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The Growth of Bones and Cartilage

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VII. Bone Growth: Cell Terms

  • Cyte =
  • Osteo =
  • Chondro =
  • Genic =
  • Blast =
  • Clast =
  • Hema =
  • Poiesis =

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Cell

Bone

Cartilage

Producing

Budding

Breaking

Blood

Production

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VII. Bone Growth: Cells

4 Types of Bone Cells

  • Osteogenic: Stem cells
  • Osteoblasts: build bone matrix
  • Osteocytes: mature bone cells
  • Osteoclasts: maintenance control

Video Link: Bone Cells

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VII. Bone Growth: Cells

1. Osteogenic cells

      • Found in the inner fibrous layer beneath the periosteum, endosteum, and larger canals containing blood vessels
      • Unspecialized stem cells
      • Only bone cells to undergo cell division
      • Develop into osteoblasts

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VII. Bone Growth: Cells

2. Osteoblasts

      • Deposit bone matrix
      • Found at margins of growing bone
      • Initiate the process of calcification.
      • Found in both the periosteum and the endosteum and in the growth plate

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Osteoblasts

The blue arrows indicate the osteoblasts. The yellow arrows indicate the bone matrix they’ve just secreted.

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VII. Bone Growth: Cells

3. Osteocytes

      • Mature bone cells.
      • trapped osteoblasts.
      • No longer secrete matrix.
      • Responsible for maintaining the bone tissue.
      • Live in their own lacunas.

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VII. Bone Growth: Cells

4. Osteoclasts

    • Numerous nuclei
    • Digest bone matrix – bone resorption – part of normal bone growth, development, maintenance, and repair.
    • Concentrated in the endosteum and in spongy bone
    • Secretes digestive enzymes and acid that break down proteins and mineral components of bone
    • Release Ca+ into the body as needed

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How do our bones grow?

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VII. Growth: Epiphyseal Plate

Articular cartilage

Epiphyseal plate

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VII. Growth: Epiphyseal Plate

Before puberty, cartilage and bone grow in the same direction at the same rate.

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After puberty, bone accelerates and eventually “catches up” to cartilage, and then the growth plate is gone and the bone doesn’t grow any longer.

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VII. Growth: Epiphyseal Plate

Divided into

  • Resting
  • Proliferating
  • Hypertrophic
  • Calcified

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Epiphyseal Plate

Images and Text © Dr Brendan Wilkins 2001 - 2005

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VII. Growth: Epiphyseal Plate

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VII. Growth: Epiphyseal Plate

  • Resting
    • Scattered Chondrocytes
    • Do not function in cell division and growth
  • Proliferating
    • Cells divided
    • Organize into “stacks of coins”

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VII. Growth: Epiphyseal Plate

  • Hypertrophic
    • Cells increase in size, swell up
  • Calcified
    • Only a few cells thick
    • Chondrocytes die off
    • Calcified cartilage is dissolved by osteoclasts
    • Osteoblasts move in to initiate bone developement

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Growth at growth plate - very cool video

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osteoporosis postmenopause

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VII. Other types of Bone Growth:

  • Endochondral Ossification
    • long bones until puberty:

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VII. Bone Growth: Endochondral Ossification

  • Pre Step 1:
    • Cartilaginous skeleton forms
  • Step 1:
    • Chondrocytes die due to slowing nutrients
    • osteoblasts move in
  • Step 2:
    • Shaft is covered in bone

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VII. Bone Growth: Endochondral Ossification

  • Step 3:
    • Vascularization
    • Spongy bone in “Primary Ossification center”
  • Step 4:
    • Shaft thickens
    • Cartilage and bone grow at the same speed
  • Step 5:
    • Secondary Ossification center forms as the epiphyseal center calcifies
    • Medullary Cavity is carved out

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VII. Bone Growth: Endochondrial Ossification

  • Step 6:
    • Puberty accelerates bone growth
    • Growth plate closes

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VII. Other types of Bone Growth:

  • Intramembranous Ossification
    • Forms flat bones between two thin membranes

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  • Appositional Growth
    • Growth in thickness including widening the medullary cavity

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Endochondral Ossification

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VII. Bone Growth: Requirements

  • Prenatal:
    • minerals and calcium salts taken from mother
  • Through Adulthood:
    • Vitamins, calcium, and phosphate
    • Vitamin D3 – liver processing produces calcitriol. Calcitriol is hormone that stimulates absorption in the digestive system
      • Rickets: Vitamin D3 deficiency resulting in bendy bones and bowed legs
      • Scurvy: Vitamin C deficiency resulting in lowered osteoblast activity causing weakened bones

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VII. Bone Growth: The Matrix

  • ⅓ organic: Collagen protein fibers create a scaffold (like rebar, except flexible) and flexibility
  • ⅔ Inorganic: Minerals like Calcium, create the more hard matrix

This bone has been demineralized (Inorganic components like calcium have been removed)