0416 - Bone and cartilage - CS Flashcards
Structural components of bone: label this diagram
Be aware of the following structural components of bone:
- diaphysis
- metaphysis
- epiphysis (proximal and distal)
- epiphyseal line
- periosteum
- compact cortical bone
- spongy bone
- articular cartilage
- medullary cavity
- marrow
- nutrient artery
Brief definitions to be added later. (Sorry!)
Explain the basic functions of bone?
- Structural
- Movement
- Protection
- Gives skeleton the necessary rigidity to function as an attachment and lever for muscles and supports the body against gravity
- Acts as a calcium reservoir and is important in calcium homeostasis. Also phosphate
- Is heavy and its architecture is optimally arranged to provide maximum strength for the least weight.
What is bone composed of?
- Cells in abundant extracellular substance (matrix)
- Extracellular matrix:
- 30% organic matrix (mostly type 1 collagen fibres - about 90%)
- 70% inorganic salts (calcium and phosphate): ground substance (osteoid) becomes mineralised by the deposition of calcium hydroxyapatite
What gives bone its tensile strength?
Type 1 collagen fibres in the extracellular matrix
What gives bone its hardness?
The ground substance (osteoid) in the extracellular matrix that becomes mineralised by the deposition of calcium hydroxyapatite
List the types of cells in bone
Osteoprogenitor cells
Osteogenic cells
Osteoblasts
Osteocytes
Osteoclasts
What is the role of osteoprogenitor cells?
Precursor cells that self replicate or differentiate into bone-forming cells
What is the role of osteoblasts?
Form bone matrix - deposit osteoid and control subsequent mineralisation
What is the role of osteocytes?
Maintain bone tissue - modified osteoblasts that become surrounded by newly formed bone and regulate homeostasis
What is the role of osteoclasts?
Resorb bone - large multinucleated phagocytic cells that resorb bone and break down calcified matrices (originate from haemopoietic stem cells)
Describe the appearance of woven (immature) bone, as seen on light microscopy
- Randomly arranged collagen fibres in the osteoid. Looks disordered.
- Produced when osteoid is produced rapidly (eg. foetal bone, healing fracture and in bone diseases such as Paget’s disease)
- Eventually remodeled to form lamellar bone
Describe structure of the two types of lamellar bone, and their appearance, as seen on light microscopy
- Mature bone (Stronger than woven bone) - regular parallel bands of collagen fibres in the osteoid
- Within mature lamellar bone, there are two subtypes: compact bone and cancellous (trabecular, spongy) bone
Compact: lamellae are organised in concentric layers of mineralised bone matrix. Haversian canals (neurovascular channels) run through the middle of lamellae (along axis of bone) and provide nutrient supply to tissue. A lamella surrounding a haversian canals is together referred to as an haversian system or osteon. Osteoblasts become encased in small hollows within matrix lacunae. Osteocytes have several thin processes, which extend from the lacunae into small channels within the bone matrix canaliculi.
Cancellous bone (also called trabecular bone or spongy bone): Has irregular lamellae. Bony trabeculae are separated by interconnecting spaces containing bone marrow. Lamellae do not form Haversian systems, though still has organisation.
In compact bone, how do osteocytes communicate with each other and exchange substances via diffusion?
Via canaliculi
Canaliculi arising from one lacuna may anastomose with those of other lacunar and eventually, with larger, vessel-containing canals within the bone
List and explain the two ways in which foetal bone development occurs.
Two ways: 1. endochondral ossification 2.intramembranous ossification.
- Both involve replacement of primitive collagenous tissue by bone. Resulting woven bone then extensively remodelled by resorption and appositional growth to form the mature adult skeleton (lamellar bone). Bone development is controlled by growth hormone, thyroid hormone and the sex hormones.
1. Endochondral ossification: Long bones, vertebrae, pelvis and bones of the base of the skull are formed this way. Bones preceded by the formation of a continuously growing cartilage model which is progressively replaced by bone. Cartilage model forms, then periosteal bone colar forms. Cartilage is calcified via deposition of asteoid by osteoblasts. Vascular mesenchyme enters. Zones of ossification form. Growth plate fuses as growth stops. The bones formed in this way are called cartilage bones.
2. Intramembranous ossification: Bones of the vault of the skull, the maxilla and most of the mandible are formed this way. Involves the deposition of bone within primitive mesenchymal tissue. The bones formed in this way are called membrane bones.
