Essentials of Human Anatomy The Skeletal System 1

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Essentials of Human Anatomy The Skeletal
System 1

• Chapter 5

Dr Fadel Naim Ass. Prof. Faculty of Medicine IUG
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Bone

• Bones are organs
• Bones are composed of all tissue types.
• Their primary component is osseous connective
  tissue.
• The matrix is sturdy and rigid due to
  calcification (also called mineralization).

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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
• Mineral storage reservoir for minerals,
  especially calcium and phosphorus
• Blood cell formation hematopoiesis occurs
  within the marrow cavities of bones
• Energy storage (fat in yellow marrow)

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Support and Protection

• Bones provide structural support and serve as a
  framework for the entire body.
• Bones protect many delicate tissues and organs
  from injury and trauma.

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Movement

• Muscles attach to the bones of the skeleton
• contract and pull on bone
• functions as a series of levers.

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Storage of Mineral and Energy Reserves

• More than 90 of the bodys reserves of the
  minerals calcium and phosphate are stored and
  released by bone.
• Calcium needed for
• muscle contraction
• blood clotting
• nerve impulse transmission.
• Phosphate needed for
• ATP utilization
• structure of nucleic acids (DNA, RNA)

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HematopoiesisBlood Cell Formation

• Blood cell production in red bone marrow
• located in some spongy bone.
• Red bone marrow contains stem cells
• form all of the blood cell types.

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Bone Classification

• Long Bones
• Short Bones
• Flat Bones
• Irregular Bones
• Sesamoid (Round) Bones

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Classification of Bones By Shape

• Long bones longer than they are wide (e.g.,
  humerus)

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Classification of Bones By Shape

• Short bones
• Cube-shaped bones of the wrist and ankle
• Bones that form within tendons (e.G., Patella)

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Classification of Bones By Shape

• Flat bones thin, flattened, and a bit curved
  (e.g., sternum, and most skull bones)

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Classification of Bones By Shape

• Irregular bones bones with complicated shapes
  (e.g., vertebrae and hip bones)

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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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Bone Structure - External

• Cartilage protection for joints

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Bone Structure - External

• Epiphyses
• Expanded ends of long bones
• Exterior is compact bone, and the interior is
  spongy bone
• Joint surface is covered with articular (hyaline)
  cartilage
• location of red bone marrow
• Epiphyseal line separates the diaphysis from the
  epiphyses

Epiphyse
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Bone Structure - External

• 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

Diaphysis
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Bone Structure - Internal

• Spongy Bone- red marrow

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Bone Structure - Internal

• Compact bone

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Compact and Spongy Bone
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Bone Structure - Internal

• Medullary Cavity-yellow marrow

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Bone Structure - Internal

• Epiphiseal Plate
• Growth Plate

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Parts of a Long Bone

• epiphysis
• distal
• proximal
• diaphysis

• compact bone
• spongy bone

• articular cartilage
• periosteum
• endosteum

• medullary cavity
• trabeculae
• marrow
• red
• yellow

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Structure of Short, Irregular, and Flat Bones

• Thin plates of periosteum-covered compact bone on
  the outside with endosteum-covered spongy bone on
  the inside
• Have no diaphysis or epiphyses
• Contain bone marrow between the trabeculae

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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 Sharpeys fibers
• Endosteum delicate membrane covering internal
  surfaces of bone

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Blood and Nerve Supply of Bone

• Periosteal arteries
• Supply periosteum
• Nutrient arteries
• Enter through nutrient foramen
• Supplies compact bone of diaphysis red marrow
• Metaphyseal epiphyseal aa
• Supply red marrow bone tissue of epiphyses

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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

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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

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Bone Markings
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, basinlike depression
• Groove furrow
• Fissure narrow, slitlike opening
• Foramen round or oval opening through a bone

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The Histologic Types

• Compact bone ( cortical)
• Spongy bone ( cancellous)
• Lamellar bone regular mature
• Woven bone irregular immature fetus -
  fracture
• Osteoid
• Callus fracture healing

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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
• Volkmanns canals channels lying at right
  angles to the central canal, connecting blood and
  nerve supply of the periosteum to that of the
  Haversian canal

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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

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Compact Bone
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Spongy (cancellous) Bone

• Does not contain osteons.
• trabeculae surrounding red marrow spaces

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Cell Types of Bone
4 types of cells in bone tissue

• Osteoprogenitor cells
• Undifferentiated cells
• Can divide become osteoblasts
• Found in inner layer of periosteum and endosteum
• Osteoblasts
• Form matrix collagen fibers but cant divide
• Osteocytes
• Mature cells that no longer secrete matrix
• Osteoclasts
• Huge cells from fused monocytes (WBC)
• Function in bone resorption at surfaces such as
  endosteum

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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 fracture repair

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Bone Growth - Ossification

• Cartilage template laid down.

• Osteoblasts (bone building cells) located in
  Ossification Centers.

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Bone Growth - Ossification

• Primary Ossification Center in diaphasis.

• Secondary Ossification Centers in epiphisis.

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Bone Growth - Ossification

• Grow toward one another, cartilage remains
  between them.

• As long as cartilage remains undamaged, growth
  can occur.

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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

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Endochondral Ossification

• Begins in the second month of development
• Uses hyaline cartilage bones as models for bone
  construction
• Requires breakdown of hyaline cartilage prior to
  ossification

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Stages of Endochondral Ossification

• Formation of bone collar
• Cavitation of the hyaline cartilage
• Invasion of internal cavities by the periosteal
  bud, and spongy bone formation
• Formation of the medullary cavity appearance of
  secondary ossification centers in the epiphyses
• Ossification of the epiphyses, with hyaline
  cartilage remaining only in the epiphyseal plates

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Stages of Endochondral Ossification
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Long Bone Growth and Remodeling

• Growth in length cartilage continually grows
  and is replaced by bone
• Remodeling bone is resorbed and added by
  appositional growth

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Bone Growth in Length

• Epiphyseal plate or cartilage growth plate
• Cartilage cells are produced by mitosis on
  epiphyseal side of plate
• Cartilage cells are destroyed and replaced by
  bone on diaphyseal side of plate
• Between ages 18 to 25, epiphyseal plates close
• Cartilage cells stop dividing and bone replaces
  the cartilage (epiphyseal line)
• Growth in length stops at age 25

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Remodeling

• Occurs all the time.
• Stresses change, bones adapt.
• Osteoclasts remove bone, Osteoblasts build bone,
  Osteocytes maintain bone
• Mineral deposits in Spongy Bone form to hold the
  stress best.
• 5-10 bone / year.

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Osteoclast in lacuna
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Control of Remodeling

• Two control loops regulate bone remodeling
• Hormonal mechanism maintains calcium homeostasis
  in the blood
• Mechanical and gravitational forces acting on the
  skeleton

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Developmental Aspects of Bones

• The embryonic skeleton ossifies in a predictable
  timetable that allows fetal age to be easily
  determined from sonograms
• At birth, most long bones are well ossified
  (except for their epiphyses)
• By age 25, nearly all bones are completely
  ossified
• In old age, bone resorption predominates

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Fracture

• A disruption in the integrity of a living bone
  involving injury to
• Bone
• Bone marrow
• Periosteum
• Adjacent soft tissues

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Types of Fractures

• green stick
• fissured
• comminuted
• transverse
• oblique
• spiral
• Pathologic
• Stress
• Occult

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Fracture Healing

• Bone is the only tissue in the human body other
  than liver that heals by regeneration instead of
  by scarring.
• For regeneration to occur the bone must be
  immobilized to allow uninterrupted formation of
  new bone.

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Fracture Healing

• Primary healing
• Non displaced fractures, fractures with
  compressive fixation across the fracture site
• Osteoblasts traverse the fracture site and lay
  down lamellar bone without forming immature bone
  when there is direct contact between cortical
  bone ends
• Secondary healing
• No compression across fracture site, motion can
  occur
• Fracture callus forms to stop motion, stage of
  consolidation and remodeling

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Primary Bone Healing
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Secondary Bone Healing

• Fracture hematoma
• (72 hours)
• Granulation tissue
• (3-14 days)
• Callus formation
• (7-14 days)
• Ossification
• (3 weeks- 6 months)
• Consolidation
• (3 weeks- 6 months)
• Remodeling
• (Up to 1 year)

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Rickets

• a generalized metabolic bone disorder
• characterized by a failure of or delay in
  calcification of the cartilaginous growth plate
  in children whose epiphyses have not yet fused.
• it is primarily a disease affecting endochondral
  calcification
• manifests clinically and radiographically with
  widening and deformation of the metaphyseal
  regions of long bones

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THE END