6.3 endochondral and intramembranous ossification

intramembranous ossification.

process by which bone forms directly from mesenchymal tissue

where do long bones contain secondary ossification centers?

within their epiphyses

most common cause of dwarfism

Achondroplasia

what bones of the body are formed by the process of endochondral ossification ?

All the bones in the body below the head, except the clavicles,

event 4 of endochondral ossification

As the medullary cavity enlarges, the remaining cartilage is replaced by bone; the epiphyses finish ossifying

primary ossification center.

During intramembranous ossification, the inner spongy bone forms before the outer compact bone, beginning at this place

event 3 of endochondral ossification

In the primary ossification center, osteoblasts replace the calcified cartilage with early spongy bone; the secondary ossification centers and medullary cavity develop

What bones develop from intramembranous ossification?

Many flat bones, including the skull and the clavicles, form during fetal development

event 2 of endochondral ossification

Osteoblasts build the bone collar on the external surface of bone. Simultaneously, the internal cartilage begins to calcify and the chondrocytes die

event 1 of intramembranous ossification

Osteoblasts develop in the primary ossification center from mesenchymal cells.

event 4 of intramembranous ossification

Osteoblasts in the periosteum lay down early compact bone

event 3 of intramembranous ossification

Osteoblasts lay down trabeculae of early spongy bone, and some of the surrounding mesenchyme differentiates into the periosteum.

event 2 of intramembranous ossification

Osteoblasts secrete organic matrix, which calcifies, and trapped osteoblasts become osteocytes.

event 1 of endochondral ossification

The chondroblasts in the perichondrium differentiate into osteoblasts.

What do fontanels in newborns represent?

areas of incomplete fusion

Where does endochondral ossification begin?

begins at primary ossification centers, and the bone laid down is primary bone that is eventually replaced with secondary bone

what does the hyaline cartilage model consist of?

consists of chondrocytes and cartilage ECM, and is surrounded by a connective tissue membrane called the perichondrium and immature cartilage cells known as chondroblasts

what is the period of endochondral ossification?

it begins during the fetal period for most bones, although some, such as those in the wrist and ankle, ossify much later. Many bones complete this ossification process by about age 7.