What are differences between cortical (or compact) bone and spongy (or cancellous) bone?
Answer
Compact bone is hard, dense tissue that forms the outer surfaces of bones, including the shafts of long bones. It consists of cylindrical structures called osteons, also called Haversian systems. Each osteon consists of a central Haversian canal containing nerve fibers and blood vessels. These canals connect to each other via perforating canals (or Volkmann's canals). The Haversian canal is surrounded by concentric layers of calcified lamellae with small spaces known as lacunae each containing an osteocyte. Tiny channels called canaliculi connect the lacunae to allow oxygen and nutrients to reach the osteocytes, while waste is removed.
Spongy bone is a porous tissue found at the end of long bones, inside the vertebrae, and flat bones. It is not highly organized like the compact bone into osteons. It consists of flattened, interconnected plates called trabeculae. Red bone marrow is found within spaces of trabeculae that produces red blood cells. There are no central canals, but osteocytes do reside in lacunae and are connected by canaliculi.