CHAPTER 7 Bone Tissue Tissues

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CHAPTER 7Bone Tissue- Tissues Organs of the
Skeletal System- Histology of Osseous Tissue-
Bone Development- Physiology of Osseous
Tissue- Bone Disorders CHAPTER 8The Skeletal
System Introduction
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Bone Tissue

• bone is osseous connective tissue
• Bone cells
• Collagen
• Calcium phosphate and other minerals made hard by
  the calcification process

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A Bone

• A bone (like the femur) is an ORGAN made of
• Osseous tissue
• Blood
• Bone marrow
• Cartilage
• Adipose tissue
• Nervous tissue
• Fibrous connective tissue

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The Skeletal system

• is the combination of all these tissues and
  includes the organs
• Bones
• Cartilage
• Ligaments

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Skeletal system functions

• TABLE 7.1
• Support of the body
• Protection of the organs
• Movement of the body
• blood formation
• electrolyte balance of blood
• acid-base balance of blood
• detoxification of blood

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Bones of the skeletal system

• Figure 8.1 and Table 8.1
• 206 bones in adult human
• But there are some variations

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The skeletal system is divided into two main
parts

• Axial skeleton
• skull
• middle ear bones
• hyoid bone
• vertebral column
• rib cage
• sternum
• Appendicular skeleton
• upper (arms) lower (legs) extremities
• pectoral (chest) pelvic (hip) girdles

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Shapes of Bones

• Long
• longer than they are wide
• act as levers for movements
• examples femur, radius, phalanges, etc.
• Short
• length is about equal to width
• examples carpals tarsals

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A. The Shape of Bones (p. 229, Fig.
8.2) B. General Features of Bones (p. 229, Fig.
8.3) C. Elaborations of Bone Structure
(p. 231, Fig. 8.4, Table 8.3)
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Shapes of Bones (cont).

• Flat
• form an enclosure protect
• examples cranium, scapulae
• Irregular
• none of the above
• examples vertebrae, certain skull bones

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General features of bones

• Long Bone Anatomy
• osseous tissue
• Compact bone
• Spongy bone
• medullary cavity
• diaphysis
• epiphysis
• articular cartilage
• nutrient foramina

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General features of bones

• Long Bone Anatomy
• osseous tissue
• Compact bone
• Spongy bone
• medullary cavity
• diaphysis
• epiphysis
• articular cartilage
• nutrient foramina

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• Periosteum
• Covers bone
• Dense irregular CT
• And bone forming cells
• Perforating fibers
• collagen fibers connect bone and periosteum
• Some of these are continuous with connective
  tissue of tendons
• Endosteum
• Lines medullary cavity
• Reticular CT
• And bone-forming cells (osteogenic cells)

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• Epiphyseal plate
• Made of hyaline cartilage
• Located between epiphysis diaphysis in children
  and teens
• Functions as a growth zone in long bones
• Disappears at age 18-20
• Adults have only epiphyseal line

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Flat bone anatomy

• Notice how flat bones also have compact and
  spongy bone.
• They are just arranged differently
• Flat bones are often found in the skull

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Bone have many dents, holes, rough spots, etc.

• elevations
• Depressions
• canals
• holes
• slits

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Four types of bone cells
Bone as a tissue..

• osteogenic cells
• osteoblasts
• osteocytes
• osteoclasts

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Osteogenic cells

• Location
• endosteum,
• inner layer of periosteum,
• central canals
• Function
• provide the source of new bone cells
• divide to form osteoblasts

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Osteoblasts

• Locations
• Inner layer of endosteum and periosteum
• Functions
• Synthesize collagen
• Mineralize bone
• Form lacunae
• do not divide

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Osteoblasts

• When osteoblasts become surrounded collagen and
  minerals (bone), they no longer produce more
  collagen.
• They are now called OSTEOCYTES

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Osteocytes

• Remain connected to other osteocytes by gap
  junctions.
• Thru gap junctions, they pass along the need for
  more bone material to the surface osteoblasts
• Osteoblasts then can make more bone tissue.

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Osteoclasts

• Function
• move minerals from bone into blood.
• dissolve matrix using acids enzymes
• Structure
• Large cells arising from white blood cells
• Monocytes (wbcs) fuse to form osteoclasts
• Howships lacunae depressions etched into bone
  surface by osteoclasts

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What is bone matrix made of?
Bone as a tissue..

• Flexible organic portion
• collagen
• Glycosaminoglycans (GAGs)
• proteoglycans glycoproteins
• Hard inorganic portion
• hydroxyapatite
• calcium phosphate
• calcium carbonate
• Mg, K, Na, OH, F,

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Osseous Tissue Matrix

• Bone without minerals bends too easily. (rickets)
• Bone without collagen breaks too easily. (brittle
  bone disease)

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Histology of Compact Bone

• Osteon
• concentric lamellae, central canals, osteocytes
  in lacunae
• Blood vessels
• in central canals nourish bone remove wastes
• Perforating canals
• connect to central canals at right angles
• Nutrient flow
• central canals to inner and outer osteocytes
• Waste flow
• outer and inner osteocytes to central canal

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Histology of compact bone (cont.)

• Canaliculi
• tiny channels in matrix containing cytoplasmic
  processes of osteocytes
• osteocytes joined by gap junctions in canaliculi

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Histology of Spongy Bone

• trabeculae instead of osteons
• lattice of spines, rods, plates
• develop along lines of stress
• still lamellar, but no central canals
• bone marrow
• in space between trabeculae
• osteocytes are close to marrow blood supply

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Bone Marrow

• soft tissue in
• medullary cavity of long bones
• between trabeculae of spongy bones
• and large central canals
• 3 kinds of marrow
• red
• yellow
• gelatinous

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Red Marrow (myeloid tissue)

• In children
• found in most bones
• In adult
• in axial skeleton
• In proximal heads of femur humerus
• hemopoietic (makes blood cells)

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Yellow Marrow

• adult
• in shafts of long bones
• arises from red marrow of childs bone
• contains fat
• no longer hemopoietic, but can revert

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Glutinous Marrow

• in geriatric adults only
• reddish, jellylike tissue
• fat mostly gone

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Formation of flat bonesIntramembranous
ossification

• intramembranous (within membrane)
• occurs in flat bones
• Some cranial bones
• ossification formation of bone

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Intramembranous ossification(flatbones)

• During fetal development a CT sheet forms
• Blood vessels grow into the CT
• Osteogenic cells form
• Osteogenic cells become osteoblasts
• Osteoblasts make trabeculae
• osteoblasts become osteocytes
• trabeculae form spongy bone
• superficial trabeculae become calcified and
  condense (remodel) into compact bone

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Osteoid Tissue soft collagenous tissue similar
to bone, except matrix has no minerals. When it
mineralizes, then its called bone tissue.
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Long bone formationEndochondral ossification

• Endowithin
• Chondralcartilage

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In fetal development

• Hyaline cartilage forms in the shape of bones
• Osteoblasts form on the surface, and make a bony
  covering around the cartilage
• chondrocytes in diaphysis multiply, grow larger,
  then die
• Calcium accumulates in matrix
• Spongy bone is formed

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Primary Ossification Center

• Osteoclasts hollow out a marrow cavity
• Marrow forms for blood production

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Secondary Ossification Center

• Secondary centers of bone formation form in both
  the epiphyses
• the epiphyses always retain spongy bone

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Typical state of a long bone at birth
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Metaphysis (growth plate)

• located between epiphysis and diaphysis)
• zone of reserve (resting) cartilage
• zone of cell proliferation -
• chondrocytes multiply, arrange into columns
• zone of hypertrophy
• Chondrocytes get larger
• zone of calcification
• Cartilage matrix starts to calcify
• zone of bone deposition
• Osteoblasts and osteoclasts (and osteogenic
  cells!) arrive
• SEE FIG 7.9

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Bone growth in the metaphysis

• Resting cartilage cells lie next to epiphysis
• Cartilage cells closer to the diaphysis
  proliferate and form long columns
• These cells enlarge and push the reserve
  cartilage toward the bone ends, making the bone
  lengthen.
• Cartilage cells start to die, and bone cells
  invade the area.
• Bone cells make new bone material, strengthening
  the elongated bone.

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• Green arrows Zone of Resting Cartilage
• Blue arrows Zone of Proliferation
• Black arrows Zone of Hypertrophy

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Red arrows Zone of calcification White arrows
point to new bone Yellow arrows point to
calcified cartilage
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BONE GROWTH

• Bones grow longer during childhood using the
  metaphysis.
• High levels of estrogen and testosterone increase
  bone lengthening during puberty
• Higher levels of estrogen and testosterone stop
  bone lengthening after puberty

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Bone remodeling

• Osteoblasts are active throughout life
• Shape and contour changes occur on the surface of
  bone or in the cavities of bone
• Broken bones can mend
• Bones cannot lengthen after puberty

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• Bone length is added by
• multiplication hypertrophy of chondrocytes
  interstitial growth
• Bone width and contours are added by
• Osteoblasts form new bone on the surface of an
  existing bone appositional growth

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Achondroplastic dwarfism

• Is a genetic disorder where chondrocytes in the
  zones of cell proliferation and cell hypertrophy
  fail to multiply and enlarge during childhood.

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mineral deposition

• When calcium and phosphate concentrations reach a
  critical point in tissues, they crystalize onto
  collagen fibers. The first hydroxyapetite
  crystals encourage more crystals to form.
• Minerals plus collagen equals bone tissue.

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Mineral resorption -- process of dissolving bone

• Calcium and phosphate from bone can be released
  back to blood for use in other areas.
• Osteoclasts use Hydrochloric acid and acid
  phosphatase to dissolve bone

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mineral resorption

• Is often caused by physical stress
• example braces on teeth
• osteoclasts resorb minerals on one side of tooth
  socket (zone of higher pressure)
• osteoblasts deposit minerals on opposite side
  (zone of reduced pressure)
• Osteocytes can detect stress on bones

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calcium phosphate homeostasis

• bone is a reservoir for these minerals
• 99 of body Calcium is in bone
• 90 of body Phosphate is in bone
• Phosphate is important for
• Calcium is needed for
• Muscle contraction, nerve, conduction, blood
  clotting

• DNA, RNA, ATP, phospholipid synthesis

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calcium phosphate homeostasis

• hypocalcemia
• Deficiency of blood calcium
• leads to tetany and spasms of muscle
• carpopedal spasm
• Laryngospasm
• death

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calcium phosphate homeostasis

• hypercalcemia
• an excess of blood calcium
• leads to depression of nervous system
• muscle weakness
• emotional upset
• cardiac arrest

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Hormonal homeostasis of calcium

• calcitonin
• a hormone secreted by thyroid
• lowers blood calcium levels
• osteoclasts are inhibited
• osteoblasts are stimulated

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Hormonal homeostasis of calcium

• parathyroid hormone
• released by parathyroid glands
• raises blood calcium levels by
• Stimulating osteoclasts
• Promotes calcium reabsorption at kidney
• promotes vitamin D synthesis and allowing vitamin
  D to raise blood calcium
• Inhibits collagen synthesis by osteoblasts,
  inhibiting deposition of calcium in bone

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Vitamin D or calcitriol

• considered a hormone
• made by combined actions of sun, skin, liver,
  kidneys
• Promotes intestinal absorption of calcium and
  phosphorous
• Prevents rickets, osteomalacia

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How vitamin D is made

• Keratinocytes contain 7-dehydrocholesterol
• Sunlight converts 7-dehydrocholesterol into
  previtamin D3 and then vitamin D3
• Transport proteins carry vitamin D3 to blood
• Vitamin D3 travels to liver and is converted into
  calcidiol
• Calcidiol travels to kidney and changed to
  calcitriol (active vitamin D).

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Other hormones

• Growth hormone
• Thyroid hormone
• Insulin
• Estrogen
• Testosterone

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Bone Disorders

• Fractures
• Rickets
• Osteomalacia
• Osteogenesis imperfecta (brittle bone disease)
• Osteoporosis
• Osteomyelitis
• Bone cancers

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Fractures -- types

• Closed
• Open
• Complete
• Incomplete
• Greenstick
• Hairline
• Comminuted
• Displaced

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Special fractures

• Colles distal end of radius
• Common in older women (assoc w/ osteoporosis)
• Pott distal end of tibia, fibula, both
• Common sports injury
• Epiphyseal fractures - in children
• Can affect ability for that bone to continue
  growing

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Healing of fractures

• Hematoma formation
• Blood vessels of bone and periosteum disrupted
  bleeding clot formation
• Granulation tissue formation
• Soft fibrous tissue - fibroblasts first repair
  cells to arrive in area local osteogenic cells
  start dividing osteoclasts, osteoblasts invade
  from periosteum and endosteum
• Soft callus formation
• Fibroblasts deposit collagen osteogenic cells
  differentiate into chondroblasts- produce
  fibrocartilage
• Hard callus formation
• Other osteogenic cells differentiate into
  osteoblasts - form boney collar
• Remodeling - over about 3 to 4 months

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Osteoporosis

• Most common bone disease
• Bones lose mass - both organic matrix and mineral
• Highest incidence in elderly white and asian
  women african americans and hispanics also
  susceptible
• Increased frequency of fractures ( about 40 of
  50 year old women will fracture a bone during
  their remaining lifetime)
• Greatest risk in post-menopausal women
• Estrogen stimulates osteoblasts
• Also occurs in amenorrheal younger women
• Boniva, Fosamax - new treatment

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osteoporosis

• What types of treatments would you suggest?
• You have all the resources you want!