Bone and Soft Tissue

Question 1

What makes up the musculoskeletal system?

Answer 1

Bone
Muscle
Connective tissue

Question 2

What is a tendon, ligament and cartilage?

Answer 2

Tendon: muscle to bone
Ligament: bone to bone
Cartilage: structure, protection, attachment

Question 3

How many bones are there in the human skeleton?

Answer 3

206 in adults

270 in children

Question 4

How is the skeleton divided?

Answer 4

Divided into 2 parts:
Axial- cranium, vertebral column and ribcage (head, neck and trunk)
Appendicular- pectoral girdle, upper and lower limbs, pelvic girdle

Question 5

What are functions of the skeleton?

Answer 5

Movement, support, protection of vital organs, calcium storage, haematopoiesis

Question 6

What are bones made up off?

Answer 6

Cells and matrix

Question 7

What kind of cells can be found in bone?

Answer 7

Osteogenic cell
Osteoblast
Osteocyte
Osteoclast

Question 8

What is the role of an osteogenic cell?

Answer 8

bone ‘stem cell’

Found in deep layers of periosteum

Question 9

What is the role of an osteoblast?

Answer 9

bone forming, secretes osteoid
Catalyse mineralisation of osteoid by producing hydroxyapatite
Found in growing portions of bone including periosteum and endosteum

Question 10

What is the role of an osteocyte?

Answer 10

Mature/ resting bone cell
Formed when osteoblast becomes embedded in secretions
Becomes mechanoreceptor that repairs old/ broken bone
Found embedded in matrix

Question 11

What is the role of an osteoclast?

Answer 11

Bone breaking
Dissolves and reabsorbs bone by phagocytosis
Derived from bone marrow
Remodels bone
Releases Ca2+ and phosphate into blood
Found at bone surface, at sites of old, injured or unneeded bone

Question 12

What makes up the bone matrix?

Answer 12

Organic compound (40%) and inorganic compound (60%)
Organic compound is made up of type I collagen (90%) and ground substance (proteoglycans, glycoproteins, cytokines and growth factors)
Inorganic compound is made up of calcium hydroxyapatite and osteocalcium phosphate

Question 13

What are the 2 bone types?

Answer 13

Bone can be woven (made first) or lamellar (replaces woven bone after mineralisation)
Woven is weak
Lamellar is strong

Question 14

What 2 kinds of bone types are found in lamellar bone?

Answer 14

Cortical- compact/dense, useful for weight bearing

Cancellous- springy/honeycomb like, not for weight bearing

Question 15

How is cortical bone structured?

Answer 15

Cortical bone= osteons
Osteons are made of concentric lamellae around central Haversian canal
Haversian canal contains blood vessels, nerves and lymphatics
Lacunae are small spaces containing osteocytes with canaliculi raiding out and filled with ECF
Volkmans canals transverse perforating cannals and connect to Haversian canals

Question 16

How is cancellous bone structured?

Answer 16

Cancellous bone = trabeculae
Also contain osteocytes in lacunae but not arranged in concentric circles
Instead they’re found in lattice like network of matrix spikes called trabeculae
Trabeculae are structural units made of porous bone lattice
Makes bone lighter so that muscles can move them more easily

Question 17

How is long bone structured?

Answer 17

Diaphysis- tubular shaft that runs between proximal and distal ends of bone
Epiphysis- wide section at end of each bone, filled with spongy bone
Metaphysis- where epiphysis meets diaphysis, narrow area that contains epiphyseal plate (growth plate- layer of hyaline cartilage)
Physis- growing area
Medullary cavity- hollow region in diaphysis thats filled with yellow bone marrow

Question 18

What is ossification?

Answer 18

Bone remodelling by osteoblasts
Theres 2 types:
- Intramembranous
- Endochondrial

Question 19

Where does intramembranous ossification occur and what is it?

Answer 19

Flat bone of skulls, clavicle and mandible
Primary method of formation for young foetus
Cartilage not present

Question 20

How does intramembranous ossification occur?

Answer 20

1. Group of mesenchymal cells within highly vascularised area of embryonic connective tissue proliferates and differentiates into osteoblast
2. Osteoblast secretes osteoid which is calcified to become woven bone. Blood vessels incorporated between woven bone trabeculae will form future haematopoietic bone marrow
3. Later woven bone is re-modelled and replaced by mature lamellar bone. Resorption and apposition take place so that cancellous bone occupies centre of mass whilst cortical bone is formed on outer surface by continuous addition of sheets by active osteoblasts
4. Osteoclasts resorb bone from the inner surface to maintain proportional thickness and shape

Question 21

Where does endochondrial ossification occur and what what is it?

Answer 21

Occurs in all other bones
Primary method of formation after young foetal stage
Development of long bone from hyaline cartilage model
Takes longer than intramembranous ossification

Question 22

What are the 2 ossification centres in endochondrial ossification?

Answer 22

Primary ossification centre- diaphysis

Secondary ossification centre- epiphysis

Question 23

What are the steps of endochondrial ossification?

Answer 23

1. Collar bone formation
   - Perichondral mesenchymal cells differentiate into osteoblasts- lay down osteoid against shaft in primary centre forming collar
2. Cavitation
   - Chondrocytes hypertrophy and calcify collar
3. Periosteal bud invasion
   - osteoprogenitor cells (that enter periosteal buds) lay down osteoid forming trabecula
4. Diaphysis elongation
   - at birth, secondary centre starts to play role in similar process
5. Epiphyseal ossification
   - cartilage in plates is replaced by bone at around 20 yrs old

Question 24

What are the 2 types of bone growths?

Answer 24

Interstitial growth- bone lengthening

Apositional growth- increases thickness

Question 25

How does interstitial bone growth occur?

Answer 25

Epiphyseal plate= zone of elongation in long bone
Epiphyseal side contains active hyaline cartilage which divides to form hyaline cartilage matrix
Diaphysis side- contains calcifying cartilage which dies and then is replaced by bone

Question 26

How does apositional bone growth occur?

Answer 26

Ridges in periosteum creates groove for periosteal blood vessels
Periosteal ridges fuse forming endosteum- lined tunnel
Osteoblasts in endosteum build new concentric lamellae inwards towards centre of tunnel forming new osteon
Bone grows outwards as osteoblast in periosteum build new lamellae
Repeats as new periosteal ridges fold over blood vessel