In which part of a child's bones is red bone marrow primarily found?

• A. Only in the periosteum
• B. Exclusively in flat bones
• C. Only in the epiphyses of long bones
• D. In the medullary cavities of long bones

Answer: (D)

Verified step by step guidance

1. Understand the function of red bone marrow: Red bone marrow is responsible for hematopoiesis, the process of producing blood cells, including red blood cells, white blood cells, and platelets.
2. Learn about the anatomy of long bones: Long bones consist of several parts, including the diaphysis (shaft), epiphyses (ends), and medullary cavity (central hollow region).
3. Recognize the location of red bone marrow in children: In children, red bone marrow is found in the medullary cavities of long bones, as their bones are actively producing blood cells to support growth and development.
4. Differentiate between red and yellow bone marrow: As children grow, red bone marrow in the medullary cavities is gradually replaced by yellow bone marrow, which primarily stores fat. However, red bone marrow remains in certain areas like flat bones and the epiphyses of long bones in adults.
5. Clarify why other options are incorrect: The periosteum is a fibrous membrane covering the outer surface of bones and does not contain red bone marrow. Flat bones do contain red bone marrow, but the question specifies long bones. The epiphyses of long bones contain red bone marrow in adults, but in children, the medullary cavities are the primary site.