BONE pg 1 Bone or osseous tissue is an organ in its own right composed of connective tissue bone nerves blood and lymph vessels and often containing adipose tissue Functions of bone include 1 Support and protection a support femur tibia fibula pelvis spinal column b protection ribs spinal column skull pelvis 2 Motility muscles attach to bone to allow movement 3 Mineral storage fat in marrow of long bones cannibals broke open long bones to get at the tasty fat calcium and phosphorous in bone itself loss of calcium taken from bone for other more important uses causes osteoporosis 4 Hematopoiesis in adults blood cells are formed in the ribs sternum skull pelvis vertebrae and femoral and humeral heads in children nearly the entire skeleton produces red blood cells Bone comes in two structural varieties compact and spongy more on these coming up bones come in four shapes SHAPES 1 Long the length is greater than the width with a hollow shaft much like a tube all bones of the extremities except for the patella and ankle and wrist bones 2 Short shaped more like a cube tarsals ankle bones and carpals wrist bones sesamoid a sesame seed shaped bone the patella is the largest one and there are 2 small ones in a tendon at the big toe others may occur other places but their only purpose is to enhance the pull or leverage of the muscle whose tendon they are located in Flat actually more curved but always quite thin skull ribs sternum scapula pelvis Irregular odd shaped vertebrae sphenoid and ethmoid bones of the skull Short flat and irregular bones are built like a spongy bone sandwich a spongy middle called the diploe the red marrow area is encased in a surrounding shell of compact bone they are active sites for hematopoiesis long bones are built quite differently like a hollow tube developing blood cell diploe spongy bone red bone marrow site of hematopoeisis cortex compact bone Architecture of long bones diaphysis the long shaft a tube of compact bone medullary cavity the hollow area in the diaphysis filled with fat called yellow marrow epiphysis the knobs at either end proximal and distal composed primarily of spongy bone these serve as areas of joints or muscle attachment metaphysis tapering area between the epiphysis and the diaphysis articular cartilage covers the ends of the epiphyses 3 3 1 2 4 5 6 pg 2 7 8 9 1 2 3 4 5 epiphyseal growth plate an area of hyaline cartilage between the epiphysis and the metaphysis growth occurs here until it closes around age 18 21 nutrient foramen foramina plural these bring blood and lymph vessels and nerves to the interior of a bone periosteum 2 layer outer covering a fibrous layer dense irregular connective tissue b osteogenic layer contains osteoblasts and clasts to develop bone thickness periosteum and muscle tendons are held to bone by perforating fibers also called Sharpey s fibers so tightly in fact that when yanked too hard they stay imbedded in the bone and the force may cause a chunk of bone to break off with the periosteum or tendon attached to it called an avulsion fracture 10 endosteum the inner lining of bone found on the medullary cavity nutrient foramina trabecullae etc it also contains osteoblasts and osteoclasts COMPACT aka lamellar or cortical bone the outer portion of most organs is called its cortex thus the term cortical HOW IS COMPACT BONE CONSTRUCTED A sequence of cylinders telescoped into one another creates compact bone The cylinders running parallel to the long axis of the bone are called lamella and create a structure called an osteon the structural unit of compact bone Osteon also called the Haversian system contains all the elements listed below lamella 3 types a concentric several together like a bull s eye target with a passageway up its center called the central or Haversian canal blood and lymph vessels run through the central canal interstitial these fill in the spaces between the adjacent osteons b c circumferential a series of lamella running around the full perimeter of the bone osteocytes mature bone cells that reside in tiny spaces called lacuna osteocytes no longer secrete matrix but sense stresses on bone and stimulate the osteoblasts or osteoclasts to either secrete or resorb calcium matrix lacuna lacunae plural found between adjacent concentric lamellae nutrition comes to them by small canals extending from the central canal called canaliculi canaliculi tiny canal blood from the capillary in the central canal gets to the osteocyte in the outer lamellae by way of these perforating or Volkman s canal brings blood from the vessel that penetrated the nutrient foramen NOTE the central canal runs parallel to the bone s long axis the perforating canal runs perpendicular to it NOTE ALSO do not confuse the central canal with the medullary cavity the central canal is microscopically small and contains a nerve blood and lymph vessels the medullary cavity is eyeball large and contains fat The osteon architecture makes bone incredibly resistant to torsion twisting stress for these reasons 1 one of bone s components is collagen fibers with great tensile strength which twist diagonally down through their lamella 2 3 the collagen fibers in each adjacent lamella run in the opposite direction from the lamella beside it the circumferential lamella around the perimeter of the bone contribute even more resistance SPONGY aka cancellous or trabecular bone Spongy bone has the same chemical and cellular make up as compact bone but a different architectural structure there are no osteons There are lamellae lacunae osteocytes and canaliculi but they are not organized as an osteon Instead the bone is laid down in structures called trabecullae like flying buttresses along stress lines Spongy bone is found as the diploe of short irregular and flat bones as well as in the epiphyses of all long bones pg 3 CHEMICAL MAKE UP OF BONE Bone is 30 35 organic material made up mostly of collagen fibers 95 of the organic matter ground substance secreted by osteoblasts The other 65 is crystalline salts primarily made of calcium and phosphate called hydroxyapatite Ca10 PO4 6 OH2 with a lot of calcium carbonate CaCO3 Collagen gives bone its tremendous tensile strength calcium salts give it its exceptional hardness traces of magnesium sodium potassium and other minerals are also necessary B ones are constructed exactly the same way reinforced concrete is constructed The steel of reinforced concrete provides the tensile strength while the cement sand and