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Connective Tissue and
More
Connective tissues, nervous, and
muscle tissues
What is connective tissue?
Connective tissues

Represent the most abundant by weight and
most widely distributed type of tissue in the
body

Generally:
Bind structures together
Fill spaces in the body
Examples: Connective tissue proper,
Cartilage, Bone, Blood

Connective Tissue
Figure 4.6
Connective Tissues –
general functions
Connect epithelium to the rest of the
body (basal lamina)
 Have no contact with environment
(usually covered by epithelium)
 Usually highly vascular (good blood
supply)
 Also:





Protect delicate organs
Provide structure and support (bone)
Insulate and store energy (fat)
Transport materials (blood)
Characteristics of
Connective Tissues


Specialized cells
Solid extracellular protein fibers


Collagen, elastic, and reticular
Fluid extracellular ground substance

unstructured material that fills the space between
cells
These latter two extracellular features are
called Matrix
The Matrix

The extracellular components of connective
tissues (fibers and ground substance):



Makes up the majority of tissue volume
Determines specialized function:
connective tissue proper  syrupy liquid



cartilage  gel-like matrix
blood  fluid matrix
bone  crystalline solid
Matrix: ground substance



Fills the spaces between cells and fibers
Functions as a molecular sieve through which
nutrients diffuse between blood capillaries and cells
Composed of



interstitial fluid
Cell adhesion proteins: serve as glue for cells to attach to
matrix
Proteoglycans: consist of a protein core with
glycosaminoglycans (GAGs) such as chondroitin sulfate
and hyaluronic acid which trap water and determine the
consistency
Ground Substance:
Proteoglycan Structure
Figure 4.7
Matrix: Protein Fibers



Collagen – tough but inelastic; provides very
high tensile strength (greater than steel)
Elastic – long, thin fibers that allow for
stretch; composed of elastin which is similar
to collagen
Reticular – branched collagenous fibers that
form delicate networks, resist force in many
directions
Elastic fibers allow a tissue to
stretch
Cells





Fibroblasts – connective tissue proper
Chondroblasts – cartilage
Osteoblasts – bone
Hematopoietic stem cells – blood
White blood cells, plasma cells,
macrophages, and mast cells
Other CTP cell types
Melanocytes
 Adipocytes – fat cells; insulation, energy,

padding

Mesenchymal cells – stem cells; can
differentiate into other mesodermal cell types
Fibroblasts


Stationary in the tissue
Secrete the protein fibers and ground
substance found in the matrix
Classification of
Connective Tissues

Connective tissue proper:


Fluid connective tissues:


connect and protect
transport
Supporting connective tissues:

structural strength
Classification of connective
tissues
Connective tissue proper
(CTP)


Contains many types of cells and
extracellular fibers in a syrupy ground
substance
Look at the cell types and the number and
types of fibers to identify the type of tissue
Categories of
Connective Tissue Proper

Loose connective tissue:



more ground substance, less fibers
e.g., fat (adipose tissue)
Dense connective tissue:

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more fibers, less ground substance
e.g., tendons
CTP: 3 types of Loose
Connective Tissues Proper

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The “packing materials” of the body
Packing material, fills spaces
Contains mesenchyme cells – leftover from
development, can differentiate into many of
the other resident cell types
3 types in adults:



areolar
adipose
reticular
Connective Tissue: Embryonic

Mesenchyme – embryonic connective tissue

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
Gel-like ground substance with fibers and starshaped mesenchymal cells
Gives rise to all other connective tissues
Found in the embryo
Loose CTP #1: Areolar

Areolar connective tissue

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Least specialized, open framework
Viscous ground substance with all three
connective tissue fibers
Fibroblasts, macrophages, mast cells, and some
white blood cells
Wraps and cushions organs
Widely distributed throughout the body
Separates skin from deeper tissues
Holds blood vessels and capillary beds:
Areolar Connective Tissue
Model
Figure 4.8
Loose CTP #1: Areolar
Figure 4.9a
Loose CTP #2: Adipose

Adipose connective tissue

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Matrix similar to areolar connective tissue with
closely packed adipocytes
Reserves food stores, insulates against heat loss,
and supports and protects
Found under skin, around kidneys, within
abdomen, and in breasts
Local fat deposits serve nutrient needs of highly
active organs
Loose CTP #2: Adipose
Figure 4.9b
Loose CTP #2: Adipose

Contains many adipocytes (fat cells)
Figure 4–10a
Adipose Cells

Adipocytes in adults do not divide:



expand to store fat
shrink as fats are released
Mesenchymal cells divide and differentiate:


to produce more fat cells
when more storage is needed
Loose CTP #3: Reticular

Reticular connective tissue

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Loose ground substance with reticular fibers
Reticular cells lie in a fiber network
Forms a soft internal skeleton, or stroma, that
supports other cell types
Found in Reticular organs: lymph nodes, bone
marrow, liver, and the spleen
Loose CTP #3: Reticular
Figure 4.9c
Loose CTP #3: Reticular

Provides support
Figure 4–10b
CTP: 3 Types of Dense
Connective Tissues


Connective tissues proper
Tightly packed with high numbers of collagen
or elastic fibers:

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
dense regular connective tissue
dense irregular connective tissue
elastic tissue
Dense CTP #1: Dense Regular

Dense Regular Connective Tissue
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Parallel collagen fibers with a few elastic fibers
Major cell type is fibroblasts
Attaches muscles to bone or to other muscles,
and bone to bone
Found in tendons, ligaments, and aponeuroses
Dense CTP #1: Dense Regular
Figure 4.9d
Dense CT #1: Dense Regular


e.g. tendons, ligaments
Attachment and stabilization
Dense CTP #2: Dense Irregular
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Dense Irregular Connective Tissue
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Irregularly arranged collagen fibers with some
elastic fibers
Major cell type is fibroblasts
Withstands tension in many directions providing
structural strength
Found in the dermis, periosteum, perichondrium,
submucosa of the digestive tract, and fibrous
organ capsules
Dense CTP #2: Dense Irregular
Figure 4.9e
Dense CT #2: Dense Irregular
Dense CT #3: Elastic Tissue

Made of mostly elastic fibers (elastin):

e.g., elastic ligaments of spinal vertebrae
Figure 4–11c
Dense CT #3: Elastic Tissue
Fluid Connective Tissues
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Fluid connective tissues:
blood and lymph

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watery matrix of dissolved proteins
carry specific cell types (formed elements)
Fluid CT: Blood
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Formed elements
Formed elements are the cells plus the
platelets (which aren’t technically cells) =
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Red blood cells (erythrocytes) = majority
White blood cells (leukocytes)
Platelets
Connective Tissue: Blood
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Red and white cells in a fluid matrix (plasma)
Contained within blood vessels
Functions in the transport of respiratory
gases, nutrients, and wastes
Fluid Elements of Blood

Extracellular:
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Plasma – fluid portion of blood
Interstitial fluid – squeezed out of capillaries
Lymph – Int. fluid entering lymph vessels
Connective Tissue: Blood
Figure 4.9j
Flow of body fluids – A Cycle
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Plasma in blood (without formed elements)
squeezes out of capillaries due to blood
pressure and small spaces between some
epithelial cells
Now in tissue spaces it is called interstitial
fluid. Passively enters lymphatic system.
Now it is called lymph. Returns to blood
through subclavian veins then to heart
Cycle repeats
Supporting
Connective Tissues
Bone and Cartilage
What do supporting
connective tissues do?
Supportive Connective
Tissues
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Function: Support soft tissues and body
weight
Types:

cartilage:
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gel-type ground substance
for shock absorption and protection
bone:
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calcified (made rigid by calcium salts, minerals)
for weight support
Supporting CT #1: Cartilage
Matrix:
 Proteoglycans derived from chondroitin sulfates
(polysaccharide) makes it gel-like
 Different cartilage types derive their properties from
the number and type of proteoglycans and the
number and type of protein fibers
Cells:
 chondrocytes, surrounded by lacunae (chambers)
 chondroblasts (progenitor of chondrocytes)
Cartilage Structure

No blood vessels:
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chondrocytes produce antiangiogenesis factor
Perichondrium (a dense irregular CTP):
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outer, fibrous layer (for strength)
inner, cellular layer (for growth and maintenance)
Cartilage Growth - Interstitial

Interstitial growth (inside-out) by
chondrocytes
Figure 4–13a
Cartilage Growth - Appositional

Appositional growth (adding to the outside)
[Adults]
Figure 4–13b
The 3 Types of Cartilage

Hyaline (glass) cartilage:
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Elastic cartilage:
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most common
translucent matrix, packed collagen
no prominent fibers
joint perichondrium
tightly packed elastic fibers
Fibrocartilage:
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very dense collagen fibers
joint pads
Connective Tissue: Hyaline
Cartilage
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Amorphous, firm matrix with imperceptible
(clear) network of collagen fibers
Chondrocytes lie in lacunae
Supports, reinforces, cushions, and resists
compression
Forms the costal cartilage (ribs)
Found in embryonic skeleton, the ends of
long bones, nose, trachea, and larynx
Connective Tissue: Hyaline
Cartilage
Figure 4.9f
Hyaline Cartilage

Reduces friction in joints

Cover the end of long bones
Figure 4–14a
Connective Tissue: Elastic
Cartilage
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Similar to hyaline cartilage but with more
elastic fibers
Maintains shape and structure while allowing
flexibility
Supports external ear (pinna) and the
epiglottis
May be stacked up
Connective Tissue: Elastic
Cartilage
Figure 4.9g
Elastic Cartilage

Flexible support

found in external ear and epiglottis
Figure 4–14b
Connective Tissue:
Fibrocartilage
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
Matrix similar to hyaline cartilage but less firm
with thick collagen fibers
Provides tensile strength and absorbs
compression shock
Found in intervertebral discs, the pubic
symphysis, and in discs of the knee joint
Connective Tissue:
Fibrocartilage
Figure 4.9h
Fibrocartilage
Joints

Most joints have both hyaline cartilage and
fibrocartilage in them
Connective Tissue: Bone
(Osseous Tissue)
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Hard, calcified matrix with flexible collagen fibers
found in bone
Osteocytes are found in lacunae and are well
vascularized:
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arranged around central canals within matrix
small channels through matrix (canaliculi) access blood
supply (no diffusion through matrix)
Supports, protects, and provides levers for muscular
action
Stores calcium, minerals, and fat
Marrow inside bones is the site of hematopoiesis
Connective Tissue: Bone
Figure 4.9i
Bone

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Very little ground substance
matrix is 2/3 Calcium salts (phosphate,
carbonate), 1/3 collagen
Bone: what to look for
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Osteon (whole circular structure)
Concentric lamellae (of matrix)
Central canal (at center of lamellae)
Osteoblasts
Osteocytes in lacunae
Canaliculi – canals for diffusion
Close Up: ostocyte and
canaliculi

Cytoplasmic extensions
Bone growth
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Appositional only (outside)
Osteocytes secrete matrix fibers and calcium
salts, forms concentric rings
Comparing Cartilage
and Bone
Table 4–2
Nervous Tissue

Also called neural or nerve tissue:
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Branched neurons with long cellular processes
and support cells
specialized for conducting electrical impulses
rapidly senses internal or external environment
process information and controls responses
Found in the brain, spinal cord, and peripheral
nerves
Nervous Tissue
Figure 4.10
Muscle Tissue: Skeletal
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Long, cylindrical, multinucleate cells with
obvious striations
Initiates and controls voluntary movement
Found in skeletal muscles that attach to
bones or skin
3 Types of Muscle Tissue
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Skeletal muscle:
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Cardiac muscle:
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large body muscles responsible for movement
found only in the heart
Smooth muscle:

found in walls of hollow, contracting organs (blood
vessels; urinary bladder; respiratory, digestive and
reproductive tracts)
Muscle Tissue: Skeletal
Figure 4.11a
Muscle Tissue: Cardiac
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Branching, striated, uninucleate cells
interlocking at intercalated discs
Propels blood into the circulation
Found in the walls of the heart
Muscle Tissue: Cardiac
Figure 4.11b
Muscle Tissue: Smooth
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Sheets of spindle-shaped cells with central
nuclei that have no striations
Propels substances along internal
passageways (i.e., peristalsis)
Found in the walls of hollow organs
Muscle Tissue: Smooth
Figure 4.11c
Developmental Aspects

Primary germ layers: ectoderm, mesoderm,
and endoderm
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Three layers of cells formed early in embryonic
development
Specialize to form the four primary tissues
Nerve tissue arises from ectoderm
Developmental Aspects
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Muscle, connective tissue, endothelium, and
mesothelium arise from mesoderm
Most mucosae arise from endoderm
Epithelial tissues arise from all three germ
layers
Body Membranes

Membranes:



are physical barriers that line or cover portions of
the body
Consist of an epithelium
Always supported by connective tissues
4 Types of Membranes
1.
2.
3.
4.
Mucous
Serous
Cutaneous
Synovial
Figure 4–16
Mucous Membrane

Mucous membranes (mucosae):
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Epithelial surfaces must be moist:

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line passageways that have external connections:
digestive, respiratory, urinary, and reproductive
tracts
Goblet cells secrete mucins  mucus
to reduce friction
to facilitate absorption and excretion
Lamina propria:

is areolar tissue
Structure of Mucous
Membrane
Figure 4–16a
Serous Membranes

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Line cavities not open to the outside; sealed
internal subdivisions of ventral body cavity,
e.g. peritoneum
Are thin and transparent but strong
Have fluid transudate to reduce friction
Epithelial part = Mesothelium (simple
squamous)
Connective tissue part = areolar tissue
Structure of Serous Membrane
Figure 4–16b
Serous Membranes
Figure 4.12c
Double Membranes

Serous membranes:
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have a parietal (wall) portion covering the cavity
and a visceral portion (serosa) covering the
organs
Serous membranes:

consist of parietal layer and visceral layer
Cutaneous Membrane

Cutaneous membrane:
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
is skin, surface of the body
thick, waterproof, and dry
Made up of epidermis and dermis (papillary and
reticular layers). What types of tissues?
Structure of
Cutaneous Membrane
Figure 4–16c
Synovial Membranes

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Line articulating (moving) joint cavities
Produce synovial fluid (lubricant, nutrients to
chondrocytes of articular cartilage)
Protect the ends of bones (which themselves
are covered in what?)
Lack a true epithelium (incomplete, no basal
lamina)
Structure of Synovial
Membranes
Figure 4–16d
Summary: Inflammation
and Regeneration
Figure 4–20
Aging
Epithelia get thinner
 CT more fragile
So bruise easily, bones more brittle

Different PGs made by chondrocytes
Proteoglycans
Summary
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Connective tissues – structures and functions
CTP (loose, dense)
Fluid (blood, lymph)
Supporting (cartilage, bone)
Nervous tissue – brief overview
Muscle tissue overview (3 types)
Membranes (4 types)