114 Anatomy & Physiology Essentials Copyright Goodheart-Willcox Co., Inc. concentric circles called lamellae (la-MEHL-ee) around the Haversian canals. Osteocytes are housed in the lacunae, which act as protective islands for these cells. Each Haversian canal, with its surrounding layers of lacunae, forms a structural unit called an osteon, or Haversian system. Within the system, there are tiny sideways canals called canaliculi (kan-a-LIK-yoo-ligh). The canaliculi connect with the lacunae, forming a comprehensive transportation matrix for the supply of How does living bone receive nourishment and get rid of waste products? Bone has what you might think of as its own subway system. An intricate array of passageways exists at a microscopic level inside the mineralized part of bone. Blood vessels and nerves course through these tiny tunnels (Figure 5.7). Major passageways running in a lengthwise direction through the bone are called Haversian canals. Tiny cavities called lacunae (la-KOO-nee) are laid out in Periosteum Periosteum C Diaphysis A Humerus B Cortical and trabecular bone Epiphysis Diaphysis Nutrient arteries Cortical bone Cortical bone Epiphysis Articular cartilage Articular cartilage Articular cartilage Endosteum Endosteum Blood vessel Yellow bone marrow Yellow bone marrow (in medullary cavity) Medullary canal Cortical bone Trabecular bone Red marrow cavities Trabecular bone © Body Scientifi c International Figure 5.6 The anatomical structure of a long bone. A—Anterior view of the humerus with the interior of the top half exposed. B—Cortical and trabecular bone of the epiphysis. C—Enlargement of the diaphysis.