Skeletal System
Functions
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Support
Protection
Movement
Storage of minerals
Production of blood
Storage of Yellow Bone Marrow
Divisions of the Skeleton
• There are 206 named
bones in the human body.
• Each bone belongs to 1 of
2 large groups:
– Appendicular
• 126 bones
– Axial
• 80 bones
Types of Bones
• 5 basic types of bones:
– long = compact bone
– short = spongy bone
except surface
– flat = plates of compact
enclosing spongy
– irregular = variable
– sesamoid = develop in
tendons or ligaments
(patella)
• Sutural bones = in joint
between skull bones
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Types of Bones – classified by shape
Parts of a Long
Bone
• Diaphysis = main part of bone
• Epiphysis = one end of a long
bone
• Metaphysis = growth plate
region, mature bone
• Articular Cartilage = over joint
surfaces, acts as friction &
shock absorber
• Medullary cavity = marrow
cavity
• Endosteum = lining of marrow
cavity
• Periosteum = tough
membrane covering the bone
but not the cartilage
Axial Skeleton
• skull, hyoid,
vertebrae, ribs,
sternum, ear
ossicles
• 80 bones
Vertebral Column
• Backbone or spine built
of 26 vertebrae
• Five vertebral regions
– cervical vertebrae (7)
in the neck
– thoracic vertebrae ( 12 )
in the thorax
– lumbar vertebrae ( 5 ) in
the low back region
– sacrum (5, fused)
– coccyx (4, fused)
Atlas & Axis (C1-C2)
• Atlas - nodding movement that signifies “yes”, supports the
skull
• Axis - pivotal movement that signifies “no”
Typical Cervical Vertebrae (C3-C7)
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Smaller bodies
Neck region
Larger spinal canal
1st and 2nd
cervical vertebrae
are unique
– atlas & axis
Thoracic Vertebrae
(T1-T12)
• Larger and stronger
bodies
• Longer
• Facets or demifacets on
body for head of rib
Lumbar Vertebrae (L1-L5)
• Strongest & largest
• Short thick spinous
& transverse
processes
– back musculature
Sacrum
• Union of 5 vertebrae (S1 - S5) by age 30
Coccyx
• Union of 4 vertebrae (Co1 - Co4) by age 30
Intervertebral Discs
• Cushion like pad b/w vertebrae that absorbs shock
• Permit various movements and support of the
vertebral column
• Fibrocartilagenous ring with a pulpy center
Herniated (Slipped) Disc
• Protrusion of the
nucleus pulposus
• Most common in
lumbar region
• Pressure on spinal
nerves causes
pain
• Surgery
Normal Curves of the Vertebral Column
• Primary curves
– thoracic and sacral are formed during fetal development
• Secondary curves
– cervical formed when infant raises head at 4 months
– lumbar forms when infant sits up & begins to walk at 1 year
Abnormal Curvature
Scoliosis - abnormal curvature
Kyphosis - hunch back assoc. with old age
Lardosis - sway back, pregnant walk
Spina Bifida – congenital defect – failure of the vertebral
laminae to unite, leaves nerve tissue unprotected, often
leads to paralysis
Thorax
– Protects vital organs
(heart, lungs, blood
vessels)
– Sternum
(breastbone)
– Ribs
• 1-7 are true ribs
(attached to sternum)
• 8-12 are false ribs
(vertebrochondral)
• 11-12 are floating
– Costal cartilages
– Bodies of the
thoracic vertebrae.
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Sternum
• Manubrium– 1st & 2nd ribs
• Body
– Midportion of ribs,
bulk of sternum
• Xiphoid
– Cartilages in youth
– ossifies by 40
– CPR position
Ribs
Fracture at site of
greatest curvature.
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Increase in length from ribs 1-7, thereafter decreasing
Head and tubercle articulate with facets
Body with costal groove containing nerve & blood vessels
Intercostal spaces contain intercostal muscles
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The Skull
• 8 Cranial bones
– protect brain & house ear ossicles
– muscle attachment for jaw, neck & facial muscles
• 14 Facial bones
– protect delicate sense organs -- smell, taste, vision
– support entrances to digestive and respiratory systems
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The 8 Cranial Bones
Frontal
Parietal (2)
Temporal (2)
Occipital
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Sphenoid
Ethmoid
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14 Facial Bones
Nasal (2)
Mandible (1)
Inferior nasal conchae (2)
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Maxillae (2)
Lacrimal (2)
Zygomatic (2)
Palatine (2)
Vomer (1)
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Maxillary bones
• Floor of orbit, floor of nasal cavity or hard palate
• Alveolar processes hold upper teeth
• Cleft palate is lack of union of maxillary bones
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Zygomatic Bones
• Cheek bones
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Mandible
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Sutures
• Lambdoid suture unites parietal and occipital
• Sagittal suture unites 2 parietal bones
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Fontanels of the Skull at Birth
• Dense connective tissue membrane-filled spaces
(soft spots)
• Unossified at birth but close early in a child's life.
• Fetal skull passes
through the birth
canal.
• Rapid growth of the
brain during infancy
• Eventually turn into
sutures
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Hyoid Bone
– U-shaped single bone
– Articulates with no other bone of the body
– Suspended by ligament and muscle from skull
– Supports the tongue & provides attachment for
tongue, neck and pharyngeal muscles
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Appendicular
Skeleton
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Pectoral girdle
Pelvic girdle
Upper limbs
Lower limbs
Pectoral (Shoulder) Girdle
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Scapula and Clavicle
Clavicle articulates with sternum
Clavicle articulates with scapula
Scapula held in place by muscle only
Upper limb attached to pectoral girdle at shoulder
Clavicle (collarbone)
• S-shaped bone with two curves
• Extends from sternum to scapula above 1st rib.
Posterior Scapula
Anterior Scapula
• Triangular flat bone
Upper Limbs
• Each upper limb = 30 bones
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humerus within the arm
ulna & radius within the forearm
carpal bones within the wrist
metacarpal bones within the palm
phalanges in the fingers
Humerus—Proximal End
• Part of shoulder
Humerus --- Distal End
• Forms elbow joint with ulna
and radius
Ulna & Radius
• Ulna (on little finger side)
• Radius (on thumb side)
8 Carpal Bones (wrist)
• Proximal row - lat to med
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scaphoid - boat shaped
lunate - moon shaped
triquetrum - 3 corners
pisiform - pea shaped
• Distal row - lateral to
medial
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trapezium - four sided
trapezoid - four sided
capitate - large head
hamate - hooked process
Metacarpals and Phalanges
• Metacarpals
– 5 total
– knuckles
• Phalanges
– 14 total
– 3 on fingers except thumb
Pelvic Girdle and Hip Bones
• Pelvic girdle = two hipbones united at pubic
symphysis
• Each hip bone = ilium, pubis, and ischium
– fuse after birth
• Bony pelvis = 2 hip bones, sacrum and coccyx
Ischium and Pubis
• Ischium
– ischial spine & tuberosity
– lesser sciatic notch
– ramus
• Pubis
– body
– superior & inferior ramus
– pubic symphysis is pad of
fibrocartilage between 2
pubic bones
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Ilium
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Iliac crest and iliac spines for muscle attachment
Iliac fossa for muscle attachment
Gluteal lines indicating muscle attachment
Sacroiliac joint at auricular surface & iliac
tuberosity
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•Tortora
Greater
notch for sciatic nerve
Pelvis
• Pelvis = sacrum,
coccyx & 2 hip
bones
• Pelvic axis = path of
babies head
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Female and Male Skeletons
• Male skeleton
– larger and heavier
– larger articular surfaces
– larger muscle
attachments
• Female pelvis
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wider & shallower
larger pelvic inlet & outlet
more space in true pelvis
pubic arch >90 degrees
Female
Male
Lower Extremity
• Each lower limb = 30 bones
– femur and patella within the
thigh
– tibia & fibula within the leg
– tarsal bones in the foot
– metatarsals within the
forefoot
– phalanges in the toes
Femur and Patella
• Femur (thighbone)
– longest & strongest bone in body
• Patella (knee cap)
– triangular sesamoid
Tibia and Fibula
• Tibia
– medial & larger bone of leg
– Weight bearing
• Fibula
– not part of knee
Tarsus
• Region of foot (contains 7 tarsal bones)
• Talus = ankle bone (articulates with tibia &
fibula)
• Calcaneus - heel bone
• Cuboid, navicular & cuneiforms
Metatarsus and Phalanges
• Metatarsus = 5 metarsals
– midregion of the foot
• Phalanges
– distal portion of the foot
– similar in number and
arrangement to the hand
– big toe is hallux
Arches of the Foot
• Function
– distribute body weight over foot
– yield & spring back when weight is lifted
• Longitudinal arches along each side of foot
• Transverse arch across midfoot region
– navicular, cuneiforms & bases of metatarsals
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Clinical Problems
• Flatfoot
– weakened ligaments allow bones of medial arch to drop
• Clawfoot
– medial arch is too elevated
• Hip Fracture
– ½ million/yr in US
– Arthroplasty to fix
Bone Formation or Ossification
• Intramembranous bone formation = formation of
bone directly from mesenchymal cells
– Forms most flat bones, bones in skull
– Growth of short bones and the thickening of long bones
– Closes the fontanels
• Endochondral ossification = formation of bone
within hyaline cartilage
– Forms most bones within the body
Endochondral Bone Formation
• Development of Cartilage
model
– Mesenchymal cells form a
cartilage model of the bone during
development
• Growth of Cartilage model
– in length by cell division and
matrix formation ( interstitial
growth)
– in width by formation of new matrix
(appositional growth)
– cells in midregion burst and
change pH triggering calcification
Developmental Anatomy
5th Week =limb bud
appears
6th Week = constriction
produces hand or foot
plate and skeleton now
totally cartilaginous
7th Week = endochondral
ossification begins
8th Week = upper & lower
limbs appropriately
named
Osteogenesis - 10 week fetus
Osteogenesis - 16 week fetus
Bone Growth in Length
• Epiphyseal plate or cartilage growth
plate
– cartilage cells are produced by
mitosis
– cartilage cells are destroyed and
replaced by bone
• Between ages 18 to 25, epiphyseal
plates close
– cartilage cells stop dividing and bone
replaces the cartilage (epiphyseal
line)
• Growth in length stops at age 25
Aging & Bone Tissue
• Bone is being built through adolescence,
holds its own in young adults, but is
gradually lost in aged.
• Demineralization = loss of minerals
– very rapid in women 40-45 as estrogens levels
decrease
– in males, begins after age 60
• Decrease in protein synthesis
– decrease in growth hormone
– decrease in collagen production which gives
bone its tensile strength
– bone becomes brittle & susceptible to fracture
Factors Affecting Bone Growth
• Nutrition
– adequate levels of minerals and vitamins
• calcium and phosphorus for bone growth
• vitamin C for collagen formation
• vitamins K and B12 for protein synthesis
• Sufficient levels of specific hormones
• promotes cell division at epiphyseal plate
• need hGH (growth), thyroid (T3 &T4) and insulin
– at puberty
• growth spurt and closure of the epiphyseal growth
plate
• estrogens promote female changes -- wider pelvis
Bone Remodeling
• Ongoing since osteoclasts carve out small
tunnels and osteoblasts rebuild osteons.
– osteoclasts form leak-proof seal around cell
edges
– release calcium and phosphorus into interstitial
fluid
– osteoblasts take over bone rebuilding
– distal femur is fully remodeled every 4 months
Bone Remodeling
Calcium Homeostasis & Bone Tissue
• Skeleton is reservoir of Calcium & Phosphate
• Calcium ions involved with many body
systems
– nerve & muscle cell function
– blood clotting
– enzyme function in many biochemical reactions
• Small changes in blood levels of Ca+2 can be
deadly
– cardiac arrest if too high
– respiratory arrest if too low
Hormonal Influences
• Parathyroid hormone (PTH)
is secreted if Ca+2 levels fall
– PTH triggers Osteoclasts (bone
cells) to break down the bone
and put calcium back into the
blood stream
• Calcitonin hormone is
secreted from cells in thyroid
if Ca+2 blood levels get too
high
– inhibits osteoclast activity
– increases bone formation by
osteoblasts
Exercise & Bone Tissue
• Pull on bone by skeletal muscle and gravity is
mechanical stress .
• Stress increases deposition of mineral salts &
production of collagen (calcitonin prevents bone
loss)
• Lack of mechanical stress results in bone loss
– reduced activity while in a cast
– astronauts in weightlessness
– bedridden person
• Weight-bearing exercises build bone mass
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Fracture & Repair of Bone
• Fracture is break in a bone
• Healing is faster in bone than in
cartilage due to lack of blood
vessels in cartilage
• Healing of bone is still slow
process due to vessel damage
• Clinical treatment
– closed reduction = restore pieces to
normal position by manipulation cast
– open reduction = surgery
Disorders of Bone
Ossification
• Rickets
• calcium salts are not deposited properly
• bones of growing children are soft
• bowed legs, skull, rib cage, and pelvic deformities
result
• Osteomalacia
• new adult bone produced during remodeling fails
to ossify
• hip fractures are common
Osteoporosis
• Decreased bone mass resulting in porous bones
• Those at risk
– thin menopausal, smoking, drinking female with family
history
– athletes who are not menstruating due to decreased body fat
& decreased estrogen levels
– people allergic to milk or with eating disorders whose intake
of calcium is too low
• Prevention or decrease in severity
-- adequate diet, weight-bearing exercise, & estrogen
replacement therapy (for menopausal women)
Osteoporosis
Clinical Conditions
• Osteomyelitis
– Osteo=bone +
myelo=marrow +
itis=inflammation.
– Inflammation of bone
and bone marrow
caused by pus-forming
bacteria that enter the
body via a wound (e.g.,
compound fracture) or
migrate from a nearby
infection.
– Fatal before the advent
of antibiotics.
Clinical Conditions
• Gigantism
– Childhood hypersecretion of
growth hormone by the
pituitary gland causes
excessive growth.
• Acromegaly
– Adulthood hypersecretion of
GH causes overgrowth of
bony areas still responsive
to GH such as the bones of
the face, feet, and hands.
• Pituitary dwarfism
– GH deficiency in children
resulting in extremely short
long bones and maximum
stature of 4 feet.