The Skeletal System

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The Skeletal System
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Osteology

• Study of bone structure and the treatment of bone
  disorders

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Function of bone and the skeletal system

• Support forms the bodys framework, supports
  organs
• Protection protects internal organs, form body
  cavities
• Movement forms levers for muscle action
• Mineral homeostasis serves as storage for
  minerals (Ca and P)
• Hematopoiesis blood cell production from red
  bone marrow
• Triglyceride storage stored in yellow bone
  marrow

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Histology of bone (osseous) tissue

• Matrix
• 25 water
• 25 collagen fibers
• 50 crystallized mineral salts
• calcium phosphate Ca3(PO4)2
• hydroxyapatite Ca10(PO4)2(OH)2
• calcification - initiated by osteoblasts

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• Hardness - crystallized inorganic mineral salts
• Flexibility collagen fibers
• Tensile strength collagen organic molecules

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Cells in bone tissue

• Osteogenic derived from mesenchyme,
  differentiate into osteoblasts, undergoes cell
  division
• Osteoblasts bone-building cells, initiate
  calcification
• Osteocytes mature bone cells, perform
  maintenance
• Osteoclasts bone resorbing cells derived from
  monocytes

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Types of osseous tissue

• Compact (cortical) bone
• Few spaces, strongest form
• Makes up bulk of diaphyses of long bone
• Protection and support
• Made of a dense regular arrangement of osteon
  (Haversian systems)

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• Spongy (cancellous) bone
• Does not contain osteons
• Consists of lamellae arranged in irregular
  lattice of thin columns called trabeculae
• Macroscopic spaces between the trabeculae makes
  bones lighter
• Can be filled with red bone marrow

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A bone is an organ

• Tissues that make up bone
• Bone or osseous tissue
• Cartilage
• Dense connective tissue
• Epithelium
• Adipose
• Nervous
• Performs the functions of the skeletal system

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Structure of Bone
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• Bone video clip

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Bone Formation

• Intramembranous ossification
• Simpler
• Bone formation from a model of fibrous connective
  tissue
• Flat bones of the skull (cranium), clavicles
  (collar bone), and mandible (lower jaw)
• Endochondral ossification
• Bone formation from a model of hyaline cartilage
• Most bones are formed this way

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Intramembranous ossification The Cranium
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Endochondral ossification

• Bone formation from a model of a cartilage
• Nearly all bones except those of the cranium are
  ossified by this process

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Bone Fractures Remodeling
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Fractures

• Open (compound) broken ends protrude through
  the skin
• Comminuted bone splinters at the site of
  impact smaller fragments lie between the two
  main fragments
• Greenstick one side of bone is broken, the
  other is bent (occurs in children)
• Impacted one end if forcefully driven into the
  interior of the other
• Potts fracture- fracture of the distal end of
  the fibula
• Colles fracture fracture of the distal end of
  the radius
• See fig. 6.9 for examples

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Closed fracture
Stress fracture
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How fractures heal

• Hematoma (huge bruise and blood clot) forms to
  protect the area
• Fibrocartilage splint forms after dead cells are
  removed by phagocytes
• Osteocytes move into area and gradually replace
  fibrocartilage with bone tissue
• Bone remodeling occure

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Steps to remodeling (wheel)

• Pre-osteoclasts are attracted to remodeling site
• Pre-osteoclasts fuse to form regular
  osteoclasts
• Osteoclasts dig out a cavity or tunnel
• Calcium dug out is reabsorbed by the blood for
  use in the body
• Osteoclasts disappear
• Osteoblasts-making cells appear in cavity created
• Stem cells turn into pre-osteoblasts
• Pre-osteoblasts mature into regularosteoblasts
• Osteoblasts release osteoid (nonmineralized ECM)
• Calcium and phosphorous are added to ECM
• Area waits for next round to happen

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What regulates this activity

• Hormones
• Chemical messengers released into blood
• Produced by glands of the endocrine system

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Hormones related to bone remodeling

• Calcitonin (made by thyroid)
• Inhibits osteoclast activity
• Increases rate of Ca 2 excretion
• PTH (parathyroid hormone made by parathyroid)
• Stimulates osteoclast
• Increase intestinal absorption of Ca2
• Decrease the rate of Ca2 excretion

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Effect of exercise and aging

• Exercise
• With stress, bone tissue becomes stronger
• Increase deposition of mineral salts
• Production of collagen fibers by osteoblasts
• Aging
• Loss of bone mass
• Demineralization (loss of Ca and other minerals)
• Brittleness
• Decreased rate of protein synthesis
• Loss of tensile strength

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Types of Bones (by shape)

• Long bones
• Arms, legs, hands, feet (metacarpals
  metatarsals)
• Mostly compact bone
• Slightly curved to absorb shock
• Short bones
• Patella, carpals, tarsals and phalanges
• Irregular, cube shaped bones

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Types of Bones (by shape)

• Flat bones
• Skull, scapula, ribs, sternum, pelvis
• Anchor muscles
• Irregular bones
• Any bone that doesnt fit into one of the other
  groups!
• Vertebrae and some facial bones

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Other bones

• Sesamoid bones
• Not complete ossified, few millimeters in
  diameter
• Patella (large)
• Palms, soles
• Sutural bones
• small bones located in sutures between cranial
  bones