Bones

Question 1

Describe Bone (tissue)

Answer 1

• A type of connective tissue
• Few cells suspended in an abundant matrix
• Made up of organic and inorganic compounds
  (30% connective tissue matrix and 65% minerals)

Question 2

Describe Bones (the organ)

Answer 2

• Made of living bone tissue
• Dynamic and responds to changes in the environment

Question 3

What do bones do?

Answer 3

Mostly biomechanical functions:
- supports body
- Acts as a system of levers for movement
- Protects soft parts

Other functions:
- mineral homeostasis (store of calcium, phosphate and ions)
- site of haematopoiesis (bone marrow)
- fat storage (bone marrow)

Question 4

What does bone contain?

Answer 4

• specialised cells
• nerve supply
• blood supply

Question 5

What do osteoblasts do and how do they form?

Answer 5

• synthesise and secrete new bone
• form from osteoprogenitor cells in bone

Question 6

What do osteocytes do and how do they develop?

Answer 6

• develop from osteoblasts that get trapped
• they are bone maintaining cells

Question 7

What do osteoclasts do?

Answer 7

• break bone substance down

Question 8

Describe what the osteon does

Answer 8

• The osteon is a structural unit of compact bone
• Formed by remodelling (reabsorption + new bone)
• Functions as pressure-resistant columns
• osteons aligned to direction of compression (long axis)
• spiralling of collagen fibres in each lamella (layers)
• Angle of spiral is opposite in adjacent lamellae
• Osteons resist compression and twisting forces

Question 9

What are the three ways we can classify bones?

Answer 9

Topically:
- cranial and postcranial
- Axial and appendicular

Ontogenetically:
- Endochondral and intramembranous bones

By shape:
- long, short, and flat bones
- sesamoids
- irregular

Question 10

What is endochondral ossification?

Answer 10

• bone development from a hyaline cartilage template
• bone grows from the centre of the hyaline cartilage to fill it and form bone

Question 11

What is intramembranous ossification?
Give examples of what bones development from this?

Answer 11

• bone development from fibrous membranes
  (flat bones of skull, mandible and clavicles (bones in feet))

Question 12

Describe long bones and give examples of long bones

Answer 12

• humerus, fibula and metacarpals
• shaft (diaphysis)
• two ends (proximal and distal epiphyses)
• growth plates (physes)
• compact and spongy bone
• medullary cavity
• bone marrow
• articular cartilage

Question 13

Describe short bones and give examples

Answer 13

• carpal and tarsal bones
• about as long as wide
• cylindrical and cubic
• compact and spongy bone
• no medullary cavity

Question 14

Describe Flat bones and give examples

Answer 14

• scapula, ribs and frontal bone
• thin, flat and wide
• compact bone surrounding spongy bone or air sinus

Question 15

Describe sesamoid bones and give examples

Answer 15

• patella, fabella, navicular
• found in tendons/ligaments
• close to joints
• formation is sensitive to biomechanical forces
  (develop in accordance with force put on them)
• similar to short bones

Question 16

Describe irregular bones and give examples

Answer 16

• vertebrae, sphenoid
• odd shapes
• jutting bones

Question 17

organ bones are …

Answer 17

• os penis
• bones in the bovine heart

Question 18

what is the periosteum (bone membrane)?

Answer 18

• covers the outside of the bone

Question 19

Describe the periosteum membrane

Answer 19

• two layers (cellular and fibrous)
• protective
• osteogenic
• site of sensory nerves, blood and lymphatics

Question 20

What is the endosteum? (bone membrane)

Answer 20

• lines inside the surface (medullary cavity)

Question 21

Describe the endosteum

Answer 21

• Single layer
• Osteogenic and osteolytic

Question 22

How do bones get a blood and nervous supply?

Answer 22

• Well vascularised
• Arteries that enter via the nutrient foramen (diaphysis)
• Arteries pass through the subchondral bone to supply calcified part of cartilage (not cartilage itself)
• Haversian and Volkmann canals supply cortical bone
• Trabecular bone supplied by the bone marrow

Question 23

Describe bone remodelling

Answer 23

• Continuous deposition and resorption of bone
• Forces such as compression, shear and tension lead to remodelling

Question 24

How is the rate of bone remodelling controlled ?

Answer 24

• Rate influenced by hormones
• PTH and Calcitonin

Question 25

Describe Wolff's Law

Answer 25

- Bone adapts to load - e.g., trabecular trajectories - e.g., diaphysis thickness - e.g., enthesophytes