Topic 30 - Chondral ossification

Question 1

There are two types of indirect ossification?

Answer 1

Perichondral

Endochondral

Question 2

Perichondral indirect ossification

Answer 2

Osteogenesis starts in the diaphysis.

A bony collar starts from the mesenchynal cells of the perichondrium.

Question 3

Endochondral indirecct ossification

Answer 3

Blood vessels with pluripotent cells intrude the diaphysis. The perivascular mesedyme differentiates into osteoblasts, and generates the primary ossification centre.

Question 4

Endochondral ossification

definition

Answer 4

• Bones form ossified hyaline cartilage.

- Forms bones of the extremities, vertebral column, pelvis, and the base of the skull.

Question 5

Endochondral ossification:

Process

Answer 5

1. Cartilage grows more quickly at the end of the the long bone.
2. Cartilage cells of the midsection mature and enlarge, releasing matrix vesciles and causing the matrix to calcify.
3. Perichondrial mesenchymal cells produce a bony collar around the diaphysis causing further metabolic difficulty in chondrocyte metabolism.
4. Capillary loop accompanied by mesenchymal cells perforates the bony collar and enters hypertrophic cartilage.
5. Chondroclasts phagocytose degenerating chondrocytesm leaving pin-shaped calcified remnants of matrix.
6. Mesenchymal cells differentiate into osteoprogenitor cells, giving rise to osteoblasts which lay down the first layers of osteoid onto the surface of the calcified remnants of the cartilage matrix

Question 6

Bone growth

Answer 6

1. The newly formed bone will develop into compact or lamellar bone.
2. Marrow cavity is enlarged by concurrent periosteal growth and endosteal reabsorption, widening the diaphysis.

Question 7

Epiphyseal plate

Answer 7

disk-shape layer of intact hyaline cartilage, ensures longitudinal growth of long bones until puberty

Question 8

Bone modeling

Answer 8

• Primitive woven bone is replaced by lamellae bone. Size and shape change until adult shape is reached.
• Drift: eccentric growth due to biomechanical demands

Question 9

Remodeling

Answer 9

does not involve anatomical surfaces, cyclic, and slower procedure. Layers are renewed several times during a lifetime

Question 10

Zones

Answer 10

• Resting zones
• Zone of proliferating
• Zone of degenerating
• Zone of ossification