Development and growth of bone

Question 1

What are the 5 functions of bone?

Answer 1

Support of the body shape 
Systems of levers for muscle action 
Protection of internal organs 
Site of blood cell formation 
Mineral storage pool

Question 2

What are the 2 mechanical properties of bone and what is responsible for these properties?

Answer 2

Cable-like flexibility + resistance to tension because the framework is collagen + osteoid
Pillar-like stiffness + resistance to compression conferred by impregnation of collagen with crystalline mineral (hydroxyapatite))

Question 3

What are the 2 main types of bone tissue?

Answer 3

Woven (immature)

Lamellar (mature)

Question 4

When is woven bone found in adults?

Answer 4

Only found in repairing fractures

Question 5

What is the technical term for the shaft of a bone?

Answer 5

Diaphysis

Question 6

What is the technical term for the head of a bone? What type of bone is found here?

Answer 6

Epiphysis

Spongy bone

Question 7

What type of bone is found around the outside of the bone?

Answer 7

Compact (cortical) bone

Question 8

What is the term given to the cavity within the bone?

Answer 8

Medullary cavity (contains bone marrow)

Question 9

What type of bone is found within the medullary cavity?

Answer 9

Trabecular/ spongy/ cancellous bone (still lamellar)

Question 10

What units are lamellar bone in the compact bone arranged into?

Answer 10

Osteons
Have a central canal containing vessels + around the vessels you have concentric layers of bone maintained by concentrically arranged osteocytes

Question 11

In what planes are osteons arranged?

Answer 11

Usually organised along pressure planes

Question 12

What provides the main blood supply to the bone marrow?

Answer 12

Nutrient artery (passing through the nutrient foramen)

Question 13

What are the 2 layers of the periosteum?

Answer 13

Fibrous

Cellular

Question 14

What are the main roles of the periosteum?

Answer 14

Bone growth + repair
Vascular
Good sensory nerve supply

Question 15

What do osteogenic cells give rise to?

Answer 15

Osteogenic cells
Osteoblasts
Osteocytes

Question 16

What lineage do osteoclasts come from?

Answer 16

Derived from immune cell lineage (modified macrophages)

Question 17

At what point in fetal life does the skeleton start to develop?

Answer 17

6 weeks

Question 18

What are the 2 types of ossification?

Answer 18

Intramembranous

Endochondral

Question 19

Describe intramembranous ossification.

Answer 19

Occurs within existing vascular connective tissue
Bone matrix is deposited around the collagen
This mineralises to form woven bone
Then remodels to form lamellar bone

Question 20

Describe endochondral ossification.

Answer 20

Occurs within existing fetal cartilage models
Cartilage calcifies + chondrocytes die
Periosteal osteoclasts cut channels for sprouting vessels
Osteoblasts enter with vessels to build bone around them

Question 21

Name 2 bones in which intramembranous ossification takes place.

Answer 21

Skull
Mandible
(Flat bones)

Question 22

At what point do the epiphyses ossify in a child’s wrist?

Answer 22

2 years

Question 23

Until what point do epiphyseal plates remain cartilaginous?

Answer 23

Until you stop growing: then epiphyseal plates will calcify

Question 24

How does bone grow in length without disrupting terminal appositional growth?

Answer 24

Shaft ossifies 1st, followed by epiphyses
Growth continues by ossification at growing cartilage plate between them
Growth cessation when cartilage growth ceases + plate is over-run by ossification

Question 25

Why is bone described as adaptable?

Answer 25

Can grow without compromising its support function
Increases/ decreases bulk + density in response to pattern of use
Can alter its external + internal shape in response to pattern of use (remodelling)
Can repair when fractured

Question 26

Describe 3 features of bone that allow for remodelling

Answer 26

Bone has a large blood supply- cells never far from nutrients + O2
Osteocytes maintain matrix but can activate osteoblasts for new bone building
Osteoclasts are giant cells specialised for destruction of bone matrix

Question 27

What is the name of growth in bone diameter? Describe this

Answer 27

Apposition: addition to exterior at periosteum
Osteoblasts + osteoclasts create ridges + grooves on surface
Blood vessels align in grooves
Osteoblasts build new osteons round vessels
Osteoclasts remove bone from endosteal surface

Question 28

What is essential for intiating repair of a fracture?

Answer 28

Haematoma

Becomes infiltrated by fibrous matrix + invaded by cartilage/ bone progenitors

Question 29

Describe the response to high blood calcium levels

Answer 29

Calcitonin released by parafolicular thyroid cells
Breakdown of bone matrix by osteoclasts INHIBITED
Uptake of Ca2+ into bone STIMULATED

Question 30

Describe the response to low blood calcium levels

Answer 30

PTH released by chief cells of parathyroid gland
Osteoclasts bone resorption activity STIMULATED
Increases Ca2+ re-absorption by kidneys