1.95 Structure of Bone

Question 1

What is the function of the Haversion system?

Answer 1

Functions in movement, support, protection, mineral storage

Question 2

Where does Haversion system derive from?

Answer 2

Mesenchyme

Question 3

What is the Haversion system?

Answer 3

Mineralised matrix containing crystals of hydroxyapatite Ca10(PO4)6(OH)2

Question 4

What makes up the inner and outer part of the bone?

Answer 4

Dense outer cortex of compact cortical bone

Inner cavity meshwork of trabecular/spongy bone with spaces between are occupied by marrow

Question 5

Which vessels enter the femur?

Answer 5

Blood vessels - circumflex and acetabulum branch of obturator archery enter this bone

Question 6

What is the periosteum?

Answer 6

Periosteum - the muscle tendons directly insert into it and are continuous with it

Question 7

What are the two phases of bone development?

Answer 7

Woven and Lamellar bone

Question 8

What is woven bone?

Answer 8

Immature
Irregular
Collagen fibrils
Laid bone first during bone formation
Irregular arrangement of collagen fibrils
Persists in adults in a few sites:
Tooth sockets / cranial suture
May be formed in fracture repair - gets laid down initially

Question 9

What makes up the lamellar bone?

Answer 9

Both compact and trabecular bone are both types o lamellar bone

Question 10

What is Haversion (lamellar) bone?

Answer 10

• Haversian bone (mature)
• Can be arranged as: 
	• Compact bone 
	• Trabecular bone 
	• Covered externally with two layers of periosteum 
	• Outer layer – collagen, blood vessels
	• Inner layer – osteoprogenitor cells
• Covered internally with endosteum
Osteoprogenitor cells, reticular fibres

Question 11

What is a Haversion system?

Answer 11

Osteoblast produce matrix - they trap theselves within the matrix and mature into osteocytes
Channel of canaliculi - communication between lacunae
• Cylindrical subunits
• Arranged around central canal
• Surrounded circumferentially by lamellae
Canaliculi are microscopic canals connecting lacunae

Question 12

What do osteoblasts do?

Answer 12

Secrete osteoid collagen

Question 13

What do vesicles deposit during bone mineralisation?

Answer 13

Hydroxyapetite

Question 14

What forms the mineralisation?

Answer 14

Osteoid + hydroxyapetite + proteoglycans + proteins
Collagen fibres start to arrange themsevles in a regular pattern - the vesicles stick onto these fibres to form this regular pattern

Question 15

What are the organic and inorganic make up the mineralised bone matrix?

Answer 15

Inorganic and organic components
Organic: osteoid collagen fibres, proteins and proteoglycans
Inorganic: hydroxyapatite
and other molecules

Question 16

What are the organic components?

Answer 16

• Collagen type I fibres
• Proteoglycans
	• Chondrotin sulfate
	• Keratan sulfate
• Other proteins
	• Osteopontin
Osteocalcin

Question 17

What osteopontin and osteocalcin?

Answer 17

Bone matrix proteins
Osteocalcin is unique to bone and is secreted by osteoblasts
Bind to hydroxyapatite crystals
Bind osteoblasts to bone matrix

Question 18

What hydroxyapetite?

Answer 18

Almost identical to calcium phosphate found in geological deposits
Hydroxyapatite forms rod-like crystals approx 40nm x 3nm
Crystals attach along length of osteoid collagen fibres

Question 19

What is mineralisation?

Answer 19

• Occurs in matrix vesicles
• Hydroxyapatite growth and seeding depends on Ca/PO4 concentration
• Bone only forms where crystal nuclei can form
Normal tissue contains factors (e.g. pyrophosphates) which prevent formation of crystal nuclei

Question 20

what is hypocalceamia?

Answer 20

Low blood calcium levels
Due to low vitamin D or PTH
Can be treated by vitamin D