intramembranous ossification

Examples of intramembranous ossification in the following topics:

• Embryonic and Fetal Bone Formation

  • During fetal development, bone tissue is created through intramembranous ossification and endochondral ossification.
  • The skull and vertebral column are produced by intramembranous ossification.
  • Intramembranous ossification is one of the two essential processes during fetal development of the mammalian skeletal system.
  • Unlike the other process of bone creation— endochondral ossification—intramembranous ossification does not involve cartilage.
  • Unlike intramembranous ossification, cartilage is present during endochondral ossification.

• Bone Development

  • Intramembranous ossification stems from fibrous membranes in flat bones, while endochondral ossification stems from long bone cartilage.
  • The development of bone from fibrous membranes is called intramembranous ossification; development from hyaline cartilage is called endochondral ossification.
  • Intramembranous ossification is the process of bone development from fibrous membranes.
  • They then differentiate into osteoblasts at the ossification center.
  • Endochondral ossification is the process of bone development from hyaline cartilage.

• Stages of Bone Development

  • The formation of bone during the fetal stage of development occurs by two processes: intramembranous ossification and endochondral ossification.
  • Intramembranous ossification mainly occurs during the formation of the flat bones of the skull, as well as the mandible, maxilla, and clavicles.
  • The steps in intramembranous ossification are:
  • Endochondral ossification begins with points in the cartilage called "primary ossification centers."
  • They mostly appear during fetal development, though a few short bones begin their primary ossification after birth.

• Development of the Skeleton

  • Early in gestation, a fetus has a cartilaginous skeleton that becomes bone in the gradual process of endochondral ossification.
  • Early in gestation, a fetus has a cartilaginous skeleton from which the long bones and most other bones gradually form throughout development and for years after birth in a process called endochondral ossification.
  • Intramembranous ossification is the direct laying of bone into the primitive connective tissue (mesenchyme).
  • Endochondral ossification involves cartilage as a precursor.
  • Chondrocytes in the primary center of ossification begin to grow (hypertrophy).

• Fontanels

  • The ossification of the bones of the skull causes the fontanelles to close over a period of 18 to 24 months; they eventually form the sutures of the neurocranium.
  • This is called intramembranous ossification.

• Growth of Bone

  • It is a layer of hyaline cartilage where ossification occurs in immature bones.
  • The newly-deposited bone tissue at the top of the zone of ossification is called the primary spongiosa.
  • The older bone at the bottom of the zone of ossification is called the secondary spongiosa.
  • At the same time, osteoblasts via intramembranous ossification, produce new bone tissue beneath the periosteum.
  • The bottom-most row is the zone of ossification which is part of the metaphysis.

• Postnatal Bone Growth

  • Secondary ossification occurs after birth at the epiphyses of long bones and continues until skeletal maturity.
  • Secondary ossification occurs after birth.
  • During postnatal bone formation, endochondral ossification initiates bone deposition by first generating a structural framework at the ends of long bones, within which the osteoblasts can synthesize a new bone matrix.
  • Zone of bone deposition (ossification): The walls between the lacunae break down and the chondrocytes die.
  • Differentiate among the zones of development from cartilage to bone in postnatal ossification

• Sutures

  • As such, the degree of ossification can be a useful tool in determining age postmortem.

• Fibrous Joints

  • Except for the mandible, all are joined together by sutures, semi-rigid articulations formed by bony ossification.

• Cartilaginous Joints: Synchodroses

  • Depletion of chondrocytes due to apoptosis leads to less ossification, and growth slows down and later stops when the cartilage has been completely replaced by bone.