The Skeletal System- Osseous Tissue & Skeletal Structure Chapter 5

The skeletal system includes: Bones Cartilage Joints Ligaments Other connective tissues

Functions of the Skeletal System Support against gravity Protection of soft internal organs Movement (Leverage) Storage Minerals (calcium, phosphorous) – within the matrix of bone tissue Energy reserve (adipose) – within the yellow marrow of long bones Blood cell production – within red marrow of spongy bone tissue

The Structure of a Typical Bone All bones have a combination of spongy (cancellous) & compact (dense) bone tissue

The Histological Features of Spongy Bone Lamellae (layers) of matrix laid down in trabeculae - branching network of bony tissue Osteocytes located within lacunae Canaliculi branch out from lacunae Many marrow cavities which contain red marrow & small blood vessels

The Histological Features of Compact Bone Osteon/Haversian system - basic functional unit of compact bone Concentric lamellae (layers) of matrix surrounding central (Haversian) canal Osteocytes located within lacunae Canaliculi branch out radially from lacunae Central canals (containing BVs) run vertically down the length of the bone Perforating (Volkmann’s) canals (containing BVs) run horizontally across the width

Bone Cells In addition to Osteocytes, the mature bone cells found within the matrix of bone tissue, there are three other cells that are associated with bones Osteoprogenitor cells Osteoblasts Osteoclasts

Bone Cells Osteoprogenitor cells Derived from mesenchymal cells Can undergo mitosis Mature into osteoblasts

Bone Cells Osteoblasts Responsible for osteogenesis – create bone tissue Mature into osteocytes

Bone Cells Osteoclasts Derived from embryological WBCs Secrete enzymes for osteolysis – resorb/break down bone tissue Necessary for calcium homeostasis

Anatomical Classification of Bones Bones are classified by their basic shape Flat bones Sutural bones Irregular bones Long bones Short bones Sesamoid bones

Structure of a Typical Long Bone diaphysis (compact bone)

The Structure of a Long Bone diaphysis epiphysis (spongy bone) epiphysis

The Structure of a Long Bone diaphysis epiphysis articular cartilage

The Structure of a Long Bone epiphysis metaphysis – location of epiphyseal plate – in children epiphyseal line – in adults diaphysis metaphysis epiphysis articular cartilage

The Structure of a Long Bone medullary cavity filled with yellow marrow in adults lined with endosteum

The Structure of a Long Bone Outer fibrous layer of dense irregular CT for attachment of tendons& ligaments; provides route for blood vessels & nerves; separates bone tissue from surrounding tissues Double layered membrane surrounding bone except at articular cartilage Inner cellular layer contains osteoprogenitor cells, osteoblasts, osteoclasts; therefore functions in bone growth & repair periosteum

Bone Formation and Growth Ossification - Process of converting other tissues to bone; begins around week 6-8 of embryological development Two types of ossification processes occur during embryological formation: Intramembranous Endochondral

Intramembranous Ossification Forms flat bones of skull, mandible, clavicle Replacement of mesenchymal membrane with osseous tissue Mesenchymal cells differentiate to osteoprogenitor cells, which then become osteoblasts Osteoblasts create spongy bone, which then remodels into compact bone where necessary

Endochondral Ossification Most bones formed this way Mesenchyme creates Cartilage model, which gets replaced by bone Replacement begins in middle (diaphysis) & follows in ends (epiphyses)

Endochondral Ossification Cartilage model grows in length (interstitial growth) & in width (appositional growth) Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies. Cartilage model Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies. Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone. Enlarging chondrocytes within calcifying matrix The perichondrium, which surrounded the cartilage model, now must be referred to as the periosteum. Epiphysis Diaphysis Bone formation Cartilage model Figure 5.7 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies. Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone. Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center. Enlarging chondrocytes within calcifying matrix Epiphysis Diaphysis Marrow cavity Primary ossification center Bone formation Blood vessel Cartilage model Figure 5.7 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

The medullary cavity begins to hollow out Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies. Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone. Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center. Bone tissue continues to replace cartilage of the diaphysis, and & continues toward each epiphysis. Enlarging chondrocytes within calcifying matrix Epiphysis Marrow cavity Diaphysis Marrow cavity Primary ossification center Blood vessel The medullary cavity begins to hollow out Bone formation Blood vessel Cartilage model Figure 5.7 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Blood vessels invade the epiphyses and osteoblasts form secondary centers of ossification. Cartilage remains only at the ends (articular cartilage) & at metaphysis (epiphyseal plate) Enlarging chondrocytes within calcifying matrix Chondrocytes at the center of the growing cartilage model enlarge and then die as the matrix calcifies. Newly derived osteoblasts cover the shaft of the cartilage in a thin layer of bone. Blood vessels penetrate the cartilage. New osteoblasts form a primary ossification center. The bone of the shaft thickens, and the cartilage near each epiphysis is replaced by shafts of bone. Cartilage model Bone formation Epiphysis Diaphysis Marrow cavity Primary ossification center Blood vessel Secondary Epiphyseal cartilage Articular

An Overview of the Skeleton There are 206 bones in the adult human body Skeletal Divisions Axial skeleton (80 bones) Skull Thoracic cage and sternum Vertebral column Appendicular skeleton (126 bones) Upper, lower limbs Pectoral girdle Pelvic girdle

Bone Markings (Surface Features) Table 5-1 General elevations & projections: process ramus Markings for articulations: head condyle facet

Bone Markings (Surface Features) Spinous process Processes for attachment: trochanter (femur only) tuberosity tubercle epicondyle crest line spinous process (vertebrae only) transverse process (vertebrae only) Transverse process

Bone Markings (Surface Features) Depressions: fossa sulcus Spinous process Transverse process Openings: foramen (canal) meatus fissure sinus

Bone Markings (Surface Features)