heart
1. Cutaneous
membrane
2. Mucous membranes
3. Serous membranes
Mucosa lining the duodenum (1st
part of the small intestine
Cutaneous Membrane
• Skin!
• It’s an organ system
consisting of a
keratinized squamous
epithelium (epidermis)
firmly attached to a
thick layer of dense
irregular connective
tissue (dermis).
• Unlike other epithelial
membranes, it is
exposed to the air and
is a dry membrane.
• Line passageways (body cavities)
that open to the external
environment.
– Digestive, respiratory, urinary, and
reproductive tracts.
• Wet membranes that are bathed
by their own secretions or, in the
case of the urinary tract, urine.
• Mucosae have 2 or occasionally
3 layers:
– Lining epithelium (simple columnar
or nonkeratinized stratified
squamous) is adjacent to the lumen
and above the:
• Layer of areolar CT called the
lamina propria which is sometimes
above a:
– Layer of smooth muscle called the
muscularis mucosae.
Mucous Membranes
(a.k.a. Mucosae)
Mucous Membranes
• Have absorptive, secretory &
protective functions.
• Often covered with mucus secreted
by goblet cells, multicellular
mucous glands, or both.
– Mucus is often involved in trapping
foreign particles (including bacteria) or
providing lubrication.
– The presence of mucus does not define
a mucous membrane however – e.g., the
mucous membrane lining the urinary
tract lacks mucus.
• Cells modified for absorption are
present in the small intestine
• Cells modified for protection are
present mainly at those positions of
the tracts closest to the exterior.
Normal stomach mucosa
Serous Membranes
(a.k.a. Serosae)
• Moist membranes found in closed
ventral body cavities – not open to
the exterior.
– Line the insides of the peritoneal,
pleural, and pericardial cavities; and
line the outer surfaces of some of the
viscera.
• Consist of a simple squamous
epithelium lying upon a thin layer of
areolar CT.
• Secrete a thin, watery fluid that
arises from the blood. It’s called
serous fluid.
Serosae
• Provide an efficient means of
lubricating cavity walls and
organ exteriors so as to reduce
the friction associated with
movement.
– Why is this essential?
• The serosa lining the pleural
cavity and the lung exterior are
the parietal and visceral pleurae,
respectively. Those of the heart
are the parietal and visceral
pericardium and those of the
abdomen are the parietal and
visceral peritoneum.
Tissue Repair
• 2 possibilities:
– Regeneration  Replacement of dead or damaged cells by the
same type of cells as before. Most skin injuries heal by
regeneration. The liver also regenerates quite well.
– Fibrosis  Replacement of damaged tissue with scar tissue,
composed mainly of collagen produced by fibroblasts. Helps hold
an organ together but does not restore normal function. Examples
include severe cuts and burns, the healing of muscle injuries, and
scarring of the lungs in tuberculosis.
Stages of Healing a Wound to the Skin
1.
Severed blood vessels
bleed into the cut. Mast
cells and cells damaged
by the cut release
histamine which dilates
blood vessels, increases
blood flow to the area,
and makes capillaries
more permeable. Blood
plasma seeps into the
wound carrying
antibodies, clotting
proteins, and blood
cells.
2.
3.
A blood clot forms,
loosely knitting the edges
of the cut together and
interfering with the spread
of pathogens. Scab forms
and seals the wound and
blocks infection. Beneath
it, macrophages begin to
clean up tissue debris.
New capillaries sprout
from nearby vessels and
grow into the wound. The
deeper portions of the clot
become infiltrated by
capillaries and fibroblasts
and transform into a soft
mass called granulation
tissue. Macrophages
remove the blood clot
while fibroblasts secrete
collagenous fibers to
replace it.
Stages of Healing a Wound to the Skin
4.
Surface epithelial cells
around the wound
multiply and migrate
into the wounded area
beneath the scab. The
scab loosens and
eventually falls off, and
the epithelium grows
thicker. Thus, the
epithelium regenerates
while the underlying
connective tissue
undergoes fibrosis.