Module 2.1: Human Osteology and Bone Biology - ARCL 228

What are the different sections of the human skeleton?

• Axial skeleton → skull and teeth + torso

• Appendicular skeleton → shoulder and hip girdles + limbs

What are bones made of?

Calcium and protein cartilage

What are the two bone tissues?

Cortical bone aka compact: dense, hard bone

• on the external surface of the bone

Cancellous bone aka spongy bone: soft bone made of trabeculae in a honeycomb structure

• on the internal part of the bone, has blood vessels and nerves

Why do bones have different proportions of each cortical and cancellous bone tissue?

Because different bones have different functions

What are the 5 types of bones?

1. long bones

2. short bones

3. flat bones

4. irregular bones

5. pneumatized bones + sesamoid bones

What are the long bones? What do they act as? What are the parts of the long bone?

• Arms + legs

• Act as levers and supports loading

• Epiphyses - joint ends

• Diaphysis - shaft

  • medullary cavity - the centre of the bone (bone marrow, blood production)

What are the short bones? What are the characteristics of them?

• Hands + feet

  • Phalanges

  • Metacarpals

  • Carpals

• Compactness, elasticity, limited motion

What are the flat bones? What do they act as?

• Cranial bones, scapulae, os coxae

• Protection and surface area for bone attachment

What are the irregular bones? What do they act as?

• Vertebrae, some hands and feet bones

• Complex and specific functions

What are pneumatized bones?

bones with air pockets in them

• face bones: eyes, cheeks, nose

What are sesamoid bones?

Small bone that is embedded within a muscle or tendon near a joint (doesn’t touch other bones, floats in soft tissue)

How is a skeleton laid out?

• flat on a table

• palms up

  • to keep forearm bones parallel

• feet down

What are the planes of the body?

• Transverse

  • Vertical

• Frontal

  • Front + back

• Sagittal

  • Horizontal

What are the directional terms?

Right + left

Cranial (head) + caudal (toe)

Proximal (the part of the body nearest the point of

attachment to the body) + distal (the part of the limb farther away from the point of attachment to the body)

Medial (centre) + lateral (out)

Anterior (front) + posterior (back)

Superior (towards the head) + inferior (towards the feet)

Cortical bone forms what part of the bone?

The less active surface and structural sections (load bearing portion)

Cancellous bone is found where? What does it contain?

In the interior of the bone

Contains bone marrow which produce WBC and RBC

Whole bones are vascularized with what? and for what reason?

Blood vessels to move blood cells out to the rest of the body

new bone cells can replace old ones

What are osteons? What are the types of osteons?

• The functional unit of bones

• Primary osteons: formed in early development

• Secondary osteons: replace primary osteons over a lifetime

What is the bony matrix within osteocytes made of?

• Fibrous collagen (protein)

• Hydroxy-apatite (calcium mineral)

What are the parts of an osteon that start with “osteo-“

Osteogenic cells: stem cells that derive into the other cells

Osteocytes: bone cell suspended in and maintaining bony matrix

Osteoblasts: lay down new osteons

Osteoclasts: break down old osteons

What are the two other parts of osteons?

Haversian canal: soft tissue that have blood vessels going through

Canaliculi:

What are the two types of bone development?

1. Initial formation ossification

• Intramembranous ossification

  • How bones of the skull and some axial skeleton form (flat bones)

• Endochondral ossification

  • How the long bones and short bones form

2. Remodelling

What are the three germ layers during embryonic development?

Ectoderm

Mesoderm

Endoderm

Which germ layer form mesenchymal stem cells which then turn into what?

Mesoderm → mesenchymal stem cells → bone cells (osteogenic cells) & cartilage cells (chondrocytes + chondroblasts)

Explain how intramembranous ossification works

• in between membrane bones

• two sheets of mesenchymal tissue sandwiched between trabeculae

• osteoblasts are laid down

How does endochondral ossification work and how can it approximate age?

In utero

• cartilage is formed before bone

• cartilage gets a blood supply forming the primary ossification centre

  • cartilage gets replaced with bone

At birth

• the shaft turns into majority bone (diaphysis), the joint ends are mostly cartilage

• secondary ossification centres form in the joint end

3-4 years old

• Diaphysis is fully formed

• Epiphysis is mostly formed

• cartilage layer between epiphysis and diaphysis is not yet fused

• still in growth phase

Adult

• Epiphysis and diaphysis are fused

Explain bone remodeling

cell turnover

secondary osteons replace primary osteons

those secondary osteons will continue to be replaced

What do osteoclasts and osteoblasts do?

Osteoclasts break down old osteons and osteoblasts put down new bone material

making up a basic muticellular unit

What are the two types of bone that make up whole bones?

Cortical bone

Cancellous bone

What are osteoblasts?

Bone producing cells

What are osteoclasts?

Bone destroying cells

Which bones form through intermembranous ossification?

Flat bones of the skull and clavical