Biology
Bone Growth
Quick fact
During childhood and adolescence, bones can grow up to several inches per year at the growth plates, but growth stops once the plates close, typically in the late teens to early twenties.
Why this is interesting
You know bones are hard and seem unchanging, but did you know they are constantly growing and remodeling throughout your life? How does your body manage to grow a structure strong enough to support you?
Read the full explanation
Understanding Bone Growth
Think of a long bone, like your thigh bone. It grows in length at special areas near the ends called growth plates or epiphyseal plates. These plates are made of cartilage—a flexible, rubbery tissue. On the plate, new cartilage cells (chondrocytes) are constantly formed, pushing the older cells toward the bone shaft. Meanwhile, the older cartilage is gradually replaced by hard bone by cells called osteoblasts. This process—endochondral ossification—lengthens the bone. For width, bone adds layers on the outside (appositional growth) while reshaping the inside. This entire system is like a construction crew: cartilage builds a temporary scaffold, and bone fills it in.
A deeper explanation
Bone growth is regulated by hormones, especially growth hormone from the pituitary gland and sex hormones from the gonads. Growth hormone stimulates the proliferation of chondrocytes in the growth plate, while sex hormones (estrogen and testosterone) eventually cause the growth plates to close, ending longitudinal growth. The process relies on a balance between cartilage formation and bone deposition. Understanding bone growth explains why children can heal fractures faster than adults (their growth plates are still active), and why aging leads to bone loss (imbalance in remodeling). This mechanism is critical for treating growth disorders and designing orthopedic implants.