When Does Bone Formation Begin?
Bone formation, or ossification, is the process by which bones form and develop. It begins in the womb and continues throughout life. During fetal development, bone formation begins around the sixth week of gestation and continues until birth.
Fetal Development
During fetal development, a process called intramembranous ossification occurs. This is when flat bones such as the skull and clavicle form from mesenchymal cells that are found in connective tissue. The cells differentiate into osteoblasts, which are responsible for forming bone. These osteoblasts secrete collagen fibers and calcium phosphate to form a hard matrix that will eventually become bone.
Postnatal Development
After birth, a process called endochondral ossification occurs. This is when long bones such as the femur and tibia form from hyaline cartilage. The cartilage is gradually replaced by bone through a process of calcification and resorption. Osteoblasts continue to secrete collagen fibers and calcium phosphate to form a hard matrix that will eventually become bone.
Bone formation continues throughout life as bones remodel themselves in response to physical activity and other environmental factors. As people age, their bones become less dense due to decreased levels of hormones such as estrogen and testosterone, leading to an increased risk of fractures.