Musculoskeletal Flashcards
What area of the embryological animal does bone arise from?
Mesenchyme - mesoderm
Which type of ossification forms flat bones?
Intramembranous
Describe intramembranous ossification.
- Remember it must be an area of high oxygen tension.
- OBs cluster in the fibrous membrane forming a COO, start secreting osteoid
- OBs secrete collagen and ECM into which Ca is secreted leading to trabeculae formation
- Appositional growth occurs as woven bone is replaced by lamellar bone
- OBs become trapped in lacunae and become OCs
- Progenitor cells on the surface differentiate to OBs
- Bone marrow fills spaces between trabeculae
- The fibrous membrane from 2 becomes the periosteum
Describe the difference between appositional and interstitial growth.
Appositional = change in width
Interstitial = change in length
Describe Endochondral ossification.
- Originates from hypoxic mesechyme
- A cartilage model is laid down covered by perichondrium
- Blood vessels penetrate model mid-shaft, this stimulates differentiation to OBs
- OBs form a collar around the bone diaphysis
- Capillary beds penetrate diaphysis cause chondrocyte hypertrophy - cells burst increasing pH and intracellular calcification
- Intracellular substance degenerates and leaves cavities - forms marrow cavity when infiltrated by blood vessels
True or false
Bones grow in width by endochondral ossification
False, they grow in length by endochondral and in width by intramembranous
How do joint cavities develop?
By apoptosis.
Which structures of the joint are covered by synovium?
Surfaces of ligaments.
Not covered are articular surfaces and synovium
Osteoid seam
The layer of superficial non-mineralised osteoid.
Osteoid
Unmineralised bone matrix initially deposited by a layer of osteoblasts.
Primary mineralisation
Occurs around 8-10 days after osteoid secretion. The initial 70-75% of mineralisation.
Secondary mineralisation
Complete bone mineralisation to final bone density. Occurs over several months
Name and describe the four cell types found in bone.
- Osteoblasts - Osteoid formation, initial mineralisation and reg factors production
- Osteocytes - Produce and absorb immediately local bone. Communication
- Osteoclasts - Reabsorption of bone. Produce low pH acid which dissolves bone salts, and proteolytic enzymes which dissolve osteoid
- Bone marrow stromal cells - haematopoietic growth factors, OB progenitor cells, PTH, strain gauge (activate remodelling)
Describe the morphological features of active and inactive OBs.
Active = Pear shaped, cuboidal cells, abundant RER and golgi, basophilic, granular cytoplasm.
Inactive = flat, similar to squamous cells, line bone surface
Describe the morphology of osteocytes.
Minimal cytoplasm, projections which communicate with immediately adjacent cells through canaliculi of bone
Describe the morphology of an osteoclast.
Large, multinucleated cells, eosinophilic cytoplasms, found on bone surface.
Found within Howship’s lacunae when actively reabsorbing bones.
Describe the morphology of bone marrow stromal cells.
What four functions do they serve?
Spindle cells, margin of bone marrow, immediately above the osteoblast layer.
- Hematopoietic growth factors Eg: EPO and CSF
- Progenitor cells of the OB
- Provide vertical orientation of bone cell
- Establish the canalicular-lacunar system.
- React to parathyroid hormone stimulation
- Attract and stimulate OCl to remove bone
- Proliferate and form fibro-osseous matrix
- Strain gauges which activate bone remodelling.
What is the embryological origin of OCls?
Monomyelocytic stem cells
What are the organic components of the bone matrix?
- Osteoid - T1 collagen
- Other proteins - proteoglycans, osteonectin, osteopontin, etc
- Growth factors - FGF & TGFbeta - cause mitogenic responses in cells
Name the two main inorganic components of the bone matrix.
- Hydroxyapatite - Calcium and phosphorous
- Carbonate, Mg, Na, Zn, F also
Cancellous bone
aka Spongy
Tarbeculae surrounded by large spaces filled with marrow. Found along entire of flat bones and in the diaphysis of long bones.
Provides support and marrow storage.
Dense bone
aka compact bone.
Trabeculae are densely packed with few spaces. Deposited in layers over cancellous bone.
They layers of compact bone are thicker at the diaphysis.
Forms osteons in thick cortex
Cancellous and compact bones are both examples of which category of bone?
Lamellar - mature - layers of lamellae
Woven bone
Immature
Randomly oriented lamellae - becomes lamellar through remodelling.
Outline the process of OCl bone reabsorption.
An acid environment is created between the cell and the bone surface. Hydrogen and bicarbonate ions are generated from CO₂ and water by carbonic anhydrase on the brush border.
An ATP-mediated proton pump actively transfers hydrogen ions into the extracellular space. The acidity of the local environment induces demineralisation of bone and enhances the activity of acid hydrolases released from osteoclasts.
Fragments of degraded matrix are endocytosed by the osteoclast.