Specialized Connective Tissue: Bone Flashcards
What is the difference between bone and bone tissue?
What is ECM? (2)
- ECM is mineralized by calcium phosphate in the form of hydroxyapatite crystals
- Serves as a storage site for calcium and phosphate and plays a role in homeostasis of blood
calcium levels
What fibres are present in ECM?
o Mostly type 1 collagen (all collagen in the bone constitutes 90% of bone matrix protein mass)
What are the Ground substance proteins? (5)
- Proteoglycans
- GAGs
- Multi-adhesive glycoproteins
- Bone-specific vitamin K-dependent proteins
- Growth factors and cytokines
- Matrix contains _____ containing an osteocyte
- Osteocytes extend processes into small tunnels called ______
- Canaliculi connect adjacent lacunae and allow for communication between _______
lacunae
canaliculi
osteocytes
Osteoprogenitor cells:
Description
Location
Function
Osteoblasts:
Description
Location
Function
Osteocytes:
Description
Location
Function
Bone-lining cells:
Description
Location
Function
Osteoclasts:
Description
Location
Function
What is Periosteum? (2)
- Sheath of dense fibrous connective tissue containing osteoprogenitor cells
- Absent on articular surfaces
What are the 2 layers of the Periosteum?
o Outer fibrous layer resembling dense connective tissue
o Inner cellular layer containing osteoprogenitor cells
* If active bone formation is not in progress, the inner layer is not well defined
* Collagen fibers of periosteum are arranged parallel to the surface of the bone
What is the Endosteum?
- layer of connective tissue cells that contains osteoprogenitor cells
What is mature bone? (3)
- Composed of structural units called osteons (Haversian systems)
- Consists of concentric lamellae of bone matrix surrounding a central canal (Haversian canal)
- Haversian canal consists of the nerve and vascular supply of the osteon
What are Canaliculi? (2)
o Contain the osteocyte processes are arranged in a radial pattern relative to the Haversian canal
o Serves for the passage of substances between the
osteocytes and blood vessels
* Interstitial lamellae- concentric around osteons
* Circumferential lamellae- follow the circumference of the shaft of the bone
What is Volkmann’s canal? (2)
o Channels which allow vessels and nerves to travel from periosteal and endosteal surfaces to the Haversian canals
o No concentric lamellae around the canal
What are the features of mature spongy bone? (3)
o Tissue arranged in trabeculae
o Matrix of the bone is lamellated
o No Haversian systems
What is immature (foetal) bone? (3)
- Lack of organized lamellar appearance
- More cells per unit area than mature bone that are randomly arranged
- Has more ground substance and is not heavily mineralized
How is bone formed? (3)
- Bone is formed by differentiation of mesenchymal cells into osteoblasts
- Occurs in flat bones, mandible and clavicle
- Occurs around 8th week of gestation
What is the process of Intramembranous Ossification? (11)
- Mesenchymal cells aggregate
- Blood vessels form and invade the mesenchymal cells —> primary ossification centre
- The cells increase in size and become rounder- osteoprogenitor cells
- Osteoprogenitor cells differentiate into osteoblasts
- Osteoblasts secrete bone matrix which forms the osteoid
- Osteoid is mineralized and trapped osteoblasts become osteocytes
- Initially, only a spicule is formed
- Osteoblasts lay down new osteoid on the spicule which later mineralizes to form bone
- Spicules grow by appositional growth around embryonic blood vessels randomly ® woven bone
- Vascularized mesenchyme condenses on the external surface of the woven bone ® periosteum
- Trabeculae just deep to the periosteum thicken and are later replaced by mature lamellar bone
What is the process of Endochondral Ossification? (9)
- Cartilage forms in the shape of the bone and the model grows in length by interstitial growth and
in width by appositional growth. - The perichondral cells in the mid-region of the cartilage model stop giving rise to chondrocytes
and osteoblasts are produced. The non-functional perichondrium is now the periosteum and a
cuff of bone is produced around the mid-region - Chondrocytes in the mid-region enlarge and become hypertrophic as the matrix calcifies
- Calcification inhibits nutrient diffusion causing the chondrocytes to die leaving lacunae empty. Lacunae fuse to form cavities
- Blood vessels grow through the thin bony collar to vascularize the cavity and mesenchymal stem
cells migrate into the cavity and differentiate into osteoprogenitor cells - When the osteoprogenitor cells come into contact with remaining calcified cartilage spicules they
become osteoblasts - Osteoblasts create osteoid ® primary ossification centre
- Cartilage near each epiphysis is replaced by shafts of bone
- Blood vessels invade the epiphyses and osteoblasts form secondary ossification centres
What is the general growth process of Endochondral Bone? (3)
- Growth in length of long bones depends on the presence of epiphyseal cartilage
- As the diaphyseal marrow cavity enlarges, a distinct zonation can be seen in the cartilage on both
ends of the cavity - The avascular cartilage is gradually replaced by vascularized bone
What are the zones of Endochondral Bone? (5)
- Zone of reserve cartilage
- Zone of proliferation
- Zone of hypertrophy
- Zone of calcified cartilage
- Zone of resorption
What is the Zone of reserve cartilage?
o Exhibits no cellular proliferation or active matrix production
What is the Zone of proliferation? (3)
o Cartilage cells undergo division and organise into distinct columns
o These cells are larger than those in the previous zone
o Actively produce collagen and other matrix proteins
What is the Zone of hypertrophy? (4)
o Greatly enlarged cartilage cells
o Clear cytoplasm shows presence of glycogen
o Metabolically active- secrete type I and X collagen, and VEGF (vascular endochondral growth
factor)
o Matrix is compressed to form linear bands between columns of hypertrophied cells
What is the Zone of calcified cartilage? (2)
o Hypertrophied cells begin to degenerate and die
o Matrix becomes calcified
What is the Zone of resorption? (4)
o Calcified cartilage is in direct contact with the connective tissue of marrow cavity
o Blood vessels invade the region occupied by dying chondrocytes
o Forms a series of spearheads, leaving the calcified cartilage as longitudinal spicules
o Invading blood vessels are the source of osteoprogenitor cells which differentiate to form
osteoblasts
