Bone & the Skeleton

Question 1

Classify bone according to shape and give examples.

Answer 1

1. Long bones - femur; humerus
2. Flat bones - scapula; cranium
3. Short/irregular bones - vertebrae; carpals
4. Sesamoid bones - patella

Question 2

Describe the macroscopic architecture of bone and explain how this organisation relates to function.

Answer 2

Long bone:
- Epiphysis present at either end of bone
- Metaphysis located between the diaphysis (main shaft of bone) and epiphysis
- Cartilage tissue on the end of the epiphysis (allows joints to form)
- Diaphysis contains a large, dense amount of cortical bone which reduces through to the epiphysis
- Medullary cavity contains the bone marrow
- Periosteum is the membrane that covers the exterior of the bone - blood vessels are carried along the periosteum to provide a blood supply and nutrients to the bone and to remove any waste
- Epiphyseal plate allows for long bone development/growth

Trabecular bone:
- Hexagonal structure allows for a high strength structure whilst still allowing airflow - this makes the bone lighter and therefore more energy efficient with movement

Flat bones:
- Flat to serve protection or provide a large surface area for muscle attachment
- No medullary cavity
- Only 2 layers of compact bone surrounding either spongy bone or air

Short/irregular bones:
Found typically in areas with lots of motion - provide a grater range of motion due to the abundance of several different joints
- No medullary cavity
- Develop from a single centre of ossification

Sesamoid bones:
- Ease tendon path
- prevent excessive tendon wear - allows for smoother tendon movement
- Increases moment arm of muscle (provides leverage to create movement) - large moment arms allow for larger loads to be lifted using less energy, yet meaning less absolute movement for a given force is applied

Question 3

Recount the anatomical relationship between peri- and endosteum. Describe the functions of these tissues.

Answer 3

Periosteum:
- Covers the outside of bone
- 2 layers
- Protective
- Osteogenic (osteoblasts) - newly formed bone added to the outside layer
- Site of sensory nerves, blood & lymphatic vessels

Endosteum:
- 1 layer
- Osteogenic (osteoblasts)
- Osteolytic (osteoclasts)

Question 4

Appreciate that bone is an organ and therefore subject to continual adaptation processes.

Answer 4

• Bone is a type of connective tissue made up of cells embedded in a matrix
• 65% mineral compound (hydroxyapatite) / 35% organic material (mostly collagen) that gives bone it’s physical properties
• Bones are made up of living tissue, hence they are dynamic and respond to changes in their environment
• Osteogenic cells - stem cells that have the potential to become bone cells
• Osteoblast - forms bone
• Osteocyte - maintains bone tissue embedded within the bone tissue - osteocytes can sense mechanical strain within bone tissue and are located near blood vessels to allow the bone efficient access to nutrition
• Osteoclasts - resorbs bone (usually unwanted/old bone or for access to nutrition)
• Blood vessels travel through canals in the length of the long bones within the bone tissue (central canals) - they also travel through canals along the short axis of the bone within canals (perforating canals)
• Lamellae are arranged around the blood vessels (like a doughnut) - the area of lamellae surrounding the blood vessels is known as the osteon
• Osteons have an important role in bone structure - they contain collagen fibres that run in different directions in neighbouring lamellae, and therefore are more resistant to a twisting force as this allows ‘give’ so the bone is not completely brittle when a force is applied.
• Surface markings allow for:
  Leverage
  Muscle attachment
  Response to strain within bone
  Articulations/joining with other bones
• Muscles that attach further from the lever of the skeleton need to generate less force for a movement to take place (more economical)