Ultrastructure of Bone

Question 1

What is haematopoiesis?

Answer 1

Formation of blood cells from haematopoietic stem cells in bone marrow

Question 2

What are the main functions of bone?

Answer 2

Haematopoiesis
Lipid and mineral storage
Support
Protection

Question 3

Where in the bone is adipose tissue stored?

Answer 3

Bone marrow

Question 4

Where in the bone is calcium stored?

Answer 4

Hydroxyapatite crystals

Question 5

What are the cellular components of bone?

Answer 5

Osteoblasts
Osteocytes
Osteoclasts

Question 6

What is the function of osteoblasts?

Answer 6

Synthesise osteoid

Question 7

What is osteoid?

Answer 7

Uncalcified/unmineralised extracellular matrix

Question 8

What is the function of osteocytes?

Answer 8

Monitor minerals and proteins to regulate bone mass

Question 9

How do osteocytes form?

Answer 9

Osteoblasts become entombed between lamellae in lacunae of mineralising osteoid > mature into osteocytes

Question 10

From what are osteoclasts derived?

Answer 10

Monocytes

Question 11

What is the function of osteoclasts?

Answer 11

Resorb bone by releasing H+ ions and lysosomal enzymes

Question 12

What is the extracellular matrix?

Answer 12

Molecules that provide biochemical and structural support to cells

Question 13

What is the main mineral salt found in the extracellular matrix of bone?

Answer 13

Ca hydroxyapatite

Question 14

What is woven bone?

Answer 14

Primary bone
Appears in
- Embryonic development
- Fracture repair
Made of
- Osteoid
- Collagen fibres arranged randomly
Temporary structure

Question 15

What is lamellar bone?

Answer 15

Secondary bone
Bone of adult skeleton
Made of
- Highly organised sheets of mineralised osteoid
Stronger than woven bone

Question 16

What are the two types of lamellar bone?

Answer 16

Compact

Spongy

Question 17

What are the two layers of connective tissue lining the external and internal surfaces of bone, respectively?

Answer 17

Periosteum

Endosteum

Question 18

Where is compact bone found?

Answer 18

Outer part of lamellar bone

Question 19

Where is spongy bone found?

Answer 19

Inner part of lamellar bone

Question 20

What is the structure of compact bone?

Answer 20

Lamellae organised into concentric circles surrounding vertical Haversian canal

Question 21

What does the Haversian canal transmit?

Answer 21

Small neurovascular and lymphatic vessels

Question 22

What is the functional unit of bone, and of what is it comprised?

Answer 22

Osteon = set of concentric circles of lamellae around Haversian canal + neurovascular and lymphatic vessels inside canal

Question 23

What are Volkmann’s canals?

Answer 23

Horizontal canals within compact bone
Connect Haversian canals
Contain small vessels that anastomose with arteries of Haversian canals
Carry vessels from periosteum

Question 24

What are trabeculae?

Answer 24

Made up of 3D network of fine columns that crosslink in irregular way

Question 25

What fills trabeculae?

Answer 25

Bone marrow

Question 26

What are the two types of bone marrow?

Answer 26

Yellow - contains adipocytes

Red - contains haematopoietic stem cells

Question 27

What are the two types of ossification?

Answer 27

Endochondral

Intramembranous

Question 28

What is endochondral ossification?

Answer 28

Hyaline cartilage replaced by osteoblasts secreting osteoid

Question 29

What is intramembranous ossification?

Answer 29

Mesenchymal/embryonic tissue condensed into bone

Question 30

Where does bone remodelling primarily occur?

Answer 30

At sites of stress and damage