Chapter 6: Skeletal System

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Skeletal Cartilage  Contains no blood vessels or nerves  Surrounded by the perichondrium (dense irregular connective tissue) that resists outward expansion  Three types – hyaline, elastic, and fibrocartilage

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Hyaline Cartilage  Provides support, flexibility, and resilience  Is the most abundant skeletal cartilage  Is present in these cartilages:  Articular – covers the ends of long bones  Costal – connects the ribs to the sternum  Respiratory – makes up larynx, reinforces air passages  Nasal – supports the nose

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Growth of Cartilage  Appositional – cells in the perichondrium secrete matrix against the external face of existing cartilage  Interstitial – lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix, expanding the cartilage from within  Calcification of cartilage occurs  During normal bone growth  During old age

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Bones and Cartilages of the Human Body Figure 6.1

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Classification of Bones  Axial skeleton – bones of the skull, vertebral column, and rib cage  Appendicular skeleton – bones of the upper and lower limbs, shoulder, and hip

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Classification of Bones: By Shape  Long bones – longer than they are wide (e.g., humerus) Figure 6.2a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Classification of Bones: By Shape  Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones) Figure 6.2c

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Classification of Bones: By Shape  Short bones  Cube-shaped bones of the wrist and ankle  Bones that form within tendons (e.g., patella) Figure 6.2b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Classification of Bones: By Shape  Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones) Figure 6.2d

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Function of Bones  Support – form the framework that supports the body and cradles soft organs  Protection – provide a protective case for the brain, spinal cord, and vital organs  Movement – provide levers for muscles

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Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Gross Anatomy of Bones: Bone Textures  Compact bone – dense outer layer  Spongy bone – honeycomb of trabeculae filled with yellow bone marrow

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of Long Bone Figure 6.3b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Structure of Long Bone  Long bones consist of a diaphysis and an epiphysis  Diaphysis  Tubular shaft that forms the axis of long bones  Composed of compact bone that surrounds the medullary cavity  Yellow bone marrow (fat) is contained in the medullary cavity

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of Long Bone  Epiphyses  Expanded ends of long bones  Exterior is compact bone, and the interior is spongy bone  Joint surface is covered with articular (hyaline) cartilage  Epiphyseal line separates the diaphysis from the epiphyses

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Structure of Long Bone Figure 6.3

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of Long Bone Figure 6.3a

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Structure of Long Bone Figure 6.3c

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Bone Markings  Bulges, depressions, and holes that serve as:  Sites of attachment for muscles, ligaments, and tendons  Joint surfaces  Conduits for blood vessels and nerves

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Bone Markings: Projections – Sites of Muscle and Ligament Attachment  Tuberosity – rounded projection  Crest – narrow, prominent ridge of bone  Trochanter – large, blunt, irregular surface  Line – narrow ridge of bone

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Bone Markings: Projections – Sites of Muscle and Ligament Attachment  Tubercle – small rounded projection  Epicondyle – raised area above a condyle  Spine – sharp, slender projection  Process – any bony prominence

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Bone Markings: Projections – Projections That Help to Form Joints  Head – bony expansion carried on a narrow neck  Facet – smooth, nearly flat articular surface  Condyle – rounded articular projection  Ramus – armlike bar of bone

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Bone Markings: Depressions and Openings  Meatus – canal-like passageway  Sinus – cavity within a bone  Fossa – shallow, basin-like depression  Groove – furrow  Fissure – narrow, slit-like opening  Foramen – round or oval opening through a bone

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Bone Membranes  Periosteum – double-layered protective membrane  Outer fibrous layer is dense regular connective tissue  Inner osteogenic layer is composed of osteoblasts and osteoclasts  Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina  Secured to underlying bone by Sharpey’s fibers

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Bone Membranes  Endosteum – delicate membrane covering internal surfaces of bone

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of Short, Irregular, and Flat Bones  Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone (diploë) on the inside  Have no diaphysis or epiphyses  Contain bone marrow between the trabeculae

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Structure of a Flat Bone Figure 6.4

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Location of Hematopoietic Tissue (Red Marrow)  In infants  Found in the medullary cavity and all areas of spongy bone  In adults  Found in the diploë of flat bones, and the head of the femur and humerus

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Chemical Composition of Bone: Organic  Osteoblasts – bone-forming cells  Osteocytes – mature bone cells  Osteoclasts – large cells that resorb or break down bone matrix  Osteoid – unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen

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Chemical Composition of Bone: Inorganic  Hydroxyapatites, or mineral salts  Sixty-five percent of bone by mass  Mainly calcium phosphates  Responsible for bone hardness and its resistance to compression

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Bone Development  Osteogenesis and ossification – the process of bone tissue formation, which leads to:  The formation of the bony skeleton in embryos  Bone growth until early adulthood  Bone thickness, remodeling, and repair

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Formation of the Bony Skeleton  Begins at week 8 of embryo development  Intramembranous ossification – bone develops from a fibrous membrane  Endochondral ossification – bone forms by replacing hyaline cartilage

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings 10 week fetus Cartilage bone of the skull Intramembranous ossification produces the roofing bones of the skull Primary ossification centers of the diaphyses (skeleton of the lower limb) Future hip bone Bone Formation  The basic shape of a long bone, such as an arm bone, is first formed as cartilage  Bone growth begins long before birth.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Bone Formation 12 week fetus 16 week fetus Ossification begins to take place up to seven months before birth

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Bone Formation  Babies are born with 350 bones, many are composed almost entirely of cartilage.  Latter the cartilage cells will be replaced by cells that form the bones. (ossification) Long bones develop and grow throughout childhood at the centers of ossification (growth plates) The SOFT SPOT of a babie’s skull will fuse around age 2, but growth of the skull continues until adulthood. The SOFT SPOT of a babie’s skull will fuse around age 2, but growth of the skull continues until adulthood.

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Structure of Bone: Compact Bone  Haversian system, or osteon – the structural unit of compact bone  Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen  Haversian, or central canal – central channel containing blood vessels and nerves  Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Structure of Bone: Compact Bone  Osteocytes – mature bone cells  Lacunae – small cavities in bone that contain osteocytes  Canaliculi – hairlike canals that connect lacunae to each other and the central canal

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Structure of Bone: Compact Bone Figure 6.6a, b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Structure of Bone: Compact Bone Figure 6.6a

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings Microscopic Structure of Bone: Compact Bone Figure 6.6b

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Microscopic Structure of Bone: Compact Bone Figure 6.6c