A haversian canal is a central canal within the haversian system — a network of canals inside compact bone. Haversian canals occur in the center of compact bone and contain blood vessels, connective tissues, nerve fibers and lymphatic vessels. Osteons, or the structure that forms compact bone, surround these canals and are the outer component of the haversian system. The terms osteons and haversian system are often used interchangeably.
Haversian systems are units of structure within mature bone. The systems run parallel to the long axis of bones. Each cylindrical unit within compact bone is an entire haversian system. The system includes lamellae, osteocytes, lacunae, canaliculi and a haversian canal.
Lamellae are the thin layers that compile and eventually form bone. They contain collagen fibers that are arranged in a parallel array. Lamellae also contain a small amount of proteoglycans in addition to collagen. This matter becomes mineralized and miniature crystals form along the collagen fibers. This process and layered arrangement creates strength in the bone.
The shaft of a long bone is made of compact bone. Compact bone is made of osteons, which produce osteocytes. These osteocytes are mature bone cells and are responsible for maintaining the integrity of the bone. Osteocytes form in tiny chambers called lacunae.
Osteocytes also are produced by converted osteoblasts. If blood calcium levels are normal, any incurred bone destruction is repaired by osteoblasts. Osteoblasts form into bone and draw calcium from the blood. These cells eventually become caught in nonliving material where they secrete and are converted into osteocytes. This process recycles old bone tissue into new bone tissue.
Lacunae form in circles around the haversian canal. Bone cells are contained within lacunae, and the blood vessels within the haversian canal carry nutrients to the bone, allowing it to renew itself. Lacunae are separated by multiple collagen fibers and mineral deposits, such as calcium and phosphorus salts.
Minute canals link the bone cells to each other and to the haversian canal, so that matter may be distributed throughout the bone. These miniature canals are called canaliculi, also known as Volkmann’s canals. These canals communicate with canals to facilitate the smooth passage of blood vessels through bone.
Haversian canals are only a tiny component of the entire, complex bone structure, but its importance to the structure is undeniable. If they didn't function properly, the bone would be unable to retain nutrients or hold essential blood vessels and nerve fibers. This would ultimately lead to the decay and destruction of compact bone.