5.2 Bone Development And Growth

• What are the two processes by which bone grows?

  Intramembranous ossification and endochondral ossification
• What is the term for bone formation?

  Osteogenesis
• What are the skeletal elements composed of from fertilization to about eight weeks of age?

  Mesenchyme or hyaline cartilage
• At what age does the bony skeleton begin to form?

  Eight weeks
• Until what age does bone growth typically continue?

  Age 25
• What is ossification?

  The process of replacing other tissues with bone
• What does calcification refer to?

  The deposition of calcium salts within a tissue
• What are the two major forms of ossification?

  Intramembranous ossification and endochondral ossification
• In which type of ossification does bone develop from mesenchyme or fibrous connective tissue?

  Intramembranous ossification
• Which bones are formed through intramembranous ossification?

  The clavicle, mandible, and flat bones of the face and skull
• What occurs during endochondral ossification?

  Bone replaces an existing cartilage model
• What type of bones develop by endochondral ossification?

  The bones of the limbs and other weight-bearing bones
• What happens at maturity that stops bone growth?

  Epiphyseal closure
• How does the diameter of a bone increase?

  Through appositional growth at the outer surface
• What do stem cells of the inner layer of the periosteum differentiate into during appositional growth?

  Osteoblasts
• What do osteoblasts do during appositional growth?

  Add bone matrix to the surface
• What happens to deeper lamellae over time during bone growth?

  They are recycled and replaced with osteons
• What happens to blood vessels and collagen fibers of the periosteum during appositional growth?

  They can become enclosed within the matrix
• What occurs as osteoblasts add bone to the outer surface?

  Osteoclasts reabsorb bone matrix at the inner surface
• What happens to the medullary cavity as the bone increases in diameter?

  It gradually enlarges
• What is a foramen?

  An opening in a bone
• What do metaphyseal vessels supply blood to?

  The inner surface of each epiphyseal cartilage
• What do epiphyseal vessels supply?

  The osseous tissue and medullary cavities of the epiphyses
• What happens to blood vessels after the epiphyses close?

  They become extensively interconnected
• What does the periosteum contain besides blood vessels?

  An extensive network of lymphatic vessels and sensory nerves
• What do lymphatic vessels collect from the bone?

  Lymph
• Why are injuries to bones usually very painful?

  Because of rich sensory innervation
• What is necessary for normal bone growth?

  A constant dietary source of calcium and phosphate salts
• How can x-rays of the femur be used to determine whether a person has reached full height?

  Epiphyseal closure indicated by the epiphyseal line or presence of cartilage
• Briefly describe major steps in intramembranous ossification.

  In fibrous connective tissue, osteoblasts secrete matrix components in ossification center. Growth occurs outward from ossification center in spicules. Assumes shape of spongy bone then maybe compact
• Describe how bones increase in diameter?

  Appositional growth, stem cells of periosteum differentiate into osteoblasts and add bone matrix to surface
• What is the epiphyseal cartilage? Where is it located? Why is it significant?

  Cartilage separating epiphysus and diaphysus, located in metaphysis. Helps to grow the length of the bone
• List and describe the roles of vitamins and hormones in bone growth and regulation.

  • Vitamins for bone growth and remodeling
  • Calcitriol for calcium and phosphate absorption into blood
  • Parathyroid hormone stimulates osteoclasts and osteoblasts, as well as increases the rate of calcium loss
  • Calcitonin inhibits osteoclasts and increases calcium loss
  • Growth hormone and thyroxine is the puberty bone growth
  • Sex hormones stimulate osteoblasts to produce and grow bones faster
• Intramembranous is less organized
• Step I of INTRAMEMBRANOUS OSSIFICATION: Differentiation of Embryonic Mesenchyme

  • mesenchyme differentiates to osteoblast to make bone
  • osteoblasts secrete osteoid
  • osteoid will calcify
  • osteoblasts get trapped in lacunae
  • osteoblasts differentiate into osteocytes
  • blood vessels grow around primary ossification centers
• Step II of INTRAMEMBRANOUS OSSIFICATION: Spicule Development

  • bone centers connect each other
  • create spicules which look like trabeculae
  • blood vessels get trapped between spicules
  • feed tissue and bring in osteoclasts
• Step III of INTRAMEMBRANOUS OSSIFICATION: Woven (Lamellar) Bone

  • create young weak spongy and compact bone
  • bone starts to become recognizable
• Step IV of INTRAMEMBRANOUS OSSIFICATION: Expansion and Increase in Ossification Center

  • sandwich with compact-spongy-compact is diploe
  • top compact is periosteum, lower compact is endosteum
  • completes part of skull
• Endochondral requires more planning and starts with the hyaline cartilage which is flexible and stiff
• Step I of ENDOCHONDRAL OSSIFICATION: Make Cartilage

  • mesoderm differentiates to mesenchyme
  • mesenchyme wants to differentiate into either chondroblasts or fibroblasts
  • chondroblasts to build cartilage, when trapped in lacuna make chondrocytes
  • fibroblasts to be part of perichondrium, when metabolism slows it makes fibrocytes