What is the epiphysis in relation to a long bone?

The epiphysis refers specifically to the end of a long bone. It is the rounded part of the bone that articulates with other bones at joints. The epiphysis is essential in the context of bone growth and development, as it contains areas for muscle and ligament attachment and often houses the trabecular, or spongy, bone that contributes to overall bone structure and function.

In growing children and adolescents, the epiphysis is separated from the main shaft (diaphysis) of the bone by the growth plate (epiphyseal plate), where new bone tissue is generated, allowing for lengthening of the bone. This demonstrates its significance in growth processes.

The other options describe different parts or aspects of a long bone that are not related to the definition of the epiphysis. The middle section of a bone is referred to as the diaphysis, while the growth zone pertains specifically to the epiphyseal plate located between the epiphysis and diaphysis. The bone surface membrane referred to is known as the periosteum, which is distinct from the epiphysis. Understanding these distinctions helps clarify the functional anatomy of long bones and their growth mechanisms.