Skeletal Tissues

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Skeletal Tissues
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Compact vs. Spongy

• Compact bone is dense and solid in appearance.
• Cancellous, or spongy, bone is characterized by
  open space partially filled by an assemblage of
  needle-like structures.

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Compact and Spongy Bone
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Four Bone Types

• Long bones extended longitudinal axis and
  expanded and often uniquely shaped articular
  ends.
• Examples are the femur and humerus
• Short Bones cube- or box-shaped structure,
  which are about as broad as they are long.
• Examples include the wrist (carpals) and ankle
  (tarsal) bones

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• Flat bones generally broad and thin with a
  flattened and often curved surface.
• Examples include some skull bones, scapulae,
  ribs, and sternum
• Irregular Bones often clustered in groups and
  come in various shapes and sizes.
• Examples include the vertebral bones that form
  the spine and facial bones

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Parts of a Long Bone

• Diaphysis main shaftlike portion
• Epiphyses both ends of a long bone have a
  bulbous shape that provides generous space near
  the joints for stability and muscle attachment.
• Articular Cartilage thin layer of hyaline
  cartilage that covers joint epiphyses and acts as
  a cushion.

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• Periosteum Dense, white fibrous membrane that
  covers bone except at joint surfaces
• Medullary (marrow) cavity tubelike hollow space
  in the diaphysis of a long bone. In adults it is
  filled with fatty yellow marrow.
• Endosteum thin epithelial membrane that lines
  the medullary cavity of long bones.

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Bone (Osseous) Tissue

• Connective tissue
• Consists of cells, fibers, and extracellular
  matrix
• Extracellular components are hard and calcified
• Matrix is more abundant that the bone cells

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Composition of Bone Matrix

• Inorganic Salt are responsible for the hardness
  of bone.
• Hydroxyapatite composed of calcium and
  phosphate
• Organic Matrix composite of collagenous fibers
  and a mixture of protein and polysaccharides
  called ground substance.

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Osteoporosis

• Age related skeletal disease that is
  characterized by loss of bone mineral density,
  increased bone fragility, and susceptibility to
  fractures
• More common in women
• May lose 4 - 8 of their bone density on a
  yearly basis

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Microscopic Structure of Bone

• Compact bone contains many cylinder-shaped
  structural units called osteons, or Haversian
  systems.
• Each osteon surrounds a canal that runs
  lengthwise through the bone.

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Main Structures of the Osteon

• Lamellae concentric, cylinder shaped layers of
  calcified matrix.
• Lacunae small spaces containing fluid and bone
  cells
• Canaliculi ultrasmall canals radiating in all
  directions from the lacunae that connects them to
  each other and the Haversian canal

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• Haversian canal Extends lengthwise through the
  center of each Haversian system contains blood
  vessels, lymph vessels and nerves
• Volkmanns canals run perpendicular to
  Haversian canals

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Structure of Compact and Cancellous Bone
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Section of Flat Bone
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Cancellous Bone

• There are no osteons in cancellous bone
• Consists of needle-like bony spicules called
  trabeculae.
• Bone cells are found within the trabaculae
• Nutrients are delivered and wastes removed by
  diffusion

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Orientation of Trabeculae
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Types of Bone Cells

• Osteoblasts synthesize and secrete a
  specialized organic matrix called osteoid, that
  is an important part of the ground substance of
  bone. (bone forming cells)
• Osteoclasts giant multinucleate cells that are
  responsible for the active erosion of bone
  minerals. (bone reabsorbing cells)

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• Osteocytes mature, non-dividing osteoblasts
  that have become surrounded by matrix and now
  within a lacunae.

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Osteoblasts and Osteocytes
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Osteoclast
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Bone Marrow

• Soft, diffuse connective tissue called myeloid
  tissue.
• Site of blood cell production
• Found in medullary cavities of certain long bones
  and in the spaces of some spongy bones.

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Red Marrow Yellow Marrow

• In a childs body, virtually all of the bones
  contain red marrow.
• Red marrow produces red blood cells.
• As an individual ages red marrow is replaced by
  yellow marrow.
• Yellow marrow has become saturated with fat and
  is no longer active in blood cell production.

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Active Marrow in Adults
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Functions of Bone

• Support supporting framework of body
• Protection protect delicate structures such as
  the brain
• Movement joints act as levers and allow
  movement in conjuction with muscular system

• Mineral Storage major reservoir for calcium,
  phosphorus, and certain other minerals
• Hematopoiesis blood cell formation

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Regulation of Blood Calcium Levels

• 98 of body calcium is stored in bone
• Osteoblasts remove calcium from blood
• Osteoclasts break down bone and calcium levels in
  the blood increases
• Calcium is important for normal blood clotting,
  nerve impulses, and muscle contraction

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Calcium in the Body

• Calcium that is consumed is absorbed through the
  intestines
• Calcium is stored and released from bone tissue
• The kidneys eliminate extra calcium and absorb
  calcium from urine if blood calcium levels get
  too low.

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Parathyroid Hormone

• When calcium levels fall below their set point,
  osteoclasts are stimulated to increase the rate
  of bone matrix breakdown.
• Calcium is released into the blood until the
  level returns to normal.

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Vitamin D (Calcitriol)

• Acts to increase blood calcium levels
• Facilitates the absorption of calcium in the
  small intestines

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Calcitonin

• Functions to reduce blood calcium levels
• Enhances excretion of calcium in urine
• Inhibits osteoclasts

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Calcium Deprivation
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Development of Bone

• Before birth, the skeleton consists of cartilage
  and fibrous structures shaped like bones.
• Cartilage is replaced with calcified bone matrix
• The combined action of osteoblast and osteoclasts
  to make bone is known as osteogenesis

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Intramembranous Ossification

• Takes place within a connective tissue membrane

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Endochondral Ossification

• Bone forms from cartilage models
• Forms from the center to the ends

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Endochondral Ossification
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Epiphyseal Fracture
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Bone Growth and Resorption

• Bone growth is from the combined action of
  osteoclasts and osteoblasts
• Osteoclasts break down bone to enlarge the
  diameter of the medullary cavity.
• Osteoblasts from the periosteum build new bone
  around the outside of the bone

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Bone Fracture Repair