Week 1: Bone Flashcards
Describe the structural organisation of bone:
- Strong and rigid CT
- Provide support and protection to the body, involved in load bearing and articulation
Describe the structural organisation of the periosteum:
Dense fibrous connective tissue/outer condensed collagen layer - absent at articular surfaces & at points of insertion of tendons and ligaments (enthesis)
Describe the structural organisation of the endosteum:
Cellular layer (osteoprogenitor cells, osteoblasts, osteoclasts etc.)
Describe the role of the medullary cavity:
Site to store hemopoietic tissue (bone marrow) and fat
Describe the overall structure of a long bone
Diaphysis, Metaphysis, Epiphysis
Define epiphysis:
Expanded articular end - protected by a layer of articular cartilage which covers the articular surface
Define diaphysis:
Shaft of the bone
Define metaphysis:
Wider part of the developing bone where the diaphysis meets the epiphysis.
- Contains epiphyseal (growth) plate.
- Once growth is complete it ossifies.
What is the role of compact/cortical bone?
- Give strength and rigidity
- Resist tensile forces/bending
- Limited to the outer parts of the bone (shaft of long bone) or to the cortex of mature bone
What is the role of trabecular/cancellous bone?
- Provide support to the bone while minimizing the weight
- Resist compressive forces/ stress applied form different directions
- Seen in epiphysis, vertebral bodies
Describe the distribution of cortical and cancellous bone in the diaphysis and epiphyses:
Diaphysis: cortical bone forms the dense walls of the diaphysis while a very small amount of cancellous bone occupies part of the central medullary cavity
Epiphyses: typically consist of a thin outer layer of compact bone while internally the bone is cancellous
Describe the distribution of cortical and cancellous bone in human vertebrae.
Why does this arrangement exist?
Vertebrae are primarily composed of cancellous bone with a thin outer layer of cortical bone. This arrangement allows the vertebrae to sustain large compressive forces with a minimal amount of bone
What is oteoporosis?
Loss of bone density - fracture, altered force distribution
What is the extracellular matrix (osteoid) made up of?
- Inorganic (60-70%)
– Mineral salts, hydroxyapatite, calcium phosphate
– Hard, resists compression, deformation - Organic (30-40%)
– Collagen fibres (synthesised by osteoblasts)
– Ground substance
– Resists tension and bending forces
What are the 3 bone cells?
- Osteoblasts: bone-forming cell, small, responsible for synthesis and secretion of organic matrix, osteoids, that undergoes mineralisation to form bone
- Osteocytes: mature bone cell derived from osteoblasts, gives integrity to bone, found in lacunae between layers of bone tissue
- Osteoclasts: bone-removing cell, large, multi-nucleated
What are lamellae? Identify the 2 different types.
Layers of ossified extracellular matrix
- Interstitial - between Haversian systems
- Circumferential - Periphery of the bone is surrounded by circumferential lamellae
What are haversian systems/osteons?
Bony tubes that lie parallel to each other along the long axis of the bones
What is the haversian canal?
- Tube in the Haversian system
- Has 1 or 2 capillaries lined by fenestrated endothelium, and a few unmyelinated axons.
What are the Volkmann’s canals?
- Communicate haversian canals with each other
- These channels connect with medullary and periosteal vessels.
What are the lacuna?
- Spaces within the Harversian system
- Each space has an osteocyte
- The lacunae are interconnected by fine canals, the canaliculi (connect osteocytes through processes).
What is the myotendinous junction?
The junction between the muscle and the tendon
What is the osteotendinous junction
The junction between the bone and the tendon
What is intramembranous ossification?
Direct formation of bones from mesenchymal stem cells that develops into osteoprogenitor cells
E.g., Skull bones, clavicle
What is endochondral ossification?
Hyaline cartilage template model is formed, which is later converted to bone
Centres of Ossification:
* One primary (diaphysis) - appear between 7th and 12th week of intrauterine life.
* Several secondary (epiphysis) - appear after birth
E.g., long bones etc.
Describe the process of bone elongation:
- Occurs at a growth or epiphyseal plate
- Cartilage proliferates continuously - elongation of bone
- Reaching maturity growth plates are replaced by bone
What happens if a growth plate injury (fracture) occurs?
It alters normal growth and development
A twelve year old netballer trips during a game, and falls heavily on her right leg, causing a fracture. The epiphyseal plate of her right tibia is severely damaged in the fracture. What are the possible consequences of such an injury?
As the patient is twelve years of age the epiphyseal plate is still patent, with growth still potentially occurring. Damage to the epiphyseal plate interferes with bone elongation. As a result, her tibia and therefore her leg may be shorter than normal
What might happen if an epiphyseal plate was subjected to considerable shear force? An example is a “slipped capital femoral epiphysis”, which occurs from trauma.
The epiphyseal plate might separate (from either the diaphysis or the epiphysis) allowing the epiphysis to slip out of alignment with the diaphysis. This can cause lifelong joint problems if not carefully managed
Why do epiphyseal (growth) plates appear as a ‘gap’ on radiograph?
Because growth plates are composed of cartilage
How do bones grow in width?
- Periosteal (external) surface: osteoblasts
- Endosteal (internal) surface: osteoclasts
As bone is being added to the outer surface through appositional growth, osteoclasts are removing and recycling lamellae at the inner surface. As a result the medullary gradually enlarges as the bone increases in diameter.
Describe 2 age-related and congenital changes in bone:
- Osteopenia
* Inadequate ossification - Osteoporosis
* Reduction in bone mass
* Microstructural changes
The activity of osteoclasts is more than osteoblasts, so more bone is being resorbed than produced. Can lead to fracture and deformity.
Why do injuries to bone typically heal quickly and well?
Because bone is well vascularised
Why are disease processes (e.g. tumour) within bone painful?
Bone is innervated via nerves which run with the blood vessels
What is the nutrient foramina?
Long bones often have a larger main artery (nutrient artery) entering the shaft. This supplies most of the marrow and cortex, its branches running in the Haversian canals of the compact bone.
What is the vascular foramina?
The ends of long bones typically have several smaller arteries entering and several veins leaving, so numerous vascular foramina are usually visible on the epiphyses of dried bones.
What is articular (hyaline) cartilage?
It is a tissue that has a high concentration of water and it covers the articulating surfaces (ends) of bones
What are the main functions of chondrocytes?
Responsible for the manufacture, secretion and maintenance of articular cartilage, a tissue which has a high concentration of water
What are 2 important functions of articular cartilage?
- Allow relative movement of opposing joint surfaces with minimal friction and wear
- Distribute loads, thereby decreasing stresses sustained by the contacting joint surfaces
Does articular cartilage have an abundant or poor blood supply? What implications this have for healing?
Avascular tissue (reflected in its pale colour) – nourished by diffusion from synovial fluid of the joint cavity. If damaged it has limited (to no) capacity to heal
What would you notice when looking at the articular cartilage from an individual with osteoarthritis compared to normal, healthy articular cartilage? What implications might this have on function of the joint?
Thinning and loss of cartilage; Cartilage softens and the smooth surface disrupted, becoming rough with gaps (fibrillation) in the tissue; changes in chondrocyte morphology and arrangement (haphazard)
Functional implications – decreased capacity to distribute forces through the joint, and increased friction with joint movement
