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
(No Transcript)
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
(No Transcript)
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
(No Transcript)
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

23
(No Transcript)
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
(No Transcript)
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?

• Strength increases, flexibility increases.
• Strength increases, flexibility decreases.
• Strength decreases, flexibility. decreases.
• 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?

• stable mass, but re-positioned matrix
• mass will not be affected
• more mass
• 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
(No Transcript)
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?

• hyaline cartilage
• fibrous connective tissue
• mesenchymal connective tissue
• osteoid tissue

60
In endochondral ossification, what is the
original source of osteoblasts?

• de novo synthesis
• cells brought with via the nutrient artery
• cells of the inner layer of the perichondrium
• 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?

• Epiphyseal plates fuse during puberty.
• Bone growth continues throughout childhood.
• Growth spurts usually occur at the onset of
  puberty.
• 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 Abnormalities1. 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?

• The individual will be taller.
• The individual will be shorter.
• Growth of the individual will be erratic and
  slow.
• Excessive growth will be limited to axial
  skeleton.

80
Why does a child who has rickets have difficulty
walking?

• Joints become fused, preventing movement.
• Bones are brittle and break under body weight.
• Bones are flexible and bend under body weight.
• Motor skills are impaired.

81
What effect would increased PTH secretion have on
blood calcium levels?

• higher level of calcium
• lower level of calcium
• uncontrolled level of calcium
• no effect on blood calcium, PTH effects calcium
  in the bones

82
How does calcitonin help lower the calcium ion
concentration of blood?

• by inhibiting osteoclast activity
• by increasing the rate of calcium excretion at
  the kidneys
• by increasing the rate of calcium uptake by
  intestinal cells
• 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
(No Transcript)
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?

• Testosterone levels decline in post-menopausal
  women.
• Older women tend to be more sedentary than older
  men.
• Declining estrogen levels lead to decreased
  calcium deposition.
• 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