Microscopic Structure of Bone

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Microscopic Structure of Bone
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Osseous Tissue

• Another name for bone tissue
• Bone is a connective Tissue
• Widely spread cells
• Matrix
• Water, Collagen Fibers, Mineral Salts

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Calcification

• Hardening of bone tissue by the deposition of
  mineral salts in the collagen fiber of the matrix

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Hardness and Flexibility

• Hardness Provided by the crystallized mineral
  salts
• Flexibility Provided by the collagen fibers
• Bones can resist being stretched or torn apart

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Cells

• There are 4 major types of cells found in osseous
  tissue
• Osteoblast
• Osteocyte
• Osteoprogenitor
• Osteoclast

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Osteoblast

• Bone building cells
• Synthesize and secrete collagen fibers and other
  organic components needed to build the matrix of
  the tissue
• Osteoblasts surround themselves with matrix,
  become trapped in their secretions and become
  osteocytes
• Do not undergo Mitosis

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Osteocyte

• Mature Bone Cell
• Main cells in bone tissue
• Maintains daily metabolism
• Do not undergo mitosis

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Osteoprogenitor

• Bone stem cells
• These cells undergo mitosis then differentiate to
  form osteoblasts

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Osteoclasts

• HUGE cells formed from the fusion of as many as
  50 monocytes
• Concentrated in the endosteum
• Release lysosomal enzymes and acids to digest the
  matrix

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Reabsorption

• Breakdown of bone matrix
• Part of the normal development, growth, repair
  and maintenance

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Categories of Bone Tissue

• Bone has many small spaces between the cells and
  matrix it is not completely solid.
• The category of tissue is based on the size and
  distribution of these spaces
• About 80 of bone is compact bone 20 is spongy
  bone

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Compact Bone Tissue

• Contains very few spaces
• Forms the external layer of all bones and the
  diaphyses of long bones
• Provides protection and support
• Resists stress produced by weight and movement

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Osteon

• Organizational Unit of Compact Bone

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Perforating Canals

• Transverse openings through which vessels from
  the periosteum penetrate the compact bone and
  eventually meet up with other vessels

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Central (Haversian) Canal

• Run longitudinally through bone
• It is the center of the osteon
• Contains blood vessels and nerves

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Concentric Lamellae

• Rings of hard calcified matrix surrounding the
  central canal

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Lacunae

• Means little lake
• Small spaces between the lamellae
• Contain osteocytes

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Canaliculi

• Minute canals that radiate off the lacunae in all
  directions.
• Contain projections of the osteocytes
• Connect lacunae creating a network throughout the
  compact bone to provide nutrients and oxygen to
  all the osteocytes and to get rid of waste

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Spongy Bone
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• Does not contain ostons
• Made of trabeculae an irregular network of thin
  columns of bone with many spaces in between
• Trabeculae contain osteocytes within lacunae
  connected by canaliculi

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• Spongy tissue makes up most of flat, short and
  irregular bones
• Forms most of the epiphyses of long bones
• Found in a narrow rim around the medullary cavity

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• Spongy tissue is light reducing the weight of
  the skeletal system
• Red bone marrow is found in the spaces between
  trabeculae
• Hemopoiesis only occurs in the hip bones, ribs,
  sternum, vertebrae and epiphyses of long bones
  where red bone marrow is found

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Bone Scan

• Radioactive Tracer is injected through an IV and
  absorbed by the bone
• A scanning device measures the amount of
  radiation emitted by the bones and translates the
  information into an x-ray
• Normal bones have a consistent gray color
• Darker/lighter areas indicate an abnormality
• Ex - Bone cancer, abnormal healing, infections,
  arthritis

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Checkpoint Questions answer these in your notes

1. What kinds of tissue make up the skeletal system?
2. How do red and yellow bone marrow differ in
   composition and function?
3. What are the types of bones?
4. Draw and label the parts of a typical long bone.
5. What are the 4 types of bone cells?
6. How are spongy and compact bone different in
   microscopic appearance, function and location?