Bones and Skeletal Tissues P A R T A

Skeletal Cartilage No blood vessels or nerves Surrounded by perichondrium that resists outward expansion Three types – hyaline, elastic, and fibrocartilage

Hyaline Cartilage Provides support, flexibility, and resilience Most abundant Locations: Articular – on ends of long bones Costal – connects the ribs to the sternum Respiratory – makes up larynx, reinforces air passages Nasal – supports the nose

Elastic Cartilage Similar to hyaline cartilage, but contains elastic fibers Found in the external ear and the epiglottis

Fibrocartilage Highly compressed with great tensile strength Contains collagen fibers Found in menisci of the knee and in intervertebral discs

Growth of Cartilage Two methods: 1. Appositional – perichondrial cells secrete matrix 2. Interstitial – lacunae-bound chondrocytes inside the cartilage divide and secrete new matrix

Bones and Cartilages of the Human Body Figure 6.1

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

Classification of Bones by Shape Four shapes of bone: Long Short Flat Irregular

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

Classification of Bones: By Shape Short bones Wrist and ankle bones Bones that form within tendons (e.g., patella) = sesamoid bones Figure 6.2b

Classification of Bones: By Shape Flat bones Thin, flattened, and a bit curved (e.g., sternum, and most skull bones) Figure 6.2c

Classification of Bones: By Shape Irregular bones Bones with complicated shapes (e.g., vertebrae and hip bones) Figure 6.2d

Function of Bones 1. Support – form the framework of the body 2. Protection – provide a protective case for the brain, spinal cord, and vital organs 3. Movement – provide levers for muscles 4. Mineral storage – reservoir for minerals, especially calcium and phosphorus 5. Blood cell formation – hematopoiesis occurs within the marrow cavities of bones

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

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

Sites of Muscle and Ligament Attachment Tubercle – small rounded projection Epicondyle – raised area above a condyle Spine – sharp, slender projection Process – any bony prominence

Projections That Help to Form Joints Head – bony expansion on a narrow neck Facet – smooth, nearly flat articular surface Condyle – rounded articular projection Ramus – armlike bar of bone

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

Bone Markings Table 6.1

Gross Anatomy of Bones: Bone Textures Compact bone – dense outer layer Spongy bone – inner layer; honeycomb of trabeculae filled with yellow bone marrow

Structure of Long Bone Long bones consist of a diaphysis and two epiphyses Diaphysis Tubular shaft that forms the axis of long bones Compact bone surrounding a medullary cavity Yellow bone marrow (fat) is contained in the medullary cavity

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 cartilage Epiphyseal line separates the diaphysis from the epiphyses

Structure of Long Bone Figure 6.3a

Structure of Long Bone Figure 6.3b

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 Secured to underlying bone by Sharpey’s fibers Endosteum – delicate membrane lining internal surfaces of bone

Structure of Long Bone Figure 6.3c

Structure of Short, Irregular, and Flat Bones Compact bone on the outside with spongy bone (diploë) on the inside Have no diaphysis or epiphyses Contain bone marrow between the trabeculae

Structure of a Flat Bone Figure 6.4

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

Microscopic Structure of Bone: Compact Bone Haversian system (osteon) Lamella – rings made 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

Microscopic Structure of Bone: Compact Bone Osteocytes – mature bone cells Lacunae – small cavities in bone that contain osteocytes Canaliculi – canals that connect lacunae to each other and to central canal

Microscopic Structure of Bone: Compact Bone Figure 6.6a, b

Microscopic Structure of Bone: Compact Bone Figure 6.6c

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

Chemical Composition of Bone: Inorganic Hydroxyapatites, or mineral salts 65% of bone by mass Mainly calcium phosphates Responsible for bone hardness and its resistance to compression

Bone Development Osteogenesis (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

Formation of the Bony Skeleton Begins at week 8 of embryo development Two main mechanisms: 1. Intramembranous ossification – bone develops from a fibrous membrane 2. Endochondral ossification – bone forms by replacing hyaline cartilage

Intramembranous Ossification Formation of most of the flat bones of the skull and the clavicles Fibrous connective tissue membranes are formed by mesenchymal cells