from wiki:
The first site of ossification occurs in the primary center of ossification, which is in the middle of diaphysis (shaft). Then:
Formation of periosteum: Once
vascularized, the
perichondrium becomes the
periosteum. The periosteum contains a layer of undifferentiated cells (osteoprogenitor cells) which later become osteoblasts.
Formation of bone collar: The osteoblasts secrete osteoid against the shaft of the cartilage model (
Appositional Growth). This serves as support for the new bone.
Calcification of matrix: Chondrocytes in the primary center of ossification begin to grow (hypertrophy). They stop secreting collagen and other proteoglycans and begin secreting alkaline phosphatase, an enzyme essential for mineral deposition.
Then calcification of the matrix occurs and apoptosis of the hypertrophic chondrocytes occurs. This creates cavities within the bone. The exact mechanism of chondrocyte hypertrophy and apoptosis is currently unknown.
Invasion of periosteal bud: The hypertrophic chondrocytes (before apoptosis) secrete Vascular Endothelial Cell Growth Factor that induces the sprouting of blood vessels from the perichondrium. Blood vessels forming the periosteal bud invade the cavity left by the chondrocytes and branch in opposite directions along the length of the shaft. The blood vessels carry hemopoietic cells, osteoprogenitor cells and other cells inside the cavity. The hemopoietic cells will later form the bone marrow.
Formation of trabeculae:
Osteoblasts, differentiated from the osteoprogenitor cells that entered the cavity via the periosteal bud, use the calcified matrix as a scaffold and begin to secrete osteoid, which forms the bone trabecula. Osteoclasts, formed from macrophages, break down spongy bone to form the medullary (bone marrow) cavity.
Secondary center of ossification
About the time of birth, a secondary ossification center appears in each end (epiphysis) of long bones. Periosteal buds carry mesenchyme and blood vessels in and the process is similar to that occurring in a primary ossification center. The cartilage between the primary and secondary ossification centers is called the epiphyseal plate, and it continues to form new cartilage,
which is replaced by bone, a process that results in an increase in length of the bone. Growth continues until the individual is about 21 years old or until the cartilage in the plate is replaced by bone. The point of union of the primary and secondary ossification centers is called the epiphyseal line.
endochondral ossification is a procedure in the development of bone in which ?
hyaline cartilage is transformed into bone
calcified cartilage is replaced by bone
osteocytes of perichondrium form bone
osteons with cartilage lamellae are formed
plz ans with little explanation .
Its still hard to say for sure after reading the wiki article, but I think that osteocytes do not from bone, osteoblasts do, and once they are done painting themselves into a room they become osteocytes.
I think that the calcified cartilage (the matrix formed AROUND the apoptotic hypertrophied chondrocytes) is not replaced by bone, but rather is the scaffolding for it.
that leaves me thinking the answer is the first option, hyaline cartilage is transformed into the bone....since endochondral ossification is with hyaline cartilage...which is the most obvious answer with all the buzz words (and sometimes i think the most straightforward buzzword filled option is the best one and you shouldn't over think things too much...)
PS you should know this too!
During endochondral ossification, four distinct zones can be seen at the light-microscope level.
Zone of resting cartilage. This zone contains normal, resting hyaline cartilage.
Zone of proliferation. In this zone, chondrocytes undergo rapid mitosis, forming distinctive looking stacks.
Zone of maturation / hypertrophy. It is during this zone that the chondrocytes undergo hypertrophy (become enlarged). Chondrocytes contain large amounts of glycogen and begin to secrete alkaline phosphatase.
Zone of calcification. In this zone, chondrocytes are either dying or dead, leaving cavities that will later become invaded by bone-forming cells. Chondrocytes here die when they can no longer receive nutrients or eliminate wastes via diffusion. This is because the calcified matrix is much less hydrated than hyaline cartilage.
