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Skeletal System
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Skeletal System



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    Skeletal System Skeletal System Presentation Transcript

    • Anatomy and Physiology, Seventh Edition Rod R. Seeley Idaho State University Trent D. Stephens Idaho State University Philip Tate Phoenix College Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Chapter 06 Lecture Outline *
    • Skeletal System Functions
      • Support . Provides structural support for the entire body. A framework for attachment of soft tissues or organs.
      • Protection . Skull around brain and inner ear; ribs, sternum, vertebrae protect organs of thoracic cavity
      • Leverage . Act as levers for muscles that contract and produce movement by pulling on bones via tendons.
      • Storage . Acts as a reservoir for calcium and phosphorous. Fat stored in marrow cavities
      • Blood cell production (Hematopoiesis) . Bone marrow gives rise to blood cells and platelets
    • Bone Shapes
      • Long bones
        • Upper and lower limbs
      • Short bones
        • Carpals and tarsals
      • Flat bones
        • - Ribs, sternum, skull, scapulae
      • Irregular bones
        • Vertebrae, facial bones
    • Long Bone Structure
      • Diaphysis
        • Tubular shaft that forms the axis
        • Composed of compact bone that surrounds the medullary cavity
        • Yellow marrow (fat) stored in medullary cavity.
        • Shaft covered with periosteum
        • Medullary cavity lined with endosteum
      • Epiphysis
        • Expanded end of the bone
        • Interior is cancellous bone (spongy bone)
        • Joint surface covered with articular (hyaline) cartilage
        • Epiphyseal line: separates diaphysis from epiphysis
          • Composed of hyaline cartilage
          • Bone growth in lengths occurs here
    • Bone Membranes
      • Periosteum – double-layered protective membrane
        • Outer fibrous layer is dense regular connective tissue
        • Inner osteogenic (bone forming) 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
      • Endosteum – delicate membrane covering internal surfaces of bone
    • Structure of Long Bone Figure 6.3
    • Structure of Short, Irregular, and Flat Bones
      • Flat Bones
        • No diaphysis or epiphysis
        • Sandwich of cancellous between compact bone
        • Periosteum covers outer surface while endosteum lines interior
      • Some flat and irregular bones of skull have sinuses lined by mucous membranes (Frontal, Maxillary, Ethmoid, and Sphenoid bones)
    • Cells of Osseous Tissue (1)
      • Osteogenic cells in endosteum, periosteum or central canals give rise to new osteoblasts
        • arise from embryonic fibroblasts
        • multiply continuously
      • Osteoblasts mineralize organic matter of matrix
        • Synthesize and secrete collagen protein and other organic compounds of matrix
        • Produce new bone in a process known as osteogenesis
      • Osteocytes are osteoblasts trapped in the matrix they formed
        • cells in lacunae connected by gap junctions inside canaliculi
    • Cells of Osseous Tissue (2)
      • Osteoclasts develop in bone marrow by fusion of 3-50 stem cells
      • Remove and recycle bone matrix
        • Secrete acid and proteolytic enzymes that dissolve matrix and release the stored minerals; called osteolysis
      • Reside in pits that they ate into the bone
    • Matrix of Osseous Tissue
      • Dry weight = 1/3 organic and 2/3 inorganic matter
      • Organic matter
        • collagen, glycosaminoglycans, proteoglycans and glycoproteins
        • Gives bone is resilience, flexibility
      • Inorganic matter
        • 85% hydroxyapatite (calcium phosphate)
        • 10% calcium carbonate
        • Other minerals (fluoride, potassium, magnesium)
        • Gives bone its hardness
      • Combination provides for strength and resilience
        • minerals resist compression; collagen resists tension
        • bone adapts by varying proportions
    • Bone Matrix
      • If mineral removed, bone is too bendable
      • If collagen removed, bone is too brittle
    • Histology of Compact Bone
      • Osteon = basic structural unit
        • cylinders formed from layers ( lamellae ) of matrix around central canal (osteonic canal)
          • collagen fibers alternate between right- and left-handed helices from lamella to lamella
        • osteocytes connected to each other and their blood supply by tiny cell processes in canaliculi
      • Perforating canals or Volkmann canals
        • vascular canals perpendicularly joining central canals
    • Microscopic Structure of Compact Bone Figure 6.6a, b
    • Structure of Cancellous (Spongy) Bone
      • Spongelike appearance formed by plates of bone called trabeculae
        • spaces filled with red bone marrow
      • Trabeculae
        • Oriented along stress lines
        • Have few osteons or central canals
        • No osteocyte is far from blood of bone marrow
      • Provides strength with little weight
        • Trabeculae develop along bone’s lines of stress
    • Bone Development
      • Osteogenesis and ossification
        • The process of bone tissue formation, which leads to:
          • Formation of the bony skeleton in embryos
          • Bone growth until early adulthood
          • Bone thickness, remodeling, and repair
      • Begins at week 8 of embryo development
      • Two major methods used:
        • 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
      • Takes place in connective tissue membrane formed from embryonic mesenchyme
      • Forms many flat bones of the skull, part of mandible, diaphyses of clavicles
      • When remodeled, indistinguishable from endochondral bone.
    • Intramembranous Ossification
      • Produces flat bones of skull and clavicle.
    • Endochondral Ossification
      • Begins in the second month of development
      • Uses hyaline cartilage as model for bone construction
      • Bones of the base of the skull, part of the mandible, epiphyses of the clavicles, and most of remaining bones of skeletal system
    • Stages of Endochondral Ossification
    • Growth in Bone Length
      • Appositional growth - growth in length
        • Interstitial growth cannot occur because matrix is solid
        • Occurs on old bone and/or on cartilage surface
      • Growth in length occurs at the epiphyseal plate
      • Involves the formation of new cartilage by
        • Interstitial cartilage growth
      • Closure of epiphyseal plate : epiphyseal plate is ossified becoming the epiphyseal line. Between 12 and 25 years of age
      • Articular cartilage: does not ossify, and persists through life
    • The Metaphysis
      • Regions of the Epiphyseal Plate
        • Zone of reserve cartilage = hyaline cartilage
        • Zone of proliferation
          • chondrocytes multiply forming columns of flat lacunae
        • Zone of hypertrophy = cell enlargement
        • Zone of calcification
          • mineralization of matrix
        • Zone of bone deposition
          • chondrocytes die and columns fill with osteoblasts
          • osteons formed and spongy bone is created
    • Growth in Bone Length
    • Long Bone Growth and Remodeling Figure 6.10
    • Bone Growth and Remodeling
      • Bones increase in length
        • interstitial growth of epiphyseal plate
        • epiphyseal line is left behind when cartilage gone
      • Bones increase in width = appositional growth
        • osteoblasts lay down matrix in layers on outer surface and osteoclasts dissolve bone on inner surface
      • Bones remodeled throughout life
        • Wolff’s law of bone = architecture of bone determined by mechanical stresses
          • action of osteoblasts and osteoclasts
        • greater density and mass of bone in athletes or manual worker is an adaptation to stress
    • Factors Affecting Bone Growth
      • Size and shape of a bone determined genetically but can be modified and influenced by nutrition and hormones
      • Nutrition
        • Lack of calcium, protein and other nutrients during growth and development can cause bones to be small
        • Vitamin D
          • Necessary for absorption of calcium from intestines
          • Can be eaten or manufactured in the body
          • Rickets : lack of vitamin D during childhood
          • Osteomalacia : lack of vitamin D during adulthood leading to softening of bones; pain when wt. put on affected bone
        • Vitamin C
          • Necessary for collagen synthesis by osteoblasts
          • Scurvy: deficiency of vitamin C
          • Lack of vitamin C also causes wounds not to heal, teeth to fall out
    • Factors Affecting Bone Growth, cont.
      • Hormones
        • Growth hormone from anterior pituitary. Stimulates interstitial cartilage growth and appositional bone growth
        • Thyroid hormone required for growth of all tissues
        • Sex hormones such as estrogen and testosterone
          • Cause growth at puberty, but also cause closure of the epiphyseal plates and the cessation of growth
    • Dwarfism
      • Achondroplastic
        • long bones stop growing in childhood
          • normal torso, short limbs
        • spontaneous mutation during DNA replication
        • failure of cartilage growth
      • Pituitary
        • lack of growth hormone
        • normal proportions with short stature
    • Calcium Homeostasis
      • Bone is major storage site for calcium
      • The level of calcium in the blood depends upon movement of calcium into or out of bone.
        • Calcium enters bone when osteoblasts create new bone; calcium leaves bone when osteoclasts break down bone
        • Two hormones control blood calcium levels- parathyroid hormone and calcitonin.
    • Calcium Homeostasis
    • Osteoporosis 1
      • Bones lose mass and become brittle (loss of organic matrix and minerals)
        • risk of fracture of hip, wrist and vertebral column
        • complications (pneumonia and blood clotting)
      • Postmenopausal white women (> 50) at greatest risk
        • by age 70, average loss is 30% of bone mass
        • black women rarely suffer symptoms
      • Risk factors include
        • Smoking - lowers blood estrogen levels
        • Body wt - thin, anorexic, heavy exercisers (runners, ballet dancers - less adipose available to make estrogen
        • Body build - short females have less total bone mass
        • Calcium deficiency
        • Vitamin D deficiency
        • Certain drugs - alcohol, cortisone, tetracycline promote bone loss
        • Family history
        • Females with eating disorders including junk food diets
    • Osteoporosis 2
      • Estrogen maintains density in both sexes (inhibits resorption)
        • testes and adrenals produce estrogen in men
        • rapid loss after menopause, if body fat too low or with disuse during immobilizaton
      • Treatment
        • ERT (estrogen replacement therapy) - slows bone resorption, but increases risk breast cancer, stroke and heart disease
        • PTH slows bone loss if given daily injection
          • Forteo increases density by 10% in 1 year
          • may promote bone cancer
        • best treatment is prevention -- exercise and calcium intake (1000 mg/day) between ages 25 and 40
    • Spinal Osteoporosis
    • Other Pathologies of Bone
      • Osteomyelitis - all infectious diseases of bone
        • Organisms spread via the blood from wounds, boils, TB
        • Pott’s disease = tuberculosis of the spine (Hunchback)
      • Osteosarcoma - malignant tumors of bone
        • Capable of metastasizing to other tissues/organs
      • Paget’s disease
        • Characterized by excessive bone formation and breakdown
        • In males more than females
        • In skull (hat size changes), pelvis, extremities
      • Myeloma - cancer of bone marrow
      • Osteogenesis imperfecta
        • Familial in nature
        • Very fragile bones; may break while turning in bed
        • Due to an inborn error of metabolism - aminoaciduria
    • Bone Fractures
      • Open (compound)- bone break with open wound. Bone may be sticking out of wound.
      • Closed (simple)- Skin not perforated.
      • Incomplete- doesn’t extend across the bone. Complete- does
      • Greenstick: incomplete fracture that occurs on the convex side of the curve of a bone
      • Hairline: incomplete where two sections of bone do not separate. Common in skull fractures
      • Comminuted fractures: complete with break into more than two pieces
    • Bone Repair
      • Hematoma formation . Localized mass of blood released from blood vessels but confined within an organ or space. Clot formation.
      • 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.
    • Bone Repair, cont.
      • 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
    • Effects of Aging on Skeletal System
      • Bone matrix decreases. More brittle due to lack of collagen; but also less hydroxyapetite.
      • Bone mass decreases.
        • Highest around 30.
        • Men denser due to testosterone and greater weight.
        • African Americans and Hispanics have higher bone masses than Caucasians and Asians.
        • Rate of bone loss increases 10 fold after menopause.
        • Cancellous bone lost first, then compact.
      • Increased bone fractures
      • Bone loss causes deformity, loss of height, pain, stiffness
        • Stooped posture
        • Loss of teeth