What happens in the epiphyseal face?
The epiphyseal face, also known as the growth plate, is a specialized region in the long bones of the body responsible for growth and development during childhood and adolescence. It is composed of a layer of cartilage that is gradually replaced by bone tissue through a process called endochondral ossification. Here's what happens in the epiphyseal face:
1. Chondrocytes Proliferation: The epiphyseal face contains columns of chondrocytes (cartilage cells) that undergo rapid division and proliferation. These chondrocytes are responsible for the growth of the bone in length.
2. Differentiation and Maturation: As chondrocytes move away from the resting zone, they undergo a series of changes in their structure and function. They differentiate into different types of chondrocytes, including pre-hypertrophic and hypertrophic chondrocytes.
3. Matrix Production: Chondrocytes secrete and deposit extracellular matrix components such as collagen, proteoglycans, and hyaluronic acid. These substances form the cartilage matrix, providing strength and flexibility to the growing bone.
4. Endochondral Ossification: This is the process by which cartilage is replaced with bone tissue. Hypertrophic chondrocytes enlarge, and the surrounding cartilage matrix becomes calcified. Blood vessels and osteoblasts (bone-forming cells) invade the calcified cartilage, breaking down the cartilage matrix. Osteoblasts then lay down new bone tissue, replacing the cartilage with bone.
5. Secondary Ossification Centers: In addition to the primary ossification center in the diaphysis (central shaft of the long bone), secondary ossification centers develop within the epiphyses (ends of the long bone). These secondary centers undergo a similar process of endochondral ossification, contributing to the growth of the bone in width.
6. Growth Plate Closure: As individuals reach skeletal maturity, usually in late adolescence or early adulthood, the epiphyseal face or growth plate gradually closes. Chondrocyte proliferation decreases, and the growth cartilage is replaced entirely by bone tissue. This closure marks the end of longitudinal growth of the long bones, and the individual's height becomes fixed.