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Chapter 6 - Bone!
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Chapter 6!Osseous Tissue and Bone Structure!
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SECTION 6-1 !The skeletal system has five primary functions!
Chapter 6 - Bone!
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Skeletal System - Elements and Functions!
Elements!• Bones of the skeleton!• Cartilages, ligaments and other connective
tissues that stabilize and interconnect bones!Functions!
1. Support (physical and physiological)!2. Storage of minerals and lipids!3. Blood cell production (hemopoiesis)!4. Protection (of soft parts)!5. Leverage (with muscles)!
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SECTION 6-2 !Bone structure!
• Don’t worry about Bone Shapes (p. 180/184)!!• Know the definitions of the Bone Markings that
you are using in lab. See Table 6-2, page 181.
Chapter 6 - Bone!
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Bone Structure Figure 6-3!
• Spongy bone!• Compact bone !• Periosteum!• Endosteum!• Articular cartilage!
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Diaphysis (Shaft)!Epiphyses (Ends of a bone)!Metaphysis!• Union between shaft and ends!• Growing bone contains epiphyseal plate (hyaline
cartilage)!Articular cartilage!• Hyaline cartilage - reduces friction, absorbs
shock!Marrow cavity!• Contains red marrow or yellow marrow!
Parts of a Typical Long Bone (1 of 4)!
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Parts of a Typical Long Bone (2 of 4)!
Periosteum (see slide #10)!• Dense irregular CT!• Everywhere but under articular cartilage!• Continuous with Sharpey’s (perforating) fibers
at origins and insertions of muscles!Functions of periosteum!• Isolates bone from other tissues!• Route for circulatory and nerve supply!• Site of bone growth!• Site of bone repair!
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Parts of a Typical Long Bone (3 of 4)!
Periosteum structure!
1. Fibrous layer = superficial layer!• Dense irregular CT!• Nerves, blood vessels!
2. Osteogenic layer = deep layer!• Elastic fibers!• Blood vessels!• Bone cells!
Osteoprogenitors, osteoblasts!
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Parts of a Typical Long Bone (4 of 4)!
Endosteum• Lines marrow cavity and trabeculae!• Incomplete cellular layer!
Osteoprogenitors, osteoblasts, osteoclasts!
Nutrient foramina!• Allow vessels and nerves to enter bone!
Marrow!• Red marrow - hemopoiesis!• Yellow marrow - fat for energy storage!
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Periosteum and Endosteum (Figure 6-9)!
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Bone Structure Figure 6-3!
• Spongy bone!• Compact bone !• Periosteum!• Endosteum!• Articular cartilage!
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Circulatory Supply to a Mature Bone Figure 6-13!
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SECTION 6-3 !Bone is composed of a matrix and several types of cells!
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Bone = bone cells + mineralized intercellular matrix containing fibers!
Mineral salts in matrix!• Provide compressional strength!
Resist crushing forces• Act like concrete in a sidewalk!• Calcium phosphate (Ca3PO4) – forms
hydroxyapatite!• Calcium carbonate, ions also present!
Osseous Tissue - Matrix (1 of 2) !
Chapter 6 - Bone!
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Osseous Tissue – Matrix and Fibers !
Proteoglycans in ground substance of matrix!• Hydrophilic!• May help regulate bone’s water content, fiber
formation!Fibers within the matrixCollagen fibers in matrix!• Provide tensile strength!
Resist twisting, bending forces• Act like rebar in a concrete floor!
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Bone Cell Types Figure 6-4!
Osteogenic cell = osteoprogenitor cell
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Osteoprogenitor (Osteogenic) Cells!
• Are stem cells (-progenitor = “gives rise to”)!• Derived from mesenchyme (like all CT)!
Mitosis + differentiation → osteoblasts!Found in:!• Osteogenic layer of periosteum!• Endosteum!• Canals containing blood vessels!
Haversian (central) canals!Volkmann’s (perforating) canals!
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Osteoblasts!
Build new bone (-blast = “germ” or “bud”)!Derived from osteoprogenitors!• Not capable of mitosis (in G0)!• Synthesize new matrix = osteoid!
!Osteoid = collagen fibers and proteoglycans!• Becomes mineralized (next slide)!• Minerals accumulate in spaces between
collagen fibers; deposited on fibers!• Formation of new bone = osteogenesis!
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Osteoblasts - Mineralization!
A high enough [Ca2+] exists in ECF that mineralization should occur spontaneously!• Normally prevented by pyrophosphate in ECF!
ATP → AMP + PPi (pyrophosphate)!1. When o’blasts (and other cells) release
pyrophosphate, ossification is prevented.!2. When o’blasts release alkaline phosphatase
from matrix vesicles, ossification occurs!• Alkaline phosphatase is thought to overcome
the inhibitory effect by cleaving (breaking) pyrophosphate!
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Osteoblast Image!http://www.mhhe.com/biosci/ap/histology_mb/!
(trabecula)
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Osteocytes - 1!
Mature bone cells!• Derived from o’blasts!• Not capable of mitosis (in G0)!• Live in lacunae – o’blasts wall themselves in!• Cytoplasmic extensions of cell body found in
canaliculi (“little canals”)!• Gap junctions interconnect osteocytes!
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Osteocytes - 2!
Functions: !1. Maintain local area of matrix!
• Do not secrete matrix (or only a tiny bit)!2. Help in fracture repair!
• Can revert to osteoblast or osteoprogenitor when released from lacuna by a fracture!
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Osteocyte Image (Is this cool or what??)!
www.hone-kenko.org!
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Break down bone (osteolysis) -clast = “to break”!Derived from monocytes!• Multinucleate cells (up to 50 nuclei per cell!)!
Found on free bone surfaces!
Activated by parathyroid hormone!
Release:!
Osteoclasts!
• Proteolytic enzymes – break down collagen!• Organic acids – dissolve inorganic matrix!
Phagocytize and digest end products!
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Osteoclast Image (1)!
www.mhhe.com/biosci/ap/histology_mb/
Osteoclast!
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Osteoclast Image (2)!
open.jorum.ac.uk/xmlui/bitstream/handle/123456789/2475/content/osteoclast_em.htm!
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SECTION 6-4 !Compact bone contains parallel osteons, and spongy bone contains trabeculae!
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Basic unit of compact (lamellar) bone is the osteon!• Osteocytes arranged around a central
(Haversian) canal!• Perforating (Volkmann’s) canals extend
between adjacent osteons!
Spongy (cancellous) bone contains trabeculae!
• Bars of bone, act like girders on a bridge!• Surrounded by red marrow!• Canaliculi open into marrow cavity!
Compact Bone and Spongy Bone !
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The Structure of Osseus Tissue Figure 6-6!
N.A.V.a.L.!
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Compact Bone (1 of 2)!
Locations:!• External layer of all bones!• Diaphysis of long bones!
General functions:!• Protection and support!
Osteons (Haversian systems)!• Haversian (central) canals!• Volkmann’s (perforating) canals!
Interconnect central canals!• Both contain N.A.V.a.L. (What’s N.A.V.a.L.??)!
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Compact Bone (2 of 2)!
Canaliculi (“little canals”) contain:!1. Cytoplasmic extensions (arms) of osteocytes!• O’cytes communicate via gap junctions!• Exchange metabolites!• Exchange control molecules!
2. “Bone fluid”!• Similar to extracellular fluid!• Located between o’cytes’ cell membranes
and bone tissue!• Circulates nutrients, wastes, hormones, etc.!
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Histology of Compact Bone Figure 6-5!
A review of what you!learned in lab!
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Spongy (Cancellous) Bone!
• Structure = bars of bone called trabeculae!• No true osteons (What is an osteon? Why
are osteons not necessary in spongy bone?)!(Hint: Fick’s equation)!
• Trabeculae surrounded by red marrow!• Osteocytes exchange nutrients, wastes with
directly with marrow!• Called diploë when found between layers of
compact bone (e.g. in parietal bone)!
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Spongy Bone !
http://medpics.ucsd.edu/!
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Spongy Bone!
http://grad.uic.edu/gallery/main.php?g2_itemId=871!
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SECTION 6-5 !Ossification and appositional growth are mechanisms of bone formation and enlargement!
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Methods of Ossification!
Ossification types:!• Intramembranous ossification!• Endochondral ossification!
Both methods:!• Begin with a connective tissue model!• Lead to same end product!
!Major difference between the two methods:!• CT model used as starting material!
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Model = fibrous CT Begins at ossification center!• Mesenchyme cells → o’progenitors →
o’blasts!• O’blasts secrete osteoid!• Mineralization occurs!• Trabeculae (dermal bone) produced!
May be remodeled into compact bone!!Flat bones of skull, clavicle and mandible!
Intramembranous (Dermal) Ossification !
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Intramembranous Ossification Figure 6-12!
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Cartilage model is gradually replaced by bone!Interstitial growth!• Increase in bone length• Involves expansion of cartilage!
Appositional growth!• Increase in bone diameter• Add new cartilage (or bone, later) to surface!
Endochondral Ossification !
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Endochondral Ossification Figure 6-11!
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Endochondral Ossification Figure 6-11b!
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Endochondral Ossification (1 of 5) !
“Step 1”!A. Chondrocytes in midsection hypertrophy
(enlarge), mature!B. Cells burst → ↑pH → calcification!
(Note that this is opposite of osteoclasts’ mechanism for breaking down bone!)!
C. Nearby chondrocytes die (↓ diffusion)!D. Thin-walled cavities left behind!E. Walls calcify!
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Endochondral Ossification (2 of 5)!
“Step 2”!A. Vessels grow around shaft!• O’progenitors in perichondrium → o’blasts!• Form periosteal collar (bone)!
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Endochondral Ossification (3 of 5)!
“Step 3”!• Nutrient artery penetrates shaft through
periosteum (nutrient foramen)!• Fibroblasts migrating with blood vessels →
o’blasts !• Replace calcified cartilage with spongy bone
in primary ossification center of shaft!• Ossification spreads towards ends of
cartilage model!
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Endochondral Ossification (4 of 5)!
“Step 4”!• Remodeling occurs!• O’clasts break down trabeculae → marrow
cavity!Also:!• Length increases - interstitial growth!• Diameter increases - appositional growth!
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Endochondral Ossification (5 of 5)!
“Step 5”!• Vessels penetrate epiphyses!• Secondary ossification center begins forming!
“Step 6”!• Epiphyses fill with spongy bone!• Cartilage remains as:!
Articular cartilage!Epiphyseal cartilage!
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Figure 6-11, Step 6 !
(University of Kansas Medical Center)
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Epiphyseal plate (University of Kansas Medical Center)!EPIPHYSIS OF BONE!
DIAPHYSIS OF BONE!
Reserve cartilage!• Anchors plate to epiphysis!• Does not participate in bone
growth!Proliferating cartilage!
• Mitosis occurring!Maturing cartilage!
• Maturing after division!Hypertrophic cartilage!
• Cells enlarging!• Enlargement pushes plate up !• Calcification begins!
Osteogenic zone!• Ossification occurring!• Cements plate to diaphysis!• Osteoblasts lay down bone on
calcified matrix!• Produces spongy bone first
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Bone Growth at Epiphyseal Cartilage Figure 6-10!
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Growth Plate: Growth and Closure!
Plate growth stimulated by:!• Growth hormone (insulin-like growth factors)!• Thyroid hormones!• Glucocorticoids!• Insulin!• Sex hormones at puberty!
Plate closure stimulated by:• Estrogen important in both sexes!
Testosterone → estrogen !Accelerates senescence of chondrocytes!
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SECTION 6-7 !Exercise, hormones and nutrition affect bone development and the skeletal system!
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Bone remodeling!
Changes in bone structure result from:!• Exercise!• Hormone levels!
• Growth hormone and thyroxine increase bone mass!
• Calcitonin and PTH control blood calcium levels, affect bone mass!
• Nutrition (e.g. Ca2+ intake)!
Bone Is Constantly Changing!
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Bone responds to physical stress!• Compact bone is located where stresses are
limited in direction!• Spongy is bone located where stresses are
weaker or multi-directional!• Remodeling takes place throughout life!
Bones and Physical Stress !
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Distribution of Forces on a Long Bone!
Figure 6-8!
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The Piezoelectric Effect!
The Piezoelectric effect during exercise may be part of bone’s response to stress :!• Stress on a crystal generates an electrical
field!• Bone contains crystals = hydroxyapatite• Electrical field thought to call osteoblasts to
points of stress!Lay down new bone → ↑ strength!!
Certain extracellular proteins are also thought to be involved in the stress → growth response!
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SECTION 6-8 !Calcium plays a critical role in bone physiology!
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Skeleton contains 99% of body’s calcium!
Blood [Ca2+] is maintained by bone, the GI tract and the kidneys!
Calcitonin and PTH regulate blood calcium levels!• Calcitonin decreases blood calcium levels!• PTH increases blood calcium levels!
!What are some ways that proper blood [Ca2+] important is important?!
Bone as a Calcium Reserve !
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Factors Affecting [Ca2+] in Body Fluids!
Don’t WASTE
Ca2+Get Ca2+ outof STORAGE
Get NEW Ca2+
Figure 6-15a!Parathyroid
hormone!
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Factors Affecting [Ca2+] in Body Fluids!
Figure 6-15b!Calcitonin!
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Nutrition and Hormonal Effects on Bone!Vitamin C!• Necessary for collagen synthesis!• Stimulates osteoblast differentiation!• Deficiency → scurvy!
Calcitriol from Vitamin D3 (see next slide)!• Required for Ca2+ uptake from gut!
Vitamin A!• Stimulates osteoblast activity!
Vitamins K and B12!• Necessary for protein synthesis!
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Vitamin D Synthesis!
Vitamin D3 inactive form
Calcitriolactive form
Liver
Kidney
www.clinuvel.com/en/blog/wp-content/uploads/2011/04/Vitamin_D_Synthesis.jpg
Epidermis
UV rays!
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Hormones Involved in Bone Growth/Maintenance!
Table 3-1!
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SECTION 6-9 !A fracture is a crack or break in bone!
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1. Fracture hematoma!2. External and internal calluses!
a. Fibrocartilaginous callus!b. Bony callus!
3. Remodeling!
Fracture Repair !
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Steps in Fracture Repair Spotlight Figure 6-16!
1. Fracture Hematoma!
2. Internal callus!
3. External callus!
4. Remodeling!
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SECTION 6-10 !Osteopenia has a widespread effect on aging skeletal tissue!
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Osteopenia!• Decreased o’blast activity!• Begins between 30 and 40 years of age.!• Women: ↓ 8% bone mass per decade!• Men: ↓ 3% bone mass per decade!
Osteoporosis!• Bone loss affects function - bones thin, break!
Effects of Aging !
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Osteoporosis Image Figure 6-17!