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Flashcards in Bone Deck (29)
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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
Clot forms
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


What are the osteoporosis risk factors?

Genetic, insufficient calcium intake and absorption of calcium and vitamin D, Exercise and cigarettes