​Bone Cells - The dissolving and depositing of bone contributes to bone density and and helps regulate blood levels of calcium and phosphorus.

• ​Osteoblasts - Form bone

• ​Osteoclasts - Dissolve unwanted bone.

• ​Osteocytes - Mature osteoblasts embedded in the hardened bone

​Matrix - collagen fibers and calcium and phosphate salts, it is hard and calcified.

​Bone Tissue/Osseous Tissue

​Types of Bone

• ​Compact

  • ​Dense and solid

  • ​Forms shafts of long bones and surfaces of other bones

• ​Spongy (cancellous)

  • ​Found in ends of long bones and middle of other bones.

  • ​Always surrounded by compact bone.

• ​Made of a latticework of bone called trabeculae

• ​Trabeculae are arranged to offer maximum strength.

• ​If stress changes the trabeculae will realign to compensate.

• ​Cavities between trabeculae are filled with red bone marrow.

​Compact bone

• Layers of matrix are arranged in concentric rings (called lamellae) around a central canal (called a haversian or osteonic canal).

• This basic structural unit (consisting of the lamellae and haversian canal) is called an osteon.

• Blood vessels and nerves run the length of the bone, through the center of the canal

• Tiny gaps between rings of the lamellae, called lacunae, contain osteocytes.

• Microscopic passageways, called canaliculi, connect the lamellae to each other

• Transverse passageways, called Volkmann’s canals,connect the haversian canals. These canals transport blood and nutrients from the bone’s exterior to the osteocytes locked inside.

​Bone Marrow

• ​Bone marrow is a type of soft tissue that fills the medullary cavity of long bones and the spaces of spongy bones.

• ​Red bone marrow is charged with producing red blood cells. Nearly all of a child’s bones contain red bone marrow.

• In an adult, red bone marrow can only be found in the ribs, sternum, vertebrae, skull, pelvis, and the upper parts of the humerus (arm) and femur (thigh). All other bones contain yellow marrow. 

​Bone Marrow

• ​Yellow bone marrow replaces red marrow over time. The cells of yellow marrow are saturated with fat and no longer produce blood cells. In cases of severe, chronic blood loss or anemia, yellow marrow can change back into red marrow.