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Connective tissue, Cartilage and Bone

This lecture explains the general concepts of connective tissue, cartilage and bone, along with their composition and types.

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Images of Compact bone
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Outline of Lecture


Is a specialised type of connective tissue.

Consists of cells and extracellular components.

Does not contain vessels or nerves.

Is surrounded by a layer of dense connective tissue, the perichondrium



More prevalent than in adult

Skeleton initially mostly cartilage

Bone replaces cartilage in fetal and childhood periods

Location of cartilage in adults

External ear


“Articular” – covering the ends of most bones and movable joints

“Costal” – connecting ribs to sternum

Larynx – voice box

Epiglottis – flap keeping food out of lungs

Cartilaginous rings holding open the air tubes of the respiratory system (trachea and bronchi)

Intervertebral discs

Pubic symphysis

Articular discs such as meniscus in knee joint

Types of cartilage

Hyaline cartilage

Elastic cartilage

Fibrous cartilage

Functions of Cartilage Tissue

Firm consistency of the extracellular matrix allows the tissue to bear mechanical stresses without permanent distortion

Supports soft tissues.

Shock-absorbing because it is resilient.

Smooth surface allows sliding .

Essential for growth, development of bone.



Located in lacunae

Extensive extra-cellular matrix

Fibers, Collagen, &elastic

Ground substance

Fibers bind together and give firm, flexible properties to tissue

Chondrocytes are mature cells found in cartilage.

These cells make up the cellular matrix of cartilage, performing a number of functions within the cartilage, including facilitating the exchange of fluids through the gelatinous layers which make up cartilage.

The progenitors of chondrocytes arise in the bone marrow, in a form of stem cell..

When they differentiate into cartilage cells, they start out as chondroblasts, actively producing secretions of chondrin, the primary substance in cartilage, to build and repair cartilage.

Once a chondroblast becomes totally surrounded, it is a mature chondrocyte.

Chondrocytes can be found in small gaps within the cartilage known as lacunae. Chondrocytes are not capable of cell division.


Produce and maintain extra cellular  matrix.

Either single or in isogenous groups .

Fat droplets, glycogen granules are found in cytoplasm.

Active  ones are more basophilic.

Cartilage matrix

Contain high concentration of bound sulfate So stains with basic dyes.

Rich in water(70-80%)

Three classes of molecules are present; Collagen, Proteoglycans and Multi adhesive glycoproteins.


Large proteoglycan molecule

Protein core Glycosaminoglycans (chondroitin4-sulfate and chondroitin 6-sulfate) attach to protein cores

100 to 200 aggrecan molecules linked non-covalently to hyaluronic acid


Dense CT that covers cartilage

Contains blood, nerve supply, lymphatics.

Source of new cartilage cells

Divided into two layers

Inner cellular

Outer fibrous

Hyaline Cartilage

Extra cellular matrix

The matrix near the isogenous groups of chondrocytes is termed territorial matrix or capsule. In H&E stained sections the territorial matrix is more basophilic, i.e. it stains darker.

The remainder of the matrix is called the interterritorial matrix.

Articular Cartilage

Hyaline cartilage of  articular surfaces do not posses a perichondrium


Similar to hyaline cartilage but has elastic fibers running in all directions in addition to collagen.(resorcin stain)

Found in auricle of ear, walls of external auditory canals, eustachian tubes, epiglottis, larynx

Maintains shape, deforms but returns to shape; flexibility of organ; strengths and supports structures.



Chondrocytes may lie singly or in pairs, but most often they form short rows between dense bundles of collagen fibres. In contrast to other cartilage types

 It is difficult to define the perichondrium because of the fibrous appearance of the cartilage and the gradual transition to surrounding tissue types.

 Types of cartilage: 3

Hyaline cartilage: flexible and resilient

Chondrocytes appear spherical

Lacuna – cavity in matrix holding chondrocyte

Collagen the only fiber

 Elastic cartilage: highly bendable

Matrix with elastic as well as collagen fibers

Epiglottis, larynx and outer ear


Fibrocartilage: resists compression and tension

Rows of thick collagen fibers alternating with rows of chondrocytes (in matrix)

Knee menisci and annunulus fibrosis of intervertebral discs



Growth of Cartilage

Growth is attributable to two processes:

Interstitial growth

Mitotic division of preexisting chrondrocytes

Synthesis of matrix

Expands cartilage matrix from within

Occurs in epiphyseal plates, articular cartilage

Appositional growth

Differentiation of perichondrial cells ®    chondroblasts

Synthesis of matrix

Increase in girth


Epiphyseal Plate (Interstitial Growth)

Appositional Growth

Repair of hyaline cartilage

Can tolerate considerable amount of stress

Limited ability to repair Because of

1. Immobility of chodrocytes

2. Less ability of chodrocytes to proliferate

3. Avascularity

4. When hyaline cartilage calcifies it is replaced by bone

Anatomy of a Long Bone


Bone is a specialized connective tissue characterized by mineralized extracellular matrix.

Bones are the organs of skeletal system; bone tissue is the structural component of bones.


Bone Matrix

35% collagen – organic

Some chondroitin sulfate, hyaluronic acid and polysaccharides

65% calcium phosphate minerals – hydroxyapetite  -inorganic


Combination provides strength and rigidity

Laid down by osteoblasts


Long cylinder parallel to long axis of diaphysis

Consists of:

Haversian canal with nerves, blood vessels; lamellae with osteocytes

Haversian canals communicate with marrow cavity, periosteum, other canals through Volkmann’s canals


90% Collagen fibers

Type 1, Type 3, Type 5, Type11, Type13

10% non collagenous protein

1. Proteoglycans

2. Multiadhesive glycopoteins

3. Bone specific vitamin k dependent proteins

4. Growth factors and cytokines



1. Osteocytes


3. Bone-lining cells

4 Osteoclasts

Osteoprogenitor cells

Located in the periosteum and endosteum. They are very difficult to distinguish from the surrounding connective tissue cells.


Osteoblasts may form a low columnar “epitheloid layer” at sites of bone deposition. They contain plenty of rough endoplasmatic reticulum (collagen synthesis) and a large Golgi apparatus


Osteocytes. Mature bone cells.


Surrounded by matrix,

can make small amounts of matrix to maintain it.


Lacunae: spaces occupied by osteocyte cell body

Canaliculi: canals occupied by osteocyte cell processes

Nutrients diffuse through tiny amount of liquid surrounding cell and filling lacunae and canaliculi. Then can transfer nutrients from one cell to the next through gap junctions.


Canaliculi between Osteocytes

States of osteocytes

Quiescent osteocytes

Paucity of rER & decrease golgi apparatus

Formative osteocytes

More abundant rER& golgi apparatus

Resorptive osteocytes

Abundant Rer, golgi apparatus and lysosomes


Bone lining cells

On external surface are called periosteal cells

Oninternal surface are called endosteal cells

Mantainance and nutritional support of osteocytes



Large multi-nucleated bone-resorbing cells.. Osteoclasts attach themselves to the bone matrix (howships lacunae) and form a tight seal at the rim of the attachment site.

Osteoclasts are stimulated by parathyroid hormone and inhibited by calcitonin

The cell membrane opposite the matrix has deep invaginations forming a ruffled border. Osteoclasts empty the contents of lysosomes into the extracellular space between the ruffled border and the bone matrix. The released enzymes break down the collagen fibres of the matrix.

Classification of bones

Compact Bone

Cancellous (Spongy) Bone



Bone is, again like cartilage, surrounded by a layer of dense connective tissue, the periosteum. A thin layer of cell-rich connective tissue, the endosteum, lines the surface of the bone facing the marrow cavity. Both the periosteum and the endosteum possess osteogenic potency.


Compact Bone

Central or Haversian canals: parallel to long axis

Lamellae: concentric, circumferential, interstitial

Osteon or Haversian system: central canal, contents, associated concentric lamellae and osteocytes

Osteons (Haversian systems)
Blood vessel-filled central canal (Haversian canal)

Concentric lamellae of bone surround central canal

Lacunae and canaliculi contain osteocytes and fluid

Perforating or Volkmann’s canal

perpendicular to long axis. Both perforating and central canals contain blood vessels. Direct flow of nutrients from vessels through cell processes of osteoblasts and from one cell to the next.

Circumferential lamellae on the periphery of a bone

Interstitial lamellae between osteons


Circulation in Bone
 Blood vessels from periosteum penetrate bone

Vessels of the central canal

Nutrients and wastes travel to and from osteocytes via

Interstitial fluid of lacunae and canaliculi

From osteocyte to osteocyte by gap junctions

Cancellous (Spongy) Bone

Trabeculae: interconnecting rods or plates of bone.  Like scaffolding.

Spaces filled with marrow.

Covered with endosteum.

Oriented along stress lines






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