Bones

Question 1

Functions of bones (4)

Answer 1

1. Weight bearing/ support
2. Protection (e.g. skull for brain, vertebrae for spinal cord, ribcage for lungs and other internal organs)
3. Mineral store (if not enough minerals are supplied through diet, the body depends on storage, malnutrition is the leading cause of lack of minerals)
4. Blood formation (red bone marrow)

Question 2

Compact bone (cortical bone)

Answer 2

Found near the cortical (hard) bone area, made up of osteons; concentric cylinders of bone tissue with a central vascular canal

Question 3

Spongy bone (trabecular bone)

Answer 3

• Typically found at ends of long bone, highly vascular and contains red marrow often
• Sponge- like
• Also called cancellous, trabecular bone or diploe
• Less dense than compact bone
• Network of lamellated trabeculae (rod-like tissue with a specific mechanical function) filled with bone marrow
• no Harversion systems present!
• Orientation of trabeculae reflect main directions of mechanical forces

Question 4

Medullary Cavity

Answer 4

Found near shaft and filled with bone marrow

Question 5

2 membranes found in bone

Answer 5

periosteum and endosteum

Question 6

Osteons/ Haversian systems

Answer 6

-Under the microscope, osteons can be seen on bone
Osteons are made of sheets of bone (concentric rings)
Compact bone organised in circular structures (osteons/ Harvasian systems

Question 7

Central Harvasian canal and horizontal perforating

Answer 7

• Harvasian canals surround blood vessels and nerve cells and communicate with osteocytes
• Osteocytes and concentric rings of bone matrix (lamellae) are found around it

Question 8

Volkmann’s canals

Answer 8

transmit blood vessels from periosteum into the bone and communicate with Harvasian canals

Question 9

Different types of bone (6)

Answer 9

1. Sutural bone, e.g. in the suture joints in the cranium (skull)
2. Irregular bone, e.g. vertebrae
3. Long bone, e.g. femur
4. Sesamoid bone: patella (kneecap), usually in hands or feet and regions with high frictions
5. Short bone, e.g. carpal (in the wrist)
6. Flat bone, e.g. frontal or scapula (shoulder blade)

Question 10

What are the 2 different bone formation types? (ossification)

Answer 10

1. Endochondral (most common type including long bone growth, growth from hyaline cartilage)
2. Intramembranous (flat bones of skulls, mandible/jaw bone, maxilla/upperjaw, clavicles/collarbones)

Question 11

Describe endochondral ossification process

Answer 11

• Bone first as a “cartilage” model first
• Blood vessels invade cartilage
• Cartilage replaced with bone
• Cartilage remains in the epiphyseal growth plate
  Growth plate eventually ossifies

Question 12

Describe intramembranous ossification process

Answer 12

• no cartilaginous phase
• most direct way of forming bone
• Mesenchymal cells develop into osteoprogenitor cells that mature into osteoblasts that start depositing bone
• Residual mesenchymal cells develop blood vessels & bone marrow
• This bone formation also occurs in adult cortical bone

Question 13

What 3 types of cells make up the bone?

Answer 13

• osteoblasts
• osteocytes
• osteoclasts

Question 14

What are the main components of the bone

Answer 14

• cells

- ECM (extracellular matrix)

Question 15

What is the component of ECM in the bone?

Answer 15

~45% hydroxyapatite crystals (complex form of calcium phosphate)
~35% Collagen (Type I)
~20% Water

Question 16

What two components give bone its strength?

Answer 16

1. Minerals (hydroxyapatite):
   - Makes bones stiff and able to support structures
   - High strength under compression (like concrete)
2. Collagen
   - Gives bone flexibility and reduces risk of fracture
   High strength under tension

Question 17

What 2 functions of the bone give it its dynamic nature?

Answer 17

• fracture healing

- mechanical adaptation

Question 18

Osteoblasts (what are they? what’s their function?)

Answer 18

• Immature bone cells created from osteopregenitor cells in periosteum and endosteum.
• Function: produces bone matrix (unmineralised matrix= osteoid) and initiates calcification (mineralises it)
• Become osteocytes once surrounded by matrix
• derived from the mesenchymal lineage, and that their differentiation is regulated by specific regulatory molecules.

Question 19

Osteocytes (what are they? what’s their function?)

Answer 19

• Mature bone found inside lacunae (small cavity within bone matrix)
• Numerous processes found in canaliculi (little network which connect cells in a network to communicate)
• Canaliculi connect lacunae to each other
• Function: not well understood, may maintain bone matrix & sense mechanical forces and adaptation

Question 20

Describe properties of ECM (4)

Answer 20

• mainly made up of minerals, collagen and water
• Modified type 1 collagen fibres
• strongly cross linked and has large gaps within fibrils for hydroxyapatite crystals
• orientation of fibres reflects orientation of mechanical forces

Question 21

Describe 3 main bone disorders of remodelling and their causes

Answer 21

1. Osteoporosis (resorption>formation): trabecular network is less spongy, more breakable and bone becomes weaker over time, can easily cause femur fractures)
2. Paget’s disease (resorption/formation): renewal and repair of bone doesn’t happen very well causing deformation and weakness, can cause loss of hearing
3. Osteopetrosis (formation> resorption): no resorption happens (no renewal), make bone abnormally dense, can cause short stature

Question 22

What mechanical loads affect the bone mass?

Answer 22

• Weightlessness (such as in astronauts) or extended bed rest can cause significant bone loss
• Higher bone material density in athletes maintains an increased bone mass due to excessive training (BMD)

Question 23

Osteoclasts (what are they and what is their function?)

Answer 23

Multinucleate cells derived from monocytes/macrophages
Found on bone surface
Large cells with ‘ruffled border’
Function: resorb bone matrix
Howship’s lacunae – resorption pits
derived from the haemopoietic lineage