CARTILAGE
CARTILAGE
Cartilage is a form of connective tissue composed of
cells called chondrocytes and a highly specialized
extracellular matrix.
Types of CARTILAGE:
• HYALINE CARTILAGE is characterized by a
homogeneous amorphous matrix
• ELASTIC CARTILAGE, whose matrix contains elastic
fibers and elastic lamellae
• FIBROCARTILAGE, whose matrix contains large
bundles of type 1 collagen
STRUCTURAL PLAN OF CARTILAGE
PERICHONDRIUM
• outer fibrous layer
• inner cell layer (chondrogenic cells + chondroblasts)
CHONDROCYTES (isogenous groups of cells located in
lacunas) with integrin (anchoring glycoprotein of plasma
membrane)
CARTILAGE MATRIX
• type II collagen fibers or elastic fibers
• ground substance consisting
- aggrecan (proteoglycan rich in hyaluronic acid +
chondroitin sulfate + keratan sulfate)
- chondronectin (anchoring glycoprotein)
LOCALIZATION OF DIFFERENT KINDS OF
CARTILAGE
• HYALINE CARTILAGE is found as the structural
framework for the larynx, trachea and bronchi; on
the anterior ends of the ribs; on the surfaces of
synovial joints. Hyaline cartilage constitutes much
of the fetal skeleton.
• ELASTIC CARTILAGE is found in the auricle of
the external ear, in the auditory tube, in the
epiglottis, and in part of the larynx.
• FIBROCARTILAGE is found at the intervertebral
discs, the symphysis pubis , and some joints.
BONE
BONES AND BONE (OSSEOUS) TISSUE
Bone is a type of connective tissue characterized by a highly
mineralized extracellular matrix (65% of calcium
hydroxyapatite crystals) + 35% of type I collagen fibers.
Non-calcified intercellular substance is called Osteoid
• Bone tissue is CLASSIFIED as:
- Primary (Woven) bone
- Secondary (Lamellar) bone
- Compact (Dense) bone
- Spongy (Cancellous) bone
• Bones are covered by Periosteum: a sheath of dense
connective tissue
• Bone cavities are lined by Endosteum: a delicate layer of
connective tissue cells and fibers
CELLS OF BONE TISSUE
• Osteoprogenitor cell is a resting cell that can
transform into an osteoblast
• Osteoblast is the differentiated bone-forming cell
that secretes bone matrix
• Osteocyte, the mature bone cell, residing in lacuna,
is enclosed by bone matrix that is previously
secreted by an osteoblast
• Osteoclast is a large multinucleated cell whose
function is resorption of bone
Light micrograph of intramembranous
ossification with different cell types
EM of bone-forming cells
Osteoclast structure and function (scheme)
STRUCTURE OF ADULT LONG BONE
Anatomy: Diaphysis + 2 Epiphyses + 2 Metaphyses
Units of diaphyseal bone structure are called OSTEONS.
Each osteon includes:
- concentric lamellae – collagen fibers arranged in
parallel manner
- Haversian canal with blood vessel, osteoblasts and
osteoprogenitor cells inside
- osteocytes located in lacunas forvarding their
processes into the bony canaliculi
Besides osteons diaphysis consists of:
• Interstitial lamellae
• Circumferential lamellae
• Perforating (Volkmann’s) canals
• Periosteum
• Endosteum
Primary (intramembranous) bone formation
STAGES OF ENDOCHONDRAL OSSIFICATION
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Formation of a hyaline cartilage template (model)
Appearance of a bony collar around the cartilage model
Calcification of cartilage matrix
Migration of periosteal cells into the cavity with growing
blood vessels
Structure of epiphyseal cartilage throughout the
growth period:
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Zone of reserve cartilage
Zone of proliferation
Zone of maturation and hypertrophy
Zone of cartilage calcification
Zone of ossification (cartilage resorption)
Anatomy of diarthrodial joint
Events in bone fracture repair