Which statements characterize the microscopic arrangement of spongy bone?
it contains parallel lamellae
it contains concentric lamellae
it contains no osteons
it contains many osteons
The correct answer and explanation is:
Correct Answer:
“It contains no osteons.”
Explanation:
Spongy bone, also called cancellous bone, is a type of osseous tissue found inside bones, particularly in areas subject to stress and strain. Unlike compact bone, which has a dense structure with osteons (Haversian systems) for strength, spongy bone has a different microscopic organization that makes it lightweight yet strong.
1. Lack of Osteons in Spongy Bone
One of the defining characteristics of spongy bone is the absence of osteons. Osteons are cylindrical structures composed of concentric lamellae (layers of bone matrix) surrounding a central Haversian canal that carries blood vessels and nerves. These structures are crucial for the strength of compact bone, but they are not necessary in spongy bone due to its unique porous architecture.
2. Trabeculae: The Key Structural Unit
Instead of osteons, spongy bone consists of a lattice-like network of trabeculae. Trabeculae are thin, bony plates and struts that are arranged along lines of mechanical stress, providing strength without excessive weight. The spaces between the trabeculae are often filled with bone marrow, which plays an essential role in hematopoiesis (blood cell production).
3. Nutrient Supply Without Osteons
In compact bone, nutrients are supplied through the Haversian canal system. However, in spongy bone, nutrients and oxygen diffuse directly through the bone marrow and surrounding blood vessels to reach osteocytes within the trabeculae. This allows for an efficient metabolic exchange without the need for a complex vascular system like that in osteons.
4. Lamellae in Spongy Bone
While spongy bone does contain parallel lamellae, they are not arranged in the concentric ring structure seen in osteons. Instead, the lamellae are randomly oriented within trabeculae, which helps distribute stress efficiently.
Conclusion
Spongy bone is uniquely designed for strength, flexibility, and metabolic function. Its lack of osteons and reliance on trabeculae make it ideal for reducing bone weight while maintaining structural integrity, particularly in areas like the ends of long bones and within vertebrae.