➢ Groups of cells with similar structure and

Epithelial tissue (epithelium) – Covering
Connective tissue – Support
Muscle tissue – Movement
Nervous tissue – Control

All of which are interweaved to form the fabric of
the body.
➢ Epithelial tissues develop from all three
primary germ layers.
➢ Epithelium, or epithelial tissue, covers and
protects surface, both outside and inside
the body
o Body coverings
o Body linings
o Glandular tissue
➢ Epithelial functions include protection,
absorption, filtration, and secretion.
Epithelium Characteristic
➢ Cells fit closely together and often form
➢ The apical surface is the free surface of the
➢ The lower surface of the epithelium rests on
a basement membrane
➢ Avascular (no blood supply)
➢ Regenerate easily if well nourished.

Classification of Epithelia
➢ Number of cell layers
o Simple- one layer
o Stratified- more than one layer
o Pseudostratified- cells lie at different
➢ Shape of cells
o Squamous- Flattened, like fish scales
o Cuboidal- Cube-shaped, like dice
o Columnar- Column-like


stretching to
distension of

Simple Squamous Epithelium
➢ Single layer of flat cells
➢ Location- usually forms membranes
o Lines air sacs of the lungs
o Forms walls of capillaries
o Forms serous membranes (serosae)
that line and cover organs in ventral
➢ Functions in diffusion, filtration, or
secretion in membranes
Cell shape




Number of layers
One layer;
More than
one layer:
Diffusion and
Secretion in
Secretion and
these tissue
ciliated types
types are rare
propel mucus
in humans
Secretion and
ciliated types
propel mucus

Simple Cuboidal Epithelium
➢ Singe layer of cube-like cells
➢ Locations:
o Common in glands and their ducts
o Forms walls of kidney tubules
o Covers the surface of ovaries
➢ Functions in secretion and absorption;
ciliated types propel mucus or reproductive
Simple Columnar Epithelium
➢ Non-ciliated or ciliated
➢ Single layer of tall cells
o Goblet cells secrete mucus
➢ Location
o Lines digestive tract from stomach
to anus
o Mucous membranes (mucosae) line
body cavities opening to the exterior
➢ Functions in secretion and absorption;
ciliated types propel mucus or reproductive
Pseudostratified Columnar Epithelium
➢ All cells rest on a basement membrane

➢ Single layer, but some cells are shorter than
other giving a false (pseudo) impression of
➢ Location:
o Respiratory tract, where it is ciliated
and known as pseudostratified
ciliated columnar epithelium
➢ Functions in absorption or secretion
Stratified Squamous Epithelium
➢ Named for cells present at the free (apical)
surface, which are flattened
➢ Functions as a protective covering where
friction is common
➢ Exist in both keratinized or nonkeratinized.
➢ Locations-ling of the:
o Skin (outer portion)
o Mouth
o Esophagus
Transitional Epithelium
➢ Composed of modified stratified squamous
➢ Shape of cells depends upon the amount of
➢ Functions in stretching and the ability to
return to normal shape
➢ Locations:
o Urinary system organs

Tight Junctions
➢ Impermeable junctions
➢ Bind cells together into leakproof sheets
➢ Prevent substances from passing through
extracellular space between cells

Cell Connections
➢ Cells are bound together in three ways:
o Glycoproteins in the glycocalyx act
as an adhesive or cellular glue
o Wavy contours of the membranes of
adjacent cells fit together in a
tongue-and-groove fashion
o Special membrane junctions are
formed, which vary structurally
depending on their roles


➢ Resist separation during contractile
➢ Contains plaque
➢ Forms an extension zone called adhesion

➢ Anchoring junctions that prevent cells from
being pulled as a result of mechanical stress
➢ Created by buttonlike thickenings of
adjacent plasma membranes

➢ Resembles desmosomes but do not link
adjacent cells but rather their basement
➢ Transmembrane proteins are integrins

Gap Junctions

➢ Allow communication between cells
➢ Hollow cylinders of proteins (connexons)
span the width of the abutting membranes.
➢ Molecules can travel directly from one cell
to the next through these channels.

Glandular epithelium
➢ One or more cells responsible for secreting
a particular product
➢ Two major gland types
o Endocrine gland
▪ Ductless; secretion diffuse
into blood vessels
▪ All secretions are hormones
▪ Examples include thyroid,
adrenals, and pituitary
o Exocrine gland
▪ Secretions empty through
ducts to the epithelial
▪ Include sweat and oil glands,
liver, and pancreas
▪ Includes both internal and
external glands

Structure of Exocrine Glands
➢ Duct portion- for transportation
➢ Secretory portion- produce the secreted
➢ Major categories
o Unicellular gland
o Multicellular simple gland
o Compound gland
▪ Glands with secretory
regions shaped as tubules
(small tubes) are called
tubular, whereas those
shaped in saclike structures
are called acinar or alveolar.

Simple Glands
➢ Simple Tubular
o Secretory part is straight
➢ Simple branched tubular
o Branched and attaches to a single
unbranched duct
➢ Simple coiled tubular
o Coiled and attaches to a single
unbranched duct

Exocrine Glands
➢ Modes of secretion
o Merocrine- release of secretory
products by exocytosis
o Apocrine- pinched-off fragments.
o Holocrine- shedding of entire cells.

➢ Simple acinar
o Rounded and attaches to a single
unbranched duct
➢ Simple branched acinar
o Rounded secretory part is branched
and attaches to a single unbranched

➢ Found everywhere in the body
➢ Includes the most abundant and widely
distributed tissues.
Connective Tissues Characteristics
➢ Variations in blood supply
o Some tissue types are well
o Some have a poor blood supply or
are avascular
➢ Extracellular matrix
o Nonliving material that surrounds
living cells.

Compound Glands
➢ Compound tubular- Tubular and attaches to
a branched duct
➢ Compound acinar- Rounded and attaches to
a branched duct
➢ Compound tubuloacinar- Both tubular and
rounded and attaches to a branched duct.

➢ Two main elements
o Ground substance- mostly water
along with adhesion proteins and
polysaccharide molecules.

Hyaluronic acid, chondroitin
sulfate, dermatan sulfate,
and keratan sulfate

o Fibers
▪ Produced by the cells
▪ Three types:
• Collagen (white)
• Elastic (yellow) fibers
• Reticular fibers (a
type of collagen)

➢ Composed of
o Osteocytes (bone cells) sitting in
lacunae (cavities)
o Hard matrix of calcium salts
o Large numbers of collagen fibers
➢ Functions to protect and support the body


Types of Connective Tissue
➢ From most rigid to softest, or fluid.
o Bone
o Cartilage
o Dense connective tissue
o Loose connective tissue
o Blood

➢ Less hard and more flexible than bone
➢ Found in only a few places in the body
➢ Chondrocyte (cartilage cell) is the major cell
➢ Types
o Hyaline
o Elastic
o Fibrocartilage

Hyaline Cartilage

Dense connective Tissue

➢ Hyaline cartilage is the most widespread
type of cartilage
➢ Composed of abundant collagen fibers and
a rubbery matrix
➢ Locations:
o Larynx
o Entire fetal skeleton prior to birth
o Epiphyseal plates
➢ Functions as a more flexible skeletal
element than bone

➢ Dense Regular Connective Tissue
o Main matrix element is collagen
o Fibroblasts are cells that make fibers
o Locations
▪ Tendons- attach skeletal
muscle to bone
▪ Ligaments- attach bone to
bone at joints and are more
elastic than tendons
▪ Dermis- lower layers of the

Elastic cartilage
➢ Provides elasticity
➢ Location
o Supports the external ear
Dense Irregular Connective Tissue

➢ Highly compressible
o Location
▪ Forms cushion like discs
between vertebrae of the
spinal column

➢ Consists predominantly of collagen fibers
randomly arranged and a few fibroblasts.
➢ Location:
o Fasciae, reticular region of dermis of
skin, periosteum of bone,
perichondrium of cartilage, joint
capsules, membrane capsules
around various organs (kidneys,
liver, testes, lymph nodes),
pericardium of the heart, and heart
➢ Provides strength
Elastic connective tissue
➢ Consists predominantly of freely branching
elastic fibers; fibroblasts are present in
spaces between fibers.
➢ Location
o Lung tissue, walls of elastic arteries,
trachea, bronchial tubes, true vocal

cords, suspensory ligaments of
penis, and some ligaments between
➢ Allows stretching of various organs.
Loose connective tissue
➢ Areolar tissue
o Most widely distributed connective
o Soft, pliable tissue like “cobwebs”
o Functions as a universal packing
tissue and ‘glue’ to hold organs in
o Layers of areolar tissue called
lamina propria underlies all
o All fiber types from a loose network
o Can soak up excess fluid (causes

o Forms stroma (internal framework)
of organs, such as these lymphoid
▪ Lymph nodes
▪ Spleen
▪ Bone marrow
Blood (vascular tissue)
➢ Blood cells surrounded by fluid matrix
known as blood plasma
➢ Soluble fibers are visible only during clotting
➢ Functions as the transport vehicle for the
cardiovascular system, carrying
o Nutrients
o Wastes
o Respiratory gases

Muscle Tissue
Adipose Tissue
➢ Matrix is an areolar tissue in which fat
globules predominate
➢ Many cells contain large lipid deposits with
nucleus to one side (signet ring cells)
➢ Functions
o Insulates the body
o Protects some organs
o Serves as a site of fuel storage
Reticular connective tissue
➢ Delicate network of interwoven fibers with
reticular cells (like fibroblasts)
➢ Locations

➢ Function is to contract, or shorten, to
produce movement
➢ Derived from mesoderm
➢ Three types:
o Skeletal muscle
o Cardiac muscle
o Smooth muscle
Skeletal muscle
➢ Voluntarily (consciously) controlled
➢ Attached to the skeleton and pull-on bones
or skin
➢ Produces gross body movements or facial
➢ Characteristics of skeletal muscle cells
o Striations (stripes)
o Multinucleate (more than one

o Long, cylindrical shape

Nervous Tissues
Cardiac muscle

Involuntarily controlled
Found only in the heart
Pumps blood through blood vessels
Characteristics of cardiac muscle cells
o Striations
o Uninucleate, short, branching cells
o Intercalated discs contain gap
junction to connect cells together.

➢ Develops from ectoderm
➢ Composed of neurons and nerve support
➢ Function is to receive and conduct
electrochemical impulses to and from body
o Irritability
o Conductivity
➢ Supports cells called neuroglia insulate,
protect, and support neurons.

Smooth (visceral) muscle
➢ Involuntarily controlled
➢ Found in walls of hollow organs such as
stomach, uterus, and blood vessels
➢ Peristalsis, a wavelike activity, is a typical
➢ Characteristics of smooth muscle cells
o No visible striations
o Uninucleate
o Spindle-shaped cells

Tissue Repair (Wound Healing)

➢ Tissue repair (wound healing) occur in two
o Regeneration- Replacement of
destroyed tissue by the same kind of
o Fibrosis- Repair by dense (fibrous)
connective tissue (scar tissue)
➢ Whether regeneration or fibrosis occurs
depends on:
o Type of tissue damaged
o Severity of the injury
➢ Clean cuts (incisions) heals more
successfully than ragged tears of the tissue
Events in Tissue Repair
➢ Inflammation
o Capillaries becomes very permeable
o Clotting proteins migrate into the
area from the bloodstream
o A clot walls off the injured area
➢ Granulation tissue forms
o Growth of new capillaries
o Phagocytes dispose of blood clot
and fibroblasts
o Rebuild collagen fibers (scar tissue)

➢ Regeneration of surface epithelium
o Scab detaches
o Whether scar is visible or invisible
depends on severity of wound

Regeneration of Tissues
➢ Tissues that regenerate easily
o Epithelial tissue (skin and mucous
o Fibrous connective tissues and bone
➢ Tissue that regenerate poorly
o Skeletal muscles
➢ Tissues that are replaced largely with scar
o Cardiac muscle
o Nervous tissue within the brain and
spinal cord
Developmental Aspects of Cells and Tissues
➢ Growth through cell divisions continues
through puberty
➢ Cell populations exposed to friction (such as
epithelium) replace lost cells throughout life
➢ Connective tissue remains mitotic and
forms repair (scar) tissue
➢ With some exceptions, muscle tissue
become amitotic by the end of puberty
➢ Nervous tissue become amitotic shortly
after birth
➢ Injury can severely handicap amitotic
➢ The cause of aging is unknown, but
chemical and physical insults, as well as
genetic programming, have been proposed
as possible causes
➢ Neoplasms, both benign and cancerous,
represent abnormal cell masses in which
normal controls on cell divisions are not

➢ Hyperplasia (increase in size) of a tissue or
organ may occur when tissue is strongly
stimulated or irritated
➢ Atrophy (decrease in size) of a tissue or
organ occurs when the organ is no longer
stimulated normally.

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