6-1 Chapter 6 Skeletal System: Bones and Bone Tissue

6-2 Functions of the Skeletal System Support. Bone is hard and rigid; cartilage is flexible yet strong. Cartilage in nose, external ear, thoracic cage and trachea. Ligaments- bone to bone Protection. Skull around brain; ribs, sternum, vertebrae protect organs of thoracic cavity Movement. Produced by muscles on bones, via tendons. Ligaments allow some movement between bones but prevent excessive movement Storage. Ca and P. Stored then released as needed. Fat stored in marrow cavities Blood cell production. Bone marrow that gives rise to blood cells and platelets

6-3 Bone Histology Bone matrix. Like reinforced concrete. Rebar is collagen fibers, cement is hydroxyapatite –Organic: collagen and proteoglycans –Inorganic: hydroxyapatite. CaPO 4 crystals If mineral removed, bone is too bendable If collagen removed, bone is too brittle

6-4 Bone Histology Bone cells –Osteoblasts –Osteocytes –Osteoclasts –Stem cells or osteochondral progenitor cells Woven bone: collagen fibers randomly oriented Lamellar bone: mature bone in sheets Cancellous bone: trabeculae Compact bone: dense

6-5 Bone Cells Osteoblasts –Formation of bone through ossification or osteogenesis. Collagen produced by E.R. and golgi. Released by exocytosis. Precursors of hydroxyapetite stored in vesicles, then released by exocytosis. –Ossification: formation of bone by osteoblasts. Osteoblasts communicate through gap junctions. Cells surround themselves by matrix.

6-6 Bone Cells Osteocytes. Mature bone cells. Stellate. Surrounded by matrix, but can make small amounts of matrix to maintain it. –Lacunae: spaces occupied by osteocyte cell body –Canaliculi: canals occupied by osteocyte cell processes –Nutrients diffuse through tiny amount of liquid surrounding cell and filling lacunae and canaliculi. Then can transfer nutrients from one cell to the next through gap junctions.

6-7 Bone Cells Osteoclasts. Resorption of bone –Ruffled border: where cell membrane borders bone and resorption is taking place. –H ions pumped across membrane, acid forms, eats away bone. –Release enzymes that digest the bone. –Derived from monocytes (which are formed from stem cells in red bone marrow) –Multinucleated and probably arise from fusion of a number of cells Stem Cells. Mesenchyme (Osteochondral Progenitor Cells) become chondroblasts or osteoblasts.

The Histology of Compact Bone

Classification of Bones by Shape

6-10 Structure of a Long Bone, cont. Periosteum –Outer is fibrous –Inner is single layer of bone cells including osteoblasts, osteoclasts and osteochondral progenitor cells –Fibers of tendon become continuous with fibers of periosteum. –Sharpey’s fibers: some periosteal fibers penetrate through the periosteum and into the bone. Strengthen attachment of tendon to bone. Endosteum. Similar to periosteum, but more cellular. Lines all internal spaces including spaces in cancellous bone.

The Histology of Compact Bone

The Structure of Osseus Tissue

6-13 Cancellous (Spongy) Bone Trabeculae: interconnecting rods or plates of bone. Like scaffolding. –Spaces filled with marrow. –Covered with endosteum. –Oriented along stress lines

The Circulatory Supply to a Mature Bone

6-15 Circulation in Bone Perforating canals: blood vessels from periosteum penetrate bone Vessels of the central canal Nutrients and wastes travel to and from osteocytes via –Interstitial fluid of lacunae and canaliculi –From osteocyte to osteocyte by gap junctions

6-16 Bone Development Intramembranous ossification –Takes place in connective tissue membrane Endochondral ossification –Takes place in cartilage Both methods of ossification –Produce woven bone that is then remodeled –After remodeling, formation cannot be distinguished as one or other

Intramembranous Ossification

6-18 Intramembranous Ossification

6-19 Structure of Flat, Short, and Irregular Bones Flat Bones –No diaphyses, epiphyses –Sandwich of cancellous between compact bone Short and Irregular Bone –Compact bone that surrounds cancellous bone center; similar to structure of epiphyses of long bones –No diaphyses and not elongated Some flat and irregular bones of skull have sinuses lined by mucous membranes.

6-20 Endochondral Ossification

6-21 Endochondral Ossification

6-22 Endochondral Ossification

6-23 Endochondral Ossification

6-24 Zones of the Epiphyseal Plate

6-25 Growth in Bone Length

6-26 Bone Remodeling Converts woven bone into lamellar bone Caused by migration of Basic Multicellular Units –Groups of osteoclasts and osteoblasts that remodel bones Involved in bone growth, changes in bone shape, adjustments in bone due to stress, bone repair, and Ca ion regulation Relative thickness of bone changes as bone grows. Bone constantly removed by osteoclasts and new bone formed by osteoblasts. Formation of new osteons in compact bone –Osteoclasts enter the osteon from blood in the central canal and internally remove lamellae. Osteoblasts replace bone –Osteoclasts remove bone from the exterior and the bone is rebuilt

6-27 Woven and Lamellar Bone Woven bone. Collagen fibers randomly oriented. –Formed During fetal development During fracture repair Remodeling –Removing old bone and adding new –Woven bone is remodeled into lamellar bone Lamellar bone –Mature bone in sheets called lamellae. Fibers are oriented in one direction in each layer, but in different directions in different layers for strength.

6-28 Bone Repair 1.Hematoma formation. Localized mass of blood released from blood vessels but confined within an organ or space. Clot formation. 2.Callus formation. Callus: mass of tissue that forms at a fracture site and connects the broken ends of the bone. –Internal- blood vessels grow into clot in hematoma. Macrophages clean up debris, osteoclasts break down dead tissue, fibroblasts produce collagen and granulation tissue. Chondroblasts from osteochondral progenitor cells of periosteum and endosteum produce cartilage within the collagen. Osteoblasts invade. New bone is formed. –External- collar around opposing ends. Periosteal osteochondral progenitor cells  osteoblasts and chondroblasts. Bone/cartilage collar stabilizes two pieces.

6-29 Bone Repair, cont. 3.Callus ossification. Callus replaced by woven, cancellous bone 4.Bone remodeling. Replacement of cancellous bone and damaged material by compact bone. Sculpting of site by osteoclasts

Steps in the Repair of a Fracture

The Effects of Osteoporosis