9/13/2013 Anatomical Location Description • Dorsal = Posterior • Ventral = Anterior • Cranial = Superior • Caudal = Inferior • Medial moves toward the midline • Lateral moves away from the midline • On the appendicular skeleton proximal moves toward the trunk and distal away from the trunk Overview of the Skeletal System • Bones: the majority of the skeleton (begin as fibrous membranes and cartilage in embryo) • Skeletal Cartilages: certain areas (nose, parts of ribs, joints) • Ligaments: connect bone to bone, reinforce joint, allow for and restrict movement • Joints: articulations between bones – Sites where 2 or more bones meet – Give mobility and hold skeleton together Basics of Skeletal Cartilage • In adults, cartilage remains where flexible skeletal tissue is needed • 80% water allows for resilience – springs back to shape after being compressed • Avascular and Aneural • Covered in Perichondrium (dense irregular connective tissue) that resists expansion when cartilage is compressed – Blood vessels deliver nutrients through matrix 1 9/13/2013 Cartilage Basics Continued • 3 Types of Skeletal Cartilage – Hyaline Cartilage – Elastic Cartilage – Firbrocartlage • Chondrocytes are encased in small cavities called Lacunae within an extracellular matrix containing jellylike ground substance and fibers Hyaline Cartilage • Most abundant skeletal cartilage • Support, flexibility, resilience • Only fiber type is fine collagen (undetectable microscopically) • Looks like frosted glass • Include: – Articular Cartilages: covers ends of long bones at moveable joints – Costal Cartilages: connects ribs to sternum – Respiratory Cartilages: skeleton of the larynx and reinforces respiratory passages – Nasal Cartilages: supports external nose Elastic Cartilage • Similar to Hyaline Cartilage, but also contains elastic fibers • Stands up to repeated bending • Found in 2 places: – External ear – Epiglottis: flap that covers larynx when we swallow 2 9/13/2013 Fibrocartilage • Highly compressible, have great tensile strength – thick and dense • Roughly parallel rows of chondrocytes alternating with thick collagen fibers • Places with heavy pressure and stretch – Menisci: pad like cartilages of the knee – Intervertebral discs Growth of Cartilage • Cartilage has a flexible matrix that can accommodate mitosis – Ideal environment to lay down embryonic skeleton and provide new skeletal growth • Grows in 2 ways: – Appositional: growth from outside – Interstitial: growth from inside • Typically cartilage growth stops during adolescence when skeleton stops growing Appositional Growth of Cartilage • Growth from outside • Cells in the perichondrium secrete matrix against the external surface of the existing cartilage – Adds layers externally – Ends of long bones 3 9/13/2013 Interstitial Growth of Cartilage • Growth from the inside • Lacunae bound chondrocytes within the cartilage divide and secrete new matrix, expanding the cartilage from within – Adds layers internally – Epiphyseal growth plates, ears, nose Classifications of Bones: Location • By Location – Axial Skeleton: forms the long axis of the body • Bones of Skull, Vertebral Column, Rib Cage – Appendicular Skeleton: bones that form the upper and lower limbs, shoulder and hip Classifications of Bones: Shape • By Shape – Long: longer than wide • All limb bones except patella, carpals, and tarsals – Short: cube shaped • Carpals and tarsals • Sesamoid: special short bones that form within a tendon sheath - patella – Flat: thin, flattened, usually somewhat curved • Sternum, scapulae, ribs, most skull bones – Irregular: complicated shapes that don’t fit other classes • Vertabrae, hip bones 4 9/13/2013 Functions of Bone • Support – framework for body and cradles soft organs • Protection – Bones of skull protect the brain, vertebrae protect the spinal cord, rib cage protects organs of the thorax • Movement – Provide levers for muscles Functions of Bone Continued • Storage – Mineral and Growth factor Storage • Reservoir for mineral, esp. calcium and phosphorous – Rleased into blood as needed • Mineralized bone matrix stores growth factors – Triglyceride (fat) storage • Stored in bone cavities and is a source of stored energy • Blood Cell Formation – Hematopoiesis occurs within the marrow cavities of bones Bone Vocabulary • Osteoblasts: bone forming cells – Secrete bone matrix • Osteocytes: mature bone cells – Mineralize bone matrix • Osteoclasts: large cells that break down (resorb) bone matrix; “bone chewers” • Osteoid: unmineralized bone matrix 5 9/13/2013 Anatomy of Bones: Compact Bone • Compact Bone: dense outer layer • Haversian System or Osteon – structural unit – Lamella: weight-bearing, column-like tubes, mainly collagen; fibers of each ring run in adjacent directions to resist twisting forces • Osteocytes occupy lacunae at junctions of lamellae • Canaliculi: hairlike canals; connect lacunae to each other and central canal – Haversian(Central) Canal: through the core of each osteon containing small blood vessels and nerve fibers – Volkmann’s(Perforating) Canals: right angles to the long axis; connect periosteal nerve and blood supply to central canal and medullary cavity Anatomy of Bones: Spongy Bone • Internal to compact bone • honeycomb of trableculae (small needle-like flat pieces) filled with marrow • Trabeculae contain irregularly arranged lamellae and osteocytes interconnected by caniculi • No osteons Coverings and Linings: Periosteum • Double layered membrane that covers the entire bone except the joint surface • Outer fibrous layer – dense irregular connective tissue • Inner osteogenic layer – against bone surface – Osteoblasts, osteoclasts and osteogenic cells (stem cells) • Provides anchoring points for ligaments and tendons • Richly supplied with nerve fibers, lymphatic vessels and blood vessels which enter diaphysis via nutrient foramina 6 9/13/2013 Coverings and Linings: Endosteum • Delicate membrane covering the internal surfaces of bone • Covers the tribeculae of spongy bone and the canals that pass through compact bone • Contains osteoblasts, osteoclasts and osteogenic cells Anatomy of a Long Bone • Diaphysis: tubular shaft forming the long axis of the bone – Thick collar of compact bone surrounding a central medullary (marrow) cavity (yellow marrow) • Epiphyses: bone ends – Compact bone exterior, spongy bone interior – Joint surface of epiphyses covered with hyaline cartilage – Epiphyseal line separates epiphyses and diaphysis • Remnant of epiphyseal plate – hyaline growth plate Short,Irregular and flat bones • On outside, thin plates of periosteum covered compact bone • On inside, endosteum covered spongy bone – Contain marrow in the spaces of the tribeculae – In flat bones spongy bone is called diploë • Bones are not cylindrical, no shaft or epiphyses 7 9/13/2013 Bone Development • Ossification and ostoegenesis – synonyms meaning bone formation • Before week 8, the skeleton of the human embryo is constructed entirely of fibrous membranes and hyaline cartilage • Intramembranous Ossification: bone developing from fibrous membrane – Fibrous connective tissue formed by mesenchymal cells • Endochondral Ossification: Ossification of the hyaline cartilage Intramembranous Ossification • Results in formation of cranial bones (frontal, parietal, occipital, temporal) and clavicles • Stages 1)Ossification centers appear in the fibrous membrane 2)Bone matrix secreted and calcified within membrane 3)Woven bone and periosteum form - precursor to spongy bone 4)Lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears. Endochondral Ossification • Uses hyaline cartilage “bones” as patterns for bone construction • Most bones develop this way • Ossification “chases” cartilage formation as cartilage calcifies, erodes and is replaced by bone – Requires breakdown of hyaline cartilage prior to ossification 8 9/13/2013 Endochondral Ossification • Formation of Bone Collar • Cavitation of Hyaline Cartialge – Form a hole inside • Invasion of internal cavity by periosteal bud and spongy bone formation • Formation of medullary cavity; appearance of secondary ossification centers in epiphyses • Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates and as articular cartilage – Growth plates Postnatal Bone Growth • During Infancy and youth • All bones grow in thickness by appositional growth • Long bones grow by interstitial growth of the epiphyseal plate cartilage and its replacement by bone – Longitudinal growth ends when the bones of the epiphysis and diaphysis fuse (epiphyseal closure) – Around 18 in females, 21 in males Bone Remodeling • Every week we recycle 5-7% of our bone mass, yet in healthy young adults total mass remains constant • Depostion and Resorption of bone – Deposits occur where bone is injured or more strength is required • Requires protein, vit C, vit D, vit A, minerals (calcium, phosphorous, magnesium, manganese) – Resorption occurs in response to systemic Calcium demands • Romodeling units – Adjacent osteoblasts and ostoeclasts deposit and resorb bone from ondosteal and periosteal surfaces 9 9/13/2013 Regulation of Remoldeling • Hormonal mechanism maintains calcium homeostasis in the blood – Calcitonin stimulates calcium salt deposit in bone – PTH (parathyroid hormone) signals osteoclasts to degrade bone matrix and release calcium • Mechanical and gravitational forces acting on the skeleton – Wolff’s Law: a bone grows or remodels in response to forces or demands placed upon it – Trabeculae form along lines of stress – Large