Skeletal System
Skeletal Anatomy
bones, cartilage and ligaments are tightly joined to
form a strong, flexible framework
each individual bone is a separate organ of the
skeletal system
bone is active tissue:
~270 bones (organs) of the Skeletal System
à5-7% bone mass/week
with age the number decreases as bones fuse
daily Calcium requirement: 1200mg/day
by adulthood the number is 206
Functions of Skeletal System:
(typical)
even this number varies due to varying numbers
of minor bones:
1. Support
strong and relatively light; 20% body weight
2. Movement
sesamoid bones – small rounded bones that form
within tendons in response to stress
framework on which muscles act
act as levers and pivots
eg. kneecap (patella), in knuckles
3. Protection
wormian bones –bones that form within the sutures of
skull
brain, lungs, heart, reproductive system
4. Mineral storage (electrolyte balance
each skeletal organ is composed of many kinds of
tissues:
99% of body’s calcium is in bone tissue
(1200-1400g vs <1.5g in blood, rest in cells)
also stores phosphate
bone (=osseous tissue)
cartilage
fibrous connective tissues
blood (in blood vessels)
nervous tissue
5. Hemopoiesis
blood cell formation
6. Detoxification
bone tissue removes heavy metals and other foreign
materials from blood
can later release these materials more slowly for excretion
but this can also have bad consequences
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General Shapes of Bones
2
= spongy (=cancellous) bone
bones can be categorized according to their general
shape:
1. long:
Biol 2401: Anatomy & Physiology I: Skeletal System; Ziser, Lecture Notes, 2016.3
the general structure of a typical longbone:
cylindrical, longer than wide
articular cartilage
rigid levers for muscle actions eg crowbars
epiphysis
periosteum
eg. arms, legs, fingers, toes
medullary cavity
diaphysis
2. short: length nearly equal width
endosteum
limited motion, gliding if any
epiphysis
eg. carpals, tarsals, patella
3. flat: thin sheets of bone tissue
epiphyses
enclose and protect organs
large surface area for muscle attachment and pivot
broad surfaces for muscle attachments
spongy bone with trabeculae;
contains red marrow (=hemopoietic tissues)
eg. sternum, ribs, most skull bones, scapula, os coxa
4. irregular: elaborate shapes different from above
eg. vertebrae, sphenoid, ethmoid
in adults red marrow is limited to vertebrae, sternum,
ribs, pectoral and pelvic girdles, proximal heads of
humerus and femur
Bone Structure
with age, red marrow is replaced by yellow marrow
bones have outer shell of compact bone
articular cartilage
usually encloses more loosely organized bone tissue
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à produces blood cells in delicate mesh of reticular
tissues
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spongy bone with trabeculae aligned along stress
lines internally
on surface of epiphyses
resilient cushion of hyaline cartilage
Microscopic Structure (Histology)
diaphysis
thick compact bone but light; hollow à medullary cavity
A. bone:
medullary cavity
connective tissue; contains cells and matrix
yellow marrow – fat (adipose) storage
bone cells = osteocytes
“fat at the center of a ham bone”
matrix predominates; ~ 1/3rd organic and
2/3rd’s inorganic
in event of severe anemia, yellow marrow can
transform back into red marrow to make blood cells
periosteum
matrix contains lots of collagen fibers
white fibrous connective tissue continuous with tendons
penetrates bone – welds blood vessels to bone
highly organized arrangement of matrix and
cells
endosteum
fibrous CT that lines medullary cavity
lacunae w osteocyte
& canaliculi
Bone Design and Stress
lamellae
the anatomy of each bone reflects the stresses placed
on it.
haversian canal
perforating canals (Volkmann canals)
interconnect the haversian canals
require the strongest structure with the least mass
periosteum provides life support system for
bone cells
these stresses are countered with:
compact bone covering the surface of the organ
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blood vessels penetrate bone and connect with
those in haversian canals
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eg. covers articular surfaces of joints, costal cartilage
of ribs, rings of tracheae, nose
B. cartilage
resembles bone:
2. fibrous
large amount of matrix
mostly collagen fibers
lots of collagen fibers
eg. discs between vertebrae, pubic symphysis
differs:
3. elastic
firm flexible gel is not calcified (hardened)
also has elastic fibers
no haversian canal system
eg. external ear, eustacean tube
no direct blood supply
à nutrients and O2 by diffusion
all bone starts out as cartilage
in bone the matrix is hardened (= ossified) by
calcification (or mineralization)
microscopic structure of cartilage:
chondrocytes in lacunae
kinds of cartilage:
(all similar matrix with lots of collagen fibers;
differ mainly in other fibers)
1. hyaline
most common
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Anatomy of Skeletal System
consists of facial and cranial bones
most bones are paired, not all
Bone Markings: any bump, hole, ridge, etc on each
bone; eg.:
bones joined at sutures
Foramen: opening in bone – passageway for nerves and blood
vessels
Fontanels
ossification of skull begins in about 3rd month of
fetal development
Fossa: shallow depression – eg a socket into which another bone
articulates
Sinus: internal cavity in a bone
not completed at birthàbones have not yet fused
Condyle: rounded bump that articulates with another bone
gaps = fontanels
Epicondyle: raised area on or above a condyle
frontal (anterior)
occipital (posterior)
2 sphenoid
2 mastoid
Tuberosity: large rough bump – point of attachment for muscle
Tubercle: small rounded projection
at this stage skull is covered by tough membrane for protection
Spine: sharp slender process
normally, bones grow together and fuse to form solid case around
brain
two main subdivisions of skeletal system:
Paranasal Sinuses
axial : skull, vertebral column, rib cage
in 4 of the bones making up the face
appendicular: arms and legs and girdles
in life lined with mucous membrane to form sinuses
The Axial Skeleton
lighten bone, warm and moisten air
A. Skull
6 sinuses:
frontal -2
maxillary -2
ethmoid -1
most complex part of the skeleton
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sphenoid -1
foramen magnum - large opening in base
through which spinal cord passes
Maxilla Bone
occipital condyles - articulation of vertebral column
cheek bones, upper teeth cemented to these bones
Sphenoid Bone –
hard palate: palatine process and palatine bones
irregular, unpaired bone
resembles bat or butterfly; keystone in floor of cranium
cleft palate à when bones of palatine process of
maxilla bones do not fuse properly
greater and lesser wings
not only cosmetic effect
can lead to serious respiratory and feeding problems in
babies and small children
today, fairly easily corrected
anchors many of the bones of cranium
contains sphenoid sinuses
sella turcica – depression for the pituitary gland
Temporal Bone
optic canal – optic nerve from eye pass through
external auditory meatus - opening to ear canal
leads to middle ear chamber
Ethmoid Bone – irregular, unpaired bone
ear ossicles:
honeycomed with sinuses
malleus = hammer
incus
= anvil
stapes = stirrup
cribiform plate – perforated with openings which
allow olfactory nerves to pass
crista galli – attachment of meninges
styloid process
perpendicular plate – divides the nasal cavity
mastoid process
nasal conchae – passageways for air; filtering,
warming, moistening
zygomatic process – joins the zygomatic bone to form the
zygomatic arch
very delicate and easily damaged by sharp upward blow to the
nose
mandibular fossa – receives the condylar process of the
mandible
can drive bone fragments through the cribriform plate
into the meninges or brain itself
Occipital Bone
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in the newborn the spinal column forms a “C”
shaped curve
can also shear off olfactory nervesà loss of smell
Mandible = lower jaw
after ~ age 3 has a double “S” shape with 4 bends
largest, strongest bone of face
cervical
thoracic
lumbar
pelvic
body and ramus
condylar process - articulates with the temporal bone
Hyoid bone –
Herneated (Prolapsed) Disc
Outer layer of disc ruptures usually due to heavy lifting
May put pressure on spinal nerve roots causing pain and numbness
Usuall resolves on its own
May cause continuous pain if small nerves that may invade the tear
single “U” shaped bone in neck just below
mandible
suspended from styloid process of temporal bone
only major bone in body that doesn’t directly articulate with
other bones
vertebral column is divided into 5 regions:
cervical
thoracic
lumbar
sacral
coccygeal
serves as point of attachment for tongue and several other
muscles
B. Vertebral Column
vertebrae of all but last two regions are similar in
structure:
main axis of body: formed by vertebrae separated
by intervertebral discs
body
each disc is a cushion-like pad of fibrous cartilage
spinous process
inner core of gelatinous pulp to absorb shocks
vertebral foramen
interlinked and surrounding vertebrae by ligaments
transverse process
column is flexible rather than rigid
superior and inferior articular process
permits foreward, backward, and some sideways movement
intervertebral foramen between each pair of vertebrae
Cervical
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(7):
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sometimes blocks birth canal, must be broken
have transverse foramena
C. Ribcage
1st and 2nd are highly modified for movement:
manubrium – jugular notch, clavicular notch
body (=gladiolus)
xiphoid process
atlas – holds head up
no body or spinous process
“yes” movement of head
sternum
axis -- dens (odontoid process) – forms pivot
“no” movement
ribs: most joined to sternum by costal cartilages
head, neck, tubercle, facets, shaft
Thoracic (12):
true ribs (7prs)
distinguished by facets smooth areas for articulation of ribs
false ribs (5 prs)
each rib articulates at two places
one on body of vertebrae
one on transverse process
Lumbar
include floating ribs (2prs)
(5):
short and thick spinous processes
modified for attachment of powerful back muscles
Sacrum (5 fused):
triangular bone formed from fused vertebrae
sacroiliac joint – lots of stress
Coccyx
(4-5, some fused):
tailbone
painful if broken
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Appendicular Skeleton
often broken when outstretched arms are used to
break a fall or while wearing a seatbelt in an auto
accident
Upper Extremeties
sternal end
shoulder (=pectoral girdle)
upper and lower arm
wrist and hand
acromial end
B. Upper Arm:
Humerus: longest and largest bone of arm
A. Pectoral Girdle:
loosely articulates with scapula by head – glenoid cavity
scapula & clavicle
large processes of scapula, (acromium and coracoid)
only attached to trunk by 1 joint (between sternum and
clavicle)
scapula is very moveable – acts as almost a 4
of limb
th
àhave muscles which help to hold in place
segment
scapula rides freely and is attached by muscles and
tendons to ribs but not by bone to bone joint
greater & lesser tubercles – attachment of rotator cuff
muscles
deltoid tuberosity – attachment of deltoid muscle
trochlea – articulates with the ulna
extensive flat areas of scapula are used as origins for
arm muscles and trunk muscles
capitulum – articulates with the radius
superior, medial & lateral borders
medial & lateral epicondyles -
spine
olecranon fossa – articulates with olecranon process of
ulna
acromion process – articulates with clavicle
C. Forearm:
coracoid process – attachment point for biceps
very mobile; adds to flexibility of hand
glenoid cavity – articulates with humerus
clavicle is the most frequently broken bone in the body,
sometimes even during birth
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consists of two bones: radius & ulna
they are attached along their length by interosseous
membrane =sheet of fibrous connective tissue
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ulna:
main forearm bone
trochlear notch - firmly joined to humerous at elbow
[right hand-ventral surface]
olecranon process - extends behind elbow joint
proximal:
acts as lever for muscles that extends forearm
distal:
radial notch – receives head of radius
thumb
head
scaphoid, lunate, triquetrum, pisiform
trapezium, trapezoid, capitate, hamate
lateral
medial
(“sally left the party
to take carmen home”)
styloid process
radius:
metacarpals also rounded for flexibility
more moveable of two
can revolve around ulna to twist lower arm and hand
head – shaft – base
phalanges, not rounded, simple hinges for grasping
head
sesamoid bones
neck
ulnar notch
styloid process
D. Hand:
attached by muscles mainly to radius provides great flexibility
large # of rounded bones (carpals) provide flexibility
carpals allow movement in all directions
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Lower Extremeties
number and arrangement of bones in the lower limb
are similar to those of the upper limb
in the lower limb they are adapted for weight
bearing and locomotion, not dexterity
pelvis is easiest part of skeleton to distinguish between
sexes
pelvis consists of a pair of coxae (=innominate bones) that
articulate with sacrum
pelvic girdle (pelvis, 2 coxal bones, sacrum, coccyx)
thigh
lower leg
feet
sacroiliac joint – strong solid connection between sacrum
and pelvis, very little movement possible
obturator foramen – only a few nerves and blood vessels
pass through, mostly covered over by fibrous membrane
acetabulum – deep socket that articulates with head of
femur
A. Pelvic Girdle
each coxa is produced by fusion of three bones:
as bipedal animals the pelvis must support most of the body
weight forms large basin of bone
ilium – upper, fan shaped
pelvis is funnel shaped; yet must remain large enough
for the birth canal
iliac crest
à origin of thigh muscles and trunk muscles
superior & inferior liliac spines (ant. & post.)
àrigid connection to axial skeleton; strength, not flexibility
greater sciatic notch
àreceptacle for many internal organs
ischium – bottom
viscera bear down on pelvic floor
ischial spine
pelvic brim – a ridge of bone that separates the false pelvis
above from the true pelvis below:
ischial tuberosity
pubis – front
false pelvis - larger flaring upper portion is part of the
abdomen and contains abdominal organs
true pelvis - smaller area inferior to pelvic brim forms a deep
bowl that contains the pelvic organs
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pubic arch
pubic symphysis: anterior joint of fibrous cartilage
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acts as kind of a bearing
àallows tendon to slide smoothly across knee joint
in women before birth it softens to allow expansion
of birth canal
if patella is lost through accident or injury get
~30% loss of mobility and strength due to > friction
B. Upper Leg (= Thigh)
made up of single bone =
body
the pelvic brim delineates the pelvic inlet à in women, the
actual space a child must fit through during childbirth
C. Lower Leg
femur; largest, longest bone in
consists of two bones: tibia and fibula
head fits in large deep socket = acetabulum of pelvis
connected by an interosseous membrane along their
length
great strength, less flexibility than humerous
tibia (=shinbone)
neck – angles laterally from head
weakest part of the femur, most easily broken (=broken
hip)
main bone, articulates with both femur and foot
àmore strength, less mobility
greater & lesser trochanters – muscle attachments
medial & lateral condyles – articulate with condyles of
femur
medial & lateral condyles – articulate with tibia
patellar surface – smooth area between condyles,
articulates with the patella
tibial tuberosity – attachment of patellar ligament
medial malleolus – forms medial bulge of ankle
intercondylar fossa – posterior to patellar surface,
between condyles
fibula
medial & lateral epicondyles – raised areas on sides of
condyles
small, offers extra support for lower leg and foot but does
not actually bear weight
kneecap = patella
head
a sesamoid bone = bones found where tension or pressure
exists; eg thumb and large toe
D. Foot
in tendons at knee joint; does not articulate directly with
any other bone
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lateral malleolus
like hand, made of many bones
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Tarsals
produced by the interlocking shapes of the foot bones
attached by strong ligaments and pulled by strong
muscle tendons while walking or running
the weight of the body is carried mainly by the two largest,
most posterior ankle bones
calcaneus – forms heel of foot, Achilles tendon articulates
here
talus – articulates with tibia and fibula
arches also furnish more supporting strength than any
other type of construction àmore stability
if ligaments and muscles weaken, arches are lost
= flatfootedness = fallen arches
à more difficult walking, foot pain, back pain
high heals redistribute the weight of footàthrow it
foreward; ends of metatarsals bear most weight
àsore feet
distal
cuboid
lateral intermediate medial
cuneiform cuneiform cuneiform
navicular
talus
calcaneous
proximal
lateral
medial
Metatarsals
Phalanges
thick angular bones; must support all the weight of the body
arches: strung with ligaments to provide double arches
= shock absorbers
the foot has 3 arches
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Articulations (joints)
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entire joint is connected by a joint capsule that
is continuous with the periosteum of each
bone
Articulations = joints between bones
often supported by ligaments
hold bones together while usually allowing some
movement
ligaments – bind bones together across joints
can be categorized into three general kinds by the
degree of movement & the structure of the joint
A. Immoveable Joints
= Synarthroses (=”joined together”, joint)
bones are joined by fibrous connective tissue
more elastic than tendons
hold joints in place
limit their range of motion
sometimes includes fluid filled bursae
bursae = synovial sacs spaced around joints
between tendons or ligaments
B. Slightly Moveable Joints
=Amphiarthroses (=on both sides, joint)
to cusion, reduce tension & friction
bones are joined by some kind of cartilage
Examples of the 3 kinds of articulations
eg. fibrous or hyaline
C. Freely Moveable Joints
= Diarthroses (through a joining)
diarthroses predominate in the limbs; synarthroses
and amphiarthroses are largely restricted to the
axial skeleton
most complex joint structure
articulation is enclosed by synovial membrane
ends of each bone are padded with articular
cartilage
Immoveable (Fibrous) Joints
eg. sutures
– only in skull
eg. gomphoses
joint cavity is filled with synovial fluid
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-teeth in socket
- provide for many different kinds of motion
eg. syndesmoses
- the shape of the articular surfaces determine the movements
allowed at a synovial joint:
- fibrous bands (ligaments) between two bones
* some syndesmoses may allow slight movement
nonaxial = adjoining bones do not move around a specific
axis
- distal tibiofibular joint
uniaxial = movement occurs around a single axis
Slightly Moveable (Cartilaginous)
biaxial = movement can occur around two axes; both front
and sagittal planes
eg. symphyses
multiaxial = movement can occur around all three axes;
frontal, sagittal and transverse planes
-fibrocartilage pad or disc
eg. plane joint (nonaxial)
-midline of body
- femur and patella at knee
-symphysis pubis
eg. pivot joint (uniaxial)
-intervertebral discs
- atlas & axis
eg. synchondroses
- radius at hand
-hyaline cartilage joins two bones
eg. hinge joint (uniaxial)
-provides strength with some flexibility
-fingers, toes, elbow
-a few may be immoveable; eg epiphyseal discs; temporary
eg. condylar joint (biaxial)
-costal cartilage between ribs and sternum
- metacarpals to phalanges
Freely Moveable (Synovial)
eg. saddle joint (biaxial)
- most body articulations
- carpometacarpal joint of thumb
- bones separated by a joint cavity, covered with articular
cartilage and enclosed within an articular capsule lined with
synovial membrane.
eg. ball and socket joints (multiaxial)
-shoulder, hip
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Selected Synovial Joints
Temporomandibular Joint
cruciate ligaments act as restraining straps to prevent over
extension or over flexion at the knee
jaw joint is a modified hinge joint
in addition to hinge-like motion can also allow side to side motion of
the jaw
because of its shallow socket the TMJ is one of the most easily
dislocated joints in the body
two menisci of fibrocartilage help absorb shock
the tendons of many muscles reinforce the joint capsule
the patella, embedded in the patellar ligament
even a deep yawn can dislocate it
Exercise and Synovial Joints
poor occlusion of teeth or teeth grinding can cause pain in ear and
face and stiffness of joint
synovial fluid is warmed by exercise and becomes thinner
àthis is more easily absorbed by articular cartilage
Shoulder Joint
àprovides more effective cushion against compression
stability has been sacrificed for dexterity; shallow glenoid cavity
this warmup and compression also helps to distribute nutrients
to cartilage cells (nonvascular tissue) and squeeze out
metabolic wastes
the head of the humerus is held in place by tendons of 4 muscles
which form the “rotator cuff” that encircles the shoulder joint.
[subscapularis, supraspinatus, infraspinatus, teres minor]
à warm up is good for you
a vigorous movement of the arm can stretch or tear the rotator
cuff
eg baseball pitchers
Knee Joint
the knee is the largest and most complex joint of the body
mainly a hinge joint
but it also permits slight medial and lateral rotation during leg
extension
collateral ligaments join the bones of the upper and lower legs
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Skeletal Physiology
1/3rd collagen and proteins (cartilage and
bone)
Composition of Bone
mixture of organic and inorganic components
allow bone to be strong without being brittle
bone is the densest tissue in the body
à only 20% water
Physiology of Bone
bone has a grain just like wood:
bone is active tissue:
grain runs longitudinally for greatest strength
as bone is remodeled old bone is eroded to accommodate new
bone but grain is preserved
à5-7% bone mass/week
mature haversian canal systems are replaced up to 10x’s
during a lifetime
bone tissue consists of cells and matrix:
àequiv. of skeletal mass is replaced every 7 years
cells: =osteocytes
most calcium in body is contained in teeth and
skeleton
cells that secrete the matrix
2 kinds: osteoblasts = bone building cells
osteoclasts = bone destroying cells
à acts as a mineral reservoir, esp for calcium,
and phosphate
calcium is used in body for:
matrix:
muscle contractions
nerve impulses
synapses
heart beat
secretions
blood clotting
cofactors for enzymes
2/3rd mineral salts (bone only)
calcium & phosphorus
(CaPO4, CaOH, CaCO3)
also Mg, Na, K
tends to accumulate metals:lead & radium
à bone cancer, leukemia
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a supply of calcium must be constantly available for all
these activities
blood calcium homeostasis is maintained by
dissolving or depositing bone tissue via
osteocytes
Ossification = conversion of cartilage or other
connective tissue into bone by depositing
calcium and other minerals
a. intramembraneous
(eg skull bones)
two kinds of bone cells:
- bone appears between two layers of sheetlike
connective tissue
bone forming cells
-CT rich in blood supply
also works alongside osteoclasts to rework bone
osteoclasts
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bone is formed in two ways:
cells = osteocytes ( in lacunae)
osteoblasts
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bone destroying cells
-some cells become osteoblasts
-form spongy bone
very large cells produced by cell fusions
contain up to 300 nuclei
b. endochondral
amoeboid movement
(eg longbones)
wraps around small section of bone then secretes
enzyme to digest it
-as masses of cells in centers of ossification
– increase in length
Fetal Bone Formation
-bone formed from hyaline cartilage
parts of skeleton begin to form in 1st few weeks of
development
in longbones ossification begins 3rd month of
development
begins in fetus as cartilage template
centers of ossification in longbones first appear
in the diaphysis
once the cartilage is laid down, it begins to turn into
bone by ossification
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at birth additional centers in epiphyses
effects of length are primarily in long bones of arms
and legs
the process of ossification gradually replaces
cartilage with bone
growth hormone plays a major role in fetal and
childhood bone development
centers of ossification appear à clusters of osteoblasts
à stimulates cartilage cells between zones of
ossification
golgi apparatus in osteoblasts synthesizes and secretes
mucopolysaccharides (cements)
as long as the cartilage is growing faster than the
process of ossification, the bones will continue to
lengthen
endoplasmic reticulum secretes collagen
mucopolysaccharides accumulate around each osteoblast
collagen fibers become embedded in this matrix
when epiphyseal cartilage disappears the bone
has completed its growth (in length)
as matrix is formed inorganic calcium salts are deposited
= calcification
deficiency of GH: dwarfism
bones grow in diameter by combined action of
osteoblasts and osteoclasts
excess of GH: gigantism, acromegaly -hands, feet,
jaw enlarge
osteoclasts enlarge diameter of medullary cavity
osteoblasts from pereosteum enlarge bone by building new
bone around outside
tension regions + chg
thyroid hormone helps bones to develop the proper
proportions during this time
head becomes proportionately smaller
affects PTH activity
compresed regions – chg
facial bones more prominent
Skeleton in Infancy & Childhood
thorax more elliptical
early development mainly involves an increase in size
and length
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cervical curve ~3mo; lifts head
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Adulthood: Bone Maintenance and Remodeling
lumber ~1 yr; standing, walking
by early adulthood the skeleton has reached its
maximum height
Puberty
at puberty the sex hormones (estrogen &
testosterone) begin to affect the process of
ossification
the skeletal system is strongest in early adulthood
bones continue to grow and remodel themselves
throughout life
stimulate epiphyseal closure
even after bone growth has stopped, osteoblasts and
osteoclasts continue working
generally stimulate osteoblast activity and bone
deposition
in adult these opposing processes balance each
other out so bone neither grows nor shrinks
generally decrease osteoclast activity
leads to masculinizing and feminizing features of
skeleton
bone destruction is not always a pathological
process:
facial features develop especially rapidly
a. bones constantly adapting to stresses
reaction to mechanical stresses
also:
strengthens weak areas
deep and funnel shaped pelvis;
b. old bone removed to reduce bulk
whole skeleton larger and heavier
female
legs proportionately longer
estrogen and testosterone continue to help maintain
skeletal health throughout adulthood
vertebral column develops two additional curves
(already had thoracic and pelvic curves)
male
pelvis larger and wide
shallow, broader and flaring pelvis
c. minerals are added or removed from reservoir
as Calcium is metabolized to maintain
constant blood levels of calcium
limbs grow more slowly
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Biol 2401: Anatomy & Physiology I: Skeletal System; Ziser, Lecture Notes, 2016.3
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Other Factors that affect Bone Homeostasis:
muscle contractions
nerve impulses
synapses
heart beat
secretions
blood clotting
cofactors for enzymes
vitamin D
needed for absorption of calcium by small intestine
Vitamin D is synthesized by from the precursor (7dehydrocholesterol) circulating in the blood when exposed to
UV light.
two hormones involved in bone maintenance and
blood calcium homeostasis
The resulting Vitamin D is not yet active. It is modified in the
liver and then in the kidney to become the active hormonal
form of Vitamin D.
Calcitonin àstimulates bone formation
(osteoblasts)
deficiency:
à lowers blood Calcium levels
PTH
àstimulates bone destruction
(osteoclasts)
poor calcification
deformed bones
rickets – poor mineralization of bone
osteomalachia – softening of bones
found in eggs and milk
also formed from precursors produced by cells of digestive tract
carried in blood to skin
à raises blood calcium levels
UV converts precursor to Vit D.
Ca++ deficiency:
vitamin A
severe neuromuscular problems
hyperexcitability
loss of function
needed for bone reabsorption
vitamin C
Ca++ excess:
needed for synthesis of collagen (collagen = ~1/3rd bone mass)
Calcium deposits in blood vessels,
kidneys and soft organs
deficiency: slender fragile bones
Gravity & Stress
bone remodels based on stress placed upon it
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deformed bones produces electrical current
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affects entire skeleton but esp spongy bone of vertebrae and
neck of femur
àseems to inhibit PTH activity at site
most serious consequence is pathologic fractures
esp in hip, wrist and vertebral column
The Skeleton in Old Age
also, as bones become less dense they compress like
marshmallows
à results in kyphosis à exaggerated thoracic curve
(widow’s hump, dowager’s hump)
reabsorption outweighs growth
à bone become brittle
suggestions:
need good bone mass by 35 or 40
plenty of weight bearing exercise, esp before menopause
good calcium uptake (850-1000 mg/d) early in life, esp 25-40
fluoridated water helps harden bones
don’t smoke
hormone replacement therapy only slows loss, doesn’t replace
lost bone
-No longer recommended, too dangerous
shaggy margins, spurs, joint problems
cartilage keeps growing: big ears
too much bone loss may lead to Osteoporosis
= a group of diseases in which bone reabsorption
outpaces bone deposition
Disorders of Skeletal System
especially in post menopausal women (esp caucasian women)
1. Fractures
sex hormones stim bone deposition, and decrease osteoclast
activity
repairs more slowly than skin; up to 6 months
a. clot (hematoma) formation
menopause causes sharp reduction in estrogen
smoking also reduces estrogen levels
hours
broken blood vessels, damaged tissues, bone cells die
by 70 yrs the average white woman has lost 30% of her bone
mass (some up to 50%)
b. soft callus (fibrocartilage)
not as drastic in men
à bone loss begins ~60 yrs and seldom exceeds 25% loss
days
growth of new capillaries
disposal of dead tissue
bones lose mass and become more brittle
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c. bony callus
outpaces bone deposition
affects entire skeleton but esp
spongy bone of vertebrae and neck of femur
weeks
spongy bone tissue grows around area and replaces
fibrocartilage
join two pieces firmly together
esp in post menopausal women
sex hormones
stim bone deposition,
decrease osteoclast activity
d. remodeling
months
dead portions of original area reabsorbed
compact bone replaces spongy bone
ends are remodeled to blend in
usually thickened area remains
misset bones may heal crooked
but weight bearing bones usually reassume proper shape
elec current speeds calcification and repair
menopause – sharp reduction in sex hormones
esp post menopausal women (esp caucasian women)
by 70 yrs the average white woman has lost 30% of her bone
mass (some up to 50%)
not as drastic in men
bone loss begins ~60 yrs and seldom exceeds 25% loss
new synthetic materials may soon be useful in replacing missing
bone
also bone grafts
smoking also reduces estrogen levels
low body fat reduces estrogen production by ovaries in young
female runners and dancers
2. Vertebral curvature
normally spine has two “S” shaped curves
most serious consequence is pathologic fractures
esp in hip, wrist and vertebral column
provides flexibility and resilient support
also, as bones become less dense they compress like
marshmallows
several types including:
scoliosis – abnormal lateral curvature
may appear spontaneously
or be result of polio, rickets or TB
à results in kyphosis à exaggerated thoracic curve
(widow’s hump, dowager’s hump)
suggestions:
need good bone mass by 35 or 40
plenty of weight bearing exercise, esp before menopause
good calcium uptake (850-1000 mg/d) early in life, esp 25-40
fluoridated water helps harden bones
don’t smoke
3. Osteoporosis
bones lose mass and become more brittle
group of diseases in which bone reabsorption
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hormone replacement therapy only slows loss, doesn’t replace
lost bone
-No longer recommended, too dangerous
4. Rickets
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7. Osteomyelitis
any infection of bone, cartilage or periosteum
localized or general
usually bacterial
8. Ruptured (herneated) disc
childhood disease: bowed legs, deformed pelvis,
due to Vit D (or Ca++) deficiency during growing years
body unable to absorb calcium from intestine
reduces calcification – bones stay soft
intervertebral discs pad vertebrae
with age outer layer thins and cracks; inner layers less firm
extra pressure can cause rupture
= herneated disc: pain, numbness, partial paralysis
5. Osteoarthritis
most common age change is degeneration of joints
=wear and tear arthritis
rarely occurs before age 40; affects 85% of those over 70
as joints age get gradual softening and loss of articular cartilage
bone formation at margin of articular cartilage
as cartilage becomes roughened by wear, joint movements may
be accompanied by crunching or cracking sounds (=crepitus)
affects especially fingers, intervertebral joints, hips and knees
bony spurs may form as cartilage wears away àdeform joint
interfere with movement, pain
6. Rheumatoid Disease
far more severe than OA
is an autoimmune attack against synovial membrane
inflammation of synovial membranes and degeneration of
cartilage
synovial membranes fill with abnormal tissue growth =
granulation tissue
may erode articular cartilage, bones and ligaments
mainly small joints of body; wrists, ankles
tends to flare up and subside periodically
affects women far more than men
typically begins between age 30 – 40
no cure, but can be slowed with steroids, cortisone, etc
Biol 2401: Anatomy & Physiology I: Skeletal System; Ziser, Lecture Notes, 2016.3
Biol 2401: Anatomy & Physiology I: Skeletal System; Ziser, Lecture Notes, 2016.3
9. Gout
group of diseases characterized by elevated uric acid in blood
forms sodium urate crystals in synovial fluid causing severe pain
exacerbated by alcoholism
10. Bursitis
inflammation of bursal sacs around joints
fills with fluid
usually caused by blow or friction
=“housemaids knee”
=“water on the knee”
11. Tendonitis
inflammation, usually due to overuse
12. Achondroplastic Dwarfism
spontaneous mutation of genes, not necessarily from parents
long bones of limbs stop growing in childhood while growth of
other bones is not affected
à results in short stature but normal sized head and trunk
not same as pituitary dwarfism, only certain cartilage cells are
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affected
13. Polydactyly & Syndactyly
too many or too few fingers and toes
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