Chapter 4
Histology: The Study of
Tissues
4-1
Tissue Level of Organization
• The classification of tissue types is
based on the structure of cells; the
composition of noncellular
substance surrounding cells
(extracellular matrix) and the
functions of the cells.
4-2
Tissues and Histology
• Tissue Level of Organization
–
–
–
–
Epithelial
Connective
Muscle
Nervous
• Histology: Microscopic Study of Tissues
4-3
Epithelium Characteristics
• Consists almost entirely
of cells
• Covers body surfaces
and forms glands
• Has free and basal
surface
• Specialized cell contacts
• Avascular
• Undergoes mitosis
4-4
Functions of Epithelia
•
•
•
•
•
Protecting underlying structures
Acting as barriers
Permitting the passage of substances
Secreting substances
Absorbing substances
4-5
Types of Epithelium
• Types of epithelium is based on the shape
of the epithelial cells:
–Squamous: cells are flat or scale-like
–Cuboidal: cells are cube-shaped; about
as wide as they are tall
–Columnar: cells are taller tan they are
wide.
4-6
Classification of Epithelium
• Simple
– Squamous, cuboidal, columnar
• Consists of a single layer of cells with
each extending from the basement
membrane to the free surface
• Stratified
– Squamous, cuboidal, columnar
• Consists of more than one layer of cells,
only one of which is attached to the
basement membrane.
4-7
Classification of Epithelium
• Pseudostratified
–Columnar
–Special type of simple epithelium
–It appears to be stratified but it is not
(false – psuedo)
–Consists of one layer of cells, with all
the cells attached to the basement
membrane.
4-8
Classification of Epithelium
• Transitional
–Cuboidal to columnar when not
stretched and squamouslike when
stretched
4-9
Simple Squamous Epithelium
• Consists of a single layer of cells,
with each cell extending from the
basement membrane to the free
surface.
• The nuclei appear as bumps when
viewed as a cross section because
the cells are so flat
4-10
Simple Squamous Epithelium
• Function: diffusion, filtration, some
protection against friction, secretion
and absorption
• Location:lining of blood and
lymphatic vessels (endothelium) and
small ducts, alveoli of the lungs, loop
of Henle in kidney tubules, lining of
serous membranes (mesothelium) and
inner surface of the eardrum.
4-11
Types of Epithelium
4-12
Simple Cuboidal Epithelium
• Cuboidal: cells are cube-shape;
about as wide as they are tall.
• Single layer of cube-shaped cells,
some cells have microvilli or cilia.
4-13
Simple Cuboidal Epithelium
• Function: active transport and
facilitated diffusion result in
secretion and absorption by cells of
the kidney tubules, secretion by cells
of glands and choroid plexus,
movement of particles embedded in
mucus out of the terminal
bronchioles by ciliated cells.
4-14
Simple Cuboidal Epithelium
• Location: kidney tubules, glands
and their ducts, choroid plexus of
the brain, lining of terminal
bronchioles of the lungs, and
surface of the ovaries
4-15
Types of Epithelium
4-16
Simple Columnar Epithelium
• Single layer of tall, narrow cells.
Some cells have cilia (in
bronchioles of lungs, auditory
tubes, uterine tubes and uterus) or
microvilli (intestines).
4-17
Simple Columnar Epithelium
• Function: movement of particles
out of the bronchioles of the lungs
by ciliated cells. It is partially
responsible for the movement of the
oocyte through the uterine tubes by
ciliated cells. Secretion by cells of
the gland, the stomach and the
intestine. Absorption by cells of the
intestine.
4-18
Simple Columnar Epithelium
• Location: Glands and some ducts,
bronchioles of lungs, auditory
tubes, uterus, uterine tubes,
stomach intestines, gallbladder,
bile ducts and ventricles of the
brain.
4-19
Types of Epithelium
4-20
Stratified Squamous Epithelium
• Consists of more than one layer of
cells, only one of which is attached
to the basement membrane
• Cells are cubodial in shape in the
basal layer and progressively
flatten toward the surface.
4-21
Stratified Squamous Epithelium
• The epithelium can be moist or
keratinized
• In most the surface cells retain a
nucleus and cytoplasm.
• In keratinized stratified epithelium,
the cytoplasm of cells at the surface
is replaced by keratin, and the cells
are dead
4-22
Stratified Squamous Epithelium
• Function: protection against
abrasion and infection.
• Location: moist-mouth, throat,
larynx, esophagus, anus, vagina,
inferior urethra, and cornea.
–Keratinized - skin
4-23
Types of Epithelium
4-24
Stratified Cuboidal Epithelium
• Multiple layers of somewhat cubeshaped cells.
• Function: secretion, absorption and
protection against infection.
• Location: sweat gland ducts,
ovarian follicular cells, and salivary
gland ducts.
4-25
Types of Epithelium
4-26
Stratified Columnar Epithelium
• Multiple layers of cells, with tall,
thin cells resting on layers of more
cubodial cells. The cells are
ciliated in the larynx
• Function: protection and secretion
• Location: mammary gland duct,
larynx and a portion of the male
urethra.
4-27
Types of Epithelium
4-28
Pseudostratified Columnar
Epithelium
• Single layer of cells; some cells are tall
and thin and reach the free surface and
other do not. The nuclei of these cells
are at different levels and appear
stratified. The cells are almost always
ciliated and are associated with goblet
cells that secrete mucus onto the free
surface.
4-29
Pseudostratified Columnar
Epithelium
• Function: synthesize and secrete
mucus onto the free surface and move
mucus (or fluid) that contains foreign
particles over the surface of the free
surface and from passages.
• Location: lining of nasal cavity, nasal
sinuses, auditory tubes, pharynx,
trachea and bronchi of the lungs.
4-30
Types of Epithelium
4-31
Transitional Epithelium
• Stratified cells that appear cubodial
when the organ or tube is not
stretched an squamous when the
organ or tube is stretched by fluid.
4-32
Transitional Epithelium
• Function: accommodates
fluctuations in the volume of fluid
in an organ or tube. Protection
against the caustic effects of urine.
• Location: lining of the urinary
bladder, ureter, and superior
urethra.
4-33
Types of Epithelium
4-34
Cell Connections
• Functions
– Bind cells together
– Form permeability
layer
– Intercellular
communication
• Types
– Desmosomes
– Tight
– Gap
4-35
Exocrine Glands
• Unicellular
– Goblet cells
4-36
Multicellular Exocrine Glands
4-37
Exocrine Glands and Secretion Types
• Merocrine
– Sweat glands
• Apocrine
– Mammary
glands
• Holocrine
– Sebaceous
glands
4-38
Connective Tissue
• Abundant
• Consists of cell separated by
extracellular matrix
• Diverse
• Performs variety of important
functions
4-39
Connective Tissue Cells
• Specialized cells produce the
extracellular matrix
–Suffixes
• -blasts: create the matrix
• -cytes: maintain the matrix
• -clasts: break the matrix down for
remodeling
4-40
Connective Tissue Cells
• Adipose or fat cells
• Mast cells that contain heparin and
histamine
• White blood cells that respond to
injury or infection
• Macrophages that phagocytize or
provide protection
• Stem cells
4-41
Extracellular Matrix
• Components
– Protein fibers
• Collagen which is most common protein in
body
• Reticular fill spaces between tissues and
organs
• Elastic returns to its original shape after
distension or compression
– Ground substance
• Shapeless background
4-42
– Fluid
Connective Tissue Categories
Adult
–
–
–
–
–
–
Loose
Dense
Connective tissue with special properties
Cartilage
Bone
Blood
4-43
Functions of Connective Tissue
• Difficult to describe general
properties of CT in the same
way as epithelial tissue.
• CT is so much more diverse.
• Some of the characteristics may
not fit all of the CT types
perfectly-- but they will fit most
of them.
4-44
Functions of Connective Tissue
• Connective tissues are typically wellvascularized
• They can usually reproduce well (to
recover from injury)
• Exception: They need a good
number of cells to help with this, and
dense connective tissue has only
sparse numbers of cells. they have a
lot of noncellular material, called
extracellular matrix material (or just
matrix).
4-45
Extracellular Matrix
• The space between cells can be called
the extracellular space/material or the
intercellular space/material.
• "Extra-" means outside of, while "inter-"
means between. We will use the term
extracellular space to prevent other
confusion
• That's because intercellular is easily
confused with another term we will be
using: intracellular. "Intra-" means within,
and we will use intracellular to discuss
what is inside the cell
4-46
Extracellular Matrix
• To the right, the extracellular space
is all in pink.
• The space is filled with material. If
the material is only liquid, the tissue
as a whole will be loose. An
example of that is in blood.
• If the material in the extracellular
space has some tough strands
(called fibers) of protein in it, that
gives the entire tissue a stronger
consistency (because the cells are
now sitting in a mesh of fibers).
4-47
Ground Substance:
• This is the liquid portion of the
extracellular matrix.
• It is never entirely watery, but more
gel-like.
• A thin ground substance is seen in
blood. The ground substance is
not just water, but it is also filled
with many dissolved solute
particles.
4-48
Extracellular Matrix Fibers:
• The number, properties, and
alignment of fibers in the
extracellular matrix will help
determine the properties of the
connective tissue. There are three
main types of connective tissue
fibers. Two are made out of a
protein called collagen, while the
third is made out of a protein called
elastin.
4-49
Extracellular Matrix Fibers:
• Collagen is a protein that forms a long
strand. If many of these strands are put
together the large resultant bundle can be
quite strong. If only a few of these strands
are intertwined, the small resultant bundle
is only somewhat strong. Collagen is has
greater properties of strength than of
elasticity.
• Elastin, on the other hand, is not so
strong, but has elastic properties.
4-50
Extracellular Matrix Fibers:
• Reticular fibers: Thin bundles of
collagen.
• They are very short, thin fibers
that branch to form a network and
appear different microscopically
from other collagen fibers.
• Not as strong as most collagen
fibers.
4-51
Extracellular Matrix Fibers:
• Elastic fibers: stretchy
branching bundles of
elastin. Also called yellow
fibers, because they tend to
look yellower than collagen
bundles do.
4-52
Extracellular Matrix Fibers:
• All of these types of
extracellular matrix fibers can
run together in different ways:
4-53
Extracellular Matrix Fibers:
• as a mixture of fiber types mainly of
one fiber type
OR
• loosely piled, with no one orientation
• densely piled, with no one orientation
• densely piled, all having the same
orientation
4-54
Connective Tissue Cell
Types
• There are three main cell types in
connective tissue. These three
cell types may appear in most of
the types of connective
tissue. There are also cell types
that are specific for certain
connective tissues (and are only
found there).
4-55
The three main cell types are:
1. Fibroblasts
2. macrophages
3. mast cells
4-56
fibroblasts
1. these important cells are
the ones that lay down the
extracellular matrix fibers!
They tend to be elongate in
appearance
4-57
macrophages
These cells are large and are derived from
blood cells.
A certain white blood cell can leave the
blood and enter tissue, and is then called
a macrophage.
This cell is a scavenger in our connective
tissues. It chews up foreign particles in
the tissue by phagocytosis, protecting
and cleaning out our bodies.
4-58
mast cells
these cells communicate chemically
with our blood.
They signal our blood by releasing
heparin and histamine, telling our
blood when it should clot or allow
inflammation of certain tissues.
That means that these cells help begin
a repair process, when needed, in
tissue.
4-59
Other cells that you may find in
specific connective tissues are
1. osteocytes-- only found in
bone
2. chondrocytes-- only found in
cartilage (or developing bone)
3. adipocytes-- only found in
adipose tissue for storing fat
4-60
Other cells that you may find in
specific connective tissues are
4. blood cells-- found only in blood (unless
you are injured)
5. reticulocytes-- found only in reticular
connective tissue. Call them
fibroblasts.
4-61
If a connective tissue has plenty of cells
within it, it is better at recovering after
injury. For example, if the skin is cut,
and the dermis is thus cut, the mast
cells will, of course, help get blood in
the area to fill the hole left by the cut
and then will also get the blood to begin
clotting. After that, however, we need
to replace the clot with more dermis.
4-62
This is possible because the
fibroblasts in the remaining dermis
begin dividing and secreting more
fibers for the matrix. As the
fibroblasts make more dermal
connective tissue, the macrophages
start removing the clot. And,
voila! The repair is done.
4-63
If, however, a connective tissue has
few cells (and/or blood supply is
limited), it is more difficult to repair that
connective tissue. An example of this
is in tendons and ligaments.
It is difficult to repair tendons and
ligaments after injury-- the healing
time is much longer than for a broken
bone
4-64
Specific Types of Connective
Tissue
• Loose connective tissue
• Dense connective tissue
• Cartilage
• Bone
4-65
Loose connective tissue
• It binds the skin to the underlying
organs and fills spaces between
muscles.
• This is composed of a mixture of
collagenous and elastic fibers within
the ground substance.
• Fibroblasts, macrophages, and mast
cells can be found within it.
4-66
Loose Connective Tissue
•
•
•
•
Also known as areolar tissue
Loose packing material of most organs and tissues
Attaches skin to underlying tissues
Contains collagen, reticular, elastic fibers and variety of cells
4-67
Dense Connective Tissue
• Dense regular
– Has abundant collagen fibers
• Tendons: Connect muscles to bones
• Ligaments: Connect bones to bones
• Dense regular elastic
• Ligaments in vocal folds
• Dense irregular
• Scars
• Dense irregular collagenous
• Forms most of skin dermis
• Dense irregular elastic
• In walls of elastic arteries
4-68
Dense connective tissue
• This tissue is made up of A LOT of
fibers. If it is regular dense connective
tissue, it is mainly made up of parallel
collagenous fibers.
• There is very little room for
vascularization.
• This is the type of tissue that makes up
tendons and ligaments.
4-69
Dense Regular Connective Tissue
4-70
If it is irregular dense connective
tissue, it is found making up the
dermis of your skin.
It has a lot of collagenous and elastic
fibers
The fibers are not oriented in parallel
bundles they are randomly arranged.
4-71
Dense Irregular Connective Tissue
4-72
Cartilage
• Composed of chondrocytes located in
spaces called lacunae
• Next to bone firmest structure in body
• Types of cartilage
– Hyaline
– Fibrocartilage
– Elastic
4-73
Cartilage
• This tissue contains chondrocytes,
and the extracellular matrix material
was secreted by them.
• They secrete a dense matrix, so
dense that after they secrete it they
end up stuck inside of it.
• There are different types of cartilage,
each having its own appearance and
elastic qualities.
4-74
Hyaline Cartilage
• Found in areas for strong support and some
flexibility
– Rib cage and cartilage in trachea and bronchi
• Forms most of skeleton before replaced by bone
in embryo
• Involved in growth that increases bone length
4-75
Fibrocartilage
• Slightly compressible and very tough
• Found in areas of body where a great deal of
pressure is applied to joints
– Knee, jaw, between vertebrae
4-76
Elastic Cartilage
• Rigid but elastic properties
– External ears, epiglottis
4-77
Connective Tissue with Special
Properties
• Adipose tissue
– Consists of adipocytes
– Types
• Yellow (white)
–most abundant, white at birth and
yellows with age
• Brown
– found only in specific areas of body as
axillae, neck and near kidneys
• Reticular tissue
– Forms framework of lymphatic tissue
4-78
– Characterized by network of fibers and cells
Adipose Tissue
4-79
Reticular Tissue
4-80
Bone
• Hard connective tissue that consists of living
cells and mineralized matrix
• Has an Organic and inorganic portion
• Types
– Cancellous or spongy bone
• Has spaces between trabeculae (plates of
bones)
– Compact bone
• More solid (almost no space)
• Many thin layers
4-81
Bone
• This tissue contains osteocytes,
which are mature bone
cells. These cells also end up
stuck inside the dense
extracellular matrix that we think
of as bone. Because bone’s
extracellular matrix is so dense,
much more so than others,
diffusion of nutrients through it is
very difficult.
4-82
Therefore, osteocytes do not use
diffusion to get their
nutrients. Instead, they extend
tiny little processes to
communicate with each other and
with the blood; the development of
these processes makes tiny little
holes in the matrix, and these
holes are called canaliculi.
4-83
Cancellous Bone
• Location: In the interior of the bones
of the skull, vertebrae, sternum and
pelvis, also found in the ends of long
bones.
• Structure: latticelike network of
scaffolding characterized by trabeculae
with large space between them filled
with hemopoietic tissue. The
osteocytes are located within lancunae
in the trabeculae.
4-84
Cancellous Bone
• Function: Acts as a scaffolding to
provide strength and support
without the greater weight of
compact bone.
4-85
Compact Bone
• Location: Outer portions of all
bones and the shafts of long bones
• Structure: Hard, bony matrix
predominates. Many osteocytes are
located within lancunae that are
distributed in a circular fashion
around the central canals.
4-86
Compact Bone
• Function: Provides great strength
and support. Forms a solid outer
shell on bones that keeps them
from being easily broken or
punctured.
4-87
Bone
4-88
Blood
• Matrix between the
cells is liquid. Blood
cells are free to move
around
• Hemopoietic tissue
– Forms blood cells
– Found in bone
marrow
• Yellow
• Red
4-89
Blood
• Location: within the blood vessels.
Produced by hemopoietic tissues.
White blood cells frequently leave
the vessels and enter the interstitial
spaces.
• Structure: Blood cells and a fluid
matrix.
4-90
Blood
• Function: Transport oxygen,
carbon dioxide, hormones,
nutrients, waste products, ad other
substances. Protects the body from
infections and is involved in
temperature regulation.
4-91
Bone Marrow
• Location: within marrow cavities
of bone. Two types: yellow
marrow (mostly adipose tissue) in
the shafts of long bones and Red
marrow (hemopoietic or bloodforming tissue) in the ends of the
long bones and in short, flat and
irregularly shaped bones
4-92
Bone Marrow
• Structure: Reticular framework
with numerous blood-forming cells
(red marrow)
• Function: Production of new blood
cells (red marrow); lipid-storage
(yellow marrow)
4-93
Bone Marrow
4-94
Muscle Tissue
• Characteristics
– Contracts or shortens with force
– Moves entire body and pumps blood
• Types
– Skeletal
• Striated and voluntary
– Cardiac
• Striated and involuntary
– Smooth
• Nonstriated and involuntary
4-95
Skeletal Muscle
4-96
Cardiac Muscle
4-97
Smooth Muscle
4-98
Nervous Tissue
• Found in brain, spinal cord and nerves
• Cells
– Nerve cells or neurons
• Consist of dendrites, cell body,
axons
– Neuroglia or support cells
4-99
Neurons
4-100
Similarities and Differences
Between Neurons and Other
Cells
Neurons are similar to other cells because neurons
have a cell membrane, a nucleus, cytoplasm,
mitochondria, organelles, and carry out processes
such as energy production.
Neurons differ from other cells because neurons
have extensions called axons and dendrites, they
communicate with each other through an
electrochemical process.
4-101
Neurons
-Nerve cells are called neurons.
-The human brain has about one billion neurons.
-Each neuron is a cell that uses biochemical
reactions to receive, process, and transmit
information.
-a neuron is a cell specialized to conduct and
generate electrical impulses and to carry
information from one part of the brain to another.
4-102
Neuroglia
4-103
Membranes
• Mucous
– Line cavities that open to
the outside of body
– Secrete mucus
• Serous
– Line cavities not open to
exterior
• Pericardial, pleural,
peritoneal
• Synovial
– Line freely movable joints
– Produce fluid rich in
hyaluronic acid
4-104
Inflammation
• Response when tissues
damaged or with an
immune response
• Manifestations
– Redness, heat, swelling,
pain, disturbance of
function
• Mediators
– Include histamine, kinins,
prostaglandins,
leukotrienes
– Stimulate pain receptor
and increase blood vessel
permeability
4-105
Tissue Repair
• Substitution of viable cells for dead cells
• Skin repair
– Primary union: Edges of wound close together
•
•
•
•
•
•
Wound fills with blood
Clot forms
Scab
Pus
Granulation tissue
Scar
– Secondary union: Edges of wound not close
• Clot may not close gap
• Inflammatory response greater
• Wound contraction occurs leading to greater scarring
4-106
Tissue Repair
4-107
Tissues and Aging
• Cells divide more slowly in older than
younger people
• Tendons and ligaments become less flexible
and more fragile
• Arterial walls become less elastic
• Rate of blood cell synthesis declines in
elderly
• Injuries are harder to heal in elderly
4-108