Question

Most of the human skeleton begins as a hyaline cartilage model, which is later replaced by bone. When chondrocytes become surrounded by mineralized matrix, they die, but when osteocytes become surrounded by mineralized matrix, they do not die. Based on your understanding of the microscopic anatomy of cartilage and bone, explain why this is the case.

Answer 1

Answer:

The process of bone formation is called osteogenesis or ossification. After progenitor cells form osteoblastic lines, they proceed with three stages of development of cell differentiation, called proliferation, maturation of matrix, and mineralization. Based on its embryological origin, there are two types of ossification, called intramembranous ossification that occurs in mesenchymal cells that differentiate into osteoblast in the ossification center directly without prior cartilage formation and endochondral ossification in which bone tissue mineralization is formed through cartilage formation first. In intramembranous ossification, bone development occurs directly. In this process, mesenchymal cells proliferate into areas that have high vascularization in embryonic connective tissue in the formation of cell condensation or primary ossification centers. This cell will synthesize bone matrix in the periphery and the mesenchymal cells continue to differentiate into osteoblasts. After that, the bone will be reshaped and replaced by mature lamellar bone. Endochondral ossification will form the center of primary ossification, and the cartilage extends by proliferation of chondrocytes and deposition of cartilage matrix. After this formation, chondrocytes in the central region of the cartilage start to proceed with maturation into hypertrophic chondrocytes. After the primary ossification center is formed, the marrow cavity begins to expand toward the epiphysis. Then the subsequent stages of endochondral ossification will take place in several zones of the bone

Answer 2

Chondrocytes die when surrounded by a mineralized matrix as their nutrient pathways and waste elimination processes stop. Osteocytes continue with these processes, so they can survive.

Chondrocytes and Osteocytes

• Chondrocytes are the functional cells of cartilage, while osteocytes are the functional cells of the bone.
• Chondrocytes undergo apoptosis- large-scale death of cells- during the ossification of bones.
• The process of bone development from hyaline cartilage is called endochondral ossification.

What happens during ossification?

• Ossification occurs during the embryonal stage.
• When the brain releases some signals, calcification of cartilage begins.
• Due to this, the passage for nutrient mobilization and waste elimination for chondrocytes gets blocked.
• On the other hand, osteocytes are formed when the precursor cells-osteoblasts- get trapped in the mineralized matrix.
• Osteocytes have minute canals called canaliculi in them.
• Canaliculi facilitate the passage of nutrients and waste products in osteocytes.
• Thus, they can survive within the bone.

Therefore, chondrocytes die in the mineralized matrix but osteocytes can survive.