Bone Flashcards
What are the functions of bone?
Act as a support to bear weight.
Act as protection (skull:brain, vertebrae:spinal cord)
Is used as a mineral store.
Is used for blood formation (red bone marrow)
Describe the gross anatomy of bone
Compact bone Spongy (trabecular) bone These are both macroscopic. Blood vessels Medullary cavity Bone marrow Membranes (periosteum is outside of bone and endosteum is inside cell)
What is the arrangement of the compact bone?
It is organised in circular structures called Osteons/haversian systems.
Central Haversian canal in the centre of an osteon with horizontal perforating Volkmann’s canals. Filled with nerve, blood and lymph passes through.
Osteocytes and concentric rings of bone matrix (lamellae) around Haversian canals.
Describe the structure of trabecular bone
Is known as cancellous/spongy/trabecular bone or diploe. It is less dense then compact bone.
It is a network of lamellated trabeculae filled with bone marrow.
The orientation of the trabeculae reflects the direction of the mechanical force.
Name six types of bone and give examples of them
Long bone (femur) Sesamoid bone (patella) Irregular bone (vertebra) Short bone (carpal) Flat bone (frontal) Sutural bone
Describe the process of endochondral ossification?
It is the most common type of growth and is used for the long bones especially.
The bone starts off as a cartilage model and the blood vessels are formed within the model. The cartilage is then replaced with bone starting from a primary ossification centre. Cartilage remains within the epiphyseal growth plate but this eventually ossifies.
Describe the process of intramembranous ossification
There is no cartilaginous phase.
Mesenchymal stem cells turn into osteoprogenitor cells that mature into osteoblasts that start depositing bone. Residual mesenchymal cells turn into blood vessels and bone marrow.
This process also occurs in adult cortical bone.
What makes up bones?
Osteoblasts
Osteocytes
Osteoclasts
These are cells
The extracellular matrix.
45% hydroxyapatite crystals (complex form of calcium phosphate)
35% Type 1 Collagen
20% water
What are the functions of hydroxyapatite and collagen?
Hydroxyapatite makes the bone stiff so it is able to support structures and it has high strength under pressure.
Collagen gives the bone flexibility to reduce fracture risk and high strength under tension.
Why is bone considered a dynamic tissue?
It’s good at repairing fractures due to the constant turnover. Mechanical adaptations mean that bones have to adapt to new regimes so the bone is thicker in more used areas.
What are osteoblasts?
They are immature bone cells created from osteopregenitor cells in the periosteum and endosteum.
They produce the bone matrix and initiate calcification. (Unmineralised bone Matrix is called osteoid)
They become osteocytes once they are surrounded by the bone matrix.
What are osteocytes?
They are mature bone cells found in lacunae(gaps).
Canaliculi connect lacunae to each other so allows for cell to cell communication.
Osteocytes may maintain the bone matrix and sense mechanical forces.
What are osteoclasts?
These are multinucleate cells derived from monocytes/macrophages and they’re found on the bone surface. They’re large cells with a ruffled borders and they resorb bone matrix and release acid that eats away at bone. Howship’s lacunae are resorption pits.
Describe the structure of the extracellular matrix
Mainly made up of minerals, protein and water with modified type one collagen fibres. These are strongly cross linked and there are large gaps within fibres which provide space for hydroxyapatite crystals. It’s the collagen fibre orientation that’s linked to mechanical forces.
Describe some bone diseases
Osteoporosis is when resorption of bone is higher than the formation so there is reduced density in the trabecular bone so the bones are weaker, different shape and more prone to fracture.
Paget’s disease is when resorption and formation of bone are too high and uncontrolled which causes deformation and pain as the bones are more likely to fracture due to lack of order and structure.
Osteopetrosis is when there isn’t enough resorption so the bone becomes like stone so is extremely dense.
