What are the two types of bone?
Spongy bone and compact bone
Spongy (cancellous) bone?
- Found in the interior medullary cavity of long and other bones where it forms a network of trabeculae between the marrow
Compact bone?
- Dense and hard
- Forms the shaft of the long bones
- Composed of Haversian systems/canals, which contain blood vessels that branch through the bone
What is the skeleton in the Vertebrates composed of?
Bone and cartilage
What do bone and cartilage provide for the body?
Mechanical support
What surrounds the Haversian canal?
Lacunae which contain osteocytes
What are the lacunae connected by and what is the purpose of it?
- Connected by the radiating canaliculi
- These allow the supply of nutrients to the osteocytes
- Radiate from the central canal outwards towards the outside of the system
What are osteoclasts?
- Bone cells
- Break down bone
- Present in small numbers
What are osteoblasts?
- Create new bone
What makes the bone so compact and strong?
- There are a lot of calcium phosphate deposits in the matrix between the lacunae in the form of calcium hydroxyapatite.
- These crystals are secreted by the osteocytes, and therefore they give the bone it’s mineral compact matrix
- There are also secretions of proteins and collagen fibres that run throughout the compact bone, between the individual osteocytes, between the lacunae, and it is mineralised to give it the strength that it has
What is bone remodelling?
- The lifelong cycle of bone maintenance (repair) and restoration
- Osteoclasts and osteoblasts working together to maintain bones throughout your life
Bone modelling?
During development of the skeleton bone, growth occurs independent of osteoclasts (only osteoblasts in very early fetal development)
Periosteum?
- Membraneous bone covering (connective tissue layer)
- Contains progenitor cells, which can differentiate into osteoblasts for healing and repair
- The periosteum repairs the bone using progenitor cells
- Periosteal damage impairs bone healing
What is cartilage?
- Semi-rigid form of supporting structure, largely made up of an extracellular ground substance of proteoglycan aggregates (Chondroitin)
- Not as strong as bone matrix
- Can either be mostly made up of elastic fibres or collagen
Hyaline cartilage?
- Most common form of cartilage (eg in the trachea)
What are the spaces in cartilage called?
- Lacunae, which contain Chondryocytes that secrete the ground substances (elastic fibres/collagen/proteoglycan)
Are there any blood vessels in cartilage?
No
Is cartilage more flexible than bone?
Yes, but it confers insufficient rigidity to withstand gravity (would not be able to support out body)
What are the two types of skeleton?
Dermal and endoskeleton
How does the dermal skeleton develop differently than the endoskeleton, and what is the process called?
In dermal bones osteoblasts from the periosteum convert foetal connective tissue to bone. This is called intarmembranous ossification
Where are dermal bones found?
- Skull
- Jaw
- Pectoral girdle
What is endochondral ossification?
The process by which growing cartilage is systematically replaced by bone to form the growing skeleton:
- Foetal cartilage models the shape of the future adult bone
- This may persist for months/years before being invaded by osteoblasts for conversion to bone
- Epiphyses are the last parts of long bone to ossify
- Until ossification is complete, the epiphyses remains separate from the shaft (diaphysis) by the epiphyseal plate which is made of hyaline cartilage
- Then the epiphyses gets fused with the diaphysis and the bone is complete
What are epiphyses?
- The ends of bone
- Last parts of long bone to ossify
Where does bone ossification begin?
The diaphysis
