Final answer:
A baby is born with around 270 bones, and through ossification, the bone count decreases to 206 by adulthood. Endochondral ossification contributes to bone length growth, which ceases when growth plates ossify around the age of 18 to 25. Bone thickness can increase throughout life due to bone remodeling and repair.
Step-by-step explanation:
A baby is born with approximately 270 bones. As they grow, some bones will naturally fuse together. By the time they are an adult, they typically have 206 bones. This reduction in bone count is due to the process of ossification, where cartilage is replaced by bone tissue as a person matures. In particular, endochondral ossification is crucial as it transforms cartilage into bone, starting from the center and working towards the ends of bones. Growth plates, which are zones of cartilage at the ends of long bones, allow for the increase in bone length during childhood. However, around the age of 18 to 25, these plates are fully ossified, and the bones stop growing.
The process of bone fusion is a part of natural growth and development, involving both intramembranous and endochondral ossification. The flexibility provided by cartilage is necessary for infants, such as permitting the deformation of the skull during birth. Eventually, most of the cartilage is replaced with bone, although some remain in areas like joints, the rib cage, and other parts of the body.
It's important to note that while the length of bones stops increasing after the age of 25, bones can continue to grow in thickness throughout an individual's life through the processes of bone remodeling and bone repair.