Bones Flashcards
Describe Bone (tissue)
- 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)
Describe Bones (the organ)
- Made of living bone tissue
- Dynamic and responds to changes in the environment
What do bones do?
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)
What does bone contain?
- specialised cells
- nerve supply
- blood supply
What do osteoblasts do and how do they form?
- synthesise and secrete new bone
- form from osteoprogenitor cells in bone
What do osteocytes do and how do they develop?
- develop from osteoblasts that get trapped
- they are bone maintaining cells
What do osteoclasts do?
- break bone substance down
Describe what the osteon does
- 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
What are the three ways we can classify bones?
Topically:
- cranial and postcranial
- Axial and appendicular
Ontogenetically:
- Endochondral and intramembranous bones
By shape:
- long, short, and flat bones
- sesamoids
- irregular
What is endochondral ossification?
- bone development from a hyaline cartilage template
- bone grows from the centre of the hyaline cartilage to fill it and form bone
What is intramembranous ossification?
Give examples of what bones development from this?
- bone development from fibrous membranes
(flat bones of skull, mandible and clavicles (bones in feet))
Describe long bones and give examples of long bones
- 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
Describe short bones and give examples
- carpal and tarsal bones
- about as long as wide
- cylindrical and cubic
- compact and spongy bone
- no medullary cavity
Describe Flat bones and give examples
- scapula, ribs and frontal bone
- thin, flat and wide
- compact bone surrounding spongy bone or air sinus
Describe sesamoid bones and give examples
- 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
Describe irregular bones and give examples
- vertebrae, sphenoid
- odd shapes
- jutting bones
organ bones are …
- os penis
- bones in the bovine heart
what is the periosteum (bone membrane)?
- covers the outside of the bone
Describe the periosteum membrane
- two layers (cellular and fibrous)
- protective
- osteogenic
- site of sensory nerves, blood and lymphatics
What is the endosteum? (bone membrane)
- lines inside the surface (medullary cavity)
Describe the endosteum
- Single layer
- Osteogenic and osteolytic
How do bones get a blood and nervous supply?
- 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
Describe bone remodelling
- Continuous deposition and resorption of bone
- Forces such as compression, shear and tension lead to remodelling
How is the rate of bone remodelling controlled ?
- Rate influenced by hormones
- PTH and Calcitonin
Describe Wolff’s Law
- Bone adapts to load
- e.g., trabecular trajectories
- e.g., diaphysis thickness
- e.g., enthesophytes
