The Skeletal System: Bone Tissue

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The Skeletal System Bone Tissue

• Chapter 6

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Functions of Bone and the Skeletal System

• Support
• Protection
• Assistance in Movement
• Mineral Homeostasis
• Blood Cell Production
• Red bone marrow
• Hemopoiesis hemo blood, poiesis making
• Triglyceride Storage
• Yellow bone marrow

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Parts of a Long Bone

• Diaphysis growing between shaft
• Epiphyses growing over
• distal and proximal ends
• Metaphyses meta between
• region where the diaphysis joins the epiphyeses
• Articular cartilage - hyaline cartilage
• covers epiphyses

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Parts of a Long Bone continued

• Periosteum peri around
• surrounds the remainder of the bone surface
• Medullary cavity medulla marrow
• space within the diaphysis
• Endosteum endo within
• Lines the medullary cavity
• Single layer of bone forming cells

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Bone Matrix

• 25 water
• 25 collagen fibers provide tensile strength
  and flexibility
• 50 crystallized mineral salts provides
  hardness
• Mainly hydroxyapatite (calcium phosphate and
  calcium carbonate)
• A framework is created by the collagen fibers and
  the mineral salts are deposited into this
  framework
• Osteoblasts initiate calcification

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Type of Cells in Bone Tissue

• Osteogenic cells
• Unspecialized cells from the mesenchyme
• Osteoblasts
• They become trapped in their secretions and
  become osteocytes
• Osteocytes mature bone cell
• Osteoclasts
• Resorption

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Types of Cells in Bone Tissue
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Compact Vs. Spongy Bone

• Bone is not completely solid
• There are spaces between cells and the matrix
  components
• The spaces are channels for blood vessels
• The size and distribution of the spaces
  determines whether it is compact bone (80) or
  spongy bone (20).

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Compact Bone

• Contains few spaces
• External layer of all bones and the bulk of the
  diaphysis
• Provides protection and support
• Resists the stresses produced by weight and
  movement

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Histology of Compact Bone

• Arranged in units called osteons (Haversian
  Systems)
• Perforating (Volkmanns canals)
• passage of blood vessels, lymph vessels and
  nerves
• Connect with the central (Haversian) canals
• Concentric lamallae rings of hard calcified
  matrix
• Lacunae little lakes lie between lamallae
• Contain osteocytes
• Canaliculi small channels
• Contain processes of osteocytes

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Bone Deposition

• Osteons in compact bone are aligned in the same
  direction along lines of stress
• The lines of stress can change
• Fracture and deformity
• Weight training
• When a person learns to walk
• Wolfes law

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Histology of Spongy Bone

• Spongy bone does not contain osteons
• Contains trabeculae irregular latticework of
  thin columns of bone
• Red Bone Marrow fills the spaces
• Bone tissue in short, flat, or irregular bones
• Epiphyses of long bones
• Spongy bone is light
• The spongy bone of the hip bones, ribs,
  breastbone, backbones, and the ends of long bones
  is the only site of red bone marrow in adults

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Bone Scan

• Radioactive tracer is injected intravenously
• The degree of uptake depends upon the amount of
  blood flow
• Normal bone appears as gray in color with uniform
  uptake of the tracer
• Darker or lighter areas suggest abnormalities
• Dark areas hot spots increased metabolism
• Bone cancer, healing fractures, abnormal bone
  growth
• Light areas cold spots decreased metabolism
• Degenerative bone disease, decalcified bone,
  fractures, bone infection, Pagets, RA

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Pagets Disease
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Pagets Disease
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Blood and Nerve Supply

• Bone is richly supplied with blood.
• Blood vessels are particularly abundant in the
  portions of bone containing bone marrow.
• They enter through the periosteum
• Nerves accompany the blood vessels that supply
  the bones rich in sensory nerves

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Blood Supply

• Periosteal arteries / veins
• Nutrient artery / vein
• Metaphyseal arteries / veins
• Epiphyseal arteries / veins

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Bone Formation

• Ossification ossi bone, fication making
• Osteogenesis
• Intramembranous ossification
• Bone forms directly on or within loose fibrous CT
• Endochondral ossification
• Bone forms within hyaline cartilage

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Intramembranous Ossification

• Development of the center of ossification
• Mesenchymal cells cluster and differentiate
• First forming osteogenic cells, then osteoblasts
• Secrete organic matrix
• Calcification
• Minerals salts are deposited into the matrix
• Formation of trabeculae
• Forms spongy bone
• Development of the periosteum
• At the periphery of the bone the mesenchyme
  condenses
• Forms a thin layer of compact bone

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Endochondral Ossification

• Development of the cartilage model
• Chondroblasts secrete cartilage matrix (hyaline)
• Growth of the cartilage model
• Interstitial growth - length
• Appositional growth - thickness
• Development of the primary ossification center
• A region where bone tissue will replace most
  cartilage
• Development of the secondary ossification center
• Formation of articular cartilage and the
  epiphyseal plate lengthwise growth in the adult

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Bone Growth

• Bones throughout the body grow in thickness by
  appositional growth.
• Long bones lengthen by the addition of material
  to the epiphyseal plate
• Bones stop growing in length at about 25,
  although they may continue to thicken.

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Growth in Length

• Epiphyseal plate layer of hyaline cartilage in
  the metaphysis of a growing bone
• 4 zones
• Zone of resting cartilage
• Zone of proliferating cartilage
• Zone of hypertrophic cartilage
• Zone of calcified cartilage

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Epiphyseal Line

• The epiphyseal plates close between the ages of
  18 and 25.
• The cells of the plate stop dividing and bone
  replaces the cartilage
• As the plate fades a bony structure called the
  epiphyseal line is left behind.
• This signifies that the bone has stopped growing

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Growth in Thickness

• Appositional growth bone grows in thickness and
  diameter by this method
• New bone tissue is being deposited on the outer
  surface of the bone and the lining of the
  medullary cavity is being resorbed, thus
  enlarging the meduallary cavity.

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Factors Affecting Bone Growth

• Vitamins and Minerals
• Calcium and Phosphorous
• Flouride, magnesium, iron, manganese
• Vitamins C, K, B12, and A
• Hormones
• Insulinlike growth factors (IGFs)
• Human Growth Hormone (hGH)
• Thyroid hormones (T3 and T4)
• Insulin
• Sex Steroids
• Estrogens (produced by ovaries)
• Adrogens (produced by testes)

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Hormonal Abnormalities

• Oversecretion of hGH in childhood produces
  gigantism
• Oversecretion of hGH in adulthood produces
  acromegaly
• Undersecretion of hGH in childhood produces short
  stature
• Men and Women who lack estrogen grow taller than
  normal (estrogen terminates growth at the
  epiphyseal plates)

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Gigantism
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Acromegaly
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Bone Remodeling

• Ongoing process
• Osteoclasts carve out small tunnels
• Osteoblasts build bone tissue
• Response to stress
• Healing of fracture sites
• 2-4 months
• Bone Resoprtion osteoclasts break down matrix
• Weak bones / bone spurs (homeostasis is disrupted)

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Types of Fractures

• Open (compound) fracture
• Closed (simple) fracture
• Comminuted fracture
• Greenstick fracture
• Impacted fracture
• Potts fracture
• Colles fracture

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Stress Fracture

• A bone fracture without physically breaking
• Due to repeated strenuous activities

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Repair of Bone

• Formation of a fracture hematoma
• Fibrocartilaginous callus formation
• Bony callus formation
• Bone remodeling

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Treatments for Bone Fractures

• Realignment of the bone fragments
• Closed skin remains intact manual
  manipulation
• Open surgical procedure
• Screws, plates, pins, rods, and wires are used
• Immobilization to maintain alignment
• Cast, sling, splint, elastic bandage, external
  fixation device
• Restoration of function
• rehabilitation

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Bone and Calcium Homeostasis

• Bone serves as a major calcium reservoir
• Parathyroid hormone (PTH) regulates Ca2 exchange
  between bone and blood
• PTH decreases kidney loss of Ca2 and stimulates
  the formation of calcitrol which helps the GI
  tract absorb Ca2
• Calcitonin inhibits osteoclasts, speeds up blood
  uptake of Ca2 by bone, and facilitates Ca2
  deposition

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Exercise and Bone Tissue

• Bone responds to the level of stress placed upon
  it.
• Wolfes law
• Increased stress leads to increased bone
  deposition
• Decreased stress leads to bone loss
• Immobilzed bones can lose up to 1 per week.
• Weight bearing exercise
• Weight training
• Incline 11 degrees or greater
• Deposition until age 35

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Effects of Aging

• Loss of bone mass
• demineralization
• Brittleness
• Decreased rate of protein synthesis

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Osteoarthritis

• Degeneration of articular cartilage such that
  bony ends touch

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Osteogenic Sarcoma

• Bone cancer that primarily effects teenagers,
  most often during their growth spurt.
• Often metastasizes to the lungs.

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Osteomyelitis

• Infection of the bone.
• Fever, sweating, chills, pain, nausea, pus
  formation, edema, warmth
• Bacteria (Staphylococcus aureus) usually causes it

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Rickets and Osteomalacia

• Bones fail to calcify
• Bones are soft and rubbery
• Rickets affects the growth plates of children
• Bowed legs, deformities of the skull and rib cage
• Osteomalacia is a condition in adults
• Brittle bones
• Both are due to insufficient Vitamin D intake

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Rickets
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Osteopenia

• Reduced bone mass
• Osteoporosis is an example