Final answer:
Chondrocytes are cartilage-forming cells that reside in lacunae and play a key role in endochondral ossification, eventually dying to give way to the formation of the medullary cavity.
Step-by-step explanation:
Chondrocytes are cartilage-forming cells that are essential for the growth and maintenance of cartilage. These cells are found in the small cavities within the cartilage matrix known as lacunae. During the process of endochondral ossification, which is how most long bones in the body develop, chondrocytes play a critical role in forming a template of hyaline cartilage. As the matrix begins to calcify due to complex developmental signals, these chondrocytes eventually die off due to lack of nutrients, as calcification prevents diffusion. This leads to the formation of cavities within the cartilage, and subsequently, blood vessels invade these spaces, bringing along osteoblasts which later mature into osteocytes and osteoclasts that remodel the calcified cartilage matrix into spongy bone and eventually form the medullary cavity.