The Skeletal System

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The Skeletal System

• Chapter 6
• Anatomy and Physiology
• Mr. Knowles
• Liberty Senior High School

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Question of the Day!

• Do bones remain the same?
• How do bones know when to stop growing? What
  happens when they dont?

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The Skeletal System! Our First System

• Cells (Osteocytes)
• Tissues (Osseous Tissue)
• Organs (Bones)
• Systems (Skeletal)

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All C.T. have Three Parts

• 1. Specialized Cells
• 2. Extracellular Protein Fibers
• 3. The Fibers above and a ground substance
  (usually a liquid)- make up the Matrix that
  surrounds cells. (most of the volume of C.T.)

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The Fibers

• Collagen Fibers- long, straight, unbranched,
  fibers of twisted protein rope-like, very
  flexible, yet strong. (Tendons and Ligaments)

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Bone (Osseous Tissue)

• G.S. almost no liquid collagen fibers
  calcium salts (CaPO4 and some CaCO3)
• Strong and flexible properties.
• Lacunae in matrix contain osteocytes.

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Bone (Osseous Tissue)

• Lacunae organized around a central canal
  (Haversian canal) which contains blood vessels.
• Diffusion cannot occur through calcium salts.
• Cytoplasm of osteocytes extend to central canal
  by canaliculi.

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A Basic Pattern in Bone Tissue

• Lacunae with osteocytes arranged around and
  connected to a central canal by radiating
  canaliculi- Osteon
• Many osteons in one bone.

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Bone-Low Mag.
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Haversian or Central Canal
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Bone-High Mag.
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Osteons
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Bone (Osseous Tissue)

• Bone surfaces covered by periosteum- fibrous
  layer of C.T. attachment for tendons and
  ligaments.
• Site of appositional growth of bone.
• Bone is constantly remodeled- grow thicker with
  stresses.

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Anatomy of Bone (4 Parts)

• 1. Diaphysis- long, tubular shaft, mostly compact
  bone.
• 2. Epiphysis- expanded areas at the ends of bone,
  mostly spongy bone.

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Anatomy of Bone (4 parts)

• 3. Marrow Cavity- core of bone with red and
  yellow marrow.
• 4. Metaphysis- area that connects the epiphysis
  and diaphysis. Contains the Epiphyseal plate-
  area of growth between epiphysis and diaphysis

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Other Parts to Bone

• Periosteum- outermost layer of bone made of
  cells and fibers.
• Provides the point of attachment for tendons
  and ligaments on the outside.
• Route for vessels to enter the bone.
• Participates in bone growth and repair.

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Other Parts of the Bone

• Endosteum- a layer of cells that lines marrow
  cavity lines trabeculae of spongy bone and
  central canal of compact bone.
• Also site of bone growth.

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Two Types of Osseous Tissue

• 1. Compact bone- dense bone, solid, more on
  surface of bone, shaft of bone.
• Function osteons are all alignedstrengthen
  bone, the tissue of bone is parallel to stresses.

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Two Types of Osseous Tissue

• 2. Spongy Bone- open network of trabeculae which
  are struts and plates in the interior of bone
  (matrix) , light in weight
• Function has no osteons withstand stress from
  a variety of directions, reduce the weight of the
  overall bone.

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Bone Development

• Skeleton begins to develop at 6 weeks after
  conception, embryo is only 12 mm (0.5 in ) long.
• Bone growth continues through the age of 25 yrs.
• Bone is continuously remodeled or reshaped.

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How do bones grow in humans?

• Can we see bone growth in a developing embryo?

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The Players in Osteogenesis

• Ossification- formation of bone is a dynamic
  process.
• Osteoblasts- produce new bone matrix.
• Osteoclasts- produce acids and enzymes to release
  the stored minerals in the matrix.
• Osteocytes- mature bone cells that do not divide.

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Bone Grows in Two Ways

• Intramembranous Ossification- bone forms from
  mesenchyme cells or fibrous connective tissue.
  Deep layers of the dermis.
• Endochondral Ossification- bone replaces a mold
  of cartilage.

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Intramembranous Growth

• Step 1 Mesenchymal cells (stem cells) cluster
  at a site (ossification center) within the dermis
  (skin layers) and secrete bone matrix (collagen
  Ca 2). These cells will become osteoblasts.
• Step 2 Bone grows outward in spicules which
  will become the struts of spongy bone. Vessels
  grow into area.
• Step 3 Osteoblasts at the outer edge become
  less active and become osteocytes.

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Intramembranous Bones

• Dermal bones of the skull- parietal, occipital,
  etc, the mandible, the clavicle, and the scapula.
• Bones that are mostly spongy tissue are made by
  intramembranous ossification.

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Osteogenesis

• Intramembranous ossification- bone growth within
  C.T. (mandible, parietal) see p. 181, 4th Ed.,
  Martini)
• Want to see what happens when this growth is
  uncontrolled? Heterotopic Bone Formation, p. 50
  of the A.M.

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Heterotopic Bone Formation
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FOP
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Endochondral Ossification

• Endo means inside -chondros means cartilage.
• Bone tissue gradually replaces a cartilage model
  or mold for the bone.
• Most bones form this way all of the appendicular
  (limb) skeletal bones.

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Endochondral Growth

• Step 1 Cartilage forms a mold and the
  chondrocytes grow very large in the center of the
  mold. Lacunae expand and the matrix thins to
  struts. Chondrocytes die.
• Step 2 Blood vessels grow into the shaft of
  cartilage cells of the perichondrium become
  osteoblasts. The perichondrium now becomes the
  periosteum.

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Endochondral Growth

• Step 3 Blood supply increases fibroblasts
  migrate to the center and become osteoblasts.
  They start to make spongy bone- Primary Center of
  Ossification.
• Step 4 As bone enlarges, osteoclasts appear and
  erode the trabeculae in the center- creates the
  marrow cavity.

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Show Me the BMU in Action!
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Endochondral Ossification

• Osteoblasts of the diaphysis and chrondrocytes of
  epiphysis continue to grow elongate bone.
• Epiphyseal Plate is the interface between the
  two.
• At puberty, the osteoblasts overcome
  chondrocytes the plate becomes more narrow-
  epiphyseal line.

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Fetal Long Bone
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Developing Long Bone
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Endochondral Ossification
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Endochondral Ossification

• Lengthening Bones-
• Hyaline chondrocytes die and leave calcified
  struts.
• Blood vessels grow at edges and perichondrial
  cells become osteoblasts.
• Osteoclasts- create a marrow cavity by dissolving
  struts

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Bone Growth

• Intramembranous
• Occurs in a layer between dermis (dermal bones).
• Mesenchymal (stem) cells ?osteoblasts.
• Spongy Bone.
• Skull bones, mandible, scapula, clavicle.

• Endochondral
• Fills in a cartilage mold in a center of
  ossification.
• Fibroblasts ?osteoblasts in the center of mold.
• Osteoclasts form a marrow cavity.
• Compact Bone.
• Most other bones long bones.

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Basic Multicellular Unit (BMU)

• A group of wandering cells that constantly reform
  or remodel bone.
• Many BMU move throughout the bones center and
  surface.
• Specific sequence of 5 events or steps.

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5 Steps to Bone Formation

• Osteoclast Recruitment- osteoclasts arrive at the
  site of repair or reformation.
• Resorption- osteoclasts resorb or release the Ca
  2 from the matrix. This forms a cavity in the
  area (2 weeks).
• Osteoid Formation- osteoclasts self-destruct and
  attract osteoblasts to the area. The osteoblasts
  secrete new collagen and Ca 2 into the cavity.

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5 Steps to Bone Formation

• Mineralization- the new osseous tissue begins to
  mineralize Ca 2 fills the cavity.
• Quiescence- the last osteoblasts develop into
  osteocytes and remain quiet in the bone tissue.
  They have long cell processes that can detect
  mechanical stresses.

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Show me Normal Bone Remodeling in Spongy Bone!
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When bones dont stop growing!
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Diseases of Bone Growth

• Read bottom of p. 48 52 of Martini, F. (1998)
  Applications Manual. 4th Ed. Prentice Hall New
  Jersey.
• Complete the Table on Bone Growth Diseases.

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Acromegaly?
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Diseases of Bone Growth

• Gigantism overproduction of growth hormone
  before puberty, growth plates still open
  pituitary tumor.
• Acromegaly overproduction of growth hormone
  after puberty, growth plates closed but abnormal
  growth of cartilage and small bones.
• Marfans Syndrome defect in fibrillin, a
  protein of C. T. matrix excessive cartilage at
  plates that is weak blood vessels are not as
  elastic genetic.

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Marfans Syndrome?
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Achondroplasia
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Diseases of Bone Growth

• Achondroplasia a without, chondro
  cartilage, plasia formation cartilage within
  the epiphyseal plates grow extremely slow
  affects appendicular skeleton more than axial
  skeleton.

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Osteoporotic Spongy Bone
Normal Spongy Bone
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Show Me Post-Menopausal Bone in Action
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The Skeletal System

• Anatomy and Physiology
• Chapters 7 and 8
• Mr. Knowles
• Liberty Senior High School

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The Skeletal System

• How many bones do women and men have?
• 206 bones in humans

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Two Divisions

• Appendicular Skeleton-
• bones of limbs (appendages), pectoral and pelvic
  girdlesattach the limbs to the trunk of the body.

• Axial Skeleton-
• bones of skull, vertebral column, ribs, and
  sternum- 80 bones

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Functions of the Skeletal System

• 1. Support- framework,
• 2. Storage of Minerals- Ca3(PO4)2, and CaCO3
• 3. Storage of Lipids- yellow marrow.

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Functions of the Skeletal System

• 4. Blood cell production- red marrow makes
  erythrocytes, leukocytes, and others.
• 5. Protection- protect vital organs. Ex. Ribs.
• 6. Leverage- change magnitude and direction of
  forces.

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Classification of Bones

• 1. Long bones- long, slender shapes (femur,
  phalanges)
• 2. Short bones- boxlike (carpal and tarsal bones)
• 3. Flat bones- thin, flat bones (sternum, ribs,
  scapula, parietal)

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Short Bones
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Carpals
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Bones of the Skull
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Classification of Bones

• 4. Irregular bones- complex shapes, notched or
  ridged surfaces vertebra(ae)
• 5. Sesamoid- like a sesame seed, small, flat, and
  inside joints patella(ae)

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Vertebra (ae) irregular bones
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The Patella (ae) a sesamoid bone
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Sesamoid Bone in Hand
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A Sesamoid Bone
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Other Sesamoid Bones!
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Classification of Bones

• 6. Sutural bones- small, flat, irregular bones of
  skull (sutural bone in skull)

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Many Irregular, Flat, and Sutural
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Your Assignment

• Finish the handouts over the tissues of bone.
• Identify all bones and structures listed in the
  outline (Refer to Table 6-2 on p. 192).
• Classify these bones into the six major types of
  bones.

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What can we learn about a persons life from
their bones?

• G. B. Dyson (2000). The Aleutian Kayak.
  Scientific American (April) 84-91.