Session3
Dr. Maria Zahiri
Lecture outline
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Overview ( special connective tissue)
Cartilage:
morphology
Type
Histogenesis
Bone:
morphology
Type
Histogenesis
Cartilage
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Cartilage:
is a flexible connective tissue in animals, including
the joints between bones, the rib cage, the ear, the nose, the bronchial
tubes and the intervertebral discs.
It is not as hard and rigid as bone, but it is stiffer and less flexible
than muscle.
 Important for:
- support to softer tissues
- formation and growth of long bones
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Because of its rigidity, cartilage often serves the purpose of holding tubes
open in an animal's body.
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Example:
rings of the trachea, such as the cricoid cartilage and carina
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cartilage
Consists of:
 Cells
 ECM
- collagen and/or elastin fibers
- proteoglycans
- water
CELLS:
CHONDROBLAST
 Progenitor of chondrocytes
 Lines border between
perichondrium and matrix
 Secretes type II collagen and other
ECM components
Chondrocytes
 Chondrocytes are chondroblasts which
are surrounded by matrix and are
quiescent
 They produce and maintain the
cartilaginous matrix, which consists
mainly of collagen and proteoglycans.
 Mature cartilage cell
 Reside in a space called the lacuna
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ECM:
Collagen provides tensile strength and durability
For example, if you inject papain (an enzyme that digests the protein cores of
proteoglycans) into the ears of a rabbit, after a few hours the ears will loose their
stiffness and droop.
The combined properties of collagens and aggrecan in articular
cartilage
MORE FEATURES OF CARTILAGE
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Cartilage is an avascular tissue and relies on diffusion of nutrients and
waste through the matrix
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The vasculature located in adjacent perichondrium and in absence of
perichondrium, synovial fluid nurishes the cartilage
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Cartilage has no innervation, and no lymphatic vessels
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Chondrocytes have low metabolic activity
Perichondrium
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Perichondrium is a vascular sheath of dense irregular connective
tissue surrounding cartilage (type I collagen)
perichondrium
perichondrium has 2 layer:
• inner cellular layer
• outer fibrous layer
The cellular layer of the perichondrium contains chondrogenic cells that undergo division
and differentiate into chondroblasts
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In embryo it serves as skeleton until replacement by bones, and form
template for many bones
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It is also exist in epiphyseal plate, nose, bronchi, ends of ribs adjacent to
sternum
MORE FEATURES OF HYALLIN CARTILAGE
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Cells:
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Outer chondrocytes are elliptical with long axis parallel to surface
Deeper ones are round, may be in groups of up to 8 - isogenous group
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Isogenous groups of chondrocytes:
are the result of mitotic divisions of the cells during interstitial growth,
several chondrocytes occupy a single lacuna.
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In epiphyseal plate chondrocytes located in rows
They are often shrunken in histological sections
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Amorphous ground substance
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Territorial matrix:
adjacent to chondrocytes stains darker than non-territorial matrix,
because matrix around lacuna is poor in collagen but rich in
chondroitin sulfate
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Interterritorial matrix:
which is the bulk of cartilage is richer in type II collage
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Pericellular capsule:
just around the lacuna is made of fine meshwork of collagen fibers
and basal lamina like substances which protects the chondrocytes
from mechanical stress
Matrix of Hyaline Cartilage
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Fiber:
collagen type II , IX, X, and XI
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Proteoglycan:
Aggrecan
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GAGs of Aggrecan is chondroitin 4-sulfate, chondroitin 6-sulfate, and
heparan sulfate
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Glycoprotein: Chondronectin
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water
Cartilage Growth
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Interstitial growth:
Existing chondrocytes
mitotic division
Isogenous groups
(enlarging cartilage from within)
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Appositional growth:
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Chondrogenic cells
(from inner layer of perichondrium)
differentiation
new chondroblasts
(That adding matrix to periphery of cartilage)
MORE FEATURES OF ELASTIC CARTILAGE
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It is similar to hyaline cartilage, but with many branching elastic fibers
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Yellow in colour
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Chondrocytes are more abundant and larger but matrix is less than hyaline
cartilage
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Perichondrium is also rich in elastic fibers
Fibrocartilage
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Usually merges with adjacent dense connective tissue
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Chondrocytes in rows or groups with thick bundles of collagen between them
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matrix is scant (rich in chondroitin and dermatan sulfate), and exhibit bundles
of type I collagen which stain acidophilic
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It has no perichondrium
Intervertebral Disks
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It is located between vertebrae
 Each disk has two components;
Nucleus pulposus and Annulus fibrosus)
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Nucleus pulposus: is a gel-like matrix rich in hyaluronic acid and cells
Annulus fibrosus: is made of fibrocartilage in overlapping layers
Herniation : results from rupture of annulus fibrosus and expulsion of nucleus pulposus
which can compress spinal cord or nerves
Bone
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Bone is a specialized connective tissue of:
 calcified bone matrix
 3 cell types:
 Osteocytes that are located in lacunae
 Osteoblasts that make new matrix and maintain old matrix
 Osteoclasts are multinucleated giant cells that phagocytose bone
matrix in remodeling bone
Osteoblasts
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Synthesize and maintain matrix (collagen, proteoglycans, and glycoproteins)
bone forming cells
typically rounded or cuboidal in shape
Osteoblasts are basophilic as a result of abundance of rough endoplasmic
reticulum
Become osteocyte when surrounded by matrix
Osteoid is newly made uncalcified matrix that separates osteoblasts and
osteocytes from the calcified matrix
Osteocyte
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mature bone cells
are connect to other osteocytes by long processes via gap
junctions
Narrow canaliculi house cytoplasmic processes of osteocytes
Canaliculi also contain extracellular fluid that carrying
nutrients and metabolites
Osteocytes maintain bone matrix
Osteocyte
Osteoclasts
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Large, multinucleated, and motile cells
responsible for resorbing bone
Their precursor located in bone marrow in common with monocytes
Acidophilic cytoplasm, many lysosomes, many mitochondria
Secrete organic acids, collagenase and other proteases that break down the
matrix
Osteoclasts
They occupy shallow depressions that is called resorption bay (Howship’s
lacunae)
ruffled membrane: The region of the osteoclastic cytoplasm adjacent to the
bone matrix which is being resorbed
This is an area of numerous microvilli closely applied to the bone that is
being hydrolyzed by the enzymes secreted by the osteoclast
CO2+H2O
H2CO3
H⁺+ HCO3⁻
Bone Matrix
Inorganic part
calcium and phosphate (Hydroxy apatite
crystals [Ca10(Po4)6(OH)2])
Organic part
Fiber: type I collagen bundles
Glycoproteins: (Osteonectin, osteopontin)
Proteoglycans: keratan sulfate and
chondroitin sulfate bind to hyaluronic acid
and form aggrecan composites
Bone sialoprotein is another matrix protein
that has binding site for integrins of bone
cells and matrix components
Periosteum
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dense irregular connective tissue that covers outer surface of bone
Sharpey’s fiber inserting periosteum to the bone
Outer fibrous layer:
contains collagen bundles and fibroblasts of periosteum,
distribute blood vessels and nerves to bone
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Inner cellular layer:
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has osteoprogenitor cells and osteoblasts
Osteoprogenitor cells can form new osteoblasts
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Endosteum
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lines all internal bone surfaces
It is a specialised thin connective tissue composed a single layer of
osteoblasts, osteoclasts, and osteoprogenitor cells
Types of Bone
There is two different kind of mature bone
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Compact bone (no cavities)
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Cancellous (spongy bone)
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Long bones
have ends (epiphyses) of spongy bone
covered by a thin layer of compact
bone;
shaft (diaphysis) is mostly compact bone
with small amount of spongy bone
around marrow cavity
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Short bones have core of spongy
bone surrounded by compact bone
Spongy bone
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Spongy bone is composed of branching bone trabeculae and spicules
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Spongy bone is lamellar but there is not any haversian system
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It is extended from inner circumferential system of compact bone into
marrow cavity
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Lamellae are arranged in irregular manner
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Spaces between lamellae contain bone marrow
bone marrow
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Red bone marrow:
where active hemopoiesis is taking place
contains stem cells
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Yellow bone marrow:
is inactive in hemopoiesis but acts as a reserve tissue
It contains many unilocular adipocytes
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