The Structure of Bone

Characteristics of bone

• Highly vascular

• Strong and durable connective tissue

• Composed of 65% calcium salts (mostly calcium phosphate)

What is the use of calcium salts found in bone?

Makes up an inorganic, intracellular matrix which makes the bone hard.

Bone matrix

• Makes bone hard

• Interposed with a system of collagenous organic fibres - collagen is strong and gives bone its slight flexibility

2 types of bone

• Compact, cortex, dense bone - forms the hard outer layers

• Cancellous, spongy bone - porous inner layers

Where is compact bone commonly found?

In the shafts of long bones where a strong tubular structure is required

What type of bone makes up the majority of the body bone mass?

Compact bone

What is compact bone made up of?

• Harversian systems - central canal contains blood, lymph, and nerve vessels

• Lamellae are concentric rings of bone around the Haversian canals (osteon)

What percentage of body bone mass is compact bone?

80%

What percentage of body bone mass is cancellous bone?

20%

Characteristics of cancellous bone

Honeycomb arrangement formed by trabeculae where red bone marrow can be found

What processes are involved in the development of bone tissue?

Osteogenesis or ossification

When does the development of bone tissue occur in the human body?

Before birth/intrauterine

At what age does the development of bone tissue finish?

Around 21 years old

How and where do long, short and irregular bones develop?

In the foetus from rods of cartilage

How and where do flat bones develop?

In the foetus from membrane models

How and where do sesamoid bones develop?

During childhood (around 8 years old) from tendon models

3 types of bone cells

• Osteoblast - bone building cells

• Osteoclast - bone re-absorbing cells

• Osteocyte - mature bone cells

Where are osteoblasts found?

Sites where bone is growing, repairing, or remodelling

Role of osteoblasts

• Bone forming cells that secret osteoid (organic bone matrix) and promote the deposition of inorganic mineral salts - mainly calcium phosphate.

• As new bone is laid around them, some osteoblasts become trapped within small spaces called lacunae and differentiate into osteocytes

Role of osteoclasts

• Breaks down bone

• Release calcium and phosphate

Where are osteoclasts usually found

Areas of bone where there is active growth, repair, or remodelling

Role of osteocytes

Monitors and maintains bone tissue

What are osteocytes

Mature bone cells that do not divide, they are nourished by tissue fluid in the canaliculi that radiate from the haversian canals