Bone Types and Histogenesis

Bone Types

• Bone is organized into two forms: compact and cancellous bone.

Compact Bone

• Sites:

  • Shaft of long bones
  • Outer part of short and flat bones
  • Outer part of epiphysis

• Structure:

  • Covered by periosteum and lined with endosteum
  • Contains osteons (Haversian systems)
  • Haversian systems are composed of a Haversian canal surrounded by concentric lamellae, with interstitial lamellae between them
  • Outer and inner circumferential lamellae are at the periosteum and endosteum, respectively

Cancellous Bone

• Sites:

  • Center of flat bones and irregular bones
  • End of long bones

• Structure:

  • Composed of irregular trabeculae of bone
  • Separated by bone marrow spaces
  • Trabeculae consist of osteocytes and intercellular substance
  • Covered with endosteum
  • Lacks Haversian systems

Histogenesis of Bone

• Bone forms in two ways:
  • Intramembranous ossification: direct mineralization of matrix secreted by osteoblasts. Occurs in flat bones (skull, clavicle)
  • Endochondral ossification: deposition of bone matrix on preexisting cartilage matrix. Occurs in short and long bones.

Intramembranous Ossification

• Site: Most flat bones, skull, clavicle, and most cranial bones.
• Steps:
  • Primary center of ossification appears in mesenchymal connective tissue.
  • Mesenchymal cells differentiate into osteoprogenitor cells, then osteoblasts.
  • Osteoblasts produce osteoid, which then calcifies.
  • Osteoblasts become osteocytes.
  • Connective tissue remains, becoming bone marrow cells within the spongy bone.

Endochondral Ossification

• Site: within a piece of hyaline cartilage, forming short and long bones.
• Steps:
  • Primary center of ossification in the middle of the diaphysis.
  • Bone tissue forms a collar around cartilage.
  • Cartilage undergoes degeneration, forming calcified cartilage.
  • Blood vessels from the periosteum invade calcified cartilage.
  • Osteoblasts form spongy bone
  • Secondary centers of ossification at the epiphyses (occur after birth).
  • Epiphyseal plate persists, maintaining bone growth. The epiphyseal plate cartilage is eventually replaced and ossifies.

Growth in length of bone

• Before adulthood, interstitial growth of cartilage in the epiphyseal plate increases bone length.
• This process stops at around 17 to 20 years, leading to closure of the epiphyseal plate.

Bone Remodeling and Repair

• Previously discussed (likely described in previous parts of the lecture).

Zones of the Epiphyseal Plate

• Five zones, described in greater detail in the lecture.

Explore the different types of bones, including compact and cancellous bone, as well as their structures and locations. Delve into the processes of bone histogenesis, including intramembranous ossification. Test your knowledge on bone anatomy and development with this comprehensive quiz.