10.6:
Spongy Bone
Spongy bone, also called cancellous or trabecular bone, is a porous tissue that forms the interior of bones, especially the epiphysis and metaphysis of long bones.
It is surrounded by a layer of dense compact bone, creating a strong but lightweight bone structure.
The spongy core comprises irregularly arranged, branched trabeculae that form a mesh-like network.
Similar to the osteons of compact bone, the trabeculae also comprise concentric lamellae of calcified bone matrix.
The lacunae, spaces between the lamellae, harbor osteocytes that are interconnected via narrow branching canals called canaliculi. The canals further open into the spaces between the trabeculae.
These spaces are filled with red bone marrow and tiny blood vessels that provide nutrition to the osteocytes via the canaliculi.
The trabecular network is dynamic, orienting its growth along the different stress lines to withstand pressure from different directions.
10.6:
Spongy Bone
All bones comprise an outer layer of compact bone, and an interior made up of spongy bone tissue, also called cancellous or trabecular bone. In long bones, spongy bone tissue is mainly found in the interior of the epiphyses (broad ends of the bone).
Spongy bone is more porous, and less dense compared to compact bone. It is composed of concentric lamellae that are arranged irregularly to form the trabecular network. In some bones, the spaces between trabeculae contain red marrow, where hematopoiesis occurs; in others, they are filled with yellow marrow. Spongy bone is highly vascular, providing nutrients to the osteocytes in the trabeculae via channels called canaliculi. The osteocytes are mature bone cells that regulate bone formation and growth. They are found between the lamellae, in spaces called lacunae.
The trabeculae may appear to be a random network, but each trabecula forms along the lines of stress. The trabecular network develops as the individual learns to walk. It may also dynamically alter when stress lines change, such as when the walking style changes after a leg injury or fracture. The mesh-like network can thus resist compression forces from different directions and provide strength to the bone. This helps transmit forces across joints without damage to the bone. The porous tissue also makes the bones lighter, so muscles can move them more easily.
Part of this text is adapted from Openstax, Anatomy and Physiology 2e, Section 6.3: Bone structure