Download Human Anatomy & Physiology I

Chapter 6
The Skeletal System
Copyright 2010, John Wiley & Sons, Inc.
Bone Function


Support
Protection
- Skull, rib cage

Assist in movements
- together with muscles &
tendons

Mineral homeostasis
- calcium, magnesium,
phosphate

Blood cell production

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Hemopoiesis in red bone marrow
Triglyceride (fat) storage
- in yellow bone marrow
2 Million year old
hand skeleton of
possible early human
ancestral hominid
Types of Bones

Long bones: longer than wide
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Short bones: almost cube shaped

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Most wrist and ankle bones
Flat bones: thin and extensive surface
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Such as thigh, leg, arm, forearm, fingers and toes
Such as cranial bones sternum, ribs and scapulas
Irregular bones: do not fit above
categories

Such as vertebrae and some facial bones
Copyright 2010, John Wiley & Sons, Inc.
Macroscopic Structure

Parts of a long bone
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Diaphysis: shaft of long bone; made up mostly of
compact bone
Epiphysis: broad end of long bone; mostly
spongy bone
Metaphysis: growth area between diaphysis and
epiphysis
Articular cartilage: hyaline cartilage at joint
Periosteum: fibrous covering over most of bone
Medullary cavity (marrow) with fat and blood cells
Endosteum: membrane lining medullary cavity
Copyright 2010, John Wiley & Sons, Inc.
Long Bones
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Long Bones
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Microscopic Structure of Bone

Matrix
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25% water, 25% collagen fibers, 50% mineral salts
Cells
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Osteogenic cells in periosteum 
Osteoblasts
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Secrete collagen fibers
Build matrix and become trapped in lacunae
Become 
Osteocytes that maintain bone
Osteoclasts are formed from monocytes

Digest bone matrix for normal bone turnover
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Histology of Bones
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Compact Bone Structure

Arranged in osteons (haversian systems)
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Central canal through center of osteon
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Cylinders running parallel to long axis of bone
Contains blood vessels, nerves, lymphatics
Concentric lamellae: layers of matrix
Lacunae: “lakes” between lamellae

Contain osteocytes (bone cells)
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Compact Bone Structure

Canaliculi (“little canals”)
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Contain extensions of osteocytes
Permit flow of ECF between central canal and
lacunae
Compact bone is covered by periosteum
Perforating (Volkmann’s) canals
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
Carry blood and lymphatic vessels and nerves from
periosteum
They supply central (Haversian) canals and also bone
marrow
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Histology of Bones
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Spongy Bone

Not arranged in osteons, but irregular
latticework of trabeculae
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These contain lacunae with osteocytes and
canaliculi
Spaces between trabeculae may contain red
bone marrow
Spongy
bone is
lighter than
compact
bone, so
reduces weight of skeleton
Copyright 2010, John Wiley & Sons, Inc.
Bone Dynamics and Tissue
Interactions Animation
Bone Dynamics and Tissue
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Bone Formation


Known as ossification
Timeline
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Initial bone development in embryo and fetus
Growth of bone into adulthood
Remodeling: replacement of old bone
Repair if fractures occur
Mesenchyme (early connective tissue) model

This initial “skeleton” model will be replaced by
bone tissue beginning at 6 weeks of embryonic life
Copyright 2010, John Wiley & Sons, Inc.
Bone Formation

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Two different methods of ossification each
result in similar bone tissue
1. Intramembranous:

Bone forms within sheets of mesenchyme that
resemble membranes
Only a few bones form by this process: flat bones of the
skull, lower jawbone (mandible), and part of clavicle
(collarbone)

2. Endochondrial:

Mesenchyme forms hyaline cartilage which then
develops into bone
All other bones form by this process


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Flat bone
of skull
Blood capillary
Ossification center
Mesenchymal cell
Osteoblast
Mandible
Collagen fiber
1 Development of ossification center
Mesenchyme
condenses
Osteocyte in lacuna
Blood vessel
Canaliculus
Spongy bone
trabeculae
Osteoblast
Osteoblast
Newly calcified bone
matrix
2 Calcification
3 Formation of trabeculae
Periosteum
Spongy bone tissue
Compact bone tissue
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4 Development of the periosteum
Intramembranous Ossification

Four steps
1.Development of ossification center
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Mesenchyme cells  osteogenic osteoblasts
Osteoblasts secrete organic matrix
2. Calcification: cells become osteocytes
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In lacunae they extend cytoplasmic processes to each other
Deposit calcium & other mineral salts
3.Formation of trabeculae (spongy bone)

Blood vessels grow in and red marrow is formed
4. Periosteum covering the bone forms from
mesenchyme
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Perichondrium
Proximal
epiphysis
Uncalcified
matrix
Hyaline
cartilage
Periosteum
Uncalcified
matrix
Diaphysis
Calcified
matrix
Primary
ossification
center
Nutrient
artery
Spongy
bone
Distal
epiphysis
Calcified
matrix
Periosteum
(covering
compact bone)
Medullary
cavity
Nutrient
artery and vein
1 Development of
cartilage model
2 Growth of
cartilage model
3 Development of
primary ossification
center
4 Development of
the medullary
cavity
Articular cartilage
Secondary
ossification
center
Epiphyseal
artery and
vein
Spongy bone
Uncalcified
matrix
Epiphyseal plate
Nutrient
artery and vein
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2010, John
5 Development
of secondary
ossification center
Wiley6&Formation
Sons, Inc.of articular cartilage
and epiphyseal plate
Endochondrial Ossification
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Six Steps
1. Formation of cartilage model of the “bone”
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As mesenchyme cells develop into chondroblasts
2. Growth of cartilage model
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Cartilage “bone” grows as chondroblasts secrete
cartilage matrix
Chondrocytes increase in size, matrix around them
calcifies
Chondrocytes die as they are cut off from nutrients,
leaving small spaces (lacunae)
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Endochondrial Ossification

Six Steps
3. Primary ossification center
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Perichondrium sends nutrient artery inwards into
disintegrating cartilage
Osteogenic cells in perichondrium become osteoblasts
that deposit bony matrix over remnants of calcified
cartilage  spongy bone forms in center of the model
As perichondrium starts to form bone, the membrane is
called periosteum
Copyright 2010, John Wiley & Sons, Inc.
Endochondrial Ossification

Six Steps
4. Medullary (marrow) cavity
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Spongy bone in center of the model grows towards
ends of model
Octeoclasts break down some of new spongy bone
forming a cavity (marrow) through most of diaphysis
Most of the wall of the diaphysis is replaced by a collar
of compact bone
Copyright 2010, John Wiley & Sons, Inc.
Endochondrial Ossification

Six Steps
5. Secondary ossification center


Similar to step 3 except that nutrient arteries enter ends
(epiphyses) of bones and osteoblasts deposit bony
matrix  spongy bone forms in epiphyses from center
outwards
Occurs about time of birth
6. Articular cartilage and epiphyseal cartilage
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Articular cartilage at ends of epiphyses becomes
articular cartilage
Epiphyseal (growth) plate of cartilage remains between
epiphysis and diaphysis until bone growth ceases
Copyright 2010, John Wiley & Sons, Inc.
Growth in Length
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Chondrocytes divide and grow more cartilage
on epiphyseal side of the epiphyseal plate
Chondrocytes on the diaphyseal side die and
are replaced by bone
Therefore bone grows from diaphyseal side
towards epiphyseal side
Growth in length stops between 18-25 years;
cartilage in epiphyseal plate is completely
replaced by bone (epiphyseal line)
Copyright 2010, John Wiley & Sons, Inc.
Growth in Thickness

As bones grow in length, they must
also grow in thickness (width)

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Perichondrial osteoblasts  osteoblasts 
lay down additional lamellae of compact
bone
Simultaneously, osteoclasts in the
endosteum destroy interior bone to
increase width of the marrow
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Remodeling and Repair

Remodeling in response to use

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Resorption of bone matrix by osteoclasts
and
Deposition of bone matrix by osteoblasts
Repair after a fracture
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Dead tissue removed
Chondroblasts  fibrocartilage 
spongy bone deposited by osteoblasts 
remodeled to compact bone
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Types of Fractures
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Partial: incomplete break (crack)
Complete: bone broken into two or more
pieces
Closed (simple): not through skin
Open (compound): broken ends break skin
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Factors Affecting Growth
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Adequate minerals (Ca, P, Mg)
Vitamins A, C, D
Hormones
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Before puberty: hGH + insulin-like growth factors
Thyroid hormone and insulin also required
Sex hormones contribute to adolescent growth
spurt
Weight-bearing activity
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Calcium Homeostasis
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Blood levels of Ca2+ controlled
Negative feedback loops
Parathyroid hormone (PTH) released by
parathyroid gland
 increases osteoclast activity + decreases
loss of Ca2+ in urine
Calcitonin decreases osteoclast activity
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Negative Feedback
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Exercise & Bone Tissue
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Bone strengthened in response to use
Bone resorbed during disuse; examples:
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During prolonged bed rest
Fracture with cast/immobilizer
Astronauts without gravity
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Divisions of Skeletal System
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Two divisions: axial and appendicular
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Axial: bones around body axis

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Examples: skull bones, hyoid, ribs, sternum, vertebrae
Appendicular: bones of upper and lower limbs
plus shoulder and hip bones that connect them

Examples: collar bone (clavicle), arm (humerus),
forearm (radius and ulna), thigh bone (femur)
Copyright 2010, John Wiley & Sons, Inc.
Divisions of the
Skeletal System
There are 206 skeletal bones in
the human skeleton
- 80 bones of the axial skeleton
- Skull (22)
- Hyoid (1)
- Auditory ossicles (6)
- Vertebral column (26)
- Rib cage (25)
- 126 bones make up the
appendicular skeleton
- Pectoral (shoulder) girdle (4)
- Upper limb bones (60)
- Pelvic (hip) girdle (2)
- Lower limb bones (48)
Bone markings

1. Bone Projections
1. Tuberosity
- large, rounded projection
e.g. Tibial tuberosity
2. Crest
- narrow bone ridge, usually prominent
e.g. Anterior crest of tibia
3. Trochanter
- very large, blunt, irregularly shaped
process, e.g. Femur
4. Line
- narrow bone ridge, less prominent than
crest; e.g. Intertrochanteric line
5. Tubercle
- small rounded projection or process
e.g. Adductor tubercle (on medial femur)
6. Epicondyle
- Raised area on or above a condyle
e.g. Medial epicondyle (on femur)
7. Spine
- sharp, slender, often pointed projection
e.g. Vertebra
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Bone markings (Contd.)

Bone depressions & Openings
1. Foramen
- round or oval bone opening
e.g. Optic foramen or Foramen magnum
2. Meatus
- canal-like passage way
e.g. External acoustic meatus (skull)
3. Fossa
- shallow, basin-like depression
e.g. Mandibular fossa
4. Groove
- slit-like furrow
e.g. Mandible
5. Fissure
- narrow, slit-like opening
6. Notch
- shallow depression
e.g. Clavicular notch
7. Body
- large, rough-surfaced depression
e.g. Body of vertebrae
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Bone markings (Contd.)
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Processes that help to form joints
1. Condyle
- large rounded bone prominence
e.g. Mandibular condyle
2. Head
- bony expansion
e.g. Head on rib bones
3. Facet
- smooth, nearly flat articular surface
e.g. Rib facets, articular facets (vertebrae)
Bone cavities
1. Sinus
- hollow sections of bones filled with
air, lined with mucous membranes
e.g. ethmoid or sphenoid sinus
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Skull & Hyoid Bone

Eight Cranial bones
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Frontal, 2 parietal, 2 temporal, occipital, sphenoid,
and ethmoid
Fourteen Facial bones
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2 nasal, 2 maxilla, 2 zygomatic, 2 lacrimal
2 palatine, 2 inferior nasal conchae, 1 mandible,1
vomer
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Skull
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Skull
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Skull
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Skull
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Sphenoid Bone
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Ethmoid Bone
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Ethmoid Bone
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Unique Features of Skull

Sutures: immovable joint between skull
bones
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Paranasal sinuses: cavities
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Coronal, sagittal, lambdoidal, squamous
Located in bones near nasal cavity
Fontanels: soft spot in fetal skull


Allow deformation at birth
Calcify to form sutures
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Sinuses

Found in four skull bones - maxillary, sphenoid,
ethmoid and frontal bone
- are mucosa-lined air cavities within the skull;
- all lead into the nasal
passages
- help to lighten the weight
of the facial bones,
- serve as resonance
chambers for speech
- may also help to insulate the
brain from cold effects
- largest is the maxillary sinus
Paranasal Sinuses
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Vertebrae

Functions
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Encloses spinal cord
Supports head
Point of attachment for muscles of back, ribs
and pelvic girdle
Regions (from superior to inferior)
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7 cervical
12 thoracic
5 lumbar
1 sacrum and 1 coccyx
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Normal Curves in Column

Four normal curves
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Cervical and lumbar curves are convex (bulge
anteriorly)
Thoracic and sacral curves are concave (bulge
posteriorly)
Curves increase strength, help in balance
and absorb shocks
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Vertebral
Column
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Vertebral Column
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Structure of Vertebra


Body: disc-shaped anterior portion
Vertebral arch: posteriorly back from body


With the body, creates a hole called vertebral foramen
Seven processes from this arch
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Transverse process extending laterally on each side
Spinous process extending dorsally
Two each of superior and inferior articular processes
that form joints with vertebrae
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Structure of Vertebra
Copyright 2010, John Wiley & Sons, Inc.
Cervical Area

Cervical (C1-C7 from superior to inferior)

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C1: atlas
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
Spinous process often bifid with transverse foramina
on transverse processes
Articulates with head, specialized to support head
Lacks body and spinous process
C2: axis


Has body and spinous process
Called dens (“tooth”) that creates a pivot for head
rotation
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Cervical
Vertebrae
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Other Vertebrae

Thoracic (T1-T12 )
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Lumbar (L1-L5)


Largest and strongest; spinous processes short and
thick
Sacrum (S1-S5 fused into one unit)
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
Larger than cervical
Have facets for articulations with ribs
Foundation for pelvic girdle
Contain sacral foramina for nerves and blood vessels
Coccyx: 4 coccygeal vertebrae fused into 1
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Sacrum bone markings

One important bony landmark of the sacrum is the
sacral cornua which allows the location of the
sacral hiatus (located between the cornua);
- anesthetic drugs that act on the sacral and
coccygeal nerves are often injected through the
sacral hiatus;
- this procedure is called caudal anesthesia or
epidural block;
- often used in the clinic to relieve pain during labor
and to provide anesthesia to the perineal area
- anesthetic drugs may also be injected through the
posterior sacral foramina
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Lumbar Vertebrae
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Sacrum and Coccyx
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Thorax


Thoracic cage: sternum, costal cartilages,
ribs and bodies of T1-T12
Sternum: form by 3 portions fused by about
age 25 years:
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Manubrium, body, xiphoid process
Ribs: 12 pairs
True ribs are #1-7: articulate with sternum
directly by costal cartilages
False ribs are #8-12: do not articulate with
sternum directly by costal cartilages
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Thorax
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Pectoral Girdle


Function: attach bones of upper limbs to axial
skeleton
Clavicles (2) and scapulas (2): bilateral
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Right Pectoral (Shoulder) Girdle
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Upper Limb

Humerus (arm bone)
- the longest and largest bone of the upper limbs
- important bone markings: deltoid tuberosity,
anatomical neck, radial fossa

Ulna
- located on the medial aspect = middle fingerside
- important bone markings are: olecranon (forms
prominence of the elbow, coronoid process,
trochlear notch, radial notch, styloid process

Radius
- located on the lateral aspect = thumb side
- bone markings: head, radial tuberosity (biceps brachii
muscle attachment), styloid process
Copyright 2010, John Wiley & Sons, Inc.
Right
Humerus
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Right Ulna
and Radius
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Right Ulna and Radius
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Wrist and Hand


Carpus (wrist): 8 bones
Metacarpals: 5 bones of palm of hand


Number 1-5 starting with thumb
Phalanges: 14 bones of fingers


Numbered 1-5 metacarpals
Each finger except the thumb has proximal,
middle and distal phalanges; thumb lacks middle
phalanx
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Carpal bones


8 bones held together by ligaments
four carpal bones in each row
top row: scaphoid, lunate, triquetrum, pisiform
“Scaphoid bone is broken in about 70% of all cases of
carpal fractures ..!"

lower row: trapezium, trapezoid, capitate, hamate
Pisiform and hamate (ulnar side) & scaphoid and
trapezium (radial side) form carpal tunnel which
allows passage of the long digital and thumb flexor
tendons and of the median nerve; narrowing causes
the painful disorder carpal tunnel syndrome
(CTS).."
Right Wrist
and Hand
Copyright 2010, John Wiley & Sons, Inc.
Pelvic (Hip) Girdle

Pelvic girdle includes two hip (coxal) bones



Joined anteriorly at pubic symphysis
Posteriorly attached to sacrum at sacroiliac joint
Basin-like pelvis is formed by two hip bones
(pelvic girdle) + sacrum and coccyx


False (greater) pelvis: broad region superior to
pelvic brim; contains abdominal organs
True (lesser) pelvis: small region inferior to pelvic
brim; contains urinary bladder + internal
reproductive organs
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Pelvic Girdle (Female)
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Pelvic Girdle (Female)
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Parts of Each Hip (Coxal) Bone

3 separate bones fuse by age 23 to form a
hip bone




Ilium: largest and most superior
Ischium: lower posterior part
Pubis: lower anterior part
Bones meet at the acetaulum of the hip bone
(socket for head of femur)
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Right
Hip
Bone
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Lower Limb

Femur (thigh bone): largest bone in the body




Patella: kneecap in anterior of knee joint
Tibia: shin bone


Articulates with hip proximally and with the tibia and
patella distally
Head (fits into acetabulum) and greater trochanter at
proximal end
Large medial, weight-bearing bone of leg
Fibula: longest, thinnest bone in body


Lateral to tibia and smaller
Does not articulate with femur
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Right Femur
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Right Tibia
and Fibula
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Ankle and Foot

Tarsus (ankle) has 7 bones



Metatarsals (foot bones)


Large talus (ankle bone) and
Calcaneus (heel bone)
Numbered 1 to 5 from medial to lateral
Phalanges (toe bones)

Big toe has proximal and distal phalanges while others
have proximal, medial and distal phalanges.
Numbered like metatarsals from 1-5
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Right
Foot
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Arches of the Right Foot
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Male and Female Differences



Males usually have heavier bones
Related to muscle size and strength
Female pelvis is wider and shallower than male
pelvis: allows for birth
Aging and Skeletal System





Birth through adolescence: more bone
formed than lost
Young adults: gain and loss about equal
As levels of sex steroids decline with age:
bone resorption > bone formation
Bones become brittle and lose calcium
Bone loss can be accelerated through
wrong life style choices, e.g. alcoholism,
caffeine consumption
Copyright 2010, John Wiley & Sons, Inc.
Terminology – Disease &
disorders affecting skeletal system

Osteology
- scientific study of bone structure & treatment of bone
disorders

Bone scan
- diagnostic procedure that measures bone
blood flow with help of radioactive tracers

Giantism
- human growth disorder caused by oversecretion of human growth hormone (hGH)
by the pituitary gland, e.g. due to a brain
tumor;
- leads to abnormally strong bone growth
and tallness

Paget’s disease
- world-wide occuring human bone disorder;
- marked by increase in osteoclast numbers
and activity throughout the skeleton
- characterized by excessive breakdown of
bone tissue;
- increased bone resorption in Paget's
disease patients is met by a
compensatory increase in bone
formation and local bone turn-over;
- clinical features involves "woven
bones" which are bulky, weak and
prone to bowing and fractures;
- scientists suspect the role of viruses of
the paramyxovirus class (measles virus?,
canine distemper virus?);

Rheumatoid arthritis (RA)

Inflammatory bone disorder which is characterized by
the progressive destruction of articular cartilage;
Also excessive subchondral bone resorption due to
overly active osteoclasts
Active macrophages are found in the inflammatory state
which accumulate in the (usually swollen) rheumatic
synovial joint membrane;
Macrophages and other immune cells release digestive
enzymes and osteoclast stimulating cytokines
(e.g. IL-1, IL-6, IL-11)
Treated with anti-inflammatory drugs, such as Vioxx,
Ibuprofen, Aspirin;




Rheumatoid arthritis (RA)
About 1% of the world's population is afflicted by
rheumatoid arthritis, women three times more often than
men. Onset is most frequent between the ages of 40 and 50
Copyright 2010, John Wiley & Sons, Inc.

Fibrodysplasia ossificans progressiva
(FOP)

very rare, horrifying genetic bone disorder;
affected human individuals grow a "second skeleton due
to overproduction of bone and connective tissue;
bone overgrowth eventually freezes mobility of the neck,
spine, hips and even the jaw; patient literally becomes
trapped into a "second
skeleton";
strong link of FOP to
mutations of Chr#2-located
ACVR1 gene;
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Copyright 2010, John Wiley & Sons, Inc.
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Cleft lip and cleft palate
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Congenital disorder caused by incomplete fusion of left and
right maxillary and palatine bones during early (week 6-8)
embryonic development
“Cleft lip" often associated with the formation of a cleft
palate);
Cleft may cause problems
with feeding, ear disease,
speech and socialization.
Cause is not known, but toxic
substances, environmental
pollutants, and nutritional
imbalance during embryogenesis
are discussed as risk factors
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Copyright 2010, John Wiley & Sons, Inc.
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Osteoporosis

Pathological reduction in bone mass and deterioration
of the bone architecture after the age of 40
Resulting bone decay leads to an increase in fragility of
bone and high susceptibility to bone fractures, especially
hip fractures (“broken hip”);
Most common cause of osteoporosis in women is the
decrease in estrogen levels that accompanies
menopause; leads to increased bone resorption and
depletion of body calcium;
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"For every 10% of bone that is lost, the risk of bone
fracture doubles."
Copyright 2010, John Wiley & Sons, Inc.
Osteoporosis
Copyright 2010, John Wiley & Sons, Inc.
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Osteoporosis in numbers
"In the U.S., an estimated 16.8 million
postmenopausal women have lost
more than 10% of their peak adult bone
mass, another 9.4 million have
lost more than 25% and 4.8 million have
already suffered an osteoporotic
bone fracture. 25 - 30% of all hip fractures
occur in men, which show an
increase in osteoporosis in recent years."
Copyright 2010, John Wiley & Sons, Inc.
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Excessive bone loss
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Pathological or life style conditions that can
contribute to excessive bone loss are:
1. Multiple myelomatosis
2. Hyperparathyroidism
3. Hyperthyroidism
4. Chronic glucocorticoid treatment
- leads to suppression of osteoblasts
- affects 30 million people in the U.S.,
80% of them are women;
5. Excessive alcohol and caffeine consumption ?
Copyright 2010, John Wiley & Sons, Inc.
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Spina bifida

Congenital defect of the vertebral column
Caused by failure of the neural tube to close during the
first month of embryonic development (often before the
mother knows she is pregnant).
Characterized by laminae
that failed to unite at the
midline
Can be surgically closed
after birth, but this does not
restore normal function to
the mostly lumbar or sacral
part of the spinal cord
Risk factors: lack of folic acid,
fever, diabetes, obesity
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Herniated discs
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Painful rupture of fibrocartilage of the intervertebral discs
(disc ring) due to injury, weakening of ligaments or over
weight;
Most disc herniations occur in lower back, most often
between the fourth and fifth lumbar vertebral bodies or
between the fifth and the sacrum.
Often emerging spinal nerves or
sciatic nerve, may become
painfully compressed
Disc ring tear may result in release
of inflammatory chemicals which
may directly cause severe pain
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Copyright 2010, John Wiley & Sons, Inc.