Flashcards in Bone Deck (29)
Where does intramembranous ossification take place?
within condensations of meenchymal tissue- tissue that can differentiate into many types of cells
What kind of bones develop by intramembranous ossification?
Flat bones e.g. skull, clavicle, scapula and pelvic bone
What else does intramembranous ossification do?
Thickens long bones
What are the stages of intramembranous ossification?
1. Small cluster of mesenchymal stem cells form a tight cluster of cells (nidus)
2. MSCs become osteoprogenitor cells (more golgi and RER)
3. Osteoprogenitor cells become osteoblasts
4. Osteoblasts lay down extracellular matrix containing type I collagen (osteoid)
5. Osteoid mineralises to form bone tissue spicules, surrounded by osteoblasts, contain osteocytes
6. Spicules form trabeculae which form woven bone and is replaced by lamellae of mature compact bone
What is the difference between bone from intramembranous ossification and bone from endochondral ossification?
Intramembranous contains osteocytes, osteons, Haversians and Volkmanns canals
What is cancellous bone?
Spongy, network of fine bony columns, spaces filled with bone marrow
What is compact bone?
External surface of bones- 80% of skeletal mass
What do haversian and Volksmann canals do?
Carry blood vessels, lymph vessels and nerves
What is the difference between immature and mature bone?
Immature has osteocytes randomly arranged
matures osteoctes are arranged in concentric lamellae of osseous
Reabsoprtion canals in mature bone run parallel with osteon long axes
What are canaliculi?
Tiny interconnecting tunnels
What are gap junctions used for?
so nutrients can be passed between osteocytes
What is the trabeculae?
The bone part of cancellous bone, same as compact bone without haversian and volkmanns canals
How is cancellous bone remodelled?
A cutting cone contains Osteoclasts which release H+ and lysosomal enzymes and creates a tunnel
What can osteons do?
Branch and terminate
What are bones made up of?
Mineral, collagen, water, non-collagen proteins
How does a bone resist fracture?
Great tensile and compressive strength and a degree of flexibility, lamellae can slip relative to each other
How is a fracture repaired? (overview)
1. Haemotoma (blood clot) is formed and granular tissue arises
2. Procallus of granular tissue is replaced by a fibrocartilaginous callus where bony trabeculae are developing
3. Endochondral and Intermembranous ossification form bony callus of cancellous bone
4. Cancellous bone is replaced by compact cortical bone until remodelling is complete
How does a haemotoma form?
Blood vessels break
Bone cells at fracture edge die
Swelling and inflammation occur
Phagocytic cells and osteoclasts remove dead and damaged cells
Macrophages will eventually remove the blood clot
How does a fibrocartilage callus form?
New blood vessels infiltrate the haemotoma
A procallus of granulation tissue develops (rich in capillaries and fibroblasts)
Fibroblasts produce collagen fibres that span the break
Chondroblasts give rise to hyaline cartilage
This matrix splints the broken bone
Osteoblasts invade and begin to reconstruct the bone- cancellous
How does a Bony callus form?
New bone trabeculae appear within a week
Fibrocartilage callus develops into hard bony callus
Endochrondral ossification replaces all cartilage with cancellous bone and intramembrous ossification produces new cancellous bone in the area
How does the bone remodel?
Callus of spongy, cancellous bone begins to rmodel into compact bone as soon as it is formed
Continues for several months
Osteoclasts remove bulging material
Same shape as before as responds to same mechanical stressors
What do bone banks do?
Supply viable bone for grafting purposes
What is an autograft?
Donor is the recipient
What is a homograft?
Donor is a different human
What is a heterograft?
Donor is a different species
What is Osteoporosis?
Metabolic bone disease where mineralised bone is decreased in mass so no longer support
What causes Osteoporosis?
Incomplete filling of osteoclast resportion bays
What is primary osteoporosis?
Type I- menopausal women, increase in osteoclasts due to oestrogen withdrawal
Type II- elderly people, decrease in osteoblast function