Bone and cartilage
Bone
- There are two basic types of bone structure
- Compact bone
- Trabecular bone
Compact bone
- Compact bone is the hard material that makes up the shaft of long
bones and the outside surfaces of other bones
- Makes up 80% of total body mass
- It consists of cylindrical units called osteons (Haversian systems)
- Each osteon contains concentric lamellae of hard, calcified matrix
with osteocytes lodged in lacunae between the lamellae.
- Smaller canals, or canaliculi, radiate outward from a central canal
(Haversian canal)
- These contains blood vessels and nerve fibres
- Osteocytes within an osteon are connected to each other and to the
central canal by fine cellular extensions
- Through these cellular extensions, nutrients and wastes are
exchanged between the osteocytes and the blood vessels.
- Perforating canals (Volkmann's canals) provide channels that allow
the blood vessels that run through the central canals to connect to the
blood vessels in the periosteum that surrounds the bone
Trabecular bone
- Trabecular or spongy bone consists of thin, irregularly shaped
plates called trabeculae
- These are arranged in a latticework network
- Trabeculae are similar to osteons in that both have osteocytes in
lacunae that lie between calcified lamellae
- As in osteons, canaliculi present in trabeculae provide connections
between osteocytes
- Each trabecula is only a few cell layers think, each osteocyte is
able to exchange nutrients with nearby blood vessels
Microstructure of bone
- Osteoblasts secrete organic bone matrix (osteoid)
- The become osteocytes when surrounded by bone matrix
- Osteoclasts are multinucleate cells derived from monocytes
- They actively resorb bone
- Bone matrix has both organic and inorganic components
- The organic component is composed or type 1 collagen and
proteoglycans
- The inorganic matric is mainly calcium and phosphate salts
- Periosteum covers bones and contains blood vessels, nerves and
lymphatics
- Its inner surface is osteogenic and contains osteoblasts and
osteoclasts
Ossification
- Bone undergoes either intramembranous or endochondral ossification
- Both result in the same microstructure
- Intramembranous ossification is directly from mesenchyme
- Occurs in flat bones such as the skull
- Endochondral ossification is the development of bone through an
intermediate cartilage stage
- Occurs in long bone
Function of bone
- Calcium homeostasis
- Haemopoiesis
- Structure and protection of internal organs
- Movement
Cartilage
Structure
- Matrix makes up over 80% of cartilage
- Primarily made of proteoglycans, type 1 and 2 cartilage and elastin
- These are large molecules with a protein back-bone and
glycosaminoglycan side chains
- Chondrocytes are mature cartilage cells
- Scattered through out cartilage matrix
Types of cartilage
- Hyaline cartilage is made up of mainly type 2 collagen
- Functions as articular cartilage in synovial joints
- Also is centre for ossification in growing bone
- Elastic cartilage is similar to hyaline cartilage
- Contains more elastin bundles
- Is found in the pinna, Eustachian tube and epiglottis
- Fibrocartilage is a tougher form of cartilage
- Found in intervertebral discs and symphyses
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