Compact bone consists of tightly packed cylinders known as what?

The correct answer is Haversian systems, which are structured within compact bone. Haversian systems, or osteons, are the fundamental functional units of compact bone, consisting of a central canal surrounded by concentric rings of bone tissue. These systems provide strength and support, allowing compact bone to withstand various stresses.

Within a Haversian system, the central canal contains blood vessels and nerves, essential for nourishing bone tissue and facilitating communication within the bone. The concentric lamellae surrounding the canal are composed of mineralized bone matrix, which gives the bone its rigidity. The spaces between these lamellae contain osteocytes, which are mature bone cells involved in maintaining the bone matrix.

It's important to note that while the term osteon is often used interchangeably with Haversian systems, Haversian systems also emphasize the inclusion of the central canal and the overall organization, hence leading to the confusion in terminology. The other terms listed—cancellous systems, lacunae, and osteons—do not accurately define the tightly packed structures found in compact bone. Cancellous bone, for example, refers to spongy bone that has a different organization and function, while lacunae are small spaces that house osteocytes within the