Tissues

TISSUES
➢ Groups of cells with similar structure and
function
FOUR PRIMARY TYPES
➢
➢
➢
➢

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
➢ Epithelial tissues develop from all three
primary germ layers.
➢ Epithelium, or epithelial tissue, covers and
protects surface, both outside and inside
the body
➢ LOCATIONS.
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
sheets
➢ The apical surface is the free surface of the
tissue
➢ 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
levels.
➢ Shape of cells
o Squamous- Flattened, like fish scales
o Cuboidal- Cube-shaped, like dice
o Columnar- Column-like

Transitional

Protection;
stretching to
accommodate
distension of
urinary
structures.

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
cavity
➢ Functions in diffusion, filtration, or
secretion in membranes
FUNCTIONS OF EPITHELIAL TISSUE RELATED TO
TISSUE TYPE
Cell shape

Squamous

Cuboidal

Columnar

Number of layers
One layer;
More than
simple
one layer:
epithelial
stratified
tissues
epithelial
tissues
Diffusion and
Protection
filtration
Secretion in
serous
membranes
Secretion and
Protection:
absorption;
these tissue
ciliated types
types are rare
propel mucus
in humans
or
reproductive
cells
Secretion and
absorption;
ciliated types
propel mucus
or
reproductive
cells

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
cells
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
cells.
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
stratification
➢ 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
epithelium
➢ Shape of cells depends upon the amount of
stretching
➢ 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

Adherens

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

Hemidesmosomes
Desmosomes
➢ 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
membrane
➢ 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
surface
▪ 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
material.
➢ 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
duct

CONNECTIVE TISSUE
➢ 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
vascularized
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)
fibers
• Elastic (yellow) fibers
• Reticular fibers (a
type of collagen)

Bone
➢ 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

Cartilage

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
type
➢ 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
fiber
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
skin

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

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

o Forms stroma (internal framework)
of organs, such as these lymphoid
organs:
▪ 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
expressions
➢ Characteristics of skeletal muscle cells
o Striations (stripes)
o Multinucleate (more than one
nucleus)

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
cells
➢ Function is to receive and conduct
electrochemical impulses to and from body
parts
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
activity
➢ 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
ways:
o Regeneration- Replacement of
destroyed tissue by the same kind of
cells
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
membranes)
o Fibrous connective tissues and bone
➢ Tissue that regenerate poorly
o Skeletal muscles
➢ Tissues that are replaced largely with scar
tissue
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
tissues
➢ 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
working

➢ 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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