ct_11. Indirect osteogenesis (replacement of cartilage with bone)
(Heidenhain’s azan)
1. Take a closer look at the general topography of bone tissue development from a cartilage model of the tubular bone (previously formed from the mesenchyme):
- epiphyses - contain hyaline cartilage, surrounded by the perichondrium;
- the outside of diaphysis is lined with the periosteum;
- towards the bone ends, the periosteum continues directly into the perichondral bone collar, perichondral bone annulus , that encircles the periphery of the growth plate.
2. Find ossification zones and take a closer look at their structure:
- formation of the bone cuff begins in the midsection of the bone diaphysis. Vascularization of the perichondrium at this site causes synthesis of osteoblasts that, in turn, secrete extracellular matrix;
- the process of endochondral bone formation occurs within the core of bone diaphysis. Endochondral ossification begins with the proliferation and aggregation of mesenchymal cells at the site of the future bone;
- find calcified cartilage remnants, on which the endochondral bone is laid down (the endochondral ossification zone), and cavities formed between them. These cavities then become fill with the hemopoietic tissue;
- learn to differentiate 4 zones of endochondral bone formation (moving from the epiphysis to the diaphysis):
- the zone of reserve/resting cartilage,
- the zone of cell columns/proliferation (in this zone, chondrocytes undergo rapid mitosis, forming distinctive looking stacks, and secrete cartilage matrix),
- the zone of cellular cartilage (in this zone, overgrown chondrocytes are either dying or dead),
- the zone of calcified cartilage (adjacent to the endochondral bone of the diaphysis).
3. Draw the epiphysis and a part of the diaphysis and point out:
-
I
- perichondral ossification zone
(1 - the periosteum, 2 - the forming woven bone), II
- endochondral ossification zone (3 - the endochondral bone, 4 - calcified cartilage remnants, 5 - the forming hematopoietic tissue),
III
- cartilage tissue remodeling zone (6 - the zone of reserve/resting cartilage, 7 - the zone of cell columns/proliferation, 8 - the hypertrophic zone).
4. Define and write significant features of the cartilaginous ossification specimen.