L4.4.3: Bone Growth

• Bone growth is controlled by hormones, such as growth hormone and sex hormones
• EPIPHYSEAL PLATE

  ● Is the area of elongation in the long bone.

  ● Includes hyaline cartilage

  ● Ossification can continue to occur:

  • Diaphyseal side
  • Epiphyseal side
• DIAPHYSEAL SIDE

  ● Cartilage calcifies then dies and replaced by bones
• EPIPHYSEAL SIDE

  ● Cartilage remains to be active and continues to divide and secretes hyaline cartilage matrix
• APPOSITIONAL GROWTH

  ● Bones grow in width

  ● Osteoblasts in the periosteum add bone matrix to the outside of the diaphysis

  ● Osteoclasts in the endosteum remove bone from the inner surface of the diaphysis
• GROWTH OF LONG BONES

  [1] Osteoblast Covering Cartilage Model w/ Bone Matrix

  ● Bone starts as a hyaline cartilage.

  ● The osteoblasts secretes the bone matrix which dominates the entire cartilage.

  ● As the embryo develops, the cartilaginous bone is replaced.
• GROWTH OF LONG BONES

  [2] Enclosed Cartilage is Digested Away

  ● In a fetus, the enclosed cartilage is digested away, opening up a medullary cavity.

  ● The shaft won’t have any cartilaginous component anymore because the bone matrix has completely replaced the hyaline cartilage.

  ● Cartilage is concentrated on the epiphysis (ends).
• GROWTH OF LONG BONES

  ● By birth, most cartilage is converted to bone except for two regions in a long bone.

  ○ Articular Cartilages

  ○ Epiphyseal Plates

  ● New cartilage is formed continuously on the external face of these two cartilages.

  ● Old cartilage is broken down and replaced by bony matrix