Chapter 6: Osseous Tissue and Bone Structure

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Chapter 6 Osseous Tissue and Bone Structure
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The Skeletal System

• Skeletal system includes
• bones of the skeleton
• cartilages, ligaments, and connective tissues

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What are the functions of the skeletal system?
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Functions of the Skeletal System

• Support
• Storage of minerals/lipids (yellow marrow)
• Hemopoiesis (red marrow)
• Protection
• Leverage

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How are bones classified?
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Classification of Bones

• Bone are identified by
• shape
• internal tissues
• bone markings

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Bone Shapes

• Long bones
• Flat bones
• Sutural bones
• Irregular bones
• Short bones
• Sesamoid bones

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• 2 Types of Bone (Osseous) Tissue
• Compact dense, solid usually on surfaces
• Spongy open network, usually interior

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Long Bones

• Diaphysis
• the shaft
• compact bone
• central marrow cavity
• Epiphysis
• wide part at each end
• articulation with other bones
• Mostly spongy (cancellous) bone
• Covered with compact bone (cortex)

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Long Bones

• The femur

Figure 62a
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Flat Bones

• The parietal bone of the skull
• Sandwich of spongy bone between 2 layers of
  compact bone

Figure 62b
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What are the types and functions of bone cells?
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Bone (Osseous) Tissue

• Dense, supportive connective tissue
• Contains specialized cells
• within lacunae organized around blood vessels
• Solid matrix of calcified ground substance around
  collagen fibers

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• Canaliculi
• form pathways for blood vessels
• exchange nutrients and wastes
• Periosteum
• covers outer surfaces of bones
• consist of outer fibrous and inner cellular layers

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Bone Cells

• Make up only 2 of bone mass
• osteocytes
• osteoblasts
• osteoprogenitor cells
• osteoclasts

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Homeostasis

• Bone building (by osteocytes) and bone recycling
  (by osteoclasts) must balance
• more breakdown than building, bones become weak
• exercise causes osteocytes to build bone

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• 2 Types of Bone (Osseous) Tissue
• Compact dense, solid usually on surfaces
• Spongy open network, usually interior

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What is the difference between compact bone and
spongy bone?
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Osteon

• The basic unit of mature compact bone
• Osteocytes are arranged in concentric rings
  around a central canal (Haversian)
• Contains blood vessels
• within lacunae surrounded by osseous tissue
• Perforating Canals
• Perpendicular to the central canal
• Carry blood vessels into bone and marrow
• Interstitial lamellae
• Circumferential lamellae

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Compact Bone
Figure 65
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Spongy Bone

• Does not have osteons
• Matrix forms an open network of trabeculae
• have no blood vessels

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• The space between trabeculae is filled with red
  bone marrow
• has blood vessels
• forms red blood cells
• supplies nutrients to osteocytes
• In some bones, spongy bone holds yellow bone
  marrow
• stores fat

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Spongy Bone
Figure 66
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Periosteum and Endosteum

• Compact bone is covered with membrane
• periosteum
• Superficial layer
• an outer, fibrous layer and an inner, cellular
  layer
• endosteum
• lines the marrow cavity
• covers trabeculae of spongy bone
• lines central canals

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Functions of Periosteum

• Isolate bone from surrounding tissues
• Provide a route for circulatory and nervous
  supply
• Participate in bone growth and repair

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Periosteum
Figure 68a
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Endosteum

• Contains osteoblasts, osteoprogenitor cells, and
  osteoclasts
• Is active in bone growth and repair

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Endosteum
Figure 68b
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What is the difference between intramembranous
ossification and endochondral ossification?
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Bone Development

• Human bones grow until about age 25
• Ossification
• process of replacing other tissues with bone
• Calcification
• process of depositing calcium salts
• Occurs during bone ossification
• Can occur in other tissues

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Ossification

• The 2 main forms of ossification are
• intramembranous ossification
• endochondral ossification

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Intramembranous Ossification

• Also called dermal ossification
• because it occurs in the dermis
• produces dermal bones such as mandible and
  clavicle

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• Mesenchymal cells aggregate
• differentiate into osteoblasts
• begin ossification at the ossification center
• develop projections called spicules

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• Blood vessels grow into the area
• to supply the osteoblasts
• Spicules connect
• trapping blood vessels inside bone

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• Spongy bone develops and is remodeled into
• osteons of compact bone
• periosteum
• marrow cavities

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Figure 611 (Step 1)
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Endochondral Ossification

• Ossifies bones that originate as cartilage
• Most bones originate as hyaline cartilage
• Growth and ossification of long bones occurs in 6
  steps

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• Chondrocytes in the center of cartilage
• enlarge
• form struts and calcify
• die, leaving cavities in cartilage

Figure 69 (Step 1)
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• Blood vessels grow around the edges of the
  cartilage
• Cells in the perichondrium change to osteoblasts
  
• producing a layer of superficial bone around the
  shaft which will continue to grow and become
  compact bone (appositional growth)

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• Blood vessels enter the cartilage
• bringing fibroblasts that become osteoblasts
• spongy bone develops at the primary ossification
  center

Figure 69 (Step 3)
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• Remodeling creates a marrow cavity
• bone replaces cartilage at the metaphyses

Figure 69 (Step 4)
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• Capillaries and osteoblasts enter the epiphyses
• creating secondary ossification centers

Figure 69 (Step 5)
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• Epiphyses fill with spongy bone
• cartilage within the joint cavity is articulation
  cartilage
• cartilage at the metaphysis is epiphyseal
  cartilage

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• Appositional growth
• Bones continue to grow in diameter
• compact bone thickens and strengthens long bone
  on outside of shaft

Figure 69 (Step 2)
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Remodeling

• The adult skeleton
• maintains itself
• replaces mineral reserves
• Remodeling
• recycles and renews bone matrix
• involves osteocytes, osteoblasts, and osteoclasts

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• Normal bone growth and maintenance requires
  nutritional and hormonal factors
• Minerals
• Vitamins

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• Minerals
• calcium and phosphate salts
• Vitamins
• Vitamin D3
• Vitamin C
• Vitamin A
• Vitamins K and B12

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• Hormones
• Calcitriol
• Growth hormone and thyroxine
• Estrogens and androgens
• Calcitonin and parathyroid hormone

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The Skeleton as Calcium Reserve

• Bones store calcium and other minerals
• Calcium is the most abundant mineral in the body
• Vital to membranes, neurons, muscle cells,
  especially heart cells

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Chemical Composition of Bone
Figure 613
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Calcium Regulation

• Calcium ions in body fluids
• must be closely regulated
• Homeostasis is maintained
• by calcitonin and parathyroid hormone
• control storage in bones, absorption in digestive
  tract, and excretion from kidneys

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Parathyroid Hormone (PTH)

• Produced by parathyroid glands in neck
• Increases calcium ion levels by
• stimulating osteoclasts
• increasing intestinal absorption of calcium
• decreases calcium excretion at kidneys

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Calcitonin

• Secreted by thyroid
• Decreases calcium ion levels by
• inhibiting osteoclast activity
• increasing calcium excretion at kidneys

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What are the types of fractures?
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Fractures

• Fractures
• cracks or breaks in bones
• caused by physical stress
• may be simple or compound

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• Comminuted fractures

Figure 616 (2 of 9)
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• Transverse fractures

Figure 616 (3 of 9)
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• Spiral fractures

Figure 616 (4 of 9)
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• Greenstick fracture

Figure 616 (7 of 9)
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• Compression fractures

Figure 616 (9 of 9)
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What are the effects of aging on the skeletal
system?
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Age and Bones

• Bones become thinner and weaker with age
• Osteopenia begins between 30 and 40
• Osteoporosis - over age 45
• Severe bone loss
• resulting in fragile limbs
• reduction in height
• tooth loss

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Congenital Disorders

• Pituitary Dwarfism
• Gigantism
• Acromegaly