The Skeletal System Osseous Tissue

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The Skeletal SystemOsseous Tissue

• Chapter 5

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Skeletal Overview

• Adult skeleton consists of about 206 bones
• Skeleton - axial and appendicular
• Axial skeleton (80 bones) forms the bodys axis
  to support and protect head, neck, and trunk
  organs
• - Skull - composed of cranial facial bones
• - Vertebral column (backbone) 26 vertebrae,
  most separated by intervertebral discs
• - Rib cage 12 rib pairs, sternum, costal
  cartilages
• Appendicular skeleton - the limb bones and their
  girdles appended or attached to the axial skeleton

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Axial Skeleton
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Appendicular Skeleton
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Skeletal System

• Made up of the skeleton and the cartilages,
  ligaments, and other CTs that stabilize them
• Bone or osseous tissue, is the major component of
  the skeletal system
• Bones are dynamic organs made up of several
  tissue types

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Functions

• Support bones are the bodys infrastructure
• Storage of minerals calcium salts, 98 of the
  bodys calcium is in the bones
• Blood cell production the bone marrow produces
  new blood cells
• Protection many delicate organs are surrounded
  by bone
• Leverage muscles pull on bone to produce
  movement

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Bone Structure

• Osseous tissue like other supporting CTs
  contains
• - specialized cells
• - EC matrix of protein fibers and a ground
  substance
• - matrix is solid and sturdy due to deposition
  of calcium salts around the protein fibers
• Outer covering called periosteum is continuous
  with the deep fascia
• Inner cellular lining is called the endosteum

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Organization of Mature Bone

• The matrix Ca3 (PO4)2 almost 2/3 of the
  weight
• - interacts with Ca(OH)2 to form hydroxyapatite
  Ca10 (PO4)6 (OH)2 crystals which in turn
  incorporate other calcium salts
• - gives bone its resistance to compression
• Collagen fibers make up 1/3 of the bone matrix
• - very resistant to stretch
• Collagen and hydroxyapatite make bone tissue
  extremely strong
• Cells make up only about 2-3 of bone tissue

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Cells of Mature Bone

• Osteocytes mature cells that maintain bone
  tissue
• Osteoblasts immature, active cells that are
  found on inner and outer surfaces of bones
• - osteoblasts produce osteoid the organic
  component of the bone matrix
• Osteogenesis process of making new bone
• Osteoprogenitor cells are found on inner and
  outer surfaces of bones
• - divide and differentiate to form new
  osteoblast
• Osteoclasts are giant multinucleated cells that
  perform osteolysis

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Histological Structure of a Typical Bone

• Fig 5.1 Bone cells

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Osteon
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Compact and Spongy Bone

• Same matrix compostition but different 3-D
  arrangement of osteocytes, canaliculi, and
  lamellae
• Compact bone is dense and solid its basic
  functional unit is the osteon
• Spongy bone forms an open network of struts and
  plates (trabeculae)
• Typical bone - compact bone forms the walls and
  an internal layer of spongy bone surrounds the
  medullary cavity, contains bone marrow, a loose
  CT
• - yellow marrow, dominated by adipocytes
• - red marrow, a mixture of red and WBCs, and
  stem cells

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Internal Organization

• Osteocytes mature bone cells
• - maintain and monitor the protein and mineral
  content of the surrounding matrix
• Lacunae small chambers occupied by osteocytes
• - sandwiched between layers of calcified matrix
  known as lamallae
• Canaliculi channels that radiate through the
  matrix from lacuna to lacuna, free surfaces, BVs
• - interconnect the osteocytes in adjacent
  lacunae
• Tight junctions interconnect canaliculi
• - provide a route for nutrient and waste
  diffusion

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Functional Differences

• Matrix composition, same in compact and spongy
  bone
• Functional differences
• Epiphyses, or ends - filled with spongy bone
• Diaphysis, or shaft with walls of compact bone
• Metaphysis, a narrow zone connecting the
  epiphyses and diaphysis

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Anatomy of a Representative Bone
Fig 5.3
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The Periosteum

• Consists of an outer fibrous layer of dense
  fibrous CT and an inner cellular layer containing
  osteoprogenitor cells
• Isolates and protects the bone from surrounding
  tissues
• Provides a route and a place for attachment for
  circulatory and nervous supply
• Actively participates in bone growth and repair
• Attaches the bone to the CT network of the deep
  fasica

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Near joints periosteum is continuous with the CT
network- surrounds and stabilizes the
jointCollagen fibers incorporated into bone
tissue from tendons are called perforating or
Sharpeys fibers

• Inside the bone, a cellular endosteum
• lines the medullary cavity contains
• osteoprogenitor cells, covers the
• trabeculae of spongy bone and lines
• inner surfaces of the central and
• perforating canals

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Bone Development and Growth

• Before 6 weeks of development the skeleton
  consists mainly of cartilage
• It is replaced with bone by a process known as
  ossification
• - calcification occurs, the process of
  depositing calcium salts into tissues
• There are 2 major forms of ossification
• - intramembranous, bone develops from mesenchyme
  (clavicle, mandible, flat bones of the face and
  skull)
• - endochondral, bone replaces cartilage (limbs
  and weight-bearing bones such as the vertebral
  column)

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Formation of the Blood Supply

• In a typical bone (humerus), 4 major sets of
  blood
• vessels develop
• The nutrient artery and nutrient vein (usually 1
  ea) enter the diaphysis through a nutrient
  foramen
• - penetrate the shaft to reach the medullary
  cavity
• - nutrient artery divides into ascending and
  descending branches, which approach the epiphyses
• - vessels re-enter the compact bone by
  perforating canals and extend along the central
  canals to supply the osteons

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Formation of the Blood Supply

• Metaphyseal vessels supply blood to the inner
  surface of the epiphyseal cartilage
• - where bone is replacing cartilage
• Epiphyseal vessels enter foramina to supply the
  osseous tissue and medullary cavities of the
  epiphyses
• Periosteal vessels, from the periosteum, provide
  blood to the superficial osteons of the shaft
• Following the closure of the epiphyses, all 3
  sets of BVs become interconnected

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Circulatory Supply to a Mature Bone
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Lymphatic Supply

• The periosteum contains an extensive network of
  lymphatic vessels
• Many of these vessels have branches that enter
  the bone and reach individual osteons through
  numerous perforating canals

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Factors Regulating Bone Growth

• Normal bone growth depends on a combination of
  nutritional and hormonal factors
• A constant dietary source of ions
• - calcium, phosphate, magnesium, citrate,
  carbonate, sodium
• Vitamins
• - Vitamins A and C (most be obtained from diet)
• - Vitamin D derivatives stimulates absorption
  and transport of calcium and phosphate ions into
  the blood
• - calcitriol, active form of vit D, synthesized
  in the kidneys depends on cholecalciferol, a
  steroid absorbed from the diet or synthesized in
  the skin from UV radiation

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Hormonal Factors

• Parathyroid hormone (PTH) acts to increase
  overall availability of calcium ions in the blood
• - increased osteoclast activity is the direct
  result of PTH
• Calcitonin is the antagonist of PTH
• - inhibits osteoclasts and increases rate of Ca
  loss in urine
• Growth hormone (pituitary) and thyroxine
  (thyroid) increase osteoblast activity
  stimulating bone growth
• Sex hormones (estrogen, testosterone) increase
  bone growth dramatically during puberty

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Fracture Repair
Fig 5.11
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Osteoporosis
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Classification of Bones

• Long bones long and slender
• - diaphysis, 2 metaphyses, 2 epiphyses,
  medullary cavity
• Flat bones thin, flat, usually curved
• - cranial bones, sternum, ribs, scapulae
• Pneumatized bones hollow or contain numerous
  sacs (ethmoid)
• Irregular bones complex shapes
• - vertebrae and hip bones
• Short bones boxlike in appearance
• - carpal bones and tarsal bones
• - sesamoid bones (patella)

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Bone Shapes
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Bone Markings
Fig 5.14
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Fracture Classifications
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Clinical Terms

• Achondroplasia
• Acromegaly
• External callus
• Fracture
• Fracture hematoma
• Gigantism
• Hyperostosis
• Internal callus
• Marfans syndrome

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Clinical Terms

• Osteoclast-activating factor
• Osteogenesis imperfecta
• Osteomalacia
• Osteomyelitis
• Osteopenia
• Osteopetrosis
• Osteoporosis
• Pagets disease (osteitis deformans)
• Pituitary growth failure
• Rickets