Bone and Bone development

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Bone Cells

  • Osteocyte: Mature bone cell
  • Osteoblast: Responsible for creating new bone
  • Osteoclast: Responsible for removing old/dead bone cell
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Bone Structure

Bones are specialised connective tissue so it is made up of standard componants:

  • Ground Substance/ Matrix: A solid matrix made up of calcium phosphate.
  • Cells: Osteocytes
  • Fibres: Collagen for stregnth and resiliance.

Made up in concentric circles (like a tree trunk) known as Lamellae arranged around a central Haversian Canal that contains nerves, blood vessels and lymphatic vessels. Osteocyes are positioned within Lacunae within lamella

There are 2 types of bone tissues:

  • Compact / Cortical Bone:
    •  Has tightly packed Haversian systems
    • Strong and dense
    • Found in cortex (outer edge)
  • Cancellous / Spongy Bone:
    • Lighter than compact bone
    • Made up of bars called trabeculae
    • Found at end of long bones and core of others 
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Haversian System

(http://cronodon.com/images/bone_2b.jpg)

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Functions

  • Support: Scaffold of the body and houses sensory organs. 
  • Locomotion: Skeletal muscles attach to the bones and pull on them for movement.
  • Protection: Form a protective cage for vital organs.
  • Storage: Calcium is stored within the bones.
  • Haematopoiesis: Blood cells are produced withing the bone marrow.
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Classification and Examples

  • Long : Humerous, Ulna, Femur, Tibia, Phalanges
  • Short : Carpal and Tarsal Bones
  • Irregular : Vertebrae
  • Flat : Scapula, Pelvic bone, Ribs
  • Sesamoid : Patella , Fabellae
  • Pneumatic / air filled : Frontal bone, Maxillary bone, some long bones in birds
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Components of Long Bones

Diaphysis  : Main shaft of bone

Epiphysis :  Ends of bone

Metaphysis : Where diaphysis and epiphysis meet. Growth plate in young animals

Articular Cartilage : Hyline cartilage that covers ends of bones

Periosteum : Membranous structure that surrounds outer surface of the bone

Nutrient Foramen : Small hole where blood vessels enter the bone 

Cortex : Outer region of compact bone

Medulla : Central cavity of bone, filled with bone marrow

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Diagram

                               Structure of a long bone (http://www.buzzle.com/images/diagrams/human-body/structure-of-a-long-bone.jpg) 

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Ossification

Endochondral: Occurs in all bones except flat bones

  • Occurs in diaphysis (primary ossification centre)
  • Osteoblasts replace cartillage with bone (develops outwards)
  • Secondary ossification centres develop in epiphysis (develops outwards towards diaphysis)
  • Osteoclasts reabsorb centre of bone forming medullary cavity
  • 2 bands of cartilage forms between diaphysis and epiphysis forming growth plates
  • When cartilage is replaced with bone, no further growth occurs

Intramembranous: Occurs in flat bones only

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