Intro to Bone and Soft Tissue

Question 1

What are the 3 components of the MSK?

Answer 1

Bone
Muscle
Connective tissue

Question 2

What are the 3 types of connective tissue?

Answer 2

Tendon - Connects muscle to bone
Ligaments - Connects bone to bone
Cartilage - Structural support, protect tissues, attachment sites

Question 3

What do the appendicular and axial skeletons consist of?

Answer 3

Appendicular - Pectoral girdle, upper and lower limbs, pelvic girdle.
Axial - Cranium, vertebral column, ribcage

Question 4

What are the functions of the skeletal system?

Answer 4

Movement 
Support 
Protection of internal organs
Site of calcium storage 
Site of haemopoiesis

Question 5

How do bones develop in utero?

Answer 5

Intramembranous Ossification - First occurs after conception → flat bones

Endochondral Ossification - Begins 2 months into utero → long bones

Question 6

Explain how intramembranous ossification leads to the development of mesenchymal to bone.

Answer 6

1. Mesenchymal stem cells aggregate and form osteoblasts by differentiation
2. Ossification centre forms
3. Osteoblasts begin to secrete osteoid
4. Peripheral mesenchymal cells continue to differentiate
5. Osteoblasts secrete osteoid inwards towards ossification centre
6. Osteoblasts become trapped in osteoid causing differentiation into osteocytes
7. Osteoid calcifies and hardens after several days
8. Osteoid continues to be deposited, assembles in random manner around embryonic blood vessels
9. Finely woven trabeculae forms
10. Mesenchyme begins to differentiate into periosteum
11. Lamellar bone replaces woven bone at outer edge creating layers. Internal spongy bone remains
12. Vascular tissue within trabecular spaces forms red marrow
13. Osteoblasts remain on bone surface to remodel when needed

Question 7

Explain how endochondral ossification leads to development of mesenchymal to cartilage to bone before birth

Answer 7

1. Perichondrium vascularised and blood vessels supply new nutrients to mesenchymal, causing differentiation
2. Newly formed osteoblasts gather at diaphysis wall to form bone collar
3. Primary ossification centre (diaphysis) forms at the centre of the bone
4. Chondrocytes within central cavity enlarge, causing matrix to calcify, making it impermeable to nutrients, causing cell death
5. Central clearing forms where cells have died (supported by bone collar)
6. Healthy chondrocytes elsewhere cause elongation
7. Periosteal bud invades cavity causing formation of spongy bone
8. Bud consists of artery, vein, lymphatics and nerves. It also delivers osteogenic cells
9. Osteoclasts degrade cartilage matrix while osteoblasts deposit new spongy bone, bone continues to elongate
10. Diaphysis continues to enlarge and osteoclasts break down newly formed spongy bone
11. Medullary cavity begins to form and cartilaginous growth now only within epiphysis causing a bony epiphyseal surface to form

Question 8

What is a joint?

Answer 8

A point at which 2 separate bone meet.

Question 9

How many bones are their in children and adults respectively?

Answer 9

206 Bones in adults + Sesamoids

270 in children

Question 10

How do bones develop in utero?

Answer 10

Intramembranous: Mesenchymal cells&raquo_space; Bone; for flat bones

Endochondral: Mesenchymal > Cartilage > Bone; for long bones

Question 11

Outline intramembranous ossification (mesenchymal to bone)

Answer 11

Condensation of mesenchymal cells which differentiate into osteoblasts - Ossification centre forms.

Secreted osteoid traps osteoblasts which become osteocytes.

Trabecular matrix and periosteum form.

Compact bone develops superficial to cancellous bone. Crowded blood vessels condense into red bone marrow.

Question 12

Which bones does intramembranous ossification form?

Answer 12

Forms flat bones of skull, clavicle and mandible.

Question 13

Which type of ossification takes longer?

Answer 13

Endochondral ossification.

Question 14

List the steps of endochondral ossification.

Answer 14

Bone collar formation
Cavitation
Periosteal bud invasion
Diaphysis elongation - Primary ossification centre
Epiphyseal ossification - secondary ossification centre.

Question 15

What are bones made up of?

Answer 15

Cells and Matrix

Question 16

List the difference types of bone cells.

Answer 16

Osteogenic cell
Osteocyte
Osteoblast
Osteoclast

Question 17

What is an osteogenic cell?

Answer 17

Bone stem cell

Question 18

What is an osteocyte?

Answer 18

‘Mature’ bone cell.
Formed when an osteoblast becomes embedded in its secretions.
Sense mechanical strain to direct osteoclast and osteoblast activity.

Question 19

What is an osteoblast?

Answer 19

Bone forming
Secretes osteoid
Catalyse mineralisation of osteoid

Question 20

What is an osteoclast?

Answer 20

Bone breaking
Dissolve and reabsorb bone by phagocytosis.
Derived from bone marrow.

Question 21

Where do you find osteogenic cells?

Answer 21

Deep layers of periosteum.

Question 22

Where do you find osteoblasts?

Answer 22

Growing portions of bone, including periosteum and endosteum.

Question 23

Where do you find osteocytes?

Answer 23

Entrapped in Matrix

Question 24

Where do you find osteoclasts?

Answer 24

Bone surfaces and at sites of old, injured or unneeded bone.

Question 25

Outline the organic component of bone matrix.

Answer 25

Organic component (40%):

• Type 1 collagen (90%)
• Ground substance (10%) > GPs, proteoglycans and cytokine and growth factors

Question 26

Outline the inorganic component of bone matrix

Answer 26

Inorganic component (60%):
Calcium hydroxyapatite and osteocalcium phosphate.

Question 27

What are the 2 different types of bone?

Answer 27

Immature/woven/disorganised

Mature bone > Well organised

Question 28

What is immature bone?

Answer 28

First bone that is produced.
Laid down in a ‘woven’ manner - relatively weak.
Mineralised and replaced by mature bone.

Question 29

What is mature bone?

Answer 29

Mineralised woven bone.

Lamellar (layer) structure - relatively strong.

Question 30

What are the types of mature bone?

Answer 30

Cancellous - Spongy (honeycomb structure), not suitable for weight bearing.

Cortical - ‘Compact’, dense; suitable for weight bearing.

Question 31

Describe the organisation of compact/cortical bones.

Answer 31

Compact bones have osteons and few spaces.

Repeated structural units - Osteons (concentric lamellae around a central ‘Haversian canal’.

Volkmans canal - transverse perforating canals

Question 32

What are lacunae?

Answer 32

Small spaces, containing osteocytes. Tiny canaliculus radiate from lacunae filled with extracellular fluid.

Question 33

What is the periosteum?

Answer 33

Connective tissue covering

Question 34

What does the medullary cavity contain?

Answer 34

Yellow bone marrow

Question 35

Where is articular cartilage of long bones?

Answer 35

On surface of bone at joint only.

Question 36

What are the 2 types of bone growth?

Answer 36

Interstitial - Long bones > Increased length

Appositional - Increased thickness and diameter

Question 37

Where does interstitial growth occur and explain the process?

Answer 37

Happens at the physis (physial plate)

Zone of elongation in long bone. Contains hyaline cartilage.

Epiphyseal side - hyaline cartilage active and dividing to form hyaline cartilage matrix.
Diaphyseal side - Cartilage calcifies and dies and then replaced by bone.

Question 38

What is appositional growth and explain the process?

Answer 38

Deposition of bone beneath periosteum to increase thickness.

Ridges in periosteum create groove for periosteal blood vessel.
Periosteal ridges fuse, forming an endosteum-lined tunnel.
Osteoblasts in endosteum build new concentric lamellae inward toward the centre of tunnel, forming a new osteon.
Bone grows outwards as periosteum build new circumferential lamellae. Osteon formation repeats as new periosteal ridges fold over blood vessel.

Question 39

Explain the role of bone in calcium homeostasis

Answer 39

Bone - 99% of body Ca2+
Calcium hydroxyapatite - structural support.

Calcium is deposited and withdrawn during bone remodelling.
Regulated by PTH and calcitriol (kidneys)
Calcitonin (Thyroid) - Stimulates calcium uptake into bone.

Question 40

3 types of joint classifications and examples of each.

Answer 40

Fibrous - sutures, syndesmosis, interosseous membrane (immovable)

Cartilaginous - Synchondroses e.g.spine, symphyses e.g.pubic
(semi-movable)

Synovial - Plane, hinge, condyloid, pivot, saddle, ball and socket
(freely movable)

Question 41

What’s the structure of synovial joints?

Answer 41

Most mobile and common

Joint capsule: 
Articular capsule (outer) - keeps bone together structurally 
Synovial membrane (inner) - contains synovial fluid 

Synovial fluid - reduce friction during movement.

Question 42

How are synovial joints stabilised?

Answer 42

Muscles/tendons
Ligaments
Bone surface congruity

Question 43

What is the function of ligaments?

Answer 43

Prevent excessive movement that could damage joint.

More ligaments and tighter ligaments > Greater stability BUT less mobility.

Less ligaments and laxer ligaments > Greater mobility BUT less stability

Question 44

What can poor stability lead to?

Answer 44

Risk of dislocation

Question 45

What can disproportionate, inappropriate or repeated stress to ligaments do?

Answer 45

Injury (athletes at risk of this)

Question 46

What happens if somebody has excessive ligament laxity?

Answer 46

Hypermobility > Greater risk of injury