Development and growth of bone

Question 1

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

Answer 2

FLEXIBILITY (like a cable), due to the protein element of bone– and resistance to tension because the framework is collagen and other bone proteins (osteoid)

Pillar-like STIFFNESS, due to minerals– and resistance to compression conferred by impregnation of collagen with crystalline mineral (hydroxyapatite – a complex calcium hydroxyphosphate)

Question 3

What are the two main types of bone tissue?

Answer 3

Woven (immature)

Lamellar (mature)

Question 4

When is woven bone found in adults?

Answer 4

It is 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?

Answer 6

Epiphysis

Question 7

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

Answer 7

Compact bone (aka 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 this cavity?

Answer 9

Trabecular/spongy/cancellous bone (this is still lamellar bone)

Question 10

What units are the outer compact/cortical bone arranged into? (in lamellar/mature bone)

Answer 10

Osteons/Haversian Systems
They have a central canal containing vessels and around the vessels you have concentric layers of bone maintained by concentrically arranged osteocytes

Question 11

In what planes are these units arranged?

Answer 11

They are 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 two layers of the periosteum?

Answer 13

Fibrous (outer)
Cellular (inner)

The fibrous layer contains fibroblasts, while the cellular layer contains progenitor cells that develop into osteoblasts. These osteoblasts are responsible for increasing the width of a long bone and the overall size of the other bone types.

Question 14

What are the main roles of the periosteum? Does it have a blood and nerve supply?

Answer 14

Bone growth and repair

It is vascular
It has a good sensory nerve supply

Question 15

What do osteogenic cells give rise to?

Answer 15

Osteogenic cells (initial stem cells) –> Osteoblasts –> Osteocytes slide 17

Question 16

What lineage do osteoclasts come from?

Answer 16

They are derived from the immune cell lineage – they are 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 two types of ossification?

Answer 18

Intramembranous 
Endochondral (within cartilage)

Question 19

Describe intramembranous ossification.

Answer 19

Occurs within existing vascular connective tissue
Bone matrix (ostein) is deposited around the collagen
This mineralises to form woven bone
It then remodels to form lamellar bone

Question 20

Describe endochondral ossification.

Answer 20

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

Question 21

List some bones in which intramembranous ossification takes place.

Answer 21

Skull bones
Jaw bones (mandible)
Part of the clavicle

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 (ie your bones stop growing) – then the epiphyseal plates will calcify. The epiphyseal plate is where your bone grows and helps the bone to lengthen.