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Chapter 4 Outline
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Epithelial Tissue
Connective Tissue
Body Membranes
Muscle Tissue
Nervous Tissue
Tissue Change and Aging
Introduction
• The body is composed of approximately
75 trillion cells.
• These cells are organized into only four
categories called tissues.
• A tissue is a group of cells performing
similar functions.
Introduction
• Tissues vary in structure, function, and the
content of their extracellular matrix
– a substance produced by the cells of a
specific tissue and can contain protein
fibers, salts, H2O, and dissolved
macromolecules
– located outside of cells
The Four Tissue Types
•
All human body cells belong to one of
these tissues:
– epithelial tissue
– connective tissue
– muscle tissue
– nervous tissue
Epithelial Tissue
• Epithelial tissue lines every body surface
and all body cavities.
• Organs are lined on the outside and inside
by epithelial tissue.
• The majority of glands are derived from
epithelial tissue.
• Epithelial tissue possesses little to no
extracellular matrix.
Characteristics of Epithelial Tissue
All epithelia share several common characteristics:
• Cellularity–composed almost entirely of cells
with little extracellular matrix. Cells are bound
together by several types of intercellular
junctions (discussed later)
• Polarity–epithelial cells have an apical (top or
exposed) surface and a basal surface where
they attach to underlying cells
Characteristics of Epithelial Tissue
•
•
Attachment–basal surface is attached to
a thin basement membrane, which is an
acellular structure produced by both
epithelial and underlying connective
tissue cells
Avascularity–all epithelial tissues lack
blood vessels; the cells receive their
nutrients by diffusion from underlying
tissues
Characteristics of Epithelial Tissue
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Innervation–epithelia are richly
innervated to detect changes in
environment at a body or organ region
Regeneration–because apical surface is
constantly exposed to the environment,
epithelial cells are frequently damaged or
die; they are replaced as quickly as they
are lost
Epithelium
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Apical (free) surface
Lateral surface
Epithelium
Basement membrane
Basal surface
Connective tissue
Blood vessel
(a) Epithelium–connective tissue junction
Figure 4.1
Functions of Epithelial Tissue
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Physical protection–from dehydration and
abrasion; and physical, chemical, and biological
agents
Selective permeability–regulates the passage of
certain molecules in or out of a certain region of
the body
Secretions–some epithelial cells called exocrine
cells produce secretions such as sweat or oil
Sensations–possess nerve endings that can
detect light, taste, sound, smell, and hearing
Basement Membrane
• A specialized structure of epithelium
• Found between the epithelium and
underlying connective tissue
• Provides physical support and anchoring
of epithelial tissue
• Acts as a barrier to regulate passage of
large molecules between epithelium and
underlying connective tissue
Intercellular Junctions
•
•
Epithelial cells are strongly bound to each
other on their lateral surfaces by sharing
membrane specializations called intercellular
junctions
There are several types of these junctions:
– tight junctions
– adhering junctions
– desmosomes
– gap junctions
Intercellular Junctions
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Apical (free) surface
Epithelium
Basement membrane
Lateral surface
Basal surface
Connective tissue
Blood vessel
(a) Epithelium–connective tissue junction
Tight junction
Membrane protein
Plasma membrane
Microfilament
Hemidesmosome
Adhering junction
Desmosome
Protein filaments
Protein plaque
Intermediate filaments
Intercellular space
Figure 4.1
Adjacent plasma
membranes
(b) Types of intercellular junctions
Intercellular space
Plasma membrane
Gap junction
Pore
Connexon
Tight Junctions
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Encircle cells near their apical surface
Prevent molecules from traveling
between epithelial cells, therefore
molecules must go through the epithelial
cells rather than in between them
“Gatekeepers” between an external and
internal environment
Tight Junctions
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Tight junction
Membrane protein
Plasma membrane
Microfilament
Hemidesmosome
Adhering junction
Desmosome
Protein filaments
Protein plaque
Intermediate filaments
Intercellular space
Adjacent plasma
membranes
(b) Types of intercellular junctions
Figure 4.1
Intercellular space
Plasma membrane
Gap junction
Pore
Connexon
Adhering Junctions
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Formed completely around the cell deep
to the tight junction
Microfilaments act like a purse string to
stabilize the apical surface of the
epithelial cell
Adhering Junctions
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Tight junction
Membrane protein
Plasma membrane
Microfilament
Hemidesmosome
Adhering junction
Desmosome
Protein filaments
Protein plaque
Intermediate filaments
Intercellular space
Adjacent plasma
membranes
(b) Types of intercellular junctions
Figure 4.1
Intercellular space
Plasma membrane
Gap junction
Pore
Connexon
Desmosomes
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•
Like a button or snap between adjacent cells
Appear at locations of mechanical stress between
cells sharing this type of junction
Consist of a thickened protein plaque on each of
the apposed cell membranes with a fine network
of proteins spanning the intercellular space
between the plaques
On the cytoplasmic side, intermediate filaments
attach to the plaques and provide support and
stability to this structure that is shared between the
two apposed cells
Desmosomes
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Tight junction
Membrane protein
Plasma membrane
Microfilament
Hemidesmosome
Adhering junction
Desmosome
Protein filaments
Protein plaque
Intermediate filaments
Intercellular space
Adjacent plasma
membranes
(b) Types of intercellular junctions
Figure 4.1
Intercellular space
Plasma membrane
Gap junction
Pore
Connexon
Gap Junctions
• Fluid-filled channels that directly connect
the cytoplasms of apposed cells sharing
these structures
• These structures allow adjacent cells to
communicate with each other by the flow
of ions and other small molecular
messengers
Gap Junctions
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Tight junction
Membrane protein
Plasma membrane
Microfilament
Hemidesmosome
Adhering junction
Desmosome
Protein filaments
Protein plaque
Intermediate filaments
Intercellular space
Adjacent plasma
membranes
(b) Types of intercellular junctions
Figure 4.1
Intercellular space
Plasma membrane
Gap junction
Pore
Connexon
Classifying Epithelia
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Many different types of epithelial tissue
Classified according to two criteria:
– number of layers of cells
– shape of the cells
Epithelial Cell Layers
• Simple epithelium–a single layer of cells with all
cells having an apical surface and attached to the
basement membrane
• Stratified epithelium–two or more layers of cells,
not all cells have an apical surface nor do all cells
attach to the basement membrane
• Pseudostratified epithelium–single layer but not
all cells reach the apical surface and their nuclei
give the appearance of multilayered, stratified
epithelium . . . but they are not
Simple vs. Stratified Epithelium
Figure 4.2
Epithelial Cell Shapes
• Squamous–flattened and similar to the
shape of a fried egg
• Cuboidal–about the same size on all
sides, the nucleus is usually centrally
located
• Columnar–taller than they are wide and
nucleus is oval and located in the basal
region of the cell
Shapes of Epithelial Cells
Figure 4.2
Types of Epithelium
• To decide the type of epithelium,
determine how many layers there are and
what is the shape of surface cells
– start with a single layer simple epithelium
– then consider multiple layered stratified
epithelium
Simple Squamous Epithelium
• Single layer of flat cells
Simple Cuboidal Epithelium
• Single layer of cube-shaped cells
Simple Columnar Epithelium
• Single layer of cells that are taller than
they are wide
Simple Columnar
Ciliated Epithelium
• Some epithelial cells possess cilia on their
apical surface (respiratory and
reproductive systems)
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Uterine tube
Cilia
Simple columnar
epithelial cell
Basement membrane
LM 100x
Cilia
Simple columnar
epithelial cell
Basement membrane
© Victor Eroschenko
Stratified Squamous Epithelium
• Multiple layers of flattened cells
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Epidermis of skin
Keratinized stratified
squamous epithelial cells
Living stratified
squamous epithelial cells
Basement membrane
Connective tissue
LM 100x
Keratinized stratified
squamous epithelial cells
Living stratified
squamous epithelial cells
Basement membrane
Connective tissue
© The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Stratified Cuboidal Epithelium
• Multiple layers of cube-shaped cells
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Duct of sweat gland
LM 100x
Cuboidal cell
Stratified cuboidal
epithelium
Basement membrane
Cuboidal cell
Stratified cuboidal
epithelium
Basement membrane
© The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser
Stratified Columnar Epithelium
• Multiple layers of cells that are taller than
they are wide
Pseudostratified Columnar
Epithelium
• Single layer of columnar epithelial cells but
layered appearance of nuclei suggest
multiple layers of cells
Transitional Epithelium
• Found lining the inside of the urinary
bladder
• Changes shape between squamous and
cuboidal depending on whether bladder is
full and its wall is stretched or empty and
its wall is contracted
Transitional Epithelium
Glands
• Glands perform a secretory function
• They produce mucin, hormones, enzymes, and
waste products
• Glands fall into two categories:
– endocrine glands do not possess ducts and
secrete directly into the interstitial fluid or the
bloodstream, derived from multiple tissues
– exocrine glands possess ducts and their cells
secrete their products into their ducts; almost all
exocrine glands are derived from epithelial tissue
Structure of Exocrine Glands
Figure 4.5
Connective Tissue (CT)
• Most diverse, abundant, widely distributed,
and structurally varied of all four tissue
types
• Function is to “connect” one structure to
another structure
• CT is the “glue” and “filler” of the body
• Examples of CT are: tendons, ligaments,
body fat, bones, and cartilage
Structural Components of
Connective Tissue
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Cells: different cells for different types of CT─bone
cells, cartilage cells, fat cells
Protein fibers: elastic fibers, collagen, reticular
fibers
Ground substance: a mixture of proteins and
carbohydrates with variable amounts of salts and
H2O
– the protein fibers and ground substance
comprise the extracellular matrix, which is
produced by the CT cells
Structural Components of
Connective Tissue
Figure 4.7
Functions of Connective Tissue
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Physical protection
Support and structural framework
Binding of structures
Storage
Transport
Immune protection
Development of
Connective Tissue
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Arises from mesoderm
Two types of embryonic CT:
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–
Mesenchyme: the source of all adult CT
Mucous: found in umbilical cord and can
contain stem cells for future use by the
individual
Embryonic Connective Tissue
Table 4.6
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Amnion
Umbilical cord
Immature
protein
fibers
Mesenchymal cells
Immature
protein
fiber
Ground
substance
Ground substance
LM 400x
Mesenchymal cells
Ground substance
Mesenchymal
cell
LM 250x
Immature
protein
fibers
Immature
protein
fiber
Ground
substance
a: © The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser; b: © Ed Reschke
Mesenchymal
cell
Classification of Connective Tissue
•
CT types present after birth can be
classified into three broad categories:
– CT proper
– Supporting CT
– Fluid CT
Classification of Connective Tissue
Figure 4.8
Cells of Connective Tissue Proper
There are two groups of cells in CT proper:
• Resident cells: include fibroblasts,
adipocytes, fixed macrophages, and
mesenchymal cells
• Wandering cells: include mast and
plasma cells, free macrophages, and
leukocytes
Cells of Connective Tissue Proper
Fibers of Connective Tissue Proper
There are three general types of protein
fibers produced by CT cells and secreted
into the extracellular matrix:
• Collagen fibers: long, unbranching,
strong, flexible, and resistant to
stretching. They make up 25% of all
protein in the human body, making
collagen the most abundant protein.
Fibers of Connective Tissue Proper
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•
Elastic fibers: thinner than collagen,
stretch easily, branch, and rejoin. These
fibers allow structures such as blood
vessels to stretch and relax.
Reticular fibers: thinner than collagen
fibers, form a meshwork-like
configuration. They are found in organs
with abundant spaces such as liver,
lymph nodes, and spleen─act as packing
material.
Ground Substance of
Connective Tissue Proper
• A combination of proteins and
carbohydrates
• Additional content such as H2O and salts
can result in a texture anywhere from
semi-fluid (adipose, fat) to hard (bone)
Connective Tissue Proper
Can be classified into two categories:
• Loose CT: has fewer protein fibers and
more ground substance
• Dense CT: has more protein fibers and
less ground substance
Categories of Connective
Tissue Proper
Loose Connective Tissue
Serves as the body’s packing material,
found in spaces around organs; there are
three types:
• Areolar CT: contains fibroblasts,
collagen, and elastic fibers; can be
distorted without damage; found
subcutaneous to skin
Areolar Connective Tissue
Loose Connective Tissue
•
Adipose CT: known as “fat,” comprised
mainly of adipocytes (fat cells) and very
little else
Loose Connective Tissue
•
Reticular CT: contains reticular fibers,
fibroblasts, and leukocytes; found in
spleen, lymph nodes, and bone marrow
Dense Connective Tissue
Strong, has fibers (mostly collagen) packed
tightly together; there are three types:
• Dense regular CT
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–
collagen fibers aligned parallel to applied
force
found in tendons (attach muscle to bone)
and ligaments (attach bone to bone)
Dense Regular Connective Tissue
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Table 4.10
Connective Tissue Proper: Dense Connective Tissue
Reticular layer
of dermis
Tendon
Ground substance
Collagen fiber bundles
Fibroblast nucleus
Collagen fibers
Fibroblast nucleus
Ground substance
LM 200x
LM 250x
Ground substance
Collagen fiber bundles
Single collagen fiber
Fibroblast nucleus
Collagen fibers
Fibroblast nucleus
Ground substance
(a) Dense Regular Connective Tissue
(b) Dense Irregular Connective Tissue
Structure
Densely packed, parallel collagen fibers; fibroblast
nuclei squeezed between layers of fibers; scarce
ground substance
Structure
Predominantly collagen fibers, randomly arranged
and clumped together; fibroblasts in spaces among
fibers; more ground substance than in dense regular
connective tissue
Function
Attaches muscle to bone and bone to bone; resists
stress applied in one direction
Function
Withstands stresses applied in all directions; durable
Location
Forms tendons, most ligaments
Location
Dermis; periosteum covering bone; perichondrium
covering cartilage, organ capsules
a: © Ed Reschke; b: © The McGraw-Hill Companies, Inc./Dennis Strete, photographer
Dense Connective Tissue
•
Dense irregular CT
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–
bundles of collagen fibers extending in
many directions
found in deep portion of the skin (dermis)
and capsules around organs such as the
liver, kidney, and spleen
Dense Irregular Connective Tissue
Dense Connective Tissue
•
Elastic CT
–
–
predominant elastic fibers provide ability to
stretch and recoil
found in the vocal cords and large/medium
arteries
Elastic Connective Tissue
Classification of Connective Tissue
Figure 4.8
Supporting Connective Tissue
Two types of supporting connective tissue:
• Cartilage
• Bone
Cartilage
• Cells are called chondrocytes. They
secrete a gel-like extracellular matrix
containing collagen and elastic fibers.
• Chondrocytes occupy small spaces
enclosed by their extracellular matrix
called lacunae.
• They provide support and withstand
deformation─for example, the nose and
the ear.
Cartilage
There are three types of cartilage:
• Hyaline cartilage
–
–
most common type but the weakest
found in fetal skeleton, at ends of bones
that articulate with each other, in trachea,
larynx, and nose
Hyaline Cartilage
Supporting Connective Tissue
•
Fibrocartilage
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–
densely interwoven collagen fibers
contribute to the durability
found in intervertebral disc, pubic
symphysis, and the menisci of the knee
• acts as shock absorber
Fibrocartilage
Supporting Connective Tissue
•
Elastic cartilage
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–
elastic fibers are main feature
found in epiglottis and external ear
• both structures need to bend and snap
back to original form
Elastic Cartilage
Bone
• Cells are called osteocytes.
• Extracellular matrix is a unique mixture of
collagen and bone salts.
• This mixture provides extreme strength
(from the bone salts) and micro-flexibility
(from the collagen).
Bone
Classification of Connective Tissue
Fluid Connective Tissue
Comprised of the following components:
• Plasma: a watery ground substance
containing protein fibers
• Erythrocytes: red blood cells
• Leukocytes: white blood cells
• Platelets: fragments of blood cells
involved in blood clotting
Fluid Connective Tissue
Muscle Tissue
• Comprised of cells called fibers
• When stimulated by the nervous system,
fibers shorten or contract
• The result of contraction is movement (i.e.,
movement of bones, blood, food, sperm)
Classification of Muscle Tissue
Three types of muscle:
• Skeletal
• Cardiac
• Smooth
Classification of Muscle
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Table 4.14
Muscle Tissue
Skeletal muscle
Muscularis of
small intestine
Heart wall
Intercalated
discs
Cardiac
muscle cell
Nuclei
Nuclei of
smooth
muscle cells
Striations
Skeletal muscle
fiber
Striations
Nuclei
Intercalated
discs
LM 500x
Cardiac
muscle cell
Nuclei of
smooth
muscle cells
Striations
Nuclei
Nuclei
Skeletal muscle
fiber
Striations
(a) Skeletal Muscle Tissue
(b) Cardiac Muscle Tissue
(c) Smooth Muscle Tissue
Structure
Fibers are long, cylindrical, striated, parallel, and
unbranched; fibers are multinucleated with nuclei
along periphery
Structure
Structure
Function
Moves skeleton; responsible for voluntary body
movements, locomotion, heat production
Function
Location
Attaches to bones or sometimes to skin (e.g., facial Location
muscles); also found in the voluntary
sphincters—lips, urethra, anus
Cells are short, bifurcated, and striated, with one
or two centrally located nuclei; intercalated discs
between cells
Involuntary contraction and relaxation pump blood Function
in heart
Heart wall (myocardium)
Location
a:© The McGraw-Hill Companies, Inc./Photo by Dr. Alvin Telser; b,c: © Victor Eroschenko
Cells are fusiform (spindle-shaped), short,
nonstriated, and contain one centrally
located nucleus
Involuntary movements and motion; moves
materials through internal organs
Walls of hollow internal organs, such as
vessels, airways, stomach, bladder, uterus
Skeletal Muscle
• Attached to bones of skeleton and some
skin
• Cells (muscle fibers) are:
– cylindrical and long (some as long as whole
muscle)
– multinucleated
– striated (striped internal appearance) and
voluntary
• Contraction causes movement of skeleton
or skin
Skeletal Muscle
Cardiac Muscle
• Found only in the wall of the heart (myocardium)
• Cells are:
– branched, Y-shaped, shorter than skeletal fiber cells
– striated and involuntary
– attached end-to-end by strong gap junctions called
intercalated discs that allow rapid passage of
electrical current from one cell to the next during each
heart beat
• Contraction causes movement of blood
Cardiac Muscle
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Heart wall
Intercalated
discs
Cardiac
muscle cell
Striations
Nuclei
Intercalated
discs
Cardiac
muscle cell
Striations
Nuclei
(b) Cardiac Muscle Tissue
Structure
Cells are short, bifurcated, and striated, with one
or two centrally located nuclei; intercalated discs
between cells
Function
Involuntary contraction and relaxation pump blood
in heart
Location
Heart wall (myocardium)
© Victor Eroschenko
Smooth Muscle
• Found in walls of most internal organs
– stomach, intestines, urinary bladder
• Cells are:
– relatively short, wide in the middle, and
tapered at the ends (fusiform)
– involuntary and non-striated
• Contraction causes movement of food,
blood, sperm
Smooth Muscle
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Muscularis of
small intestine
Nuclei of
smooth
muscle cells
Nuclei of
smooth
muscle cells
(c) Smooth Muscle Tissue
Structure
Cells are fusiform (spindle-shaped), short,
nonstriated, and contain one centrally
located nucleus
Function
Involuntary movements and motion; moves
materials through internal organs
Location
Walls of hollow internal organs, such as
vessels, airways, stomach, bladder, uterus
© Victor Eroschenko
Nervous Tissue
•
Contains two types of cells:
– Neurons: nerve cells that are capable
of initiating and conducting electrical
activity throughout the body
– Neuroglia: cells that support the
neurons
• Function is communication and control of
body functions
Neuron
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Dendrite
Cell body
of neuron
Axon
Nuclei of
glial cells
Tissue Change and Aging
Tissues can undergo change in form, size, or
number during the aging process:
•Metaplasia: epithelia lining the respiratory airways of
people who smoke change from pseudostratified ciliated to
stratified squamous
•Hypertrophy: an increase in the size of existing cells
•Hyperplasia: an increase in number of cells in a tissue
•Neoplasia: out-of-control growth, which forms a tumor
•Atrophy: shrinkage of tissue by cell size or number