Bone

• Bone is one of the hardest tissues of the human body and second only to cartilage in its ability to withstand stress..

  • It supports fleshy structures
  • Protects vital organs
  • Contains bone marrow
  • Composed of intercellular calcified material, the bone matrix.

   
• Osteoblasts (blasts immature osteocytes)

  • Which produce the organic components of the matrix, collagen and glycoprotein
  • Exclusively located on surfaces of bone tissue, side by side (look like simple epithelium)
  • Newly produces, not yet calcified matrix adjacent to the osteoblasts is termed osteoid
• Osteocytes

  • Found in cavities within bone matrix
  • Encapsulated in laminas of the mineralised bone matrix
• Osteoclasts

  • Multinucleated giant cells involved in reabsorption and remodel of bone
  • Very large, extensively branched motile cells.
  • Branches of cell are irregular and vary in both thickness and shape
• Decalcification of Bone

  Bone is hard so is difficult to section with a microtome - require special techniques such as decalcification.

  Following fixation in a standard fixative, the mineral component of the bone is removed by immersion in a dilute acid solution, such as 5% nitic acid

  Calcium chelating substances such as EDTA can also be used.

   
• Layers of Bone

  Inorganic matter represents about 50% of dry weight of matrix.

  Calcium and phosphorous are especially abundant, but bicarbonate, citrate, magnesium, potassium and sodium can be found.

   

  Periosteum & Endosteum

  • Internal and external surfaces of the bone are covered by layers of connective tissue
• Types of Bone

  Gross observation of bone in cross section shows:

  • Dense areas without cavities, corresponding to compact bone
  • Areas with numerous interconnective cavities -> spongy bone

  In long bones, the bulbous ends, called epiphyses, are composed of spongy bone covered by a thin layer of compact bone.

  The cylindrical part, the diaphysis, is almost totally composed of compact bone, with a small component of spongy bone in its inner position around the bone marrow cavity.
• Spongy Vs Compact

  Short bones usually have a core of spongy bone completely surrounded by compact bone.

  First bones have 2 layers of compact bone called plates, separated by a layer of spongy bone called the diploe.

  Irregular bones vary in shape and structure and therefore do not fit into any other category (flat, short, long or sesamoid). Often have a fairly complex shape, which helps protect internal organs.
• Pain


  • Stimulation of nerve endings in bone due to inflammation
  • Trauma (fracture)
  • Tumour
  • Pathological increase in bone reabsorption (e.g. Paget's disease)
• Fracture after trivial injury

  • Bone weakened due to congenital disorders of bone integrity
  • Metabolic bone disease
  • Erosion of bone by tumour
• Deformity


  • Abnormal bone growth/remodelling due to congenital disorders of bone integrity
  • Metabolic bone disease
  • Mal-union of a fracture
  • Hypercalcaemia
  • Extensive bone erosion by tumour deposits
  • Secretion of parathyroid hormone by parathyroid adenoma
  • Secretion of PTH-related peptide by visceral tumours e.g. carcinoma of the bronchus
• 2 varieties of bone tissue:

  • Immature, primary or woven bone.
  • Mature, secondary or lamellar bone
• Primary bone tumours are quite rare. Most common tumour found in bone is metastatic carcinoma in particular:

  • Breast
  • Kidney
  • Thyroid
  • Lung
  • Prostate
• Important primary malignant bone tumours are:

  • Osteosarcoma
  • Chondrosarcoma
  • Ewing's sarcoma
•  

  1. Benign tumours

  • Osteochondroma (bone - cartilage - benign)
  • Enchondroma
  • Chondroblastoma (cartilage - immature bone cells - benign)
  • Chondromyxoid fibroma
  • Osteoma
  • Osteoid osteoma

  1. Borderline tumours

  • Giant cell tumour
  • Osteoblastoma
  • Chordoma
  • Adamantinoma

  1. Malignant tumours

  • Osteosarcoma
  • Chondrosarcoma (malignant tumour of cartilage)
  • Fibrosarcoma
  • Malignant fibrous histiocytoma
  • Ewing's sarcoma

  1. Metastases (to bone)

  • Breast
  • Lung
  • Prostate
  • Kidney
  • Thyroid

  1. Myeloma

  • Multiple myeloma
  • Solitary plasmacytoma