The functional unit of spongy bone is known as the trabecula.
Trabeculae are small, rod-like structures that form the lattice-like framework of spongy bone. This structure provides support and strength to the bone while still keeping it lightweight. The spaces between the trabeculae are filled with bone marrow, which plays a crucial role in the production of blood cells. The arrangement of trabeculae allows the bone to withstand various stresses and is an adaptation that enables spongy bone to effectively distribute forces across the skeletal system.