Which of the following describes the endosteum?

The endosteum is a thin, vascular membrane that lines the inner surface of the bone, particularly the medullary cavity, and key areas such as the trabecular (spongy) bone. One of its important functions is to contain and nurture yellow bone marrow, which is primarily composed of fat cells. Yellow bone marrow is critical in energy storage and plays a role in the metabolism of fats.

In contrast, the other choices describe different structures or functions associated with bones. The outer surface of the bone is protected by the periosteum, not the endosteum, which explains why the covering option is not appropriate for describing the endosteum. The ends of long bones contain articular cartilage and epiphyseal plates but are not defined by the endosteum. Similarly, while bones do provide structure and strength, the characterization of the endosteum as primarily responsible for strength does not apply, as this structure primarily functions in the maintenance and growth of bone tissue rather than imparting strength directly.

In summary, the correct answer effectively identifies the endosteum’s specific role in housing yellow bone marrow, distinguishing it from other bone structures and functions.