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Connective Tissue
• Most abundant and widely distributed of
primary tissues
• Four main classes
– Connective tissue proper
– Cartilage
– Bone
– Blood
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Table 4.1 Comparison of Classes of Connective Tissues (1 of 2)
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Table 4.1 Comparison of Classes of Connective Tissues (2 of 2)
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Major Functions of Connective Tissue
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Binding and support
Protecting
Insulating
Storing reserve fuel
Transporting substances (blood)
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Characteristics of Connective Tissue
• Three characteristics make connective
tissues different from other tissues
– Have varying degrees of vascularity (blood
vessels)
– Have extracellular matrix
• Connective tissue not composed mainly of cells
• Largely nonliving extracellular matrix separates
cells
– So can bear weight, withstand tension, endure abuse
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Structural Elements of Connective Tissue
• Three elements
– Ground substance
– Fibers
– Cells
• Composition and arrangement varies in
different connective tissues
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Ground Substance
• Unstructured material that fills space between
cells
– Medium through which solutes diffuse between blood
capillaries and cells
• Components
– Interstitial fluid
– Cell adhesion proteins ("glue" for attachment)
– Proteoglycans
• Protein core + large polysaccharides (chrondroitin sulfate
and hyaluronic acid)
• Trap water in varying amounts, affecting viscosity of ground
substance
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Connective Tissue Fibers
• Three types of fibers provide support
– Collagen
• Strongest and most abundant type
• Tough; provides high tensile strength
– Elastic fibers
• Networks of long, thin, elastin fibers that allow for
stretch and recoil
– Reticular
• Short, fine, highly branched collagenous fibers
(different chemistry and form than collagen fibers)
• Branch, forming networks that offer more "give"
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Cells
• "Blasts" cells
– Immature forum; mitotically active; secrete ground
substance and fibers
– Fibroblasts in connective tissue proper
– Chondroblasts in cartilage
– Osteoblasts in bone
– Hematopoietic stem cells in bone marrow
– "Cyte" cells
– Mature form; maintain matrix
– Chondrocytes in cartilage
– Osteocytes in bone
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Other Cell Types in Connective Tissues
• Fat cells
– Store nutrients
• White blood cells
– Neutrophils, eosinophils, lymphocytes
– Tissue response to injury
• Mast cells
– Initiate local inflammatory response against foreign
microorganisms they detect
• Macrophages
– Phagocytic cells that "eat" dead cells,
microorganisms; function in immune system
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Figure 4.7 Areolar connective tissue: A prototype (model) connective tissue.
Cell types
Macrophage
Fibroblast
Lymphocyte
Fat cell
Mast cell
Neutrophil
Capillary
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Extracellular
matrix
Ground substance
Fibers
• Collagen fiber
• Elastic fiber
• Reticular fiber
Types of Connective Tissues: Connective
Tissue Proper
• All connective tissues except bone, cartilage and
blood
• Two subclasses
– Loose connective tissues
• Areolar
• Adipose
• Reticular
– Dense connective tissues (also called fibrous
connective tissues)
• Dense regular
• Dense irregular
• Elastic
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Areolar Connective Tissue
• Support and bind other tissues
– Universal packing material between other tissues
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Most widely distributed
Provide reservoir of water and salts
Defend against infection
Store nutrients as fat
Fibroblasts
Loose arrangement of fibers
Ground substance
When inflamed soaks up fluid  edema
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Figure 4.8a Connective tissues.
Connective tissue proper: loose connective tissue, areolar
Description: Gel-like matrix with
all three fiber types; cells:
fibroblasts, macrophages, mast
cells, and some white blood cells.
Function: Wraps and cushions
organs; its macrophages
phagocytize bacteria; plays
important role in inflammation;
holds and conveys tissue fluid.
Location: Widely distributed
under epithelia of body, e.g., forms
lamina propria of mucous
membranes; packages organs;
surrounds capillaries.
Elastic
fibers
Ground
substance
Fibroblast
nuclei
Collagen
fibers
Epithelium
Lamina
propria
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Photomicrograph: Areolar connective
tissue, a soft packaging tissue of the body (340x).
Adipose Tissue
• White fat
– Similar to areolar but greater nutrient storage
– Cell is adipocyte
• Stores nutrients
– Scanty matrix
– Richly vascularized
– Shock absorption, insulation, energy storage
• Brown fat
– Use lipid fuels to heat bloodstream not to
produce atp
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Figure 4.8b Connective tissues.
Connective tissue proper: loose connective tissue, adipose
Description: Matrix as in areolar,
but very sparse; closely packed
adipocytes, or fat cells, have
nucleus pushed to the side by
large fat droplet.
Function: Provides reserve food
fuel; insulates against heat loss;
supports and protects organs.
Nucleus of
adipose
(fat) cell
Location: Under skin in
subcutaneous tissue; around
kidneys and eyeballs; within
abdomen; in breasts.
Adipose
tissue
Fat droplet
Photomicrograph: Adipose tissue from
the subcutaneous layer under the skin (350x).
Mammary
glands
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Reticular Connective Tissue
• Resembles areolar but fibers are reticular
fibers
• Fibroblasts called reticular cells
• Supports free blood cells in lymph nodes,
the spleen, and bone marrow
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Figure 4.8c Connective tissues.
Connective tissue proper: loose connective tissue, reticular
Description: Network of reticular
fibers in a typical loose ground
substance; reticular cells lie on
the network.
Function: Fibers form a soft
internal skeleton (stroma) that
supports other cell types including
white blood cells, mast cells, and
macrophages.
White blood
cell
(lymphocyte)
Location: Lymphoid organs
(lymph nodes, bone marrow, and
spleen).
Spleen
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Reticular
fibers
Photomicrograph: Dark-staining network
of reticular connective tissue fibers forming
the internal skeleton of the spleen (350x).
Dense Regular Connective Tissue
• Closely packed bundles of collagen fibers
running parallel to direction of pull
– White structures with great resistance to
pulling
– Fibers slightly wavy so stretch a little
• Fibroblasts manufacture fibers and ground
substance
• Few cells
• Poorly vascularized
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Figure 4.8d Connective tissues.
Connective tissue proper: dense connective tissue, dense regular
Description: Primarily parallel
collagen fibers; a few elastic fibers;
major cell type is the fibroblast.
Function: Attaches muscles to
bones or to muscles; attaches
bones to bones; withstands great
tensile stress when pulling force is
applied in one direction.
Collagen
fibers
Location: Tendons, most
ligaments, aponeuroses.
Nuclei of
fibroblasts
Shoulder
joint
Ligament
Tendon
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Photomicrograph: Dense regular connective
tissue from a tendon (430x).
Dense Irregular Connective Tissue
• Same elements but bundles of collagen
thicker and irregularly arranged
• Resists tension from many directions
– Dermis
– Fibrous joint capsules
– Fibrous coverings of some organs
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Figure 4.8e Connective tissues.
Connective tissue proper: dense connective tissue, dense irregular
Description: Primarily irregularly
arranged collagen fibers; some
elastic fibers; fibroblast is the
major cell type.
Nuclei of
fibroblasts
Function: Withstands tension
exerted in many directions;
provides structural strength.
Location: Fibrous capsules of
organs and of joints; dermis of the
skin; submucosa of digestive tract.
Collagen
fibers
Shoulder
joint
Fibrous
joint
capsule
Photomicrograph: Dense irregular connective
tissue from the fibrous capsule of a joint (430x).
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Elastic Connective Tissue
• Some ligaments very elastic
– Those connecting adjacent vertebrae
• Many of larger arteries have in walls
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Figure 4.8f Connective tissues.
Connective tissue proper: dense connective tissue, elastic
Description: Dense regular
connective tissue containing a
high proportion of elastic fibers.
Function: Allows tissue to recoil
after stretching; maintains pulsatile
flow of blood through arteries; aids
passive recoil of lungs following
inspiration.
Location: Walls of large arteries;
within certain ligaments associated
with the vertebral column; within
the walls of the bronchial tubes.
Elastic
fibers
Aorta
Heart
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Photomicrograph: Elastic connective tissue
in the wall of the aorta (250x).
Cartilage
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Chondroblasts and chondrocytes
Tough yet flexible
Lacks nerve fibers
Up to 80% water - can rebound after
compression
• Avascular
– Receives nutrients from membrane surrounding it
• Perichondrium
• Three types of cartilage:
– Hyaline cartilage
– Elastic cartilage
– Fibrocartilage
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Figure 4.8g Connective tissues.
Cartilage: hyaline
Description: Amorphous but firm
matrix; collagen fibers form an
imperceptible network;
chondroblasts produce the matrix
and when mature (chondrocytes)
lie in lacunae.
Function: Supports and reinforces;
serves as resilient cushion; resists
compressive stress.
Chondrocyte
in lacuna
Location: Forms most of the
embryonic skeleton; covers the
ends of long bones in joint cavities;
forms costal cartilages of the ribs;
cartilages of the nose, trachea, and
larynx.
Costal
cartilages
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Matrix
Photomicrograph: Hyaline cartilage from
a costal cartilage of a rib (470x).
Figure 4.8h Connective tissues.
Cartilage: elastic
Description: Similar to hyaline
cartilage, but more elastic fibers
in matrix.
Function: Maintains the shape of
a structure while allowing great
flexibility.
Chondrocyte
in lacuna
Matrix
Location: Supports the external
ear (pinna); epiglottis.
Photomicrograph: Elastic cartilage from
the human ear pinna; forms the flexible
skeleton of the ear (800x).
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Figure 4.8i Connective tissues.
Cartilage: fibrocartilage
Description: Matrix similar to but
less firm than that in hyaline
cartilage; thick collagen fibers
predominate.
Function: Tensile strength allows
it to absorb compressive shock.
Location: Intervertebral discs;
pubic symphysis; discs of knee
joint.
Chondrocytes
in lacunae
Intervertebral
discs
Collagen
fiber
Photomicrograph: Fibrocartilage of an
intervertebral disc (125x). Special staining
produced the blue color seen.
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Bone
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Also called osseous tissue
Supports and protects body structures
Stores fat and synthesizes blood cells in cavities
More collagen than cartilage
Has inorganic calcium salts
Osteoblasts produce matrix
Osteocytes maintain the matrix
Osteons – structural units
Richly vascularized
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Figure 4.8j Connective tissues.
Others: bone (osseous tissue)
Description: Hard, calcified
matrix containing many collagen
fibers; osteocytes lie in lacunae.
Very well vascularized.
Function: Supports and protects
(by enclosing); provides levers for
the muscles to act on; stores
calcium and other minerals and
fat; marrow inside bones is the
site for blood cell formation
(hematopoiesis).
Central
canal
Lacunae
Lamella
Location: Bones
Photomicrograph: Cross-sectional view
of bone (125x).
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Blood
• Most atypical connective tissue – is a fluid
• Red blood cells most common cell type
• Also contains white blood cells and
platelets
• Fibers are soluble proteins that precipitate
during blood clotting
• Functions in transport
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Figure 4.8k Connective tissues.
Connective tissue: blood
Description: Red and white blood
cells in a fluid matrix (plasma).
Red blood
cells
(erythrocytes)
Function: Transport respiratory
gases, nutrients, wastes, and other
substances.
White blood
cells:
• Lymphocyte
• Neutrophil
Location: Contained within blood
vessels.
Plasma
Photomicrograph: Smear of human blood
(1670x); shows two white blood cells
surrounded by red blood cells.
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Muscle Tissue
• Highly vascularized
• Responsible for most types of movement
• Three types
– Skeletal muscle tissue
• Found in skeletal muscle
• Voluntary
– Cardiac muscle tissue
• Found in walls of heart
• Involuntary
– Smooth muscle tissue
• Mainly in walls of hollow organs other than heart
• Involuntary
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Figure 4.9a Muscle tissues.
Skeletal muscle
Description: Long, cylindrical,
multinucleate cells; obvious
striations.
Part of
muscle
fiber (cell)
Function: Voluntary movement;
locomotion; manipulation of the
environment; facial expression;
voluntary control.
Nuclei
Location: In skeletal muscles
attached to bones or occasionally
to skin.
Striations
Photomicrograph: Skeletal muscle
(approx. 440x). Notice the obvious banding
pattern and the fact that these large cells are
multinucleate.
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Figure 4.9b Muscle tissues.
Cardiac muscle
Description: Branching, striated,
generally uninucleate cells that
interdigitate at specialized
junctions (intercalated discs).
Intercalated
discs
Function: As it contracts, it
propels blood into the circulation;
involuntary control.
Striations
Location: The walls of the heart.
Nucleus
Photomicrograph: Cardiac muscle (900x);
notice the striations, branching of cells, and
the intercalated discs.
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Figure 4.9c Muscle tissues.
Smooth muscle
Description: Spindle-shaped
cells with central nuclei; no
striations; cells arranged closely
to form sheets.
Function: Propels substances or
objects (foodstuffs, urine, a baby)
along internal passageways;
involuntary control.
Nuclei
Location: Mostly in the walls of
hollow organs.
Smooth
muscle
cell
Photomicrograph: Sheet of smooth
muscle (720x).
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Nervous Tissue
• Main component of nervous system
– Brain, spinal cord, nerves
– Regulates and controls body functions
• Neurons
– Specialized nerve cells that generate and conduct
nerve impulses
• Neuroglia
– Supporting cells that support, insulate, and protect
neurons
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Figure 4.10 Nervous tissues.
Nervous tissue
Description: Neurons are
branching cells; cell processes
that may be quite long extend from
the nucleus-containing cell body;
also contributing to nervous tissue
are nonexcitable supporting cells.
Nuclei of
supporting
cells
Neuron processes Cell body
Axon Dendrites
Cell body
of a neuron
Function: Neurons transmit
electrical signals from sensory
receptors and to effectors (muscles
and glands) which control their
activity; supporting cells support
and protect neurons.
Neuron
processes
Location: Brain, spinal
cord, and nerves.
Photomicrograph: Neurons (350x).
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Covering and Lining Membranes
• Composed of at least two primary tissue
types
– An epithelium bound to underlying connective
tissue proper
– Are simple organs
• Three types
– Cutaneous membranes
– Mucous membranes
– Serous membranes
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Cutaneous Membranes
• Skin
• Keratinized stratified squamous epithelium
(epidermis) attached to a thick layer of
connective tissue (dermis)
• Dry membrane
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Figure 4.11a Classes of membranes.
Cutaneous membrane
The cutaneous membrane
(the skin) covers the body surface.
Cutaneous
membrane (skin)
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Mucous Membranes
• Mucosa indicates location not cell composition
• All called mucosae
– Line body cavities open to the exterior (e.g.,
Digestive, respiratory, urogenital tracts)
• Moist membranes bathed by secretions (or
urine)
• Epithelial sheet lies over layer of connective
tissue called lamina propria
• May secrete mucus
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Figure 4.11b Classes of membranes.
Mucous membranes
Mucous membranes line body
cavities that are open to the
exterior.
Mucosa of
nasal cavity
Mucosa of
mouth
Esophagus
lining
Mucosa of
lung bronchi
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Serous Membranes
• Serosae—found in closed ventral body cavity
• Simple squamous epithelium (mesothelium)
resting on thin areolar connective tissue
• Parietal serosae line internal body cavity walls
• Visceral serosae cover internal organs
• Serous fluid between layers
• Moist membranes
• Pleurae, pericardium, peritoneum
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Figure 4.11c Classes of membranes.
Serous membranes
Serous membranes line body cavities that are
closed to the exterior.
Parietal
pleura
Visceral
pleura
Visceral
Parietal
pericardium pericardium
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Parietal
peritoneum
Visceral
peritoneum
Tissue Repair
• Necessary when barriers are penetrated
• Cells must divide and migrate
• Occurs in two major ways
– Regeneration
• Same kind of tissue replaces destroyed tissue
• Original function restored
– Fibrosis
• Connective tissue replaces destroyed tissue
• Original function lost
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Steps in Tissue Repair: Step 1
• Inflammation sets stage
– Release of inflammatory chemicals
– Dilation of blood vessels
– Increase in vessel permeability
– Clotting occurs
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Figure 4.12. Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
Slide 1
Scab
Epidermis
Vein
Blood clot in
incised wound
Inflammatory
chemicals
Migrating white
blood cell
Artery
1 Inflammation sets the stage:
• Severed blood vessels bleed.
• Inflammatory chemicals are released.
• Local blood vessels become more permeable, allowing white blood cells,
fluid, clotting proteins, and other plasma proteins to seep into the injured area.
• Clotting occurs; surface dries and forms a scab.
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Steps in Tissue Repair: Step 2
• Organization restores blood supply
– The blood clot is replaced with granulation
tissue
– Epithelium begins to regenerate
– Fibroblasts produce collagen fibers to bridge
the gap
– Debris is phagocytized
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Figure 4.12. Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
Slide 2
Regenerating
epithelium
Area of
granulation
tissue
ingrowth
Fibroblast
Macrophage
Budding capillary
2 Organization restores the blood supply:
• The clot is replaced by granulation tissue, which restores the vascular
supply.
• Fibroblasts produce collagen fibers that
bridge the gap.
• Macrophages phagocytize dead and dying cells and other debris.
• Surface epithelial cells multiply and migrate over the granulation tissue.
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Steps in Tissue Repair: Step 3
• Regeneration and fibrosis
– The scab detaches
– Fibrous tissue matures; epithelium thickens
and begins to resemble adjacent tissue
– Results in a fully regenerated epithelium with
underlying scar tissue
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Figure 4.12. Tissue repair of a nonextensive skin wound: regeneration and fibrosis.
Regenerated
epithelium
Fibrosed area
3 Regeneration and fibrosis effect permanent repair:
• The fibrosed area matures and contracts; the epithelium thickens.
• A fully regenerated epithelium with an underlying area of scar tissue
results.
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Slide 3
Regenerative Capacity in Different Tissues
• Regenerate extremely well
– Epithelial tissues, bone, areolar connective tissue,
dense irregular connective tissue, blood-forming
tissue
• Moderate regenerating capacity
– Smooth muscle and dense regular connective tissue
• Virtually no functional regenerative capacity
– Cardiac muscle and nervous tissue of brain and
spinal cord
– New research shows cell division does occur
• Efforts underway to coax them to regenerate better
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Aging Tissues
• Normally function well through youth and middle
age if adequate diet, circulation, and infrequent
wounds and infections
• Epithelia thin with increasing age so more easily
breached
• Tissue repair less efficient
• Bone, muscle and nervous tissues begin to
atrophy
• DNA mutations possible  increased cancer
risk
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