Skeletal System
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_____________ cells- unspecialized stem cells
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only bone cells to undergo cell division
daughter cells become osteoblasts
__________________- bone building cells
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figure 6.2
synthesize & secrete collagen fibers & other organic
components to build matrix
Initiate calcification
Become osteocytes= mature bone cells
____________- huge cells, fusion of monocytes
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digest protein and mineral of underlying bone
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Resorption- normal develop, growth, maintanance & repair
Skeletal system
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figure 6.1
Supports soft tissues & attachment for muscle
Protects internal organs
Provides movement
Stores & releases minerals
Contains:
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___________________ - produce blood cells
____________________- stores fat, few blood cells
Bone defined
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________- matrix is abundant w/ inorganic
mineral salts (50%), 25% water, 25%
collagen
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Hydroxyappatite- main mineral salt
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calcium phosphate and calcium carbonate
__________________ - crystallization or
hardening of the matrix
Is a connective tissue
AKA – osseous tissue
Types of bones
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________bones- greater length than width
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Shaft and extremities, curved for strength
Femur, tibia, fibula, humerus, radius, ulna
_______ bones- somewhat cube shaped
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figure 7.2
= length and width
Carpals, tarsals
_____ bones- thin, composed of 2 parallel
plates of compact bone (spongy inside)
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Sternum, ribs, scapula
Types of bones
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_____________ bones- complex shapes
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figure 7.2
Cannot be grouped into previous categories
Varying amt of spongy and compact
Vertebrae, some facial bones
________ bones- shape like sesame seed
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Develop in certain tendons where  friction,
tension, & physical stress
Palms, soles (usually few mm, except patella)
Haversian System
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Haversian system __________ – units of
_____________________
Haversian or central canal – longitudinal thru
center of osteon
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fig 6.3
contains b.v., lymphatic vessels & nerves
_______ –concentric rings of calcified matrix
___________ – small, hollow space in which
osteocytes lie
________ – small canals connecting lacunae
Haversian system = osteon
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Osteocyte – mature cell, maintains daily activity
_____________ – membrane lining marrow cavity
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consists of osteogenic cells & scattered osteoclasts
Perforating or Volkmann’s canal – small
passageway by which b.v. & nerves from
periosteum penetrate into compact bone
________ – membrane covering bone, consists of
CT, osteoprogenitor cells & osteoblasts
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essential for growth, repair, & nutrition
Compact bone tissue
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Contains few spaces, arranged in osteons
____________________________
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Bulk of diaphyses of long bones
Provides protection and support
Resists stresses produced by weight and
movement
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Osteons __________________ (such as long
axis of a bone) to resist bend or fracture
Spongy bone
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Spongy bone does NOT contain osteons
_____________ of thin columns= _________
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figure 6.3
microscopic spaces between filled w/ RB marrow
Within each trabecula: osteocytes lie in
lacunae
Canaliculi radiate from lacunae
Spongy bone (2)
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Osteocytes receive nourishment directly
from blood vessels in the medullary
(marrow) cavity
Trabeculae are oriented along stress lines
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_____________________________
Spongy tends NOT to be located in
heavily stressed areas
Long bone parts
Figure 6.1
1. Diaphysis- bone shaft; long, cylinderal
2. Epiphyses- distal & proximal ends
3. Metaphyses- region of mature bone where 1
and 2 meet
*in growing bone contains: epiphyseal plate- layer of
hyaline cartilage allowing the diaphysis to grow in
length, not width
4. ______________- thin layer of hyaline cartilage
covers epiphysis,reduce friction, shock absorbtion.
5. _____________- tough sheath of dense irregular CT
surrounding bone surface where not covered by
articular cartilage, grows in thickness not length;
protects; nourishes; repairs; attach ligaments &
tendons.
6. Medullary cavity= marrow cavity, space in diaphysis
containing YBM
7. ______________- lines medullary cavity, osteogenic
cells & osteoclasts
Bone marrow functions
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Red bone marrow
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Produces RBC, WBC, platelets=________________
Consists of blood cells, adipocytes, fibroblasts,
macrophages
Developing bones of fetus; pelvis, ribs, sternum,
vertebrae, skull, ends of some long
Yellow bone marrow
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________________ storage in fat cells
Few blood cells
With  age much red turns to yellow
Types of ossification
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Endochondral ossification- bone forms
from cartilage
Intramembranous ossification- bone forms
directly on or within CT, does not form
from cartilage
Intramembranous ossification, 6.5
Intramembranous Ossification
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Formation of bone directly on or within fibrous
CT
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form directly from mesenchyme without going thru
cartilage stage
fewer steps than endochondral:
1. Mesenchymal cells condense & differentiate:
osteogenic cells  __________________
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-center of ossification
-Osteoblasts secrete organic matrix of bone until
completely surrounded by it
2. Matrix secretion stops. Osteoblasts become
________________. Calcium & mineral salts
deposited, matrix hardens
3. Matrix develops into trabeculae, which fuse &
form spongy bone
-BV grow into spaces between trabeculae &
mesenchyme along surface
-CT assoc w/ b.v. in trabeculae differentiates into
RB marrow
4. On outside, mesenchyme condenses &
develops into _______________
-most layers of superficial spongy bone
replaced by compact bone
-remains spongy at center
-much of this bone remodeled (destroyed &
reformed)  transform into adult size & shape
Endochondral ossification
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_________________________ by bone
most bones are formed this way
1. Development of cartilage:
-mesenchymal cells crowd together in the shape of
future bone & differentiate into chondroblasts
-Chondroblasts produce a hyaline cartilage matrix,
- Perichondrium is around outside cartilage
2. Growth of cartilage:
-chondroblasts buried in matrix become chondrocytes
-cartilage grows in _________ by cell division &
secretion of matrix = ______ growth – “from within”
-Growth in __________by addition of matrix on
periphery by chondroblasts in perichondrium =
___________ growth
-Chondrocytes increase in size, may burst  release
contents   pH
*Change in pH causes calcification, other chondrocytes will
die: essential materials cannot diffuse thru new matrix
3. Nutrient artery penetrates perichondrium & calcifying
cartilage, stimulating osteogenic cells to differentiate into
osteoblasts
-Under perichondrium- thin shell of compact bone
secreted= periosteal bone collar
-periochondrium is developing bone = periosteum
__________ ossification center = region where bone will
replace most cartilage _________ from external surface
-Osteoblast secrete bone matrix
-Trabeculae form
-Osteoclast breakdown trabeculae leaving medullary
cavity
4. _____________ oss center forms - b.v. enter
epiphyses, @ birth. Spongy bone remains at
center of epiphyses- no medullary cavities &
ossif proceeds _________
5. Hyaline cartilage covering epiphyses becomes
________________
-Prior to adulthood: hyaline cartilage between
epiphysis & diaphysis = epiphyseal plateresponsible for lengthwise growth
Endochondral
ossification
Lengthening of bone
fig 6.7
Epiphyseal plate is a layer of hyaline in the
metaphysis of growing bone = 4 zones:
1. _________cartilage -layer nearest
epiphysis, small scattered chondocytes
-no function in bone growth, anchor epiphyseal
plate to bone of epiphysis
2. ____________ cartilage - slightly larger
chondrocytes
-zone arranged like stack of coins,
chondrocytes divide, replacing dying ones
at diaphyseal side
3. ____________ cartilage - chondrocytes
larger & remain arranged in columns
-lengthening of diaphysis = result of cell
division and maturation here
4. __________ cartilage- final zone, few cells, thick
-mostly dead chondrocytes: calcified matrix
-Calcified cartilage dissolved by osteoclasts &
invaded by osteoblasts & capillaries
-Osteoblasts lay down bone matrix, diaphyseal
border of epiphyseal plate firmly cemented to
diaphysis
*between the ages of 18-25 the epiphyseal plates
close, plate fades, leaving a line
Zones- lengthening
Thickness (appositional) fig 6.8
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At surface periosteal cells differentiate into
osteoblasts- secrete collagen fibers & other
molecules to form matrix
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Surrounded with matrix they become osteocytes
Bone ridges form on sides of periosteal b.v. and
enlarge to leave groove for b.v.
Ridges fuse, form tunnel
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Periosteum now endosteum in tunnel
Thickness (appositional) fig 6.8
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Osteoblasts in endosteum deposit matrix
forming new lamellae
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Proceeds inward toward b.v. filling in tunnel
Osteon is formed
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Osteoblasts deposited a new lamellae  thick
Appositional growth, fig 6.8
Remodeling of bone
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Bone is continually renewed
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Remodeling purposes:
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Osteoclasts carve out tunnels in old bone
Osteoblasts rebuild new
In different parts of skeleton full cycle= 2-3 months or
much longer
Renew ________________
Redistribute matrix along lines of mechanical stress
Remodeling is the way injured bone heals.
Remodeling of bone
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Bone reabsorption= breakdown of matrix by
osteoclasts
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Attach to endosteum or periosteum
Form leak proof seal (ruffled border)
Release protein digestion lysosomal enzymes (digest
collagen) and acids (dissolve minerals) into pocket
Proteins and minerals: mainly Ca2+ and P are
endocytosed, then exocytosis from other side
Vesicle of proteins and minerals absorbed into blood
Osteoblasts move in
Bone building must = bone reabsorption
Nutrients for bone
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Calcium and phosphorus while growing
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And lesser amt of fluoride, magnesium, iron &
manganese
Vitamin C for collagen synthesis &
differentiation of osteoblastsosteocytes
Vitamin K and B12 for protein synthesis
Vitamin A stimulates osteoblast activity
Sex hormones and bone
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At puberty: estrogens and androgens cause an 
osteoblast activity & matrix synthesis
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Cause growth spurt
___________________ widening of pelvis
Shut down epiphyseal growth plate in both sexes
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Females close earlier because  estrogen levels than men
Those lacking estrogen or its receptor grow taller before closure
During adulthood: sex hormones- slow reabsorption
of old & deposition of new
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Estrogens promote osteoclast apoptosis
BUT, post-menopause, no estrogen, osteoblasts not
stimulated  osteoporosis
Growth hormone and bone
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_____ = insulin like growth factor: most imp in
stimulation bone growth as children
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Produced by bone tissue and liver
Promote cell division at epiphyseal plate & periosteum
Enhance protein synthesis need for new bone
Production stim. by human growth hormone (hGH)
Oversecretion of hGH in childhood= __________
Undersecretion of hGH = _____________
Parathyroid hormone (PTH)
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Most imp hormone in regulation Ca2+ exchange
between ____________________
From parathyroid glands
Secretion via negative feedback
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 PTH cause  osteoclast activity
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If Ca2+ in blood , parathyroid receptors detect &
cause  cAMP, detected  PTH
Ca2+ reabsorbed into blood
PTH works on kidneys to  loss of Ca2+ to urine
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Stimulates calcitrol to  Ca2+ absorbtion from GI tract
Calcitonin (CT)
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Secreted by parafollicular cells of
parathyroid when __________________
Inhibits activity of osteoclasts
 uptake of blood Ca2+ by bone
Accelerates Ca2+ deposition in bone
Promotes bone formation &  blood Ca2+
Harvested from salmon for osteoporosis
Bone fracture types
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Open (compound) = broken ends protrude thru
skin
Closed (simple) = do not break skin
Comminuted “together crumbled” = bone splinters
at site of impact
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fig 6.9
Fragments between 2 larger pieces
Greenstick = partial fracture, one side of bone is
broken & other side bends
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Only in children- not fully ossified
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Impacted = one end of fractured bone
forcibly driven into interior of another
Pott’s = fracture at distal end of fibula with
serious injury at distal tibial articulation
Colle’s = fracture of distal end of radius &
distal fragment displaced posteriorly
Bone fracture repair
fig 6.10
1. Formation of __________________ –
-B.V. crossing the fracture are broken
-Clot forms in 6-8 hrs
-circulation in that areas stopsosteocytes die
swelling and inflammation
-capillaries grow into clot, macrophages &
osteoclasts remove dead & damaged tissue
-may take several weeks
2. _________________ _________ forms –
-new capillaries organize growing CT=
procallus
-fibroblasts & osteogenic cells invade procallus
produce collagen to connect broken ends
osteogenic cells chondroblasts secrete
fibrocartilage
-phagocytes removing debris
-this stage = 3 weeks
3. __________________ formation- in well
vascularized areas closer to healthy bone tissue.
osteogenic cells  osteoblasts produce
trabeculae
Fibrocartilagespongy bone
- this stage = 3-4 months
4. ____________________- dead portions of old
fragments reabsorbed by osteoclasts
-Compact bone replaces spongy
healed area may now be thicker, stronger
Diseases
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____________- condition of porous bones
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Bone reabsorption outpaces bone deposition,
largely due to depletion of calcium in the body
(lost in urine, feces, and sweat rather than
absorbed from the diet).
Bone mass becomes so depleted that bones
often fracture
causes shrinkage of vertebraeheight loss
hunched back and bone pain
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Rickets and Osteomalacia- bones fail to
calcify, organic matrix is produced but
calcium salts are not deposited
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bones soft, rubbery and easily deformed
___________- in children- forming bone;
_______________- in adults- new bone
formed during remodeling fails to calcify.
Pain, tenderness, possible fracture from
minor trauma.
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________________- infection of bone
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Characterized by high fever, sweating, chills,
pain, and nausea
Pus formation, edema, and warmth over
affected bone and overlying muscle
Bacteria reach bone thru
Open fracture
 penetrating wounds
 orthopedic procedures
 Other sites of infection
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Medical terms/disorders
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Kyphosis- “lump” “condition”
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Exaggeration of the thoracic curve of vertebral column
In elderly can be caused by degeneration of
intervertebral discs
Other causes= ricket, poor posture, female advanced
osteoporosis, tuberculosis of the spine
Lordosis – “bent backwards” AKA swayback
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Exaggeration of lumbar curve
Causes:  wgt of abdomen– pregnancy or obesity, poor
posture, rickets, tuberculosis of the spine
Medical terms/disorders

Scoliosis- “crooked,” lateral bending of vertebral
column (usually thoracic)
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Causes: congenitally malformed vertebrae, chronic
sciatica, paralysis of muscles on one side of vertebral
column, poor posture, one leg shorter than other.
Herniated (slipped) disc- ligaments holding
intervertebral disc are injured or weakened
causing the nucleus pulposus (inner portion) to
herniate (protrude).
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Usually in lumbar region- wgt bearing
Slip towards spinal cord or spinal nerves pain
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_________skeleton- bones arranged along axis of the
skeleton
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80 bones
Skull, hyoid, auditory ossicles, vertebral column, thorax
______________ skeleton- bones of upper & lower
limbs, & girdles connecting the limbs to the axial.
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126 bones
Pelvic girdle- connect legs to axial skeleton
Pectoral girdle- connect arms to axial