Ch 6 Bone Tissue

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Ch 6 Bone Tissue

Bone Tissue Anatomy

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Resilient tissue that is poorly vascularlized
Hyaline Cartilage
-Articular cartilages and coastal (rib) cartilage, larynx, trachea, and nose
-Rich in collagen fibers and appear glassy
-Most abundant cartilage
-Support and flexibility and resisting compression
-Forms embryonic skeleton
Elastic Cartilage
-Ear pinna and epiglottis
-Contains many elastic/collage fibers
-Able to tolerate repeated bending
-Intervertebral discs, knee menisci, pubic symphysis
-Inermediate between hyaline and elastic cartilage
-Resists strong compression and strong tension (pulling pressures)
Chondocyte in Lacunae
Produce additional cartilage tissue
Round; membrane of fibrous connective tissue that surrounds the external surface of cartilage
Appositional Growth

Think: new cartilage
Chondoblasts in surrounding perichondrium produce new cartilage; produce cartilage inside
-Growth of bone by addition of bone tissue to its surface
Interstitial Growth

Think: matrix
Chondrocytes within cartilage divide and secrete new matrix
Tissue in Bones
-Come from mesoderm
-Dominated by bone connective tissue
-Contain nervous tissue (ectoderm) and blood connective tissue
-Contain cartilage in articular cartilages
-Contain epithelial tissue lining blood vessels
What germ layer is the inside layer of bone made out of?
Function of Bones
-Support, movement, protection, mineral storage, bone-cell formation (bone contains bone red marrow), energy metabolism (osteoblasts secrete osetocalcin)
Stimulates pancreas to produce more insulin and fat cells to become insulin sensitive
Extracellular Matrix
35% organic
-Rich in collagen - provides tensile strength; contributes to flexibility

65% inorganic
-Mineral salts (ex: calcium phosphate) lie around collagen fibrils
-Mineral salts pack tightly to give bone its hardness to rest compression
-Bones don't resist torsion forces well
Osteogenic cells
-Stem cells that differentiate into osteoblasts
-From or composed of any tissue concerned in bone growth or repair
Actively produce and secrete bone matrix (ground matrix and collagen fibrils)
-Bone matrix is osteoid
-Within weeks of secretion, inorganic calcium salts crystallize within osteoid
-Add bone tissue to external surface along diaphysis
-Keep bone matrixes healthy
-Mature bone cells
-Spider shaped that occupy lacunae (small cavities in solid matrix); "legs" occupy thin tubes called canaliculi
-Receive nutrients from capillaries in endosteum surrounding trabeculae via connections from canaliculi
Bone matrix secreted by osteoblasts and crystallized by salts
-Resorption of bones
-Derived from white blood cells
-Secrete HCl and lysosomal enzymes
-Remove Bone from internal surface along diaphysis
-Bone-degrading cell
-Many nuclei
-Derive from hematopoietic stem cells
Long bones
Longer than wide; shaft plus 2 ends
Common on extremities
Short Bones

Think: Cube
-Roughly cube-shaped
-Wrist and ankles
-Sesamoid bones: special type of short bone which are sesame seed shaped and include knee caps
Flat bones
Thin and flattened, usually curved
Ex: ribs, sternum, scapula, and some cranial bones
Irregular Bones
Various shapes, don't fit in other categories
Ex: vertebrae and hip bones
Compact Bone
Dense outer layer of bone
Spongy bone (cancellous or trabecular bone)
-internal 3D network of bone with small needle-like or flat pieces called traceculae are filled with red bone marrow (mainly hematopoietic cells) or yellow bone marrow (mainly adipose)
-Trabeculae = too small to contain osteons or its own blood vessels; although they have several layers of lamellae and osteocytes
-Less complex than compact bone
Red bone barrow
Mainly hematopooetic cells
Yellow bone marrow
Mainly adipose cells

Structure of Long Bone
• Diaphysis—“shaft” long axis of a bone
• Epiphysis—ends of a bone with joint surfaces typically
covered with a thin layer of hyaline cartilage called
articular cartilage
• Epiphyseal line runs in between the diaphysis and
epiphysis in adults and is the remnant of the epiphyseal
• Blood vessels—unlike cartilage, bones are well
vascularized; nutrient arteries and nutrient veins service
the bone
• Medullary cavity—interior of all bones consists largely of
spongy bone with marrow in between trabeculae, however,
the very center of the diaphysis has no spongy bone and
is filled with yellow bone marrow
• Membranes--Periosteum, perforating fibers (Sharpey’s
fibers), and endosteum
Shaft - Long axis of bone
Very center has no spongy bone and is filled with yellow bone marriw
Ends of a one with joint surfaces typically covered with think later of hyaline cartilage called articular cartilage
Epiphyseal line
Runs in between diaphysis and epiphysis in adults and is remnant of epiphyseal
Blood vessels
Unlike cartilage, bones are well vascularized; nutrients arteries and nutrient veins service the bone
What's a big difference between cartilage and bone?
Bones are well vascularized
Medullary cavity
Interior of all bones consists largely of spongy bone with marrow in between traceculae
Periosteum, perforating fibers (Sharpey's fibers) and endosteum (inside medullary cavity)
Periosteum and Perforating Fibers

Think: external surface
-Connective tissue and membrane which covers external surface of bone, except the ends of epiphyses which are covered with articular cartilage
-2 layers: 1) Superficial outer periosteum
                  2) Deep inner periosteium layer
-Perforating fibers (Sharpey's fibers)
-Provides insertion points for tendons and ligaments with dense concentrations of perforating fibers at these insertion sites
Superficial outer periosteum
Layer of dense irregular connective tissue which resists tension placed on bone
Deep inner periosteium layer
Abuts compact outer surface of compact bone; deep later is osteogenic and forms osteoblasts and osteoclasts
Perforating Fibers (Sharpey's Fibers)
Secure periosteum to underlining bone with thick bundles of collagen that run from periosteium into bone matrix

Think: Internal surface
-Thin connective tissue membrane layer which lines internal bone surfaces including trabeculae of spongy bone and inner surface of central canals of osteons
-Will line spongy bone and medullary cavity
-Osteogenic; Osteoblast and osteoclast working with spongy bone
Osteons (Haverson System)

Lamellae + Central = osteon
-Long cylindrical structures which run along axis of bone
-Function in support
-Structurally - transverse cross-section of individual osteons resembling rings of a tree
-Group of concentric tubes

Contain: lamellae (look like pineapples/concentric ring), central canal, perforating canals, canaliculi

Microscopic Structure of Compact Bone
Long tube gives structural strength

Smallest --> Biggest
Structure of Short, irregular, and flat bones
-No diaphysis
-No epiphysis
-Hard dense compact outer layer of bone
-Diploe: Internal spongy bone with trabeculae flat bones
-No deep marrow (medullary cavity present)
Long bone vs. Short bone
Long Bone Short Bone -Diaphysis -Epiphysis -Medullar Cavity -No diaphysis -No Epiphysis -No medullar cavity
Trabeculae - Connective Tissue
-bony spicules in cancellous bone which form a meshwork of intercommunicating spaces that are filled with bone marrow.
-Trabeculae of spongy bones align along lines of stress in an organized pattern to provide structural support
Bone Design: Compression and tension
Anatomy of bone reflects stresses
-Compression and tension greatest at external surfaces
-Compression lines: vertical
-Tension lines: horizantal
Bone Markings
1. Projections for muscle and ligament attachment
2. Surfaces that form joints
3. Depressions and Openings

Projections for muscle and ligament attachment
1. Tuberosity - Large rounded project; may be roughened
2. Crest - Narrow ridge of bone; usually prominent
3. Trochanter - Very large, blunt, irregularly shaped process (only example: femur)
4. Narrow ridge of bone; less prominent than crest
5. Tubercle - small rounded projection or process
6. Epicondyle - raised area on or above condyle
7. Spine - sharp, slender often pointed projection
8. Process - any bony prominence

Surfaces that form joints
1. Head - any bony expansion carried on a neck
2. Facet - smooth, nearly flat articular surface
3. Condyle - rounded articular projection; often articulates with surrounding fossa

Depressions and Openings
1. Foreamen - round or oval opening through a bone
2. Groove - furrow
3. Fissure - narrow, slit-like opening
4. Notch - indentation at edge of structure
5. Fossa - Shallow basin-like depression in a bone; often serving as articular surface
6. Meatus - canal-like passageway
7. Sinus - Cavity within a bone; filled with air and line with mucous membrane
Compact Bone
-Contains passage ways for blood vessels, lymph vessels, and nerves
-Osteons that function in support
Concentric Tube
Compact Bone
Each tube is a lamella with layer of bone matrix in which collagen fibers and mineral crystals align and run in single direction
-These fibers and crystals next to lamella run in opposite direction creating an alternating pattern optimal for withstanding torsion (twisting) stresses and inhibiting crack propagation and fracture development
Central Canal (Haversion System)
-Runs through each osteon
-Lined with osteogenic endosteum layer with osteoblast
-Lamella added to inner surface of osteon --> decreases diameter of inner canal
-Perforating (Volmann's) canals -right angle to central canals and central marrow cavity and connect blood nerve supply of periosteum to these arrows
-Connect neighboring lacunae to one another and to capillaries for nutrient supply
-There are extensions of osteocytes that touch and form gap junctions for nutrient exchange
-Communication system
Some Lamellae not found in Osteons
1. Interstitial lamellae
2. Circumferential lamellae
Interstitial Lamellae
-Between osteons
-Groups of incomplete lamellae which lie between osteons; remains of old osteons cut through by bone remodeling
Circumferential Lamellae
Extends around the entire circumference of diaphysis
Bone-tissue formation
-Membrane bones
-Endochondrial bones
Membrane Bones
Ex: Cranial bones, clavicles

Formed directly from mesenchyme (from mesoderm) without first being modeled in cartilage through intramembranous ossification
Endochondrial Bones
Develop initially from hyaline cartilage which is replaced by a bone through endochondral ossification

Intramembranous Ossification
1. Ossification center appears in the fibrous  of connective tissue membrane
-Mesenchymal cells cluster and differentiate into osteblasts
-Form ossification center

2. Bone matrix (osteoid) secreted within fibrous membrane and calcifies
-Osteoblasts secrete osteoid (calcified within a few days)
-Trapped osteoblasts become osteocytes

3. Woven bone and periosteum form
-Accumulating osteoid --> network (instead of lamellae) of trabeculae called woven bone
-Vascularized mesenchyme condenses and becomes periosteum

4. Lamellar bone replaces woven bone. Red marrow appears.
-Periosteum thicken and are replaced with mature lamellar bone, forming compact plates
-Spongy bone: consisting of distinct trabeculae --> vascular tissue becomes red marrow

Endochondrial Ossification
-All bones except skull and clavicles
-Modeled by hyaline cartilage
-Forms late in second month of embryonic development
-Forms into early adulthood

1. Bone collar forms around hyaline cartilage model
2. Cartilage in center of diaphysis calcifies and develops cavities.
3. Periosteal invades internal cavities and spongy bone begins to form.
4. Diaphysis elongates and medullary cavity forms as ossification continues. Secondary ossification centers appear in epiphysis to prepare for stage 5.
5. Epiphyses ossify. When completed, hyaline cartilage remains only in epiphyseal plates and articular cartilages.

Epiphyseal Plates
-Cartilage organized for quick, efficient growth
-Cartilage cells form tall stacks (chondroblasts)
-Pushes epiphysis away from diaphysis
-Bone lengthens
-Maintain thickness
Resting Zone

Epiphyseal Plates
-Cells nearest to epiphysis that are small and inactive
Proliferation Zone

Epiphyseal Plates
-Made up of chondroblasts at top of stack which divide quickly, pushing epiphysis away from diaphysis --> bone elongates
-Cartilage cells undergo mitosis
Hypertrophic Zone

Epiphyseal Plates
-Older chondrocytes deep in stack signals around cartilage matrix
-Older cartilage cells enlarge
Calcification Zone
Matrix becomes calcified; cartilage cells die; matrix begins deteriorating
Ossification Zone
 New Bone formed
Postnatal Endochondrial Bones
-Bones lengthen by epiphyseal plates; they maintain constant thickness
-Cartilage replaced w/ bone connective tissue as quickly as it grows

Growing bones widen as they lengthen
 -Osteoblasts: add bone tissue to external surface along diaphysis 
-Osteoclasts: remove bone from internal surface along diaphysis
Osteoblast vs. Osteoclast
Osteoblast - add; external; bone deposition
Osteoclast - remove; internal; bone resorption
Growth Hormone
-Produced by pituitary gland
-Stimulates epiphyseal plates
Thyroid Hormones
-Ensure skeleton retains proper proportions
Sex Hormones (estrogen and testosterone)
-Promote bone growth
-Induce closure of epiphyseal plates
What happens to long bones as adolescence ends?
Long bone stops lengthening when diaphysis and epiphysis fuse.
-epiphyseal plates become thinner and are replaced by bone tissue
-cartilage stops growing
-chondroblasts dive less often
Bone remodeling
-500 mg calcium
-Canellous (spongy) bone replaced every 3-4 yrs
-Compact bone replaced every 10 yrs
-Maintains constant levels of Ca+ and PO43- in body fluids, which is important since Ca+ is critical for muscle contraction
Where do bone deposit and resorption occur?
Periosteal (perosteum) and endoesteal (endosteum)
Simple fracture
Bone fracture without penetrating skin
Compound fracture
Bone fracture injury that breaks skin
-Likelihood of infection increases
-Treat with antibiotics
Treatment by reduction
Closed: hands
Open: surgically set with pins and wires
Phases of healing simple fracture
1. Hematoma formation: blood vessels break in periosteum and inside bone

2. Fibrocartilage callus formation: w/i few days new blood vessels form the periosteum and endosteum grow into clot filling it with fibrous granulation tissue called soft fibrocartilage callus

3. Bony callus formation: w/i week, trabeculae bone begin to form

4. Bone remodelling: over months bone callus remodeled
Mesoderm --> embryonic mesenchyme cells

Mesenchyme --> membranes and cartilate that form embryonic skeleton

Ossification --> membranes and cartilage start to form 8-12 weeks gestation
Paget's Disease: makes bones soft and deformed
-Excessive rate of bone resorption and formation
        -Lots of remodelling
-Abnormally high ratio of immature woven bone to mature compact bone
-Reduced mineralization that makes bones soft and deformed
Bone cancer that occurs in long bones of lower or upper extremity
Osteomalcia "soft bones"
Bones inadequately mineralized
-Children w/ inadequate Vitamin D
-B/c bones soft, child may have bowed legs and cranial form deformity
-Low bone mass
-Resporption faster than deposition
-Increased ratio of osteclasts/osteoblasts
-Compact bone = thinner, less dense, and spongy bone has fewer trabeculae
-Occurs often in women after menopause, due to reduction in estrogen