What is primarily contained in the secondary spongiosa?

The secondary spongiosa is primarily composed of spicules of lamellar bone. This structure is integral to the organization and strength of bone, particularly in the areas subjected to weight-bearing. Lamellar bone is characterized by its layered structure, which enhances the bone’s tensile strength and resistance to stress.

The term "secondary spongiosa" refers to the trabecular (or cancellous) bone that is formed after the initial cortical bone. In this context, the spicules are small, rod-like structures that provide mechanical support while also allowing for the space necessary for bone marrow and blood vessels. This is particularly important for the bone's metabolic activities.

In contrast, other choices present elements that do not characterize the secondary spongiosa directly. Fluid-filled sacs pertain to synovial structures in joints or possibly other anatomical features but do not pertain to spongy bone composition. Densely packed connective tissues refer more to fibrous tissues or tendons rather than the unique structure and composition of spongiosa. Cartilage cells, or chondrocytes, are relevant to cartilaginous tissues but not to the lamellar bone structures found in the secondary spongiosa. Thus, the correct understanding centers on the unique role