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Chapter 6: Osseous Tissue and Bone Structure

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Title: Chapter 6: Osseous Tissue and Bone Structure


1
Chapter 6 Osseous Tissue and Bone Structure
2
The Skeletal System
  • Skeletal system includes
  • bones of the skeleton
  • cartilages, ligaments, and other connective
    tissues that stabilize the bones

3
Skeletal System
  • Functions
  • 1. Support framework structure of body
  • 2. Storage of minerals and lipids
  • Minerals calcium and phosphate
  • - for osmotic regulation, enzyme
    function,
  • nerve impulses
  • Yellow marrow triglycerides
  • 3. Blood cell production all formed elements
  • - red marrow stem cells ? hematopiesis
  • 4. Protection surround soft tissues
  • 5. Leverage for movement
  • - levers upon which skeletal muscles act

4
Classification of Bones
  • Bone are identified by
  • shape
  • internal tissues
  • bone markings
  • SHAPE
  • Long bones
  • Flat bones
  • Sutural bones
  • Irregular bones
  • Short bones
  • Sesamoid bones

5
Shape of Bones
  • Long Bones
  • Longer than wide, consist of shaft and 2 ends
  • e.g. bones of appendages
  • Short Bones
  • Approx. equal in all dimensions
  • e.g. carpals, tarsals
  • Flat Bones
  • Thin, 2 parallel surfaces
  • e.g. skull, sternum, ribs, scapula

Figure 61a
6
Shape of Bones
  • Irregular Bones
  • Complex shapes
  • E.g. vertebrae, os coxa
  • Sesamoid Bones
  • Seed shaped, form in tendon
  • E.g. patella, total number can vary
  • Sutural Bones
  • - Extra bones in sutures of skull

7
Bone Structure
  • A bone is an organ consisting of many tissue
    types
  • Osseous, nervous, cartilage, fibrous CT, blood,
    etc.
  • All bones consist of 2 types of bone tissue
  • Compact bone
  • - solid, dense bone, makes up surfaces and
    shafts
  • Spongy Bone/Cancellous bone
  • - meshy, makes up interior of bones, houses red
    marrow in spaces

8
Bone Markings
  • Bones are not flat on the surface
  • Have projections, depressions, and holes for
    muscle attachment, blood nerve supply
  • Depressions or grooves
  • along bone surface
  • Projections
  • where tendons and ligaments attach
  • at articulations with other bones
  • Tunnels
  • where blood and nerves enter bone

9
Bone Markings
Table 61 (2 of 2)
10
Long Bones Structure
  • Diaphysis
  • - Hollow shaft of compact bone
  • Medullary (marrow) cavity
  • Center of diaphysis, contains yellow marrow
  • Triglycerides for energy reserve
  • Epiphysis
  • Expanded end of bone, surface of compact bone
  • Center filled with spongy bone with red marrow in
    spaces
  • Produces blood cells

Figure 62a
11
Long Bones Structure
  • Epiphyseal line or plate
  • Cartilage that marks connection of diaphysis with
    epiphysis
  • Line adults, narrow (aka metaphysis)
  • Plate thick, allows growth during childhood
  • Periosteum
  • 2 layer covering around outside of bone
  • Outer Fibrous Layer
  • Inner Cellular Layer
  • Endosteum
  • Cellular layers, covers all inside surfaces

12
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13
  • Articular Cartilage
  • Hyaline cartilage on end where bone contacts
    another, no periosteum or perichondrium
  • Joint/Articulation
  • - connection between two bones, surrounded by
    CT capsule, lined with synovial membrane
  • Joint cavity filled with synovial fluid to reduce
    friction on articular cartilage

14
Flat Bone Structure
  • Thin layer of spongy bone with red marrow between
    two layers of compact bone
  • Covered by periosteum and endosteum
  • Site of most hematopoiesis
  • Production of blood cells and cell fragments that
    are suspended in plasma (RBC, WBC, and platelets

15
Characteristics of Bone Tissue
  • Periosteum
  • covers outer surfaces of bones
  • consist of outer fibrous and inner cellular
    layers
  • Endosteum
  • Inner, cellular layer of periosteum

16
Bone Histology
  • Bone osseous tissue, supporting CT
  • Consists of specialized cells in a matrix of
    fibers and ground substance
  • Characteristics of bone
  • Dense matrix packed with calcium salts
  • Osteocytes in lacunae
  • Canaliculi for exchange of nutrients and waste
  • Two layer periosteum, covers bone except at
    articular surfaces

17
Bone Histology
  • Matrix 98 of bone tissue
  • 1/3 osteoid organic part
  • Collagen fibers ground substance
  • Tough and flexible
  • 2/3 densely packed crystals of hydroxyapatite
    (calcium salts, mostly calcium phosphate)
  • Hard but brittle
  • Cells only 2 of bone
  • Osteocytes
  • Osteoblasts
  • Osteoprogenitor cells
  • Osteoclasts

18
Cells located in Bones
  • Osteocytes mature bone cells
  • -no cell division
  • -located in lacunae between layers of matrix
    called lamellae
  • -canaliculi link lacunae to each other and blood
    supply
  • -osteocytes linked to each other via gap
    junctions on cell projections in canaliculi
  • - allow exchange of nutrients and wastes
  • -Function
  • 1. To maintain protein and mineral content of
    matrix
  • 2. Can also participate in bone repair
  • -become stem cell like when broken free of
    lacuna

19
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20
Cells located in Bones
  • Osteoblasts - Immature bone cells
  • Perform osteogenesis
  • Formation of new bone matrix
  • Produce osteoid
  • Organic components of matrix that is not yet
    calcified to form bone
  • Promote deposit of calcium salts which
    spontaneously form hydroxyapatite
  • Once enclosed in lacuna by matrix, osteoblast
    differentiates into osteocyte and no longer
    produces new matrix

21
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22
Cells located in Bones
  • 3. Osteoprogenitor Cells mesenchymal cells
  • - bone stem cell that produces daughters
  • - daughters become osteoblasts for repair
    and growth
  • - located in endosteum and inner periosteum

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24
Cells located in Bones
  • 4. Osteoclasts
  • - large, multinuclear
  • - derived from monocytes (macrophages)
  • - perform osteolysis
  • - digest and dissolve bone matrix
  • - release minerals
  • 1. For use in blood or
  • 2. Recycling during bone remodeling

25
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26
Cells located in Bones
27
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

28
How would the strength of a bone be affected if
the ratio of collagen to hydroxyapatite increased?
  1. Strength increases, flexibility increases.
  2. Strength increases, flexibility decreases.
  3. Strength decreases, flexibility. decreases.
  4. Strength decreases, flexibility increases.

29
If the activity of osteoclasts exceeds the
activity of osteoblasts in a bone, how will the
mass of the bone be affected?
  1. stable mass, but re-positioned matrix
  2. mass will not be affected
  3. more mass
  4. less mass

30
The difference between compact bone and spongy
bone.
31
Structure of Compact Bone
  • Consists of osteons
  • Parallel to surface
  • Each osteon is around a central canal
  • Contains blood vessels and nerves
  • Perforating canals perpendicular to osteons act
    to connect the osteons
  • Osteon is built of layers of matrix secreted by
    osteoblasts
  • Each layer concentric lamella
  • Osteocytes are located in lacunae between
    lamellae
  • Ostocytes are connected to neighboring cells and
    central canal via canaliculi

32
Structure of Compact Bone
  • Interstitial lamellae fill spaces between osteons
  • Circumferiential lamellae run perimeter inside
    and out in contact with
  • endosteum and periosteum
  • Compact bone is designed to receive stress from
    one direction
  • Very strong parallel to osteons
  • Weak perpendicular to osteons

33
Compact Bone
Figure 65
34
Structure of Spongy Bone
  • Lamellae meshwork called trabeculae (no
    osteons)
  • Red marrow fills spaces around trabeculae
  • Osteocytes in lacunae are linked by canaliculi
  • No direct blood supply (no central canals)
  • Nutrients diffuse into canaliculi in trabeculae
    from red marrow
  • Spongy bone make up
  • low stress bones
  • Areas of bone where stress comes from multiple
    directions
  • Provide light weigh strength

35
Bone Marrow
  • Red Marrow
  • Located in space between trabeculae
  • Has blood vessels
  • Forms red blood cells
  • Supplies nutrients to osteocytes
  • Yellow Marrow
  • In some bones, spongy bone holds yellow bone
    marrow
  • is yellow because it stores fat

36
Structure of Spongy Bone
37
Periosteum and Endosteum
  • Compact bone is covered with membrane
  • periosteum on the outside
  • endosteum on the inside

38
Periosteum
  • Fibrous outer layer
  • - Dense irregular CT
  • Cellular Inner layer
  • Osteoprogenitor cells
  • Functions
  • Isolate bone from surrounding tissues
  • Site for attachment for tendons and ligaments
  • Route for nerves and blood vessels to enter bone
  • Participates in bone growth and repair

39
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40
Endosteum
  • Thin cellular layer
  • Lines medullary cavity, central canals, and
    covers trabeculae
  • Consists of
  • osteoblasts, osteoprogenitor cells, and
    osteoclasts
  • Cells become active during bone growth and repair

41
Endosteum
Figure 68b
42
Bone Growth
  • Begins 6-8 weeks post fertilization
  • Continues through puberty (18-25 y)
  • Osteogenesis ossification formation of bone
  • Not calcification
  • Hardening of matrix or cytoplasm with calcium
  • Can happen to many tissues
  • Two types of Ossification
  • Intramembranous forms flat bones
  • Endochondrial forms long bones

43
Bone Development
  • Human bones grow until about age 25
  • Osteogenesis
  • bone formation
  • Ossification Deposition of calcium salts
  • the process of replacing other tissues with bone

44
The difference between intramembranous
ossification and endochondral ossification.
45
Intramembranous Ossification
  • Bone develops from mesenchyme or fibrous CT in
    deep layers of dermis
  • Also called dermal ossification
  • because it occurs in the dermis
  • produces dermal bones such as mandible and
    clavicle
  • Produces skull bones
  • There are 4 main steps in intramembranous
    ossification

46
Intramembranous Ossification Step 1
  • Ossification center appears in the fibrous CT
    membrane
  • Mesenchymal cells aggregate
  • Differentiate into osteoblasts
  • Begin ossification at the ossification center

47
Intramembranous Ossification Step 2
  • Bone matrix (osteoid) is secreted within the
    fibrous membrane
  • Osteoblasts begin to secrete osteoid, which is
    mineralized within a few days
  • Trapped osteoblasts become osteocytes

48
Intramembranous Ossification Step 3
  • Woven bone and periosteum form
  • Accumulating osteoid is laid down between
    embryonic blood vessels, which form a random
    network
  • Vascularized mesenchyme condenses on the external
    face of the woven bone and becomes periosteum
    around spongy bone

49
Intramembranous Ossification Step 4
  • Bone collar of compact bone forms and red marrow
    appears
  • Trabeculae just deep to the periosteum thickens,
    forming a woven bone collar that is later
    replaced with mature lamellar bone
  • Spongy bone, consisting of distinct trabeculae,
    persists internally and its vascular tissue
    becomes red marrow

50
Endochondral Ossification
  • Ossifies bones that originate as hyaline
    cartilage
  • Most bones originate as hyaline cartilage
  • Cartilage grows by interstitial and appositional
    growth
  • Cartilage is slowly replaced from the inside out

51
Endochondral Ossification
  • Growth and ossification of long bones occurs in 6
    steps

52
Endochondral Ossification Step 1
  • Primary ossification center begins to form
  • Chondrocytes in the center of hyaline cartilage
  • Enlarge in diaphysis
  • Surrounding matrix calcifies killing the enclosed
    chondrocytes
  • die, leaving cavities in cartilage

Figure 69 (Step 1)
53
Endochondral Ossification Step 2
  • Blood vessels grow around the edges of the
    cartilage
  • Cells in the perichondrium change to osteoblasts
  • Secrete osteoid
  • Osteiod is mineralized and produces a layer of
    superficial bone around the shaft which will
    continue to grow around the diaphysis and become
    compact bone (appositional growth)

Figure 69 (Step 2)
54
Endochondral Ossification Step 3
  • Capillaries and fibroblast migrate into the
    primary ossification center
  • Blood vessels enter the cartilage
  • Bringing fibroblasts that become osteoblasts and
    secrete osteoid
  • Mineralized into rebeculae
  • Spongy bone develops at the primary ossification
    center and continues to growth toward the
    epiphysis

Figure 69 (Step 3)
55
Endochondral Ossification Step 4
  • Remodeling creates a marrow cavity
  • Osteoclasts degrade trabeculae in the center to
    create the marrow cavity
  • Bone increases in length by interstital growth of
    the epiphyseal plate followed by replacement of
    plate cartilage by spongy bone
  • Cartilage continues to grow on epiphyseal side
    and is replaced by bone on diaphysis side
  • Bone increases in diameter by appositional growth
    from cellular layers of peristeum

Figure 69 (Step 4)
56
Endochondral Ossification Step 5
  • Secondary ossification centers form in epiphyses
  • Capillaries and osteoblasts enter the epiphyses
  • creating secondary ossification centers

Figure 69 (Step 5)
57
Endochondral Ossification Step 6
  • Epiphyses become ossified with spongy bone
  • Hyaline cartilage remains on articular surfaces
    (not calcified or ossified)
  • Ossification continues at both 1and 2
    ossification centers until all epiphyseal
    cartilage has been replaced with bone ?
    epiphyseal closure
  • Adult bone retains the epiphyseal line

Figure 69 (Step 6)
58
Endochondral Ossification
  • Appositional growth
  • compact bone thickens and strengthens long bone
    with layers of circumferential lamellae

Figure 69 (Step 2)
59
During intramembranous ossification, which
type(s) of tissue is/are replaced by bone?
  1. hyaline cartilage
  2. fibrous connective tissue
  3. mesenchymal connective tissue
  4. osteoid tissue

60
In endochondral ossification, what is the
original source of osteoblasts?
  1. de novo synthesis
  2. cells brought with via the nutrient artery
  3. cells of the inner layer of the perichondrium
  4. chondrocytes from the original model

61
The characteristics of adult bones.
62
Epiphyseal Lines
Figure 610
63
Epiphyseal Lines
  • When long bone stops growing, after puberty
  • epiphyseal cartilage disappears
  • is visible on X-rays as an epiphyseal line

64
A child who enters puberty several years later
than the average age is generally taller than
average as an adult. Why?
  1. Epiphyseal plates fuse during puberty.
  2. Bone growth continues throughout childhood.
  3. Growth spurts usually occur at the onset of
    puberty.
  4. All of the above.

65
The skeletal system remodels and maintains
homeostasis. The effects of nutrition,
hormones, exercise, and aging on bone.
66
Bone Remodeling
  • Bones are not static constantly recycled and
    renewed
  • 5-7 of skeleton is recycled/week
  • Osteoclasts secrete
  • Lysosomal enzymes digest osteoid
  • Hydrochloric acid solubilize calcium salts
  • Osteoblasts secrete
  • Osteoid (organic matrix)
  • Alkaline phosphatase induces mineralization of
    osteoid
  • - Complete mineralization takes 1 week

67
Bone Remodeling
  • Bones Adapt
  • Stressed bones grow thicker
  • Bumps and ridges for muscle attachment enlarge
    when muscles are used heavily
  • Bones weaken with inactivity up to 1/3 or mass
    is lost with few weeks of inactivity
  • Heavy metals can get incorporated
  • Condition of bones depends on interplay between
    osteoclast and osteoblast activity

68
Skeleton as a Calcium Reserve
  • Calcium is important for normal function of
    neurons and muscle
  • Blood calcium 9-11 mg/100ml
  • If blood levels are too high
  • Nerve and muscle cells are non responsive
  • If blood levels are too low
  • Nerve and muscle cells are hyper-excitable ?
    convulsions, death

69
The Skeleton as Calcium Reserve
  • Bones store calcium and other minerals
  • Calcium is the most abundant mineral in the body
  • Calcium ions are vital to
  • membranes
  • neurons
  • muscle cells, especially heart cells

70
Skeleton as a Calcium Reserve
  • Calcium homeostasis depends on
  • Storage in the Bones
  • Absorption in the GI
  • Excretion at the Kidneys
  • These factors are controlled by hormones to
    regulate blood calcium levels

71
If blood calcium levels Low
  • Parathyroid hormone (from parathyroid gland)
    triggers
  • Increase osteoclast activity
  • - decrease storage
  • Enhanced calcitriol action
  • - increase absorption
  • Decreased calcium excretion at the kidneys

72
If Blood Calcium levels High
  • Calcitonin (from thyroid gland) triggers
  • Inhibition of osteoclast activity
  • Increased calcium excretion at the kidneys

73
Nutritional and Hormone Effects on Bone
  • Many nutrients and hormones are required for
    normal bone growth and maintenance
  • Calcium and phosphate salts
  • Calcitriol
  • Vitamin C
  • Vitamin A
  • Vitamin K and B12
  • Growth Hormones
  • Thyroxin
  • Estrogens and Androgens
  • Calcitonin
  • Parathyroid Hormone

74
Nutritional and Hormone Effects on Bone
  • Calcium and phosphate salts
  • - From food, for mineralization of matrix
  • Calcitriol
  • - From kidneys, for absorption of calcium and
    phosphate
  • Vitamin C
  • - From food, for collagen synthesis and
    osteoblast differentiation
  • Vitamin A
  • - From carotene in food, for normal bone growth
    in children
  • Vitamin K and B12
  • - From food, for synthesis of osteoid proteins

75
Nutritional and Hormone Effects on Bone
  • Growth Hormones
  • - From pituitary gland, for protein synthesis and
    cell growth
  • Thyroxin
  • - From thyroid gland, for cell metabolism and
    osteoblast activity
  • Estrogens and Androgens
  • - From gonads, for epiphyseal closure
  • Calcitonin
  • - From thyroid gland AND
  • Parathyroid Hormone
  • From parathyroid gland, to regulate calcium and
    phosphate levels in body fluids
  • Affects bone composition

76
Hormones for Bone Growth and Maintenance
Table 62
77
Abnormalities
  • Genetic/Physiological Abnormalities 1. Giantism
  • too much Growth hormone prior to epiphyseal
    closure, bones grow excessively large
  • 2. Acromegaly
  • - too much GH after closure, bones dont
  • grow but all cartilage does
  • - ribs, nose, ears, articular cartilage
  • 3. Pituitary Dwarfism
  • - not enough GH, bones fail to elongate

78
Abnormalities
  • Diet Related Abnormalities
  • 1. Scurvy
  • - lack of Vit. C
  • - causes low collagen content, reduced bone
  • mass, bones brittle
  • 2. Osteomalacia
  • - lack calcitriol, osteoid produced but
  • not mineralized, bones flexible
  • -Called Rickets in children and leads to
  • permanent deformity

79
A seven-year-old child has a pituitary tumor
involving the cells that secrete growth hormone
(GH), resulting in increased levels of GH. How
will this condition affect the childs growth?
  1. The individual will be taller.
  2. The individual will be shorter.
  3. Growth of the individual will be erratic and
    slow.
  4. Excessive growth will be limited to axial
    skeleton.

80
Why does a child who has rickets have difficulty
walking?
  1. Joints become fused, preventing movement.
  2. Bones are brittle and break under body weight.
  3. Bones are flexible and bend under body weight.
  4. Motor skills are impaired.

81
What effect would increased PTH secretion have on
blood calcium levels?
  1. higher level of calcium
  2. lower level of calcium
  3. uncontrolled level of calcium
  4. no effect on blood calcium, PTH effects calcium
    in the bones

82
How does calcitonin help lower the calcium ion
concentration of blood?
  1. by inhibiting osteoclast activity
  2. by increasing the rate of calcium excretion at
    the kidneys
  3. by increasing the rate of calcium uptake by
    intestinal cells
  4. 1 and 2

83
Types of fractures and how do they heal.
84
Fractures
  • Fractures
  • cracks or breaks in bones
  • caused by physical stress
  • Bones break in response to excessive stress
  • Bones are designed to heal
  • Fractures are repaired in 4 steps

85
Fracture Repair Step 1
  • Bleeding
  • produces a clot (fracture hematoma)
  • Seals off dead osteocytes and broken blood vessels

Figure 615 (Step 1)
86
Fracture Repair Step 2
  • Cells of the endosteum and periosteum
  • Divide and migrate into fracture zone
  • Cells of Periosteum
  • create external callus of fibrocartilage
  • Cells of Endosteum
  • create internal callus of spongy bone
  • Calluses stabilize the break
  • external callus of cartilage and bone surrounds
    break
  • internal callus develops in marrow cavity

Figure 615 (Step 2)
87
Fracture Repair Step 3
  • Osteoblasts
  • replace cartilage with spongy bone
  • Fracture gap is now filled with all spongy bone

Figure 615 (Step 3)
88
Fracture Repair Step 4
  • A bulge from the callus marks the fracture point
  • Osteoblasts and osteocytes remodel the fracture
    for up to a year
  • Spongy bone is replaced with compact bone and
    excess callus material is removed

Figure 615 (Step 4)
89
The effects of aging on the skeletal system.
90
Effects of Aging
  • Bones become thinner and weaker with age
  • 1. Osteopenia reduction in bone mass
  • All adults suffer in some degree
  • Osteoclasts out-work osteoblast
  • sex hormones in youth inhibit osteoclasts
  • Women 8/decade after 40
  • Men 3/decade after 40

91
Effects of Aging
  • 2. Osteoporosis reduction in bone mass that
    compromises function
  • More common in women
  • Over age 45, occurs in
  • 29 of women
  • 18 of men
  • Thinner bones to start
  • Greater rate of osteopenia

92
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93
Effects of Bone Loss
  • The epiphyses, vertebrae, and jaws are most
    affected
  • resulting in fragile limbs
  • reduction in height
  • tooth loss

94
Hormones and Bone Loss
  • Estrogens and androgens help maintain bone mass
  • Bone loss in women accelerates after menopause

95
Why is osteoporosis more common in older women
than in older men?
  1. Testosterone levels decline in post-menopausal
    women.
  2. Older women tend to be more sedentary than older
    men.
  3. Declining estrogen levels lead to decreased
    calcium deposition.
  4. In males, androgens increase with age.

96
SUMMARY (1 of 2)
  • Bone shapes, markings, and structure
  • The matrix of osseous tissue
  • Types of bone cells
  • The structures of compact bone
  • The structures of spongy bone
  • The periosteum and endosteum
  • Ossification and calcification
  • Intramembranous ossification
  • Endochondrial ossification

97
SUMMARY (2 of 2)
  • Blood and nerve supplies
  • Bone minerals, recycling, and remodeling
  • The effects of exercise
  • Hormones and nutrition
  • Calcium storage
  • Fracture repair
  • The effects of aging
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