SKELETAL SYSTEM rev 9-11
• Bone or Osseous Tissue
– consists primarily of nonliving extracellular
crystals of calcium minerals which make the
bone hard
– contains several types of living bone cells,
nerves, and blood vessels
– Is classified as a connective tissue
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Bones perform 5 important functions:
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support
movement
protection
formation of blood cells
mineral storage
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Bones can be classified into 4 categories
• Long--bones of the limbs and fingers
– are longer than they are wide
– consist of a hollow, cylindrical shaft called the
diaphysis and
– an enlarged knob at each end called the
epiphysis
– An internal marrow space or cavity
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• Short--bones of the wrists
• Flat--including the cranial bones, sternum and ribs
• Irregular--hip bones and vertebrae
• All bones contain 2 types of osseous tissue
– a solid, compact tissue
– a spongy tissue with trabeculae
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Periosteum covers the outer surface of all bones
• is a tough connective tissue
• the outermost layer is dense irregular connective
tissue
– is supplied with nerve fibers, lymphatic vessels
and blood vessels which enter the bone through
openings called nutrient foramen
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– provides insertion or anchoring points for the
tendons and ligaments
– contains bone forming cells
– if the end of a long bone forms a movable joint,
the joint surface is covered by articular or
hyaline cartilage
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The internal part of the bone surface is covered by
endosteum
• this covers the trabeculae in the marrow cavities
of the spongy bone
– lines the canals that pass through compact bone
– contains osteoblasts (bone forming cells),
osteoclasts (bone resorption cells), and
osteocytes (bone cells)
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Long bones
• Compact bone forms the external layer
• central cavity of the shaft of long bones is called
the medullary cavity
– this cavity is filled with red marrow in children
and with yellow bone marrow in adults
• Compact bone consists of calcium phosphate laid
in a pattern around the central cavity
Structural Unit of Compact bone is the
– Osteon (or Haversian system) this forms a
pattern of hollow tubes like the growth rings of
a tree trunk
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• Parts of the Haversian system:
– each ring of bone tissue in the hollow tube is
called a lamellae
– Haversian or Central canal: middle cavity in
a Haversian system. Contains the blood
vessels and nerve fibers
– lacunae: found at the junctions of the lamellae
and is filled with bone cells called osteocytes
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• canaliculi: thin canals in bone tissue which
connect the lacunae to each other and to the
central canal
• Volkmann’s canals lie at right angles to the long
axis of the bone and connect the blood and nerve
supply of the periosteum to those in the central
canals and the medullary cavity
– this allows all osteocytes to get nutrients
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Spongy bone
• Is found inside the epiphysis
• spongy bone is less dense than compact bone
• spongy bone is a honeycomb of hard, strong
pieces called trabeculae
• blood cell formation (hemopoiesis) takes
place in the spongy bone
– Contains the epiphyseal plate
• When bone length growth is completed, the
epiphyseal plate becomes ossified
(hardened) and leaves an epiphyseal line
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SKELETAL SYSTEM
• Skeleton
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provides support
protects internal organs
produces blood cells
stores minerals
stores energy
Permits movement via muscle attachments
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Skeletal system contains 3 types of connective
tissue:
• bone--hard elements of the skeleton
• ligaments--dense fibrous connective tissue that
binds the bones to each other
• cartilage--specialized connective tissue consisting
primarily of fibers of collagen and elastic in a gellike fluid called ground substance
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The Skeleton is organized into the
• Axial skeleton and the Appendicular skeleton
• Axial skeleton
– forms the long axis of the body which supports the
head, neck and trunk
– consists of the
– skull,
**bones of the ear
– vertebral column,
**hyoid bone (in the throat)
– ribs and
**these bones are
– sternum
also parts of the axial
skeleton
Appendicular skeleton
• bones which help get us from place to place
(locomotion) and enable us to manipulate our
environment
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The Skull includes the bones of the face, the cranial
bones and the jaws
– Frontal bone (forehead)
– Parietal bones (behind the frontal bone)
– Occipital bone (forms the back of the skull)
• near the base of this bone is an opening
called the foramen magnum.
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– Occipital condyles--2 rounded bumps at the
base of the skull which pivot on the 1st
vertebrae (as in nodding the head to say “yes”)
– Temporal bones
– Sphenoid bone
– Ethmoid bone
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• Facial bones and jaws-comprise the front of the
skull
• zygomatic bones
• nasal bones
• lacrimal bones
• maxillary bones form part of the eye sockets,
anchors the upper row of teeth, and forms part
of the upper palate
• Mandible or lower jaw anchors the lower teeth
• Hyoid bone: not really part of the skull
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– Ear bones
• present in the middle ear and move when air
vibrations bend the eardrum inward
– called the malleus (hammer), incus (anvil) and
stapes (stirrup)
• Several of the cranial and facial bones contain air
spaces which form the sinuses
• Vertebral column or spine
– supports the head, protects the spinal cord and serves as
the attachment for each of our arms and legs and the
body’s muscles
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– Is a column of 33 vertebrae which extends from
the skull to the pelvis
– is classified into 5 anatomical regions
• cervical (neck)
• thoracic (chest or thorax)
• lumbar (lower back)
• sacral (sacrum/upper pelvic region)
• coccygeal (coccyx or tailbone)
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– The first cervical vertebrae is called the Atlas
• it articulates with the occipital condyles
– The second cervical vertebrae is called the Axis
– vertebrae share 2 points of contact called
articulations
– vertebral bodies are separated from each other
by intervertebral disks
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• Ribs and sternum (breastbone)
– Sternum is actually 3 fused bones
– protect the chest cavity
– we have 12 pairs of ribs
• the upper 7 pairs, called “true” ribs,
• “False ribs:
– pairs 8-10 are joined to the 7th rib by
cartilage and are thus indirectly attached
to the sternum
• Floating ribs: pairs 11 and 12: don’t attach
to the sternum at all.
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Appendicular skeleton
• bones which help get us from place to place
(locomotion) and enable us to manipulate our
environment
– includes the:
– Pectoral Girdle is a supportive frame for the
upper limbs
– Arms (the humerus, ulna, radius, wrist bones,
the palm, and the fingers)
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– The Pelvic Girdle consists of the 2 pelvic
bones and the sacrum and coccyx
– they meet in front at the pubic symphysis
where cartilage joins the 2 bones
• primary purpose is to support the weight of the
upper body against the force of gravity
• in adult women, the pelvic girdle is
– broader and shallower than in men and
– the pelvic opening is wider/rounder--to allow for
childbirth
– the sacrum is flatter
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– The leg bones:
• Femur
• Patella
• Tibia
• Fibula
• Tarsals
• Metatarsals
• Phalanges (toes)
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Mature Bone Remodeling and Repair
• Changes in shape, size, strength:
– Dependent on diet, exercise, age
• Bone cells regulated by hormones:
– Parathyroid hormone (PTH): removes calcium
from bone
– Calcitonin: adds calcium to bone
• Repair: hematoma and callus formation
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• Joints or Articulations
– are sites where 2 or more bones meet
– give our skeleton mobility
– hold the skeleton together
– are the weakest parts of the skeleton
• ligaments and tendons are connective tissues that
stabilize each joint
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• Joint types
– freely movable or synovial --bones are separated by a
thin fluid filled synovial cavity which secretes synovial
fluid
• Synovial membrane lines the interior surfaces of the
joint.
• Hyaline cartilage lines the articulating surfaces of
the bones
Types of synovial joints:
• Ball and socket--the ball end of one bone fits into
the socket of another bone: shoulder and hip joints
• Hinge joint —allows movement in one plane
– Knee and elbow joints
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• Slightly Movable or Cartilaginous --has no
synovial cavity and permit only slight movement
– has a pad of fibrocartilage between 2 bones
• Pubic Symphysis
• intervertebral discs
• sacroiliac
• joint connecting the lower ribs to the
sternum
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• Immovable or Fibrous Joints
– flat bones in a baby’s skull
• at birth these bones are separated by space
filled with fibrous connective tissue. These
“soft spots” are called fontanels
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Diseases and Disorders of the Skeletal System
• Sprains: stretched or torn ligaments
– Partially torn ligaments will repair themselves but take
a long time due to poor vascularization
– Completely torn ligaments require surgery to repair
• Cartilage injuries usually due to overuse
– Require surgery to remove damaged cartilage
• Bone dislocation: occurs when bones are forced
out of alignment
– Subluxation is a partial dislocation
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• Bursitis: inflammation of the part of the joint
which contains the synovial fluid
– Falling on your knees, repeated leaning on your elbows
• Inject with anti-inflammatory drugs
• Remove some excess fluid by needle aspiration to
relieve pressure in the joint
• Tendinitis: inflammation of the tendon sheath
– Typically caused by overuse
• Arthritis: inflammation of joints
– Rheumatoid Arthritis
– Osteoarthritis= Degenerative Joint Disease (DJD)
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Rheumatoid Arthritis
• Thought to be an autoimmune disease that causes chronic
joint inflammation as well as inflammation of tissue
around the joints
– Inflammation in other body organs
• ? Genetic cause, environmental, viral, bacterial
• Exacerbations and remissions
• Chronic inflammation leads to destruction of cartilage,
bone and ligamentsjoint deformity
• Symptoms: fatigue, energy loss, decreased appetite, lowgrade fever, muscle and joint aches and stiffness (worse in
mornings)
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Treatment: ---REST
– reduce joint inflammation and pain
– Patient education to maximize joint function
– Prevent joint destruction and deformity
• Medications:
– Aspirin and corticosteroids, NSAIDs (non-steroidal
anti-inflammatory drugs), to decrease pain and
inflammation
• No known cure
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Homeostatic Imbalances
• Osteomalacia (in adults)
– Bones are inadequately mineralized causing
softened, weakened bones
– Main symptom is pain when weight is put on
the affected bone
– Caused by insufficient calcium in the diet, or by
vitamin D deficiency
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Homeostatic Imbalances
• Rickets
– Bones of children are inadequately mineralized
causing softened, weakened bones
– Bowed legs and deformities of the pelvis, skull,
and rib cage are common
– Caused by insufficient calcium in the diet, or by
vitamin D deficiency
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Homeostatic Imbalances
• Osteoporosis
– Group of diseases in which bone reabsorption
outpaces bone deposit
– Spongy bone of the spine is most vulnerable
– Occurs most often in postmenopausal women
– Bones become so fragile that sneezing or
stepping off a curb can cause fractures
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Osteoporosis: Treatment
• Calcium and vitamin D supplements
• Increased weight-bearing exercise
• Hormone (estrogen) replacement therapy
(HRT) slows bone loss
• Natural progesterone cream prompts new
bone growth
• Statins increase bone mineral density
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Paget’s Disease
• Characterized by excessive bone formation and
breakdown;
– Initially have excessive bone resorption (osteoclastic
phase) followed by a reactive phase of excessive,
abnormal bone formation (osteoblastic phase)
• Pagetic bone is chaotic, fragile and weak and
tends to have reduced mineralization
• Usually localized in the skull, spine, pelvis, femur,
• Unknown cause (possibly viral)
• Treatment includes the drugs Didronate and
Fosamax
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Bone Fractures (Breaks)
• Bone fractures are classified by:
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The position of the bone ends after fracture
The completeness of the break
The orientation of the bone to the long axis
Whether or not the bones ends penetrate the
skin
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Types of Bone Fractures
• Nondisplaced – bone ends retain their normal
position
• Displaced – bone ends are out of normal
alignment
• Complete – bone is broken all the way through
• Incomplete – bone is not broken all the way
through
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Types of Bone Fractures
• Compound (open) – bone ends penetrate the skin
• Simple (closed) – bone ends do not penetrate the skin
• Comminuted – bone breaks into three or more
pieces; common in the elderly
• Oblique - a fracture which goes at an angle to the axis
• Epiphyseal – epiphysis separates from diaphysis
along epiphyseal plate; occurs where cartilage
cells are dying
• Greenstick – incomplete fracture where one side
of the bone breaks and the other side bends;
common in children
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