Bone Health

Question 1

What are the 3 main components of bone = connective tissue?

Answer 1

• Cells ( osteoclasts, osteoblasts, osteocytes)
• Protein fibres
• Ground substance: Viscous fluid with proteoglycans cross linked by protein fibres

Question 2

What are the 3 main protein fibres?

Answer 2

Collagenous = bundles of collagen fibrils to strengthen the tissue
Reticular - join connective tissue to other tissues
Elastic - made of elastin fibres for stretch

Question 3

What are the main functions of bone?

Answer 3

1: Mechanical - protection, rigid stability of the limbs, act as levers
2: Mineral storage - storage of minerals e.g Ca2+ and phosphate, bone marrow for haematopoesis

Question 4

What are the 2 main types of bone?

Answer 4

Cortical hard bone = mechanical functions

Cancellous spongy bone = lattice of trabeculae, large SA so is very metabolically active

Question 5

What is appositional growth?

Answer 5

How bone grows by osteoblast activity

It is the deposition of new matrix on the exisiting surface

Question 6

What are the 2 main types of bone formation?

Answer 6

Intramembranous ossification: From fibrous membranes

Endochondral ossification: From hyaline cartilage

Question 7

Describe the process of intra membranous ossification

Answer 7

• Osteoblasts can form ossification centres
• Osteoblasts can secrete ECM, Ca2+ to harden the matrix
• Osteoid forms along with the periosteum
• Osteoid forms around blood vessels to create spongy bone
• Spongy bone crowds the blood vessels to condense into red marrow
• Spongy bone is remodelled to be covered by a thin layer of cortical bone

Question 8

Describe the process of endochondral ossification

Answer 8

• Mesenchymal stem cells -> chondrocytes
• Perichondrium forms
• Perichondrium becomes infiltrated with blood vessels, cells and osteoblasts
• Osteoblasts can convert the perichondrium -> periosteum

Question 9

What blood vessels supply the bone?

Answer 9

Nutrient arteries
Periosteal arteries
Metaphyseal arteries
Perforating arteries, anastamose with branches of the nutrient arteries to supplY the marrow space

Question 10

What are Haversian canals?

What are Volkman canals?

Answer 10

Central canals of the bone lying parallel to the bone axis, they contains lymphatics, nerves and vasculature
Volkman canals connect the haversian canals and are perpendicular to the bone axis.

Question 11

Where are osteoblasts and osteocytes derived from?

What other cells do they give rise to?

Answer 11

Osteoprogenitor cells ( mesenchymal stem cells) 
Myoblasts, fibroblasts, adipocytes

Question 12

What are osteocytes?

Answer 12

Major cells of the bones

They are supportive cells that maintain the bone matrix

Question 13

What are the main functions of osteoblasts?

Answer 13

• Form the organic matrix by depositing ECM, collagen and special proteins ( osteoclastin and osteonectin)
• Mineralisation via deposition of hydroxypatite between the collagen fibrils

Question 14

Describe mineralisation

Answer 14

• Osteoblasts remove ions e.g Ca2+ and phosphate from the mitochondria and cytoplsm and release these onto the organic matrix
• They have vesicles to concentrate the ions until hydroxyapatite forms
• The crystals have nucleation sites allowing for more apatite crystals to form

Question 15

What are the main components of the organic matrix?

Answer 15

88% Type 1 collagen
10% proteins : Osteocalcin + osteonectin
1-2% : Glycosaminoglycans and lipids

Question 16

What do osteoblasts secrete to prevent RANK + RANKL activation?

Answer 16

Osteoprotegerin

Question 17

What are the 3 main factors needed for osteoclast activity?

Answer 17

RANK
RANKL
Macrophage colony stimulating factor
RANK + RANKL -> NKFB singalling

Question 18

How does osteoclastogenesis occur?

Answer 18

• Cell attaches to the bone via integrins
• Extracellular compartment is isolated between the bone and ruffled membrane
• Proton pump acidifies acompartment to pH 4.5
• Releases bone minerals as lysosomes degrade the bone

Question 19

What is protected from osteoclastic activity?

Answer 19

Non mineralised bone = osteoid