Chapter 7 The Skeletal Sx.

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Chapter 7 The Skeletal Sx.

• Bones, Bones, Bones

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The Skeletal Sx.

• Bone Classification
• Long bones
• Short bones
• Flat bones
• Irregular bones
• Sesmoid bones
• Wormian bones

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The Skeletal Sx.

• Long bone structure
• The Epiphysis of a bone is the distal ends which
  are usually wider than the shaft. Each long bone
  usually has a proximal and distal epiphysis.
• Each epiphysis of a long bone is usually capped
  with Articular Cartilage which is histologically
  hyaline cartilage. This cartilage cap on the
  epiphysis helps to decrease friction during
  movement of the joint.

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The Skeletal Sx.

• The Diaphysis of a bone is the area commonly
  referred to as the shaft. It is generally
  thinner than the epiphysis.
• The Periosteum of a bone is a fiberous outer
  covering of the bone that forms attachments for
  ligaments and tendons.

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The Skeletal Sx.

• Compact Bone is very tightly packed osseous
  tissue usually found in the area of the
  diaphysis.
• Spongy Bone consist of many branching bony plates
  or spicules called trabeculae.
• The Medullary Cavity is a hollow space inside the
  diaphysis of a long bone. It is usually lined
  with an Endosteum, which is a thinner version of
  the periosteum.

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The Skeletal Sx.

• Bone Marrow comes in two types
• Red this marrow is usually found in the ends of
  long bones. It is largely responsible for blood
  cell formation of all types of blood cells.
• Yellow this marrow is usually found in the
  diaphysis of a long bone and is composed largely
  of adipose tissue. In times of need, yellow
  marrow can convert to red marrow for purposes of
  blood cell formation.

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The Skeletal Sx.

• The Osteon
• The Osteon, aka the Haversian Canal, is the
  functional unit of bone on a microscopic level.
  It has a few constituent parts
• Central Canal, aka Haversian Canal provides
  passage for minute blood vessels to get to and
  from the Osteocytes
• Lacunae small chambers or recesses in which the
  Osteocytes reside
• Caniliculi connect the lacunae to each other
  and to the central canal
• Volkmanns Canal, aka perforating canal connect
  the central canals to each other

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The Skeletal Sx.

• Bone Development
• All osteocytes develop from immature cells called
  Osteoblasts. These cells lay down the bony
  matrix of calcium and phosphorus salts that we
  associate with bone tissue.
• Bone tissue is developed in two ways
• Intramembranous Ossification takes place when a
  bone develops from sheets of connective tissue.
  The osteoblasts lay down a calcium matrix over
  the top of membranes of connective tissue that is
  well vascularized. Once secluded in their
  recesses in the matrix, they are considered
  osteocytes. Only a few bones develop in this
  manner (i.e., clavicle and skull).

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The Skeletal Sx.

• Endochondral Ossification is the process whereby
  bone is created from a pre-existing cartilaginous
  model most bones are created in this fashion.
  After a period of considerable growth, the
  chondrocytes begin to die, leaving behind the
  gelatinous matrix of which the cartilage was
  made. Undifferentiated connective tissue cells
  then infiltrate the area and begin to make
  further changes. Some become the fiberous
  periosteum, others differentiate into osteoblasts
  and begin to put down the calcium salts that are
  characteristic of bony matrix. Once secluded in
  their lacunae, these cells are considered
  osteocytes.

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The Skeletal Sx.

• The Primary Ossification Center in a long bone is
  in the center of the diaphysis early on, thus
  bone develops in the center of the diaphysis
  first. See Figure 7.8 p.198
• Secondary Ossification Centers appear in the
  epiphyses. These are the Ephyseal Plates (aka
  growth plates). They are composed of hyaline
  cartilage. The side of the growth plate next to
  the epiphysis is relatively quiescent and anchors
  the rest of the growth plate to the epiphysis.
  Growth occurs on the side of the epiphyseal plate
  closest to the diaphysis. These chondrocytes are
  undergoing cell division, enlarging, calcifying,
  and ultimately dying to be replaced by
  osteoblasts that will become osteocytes.

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The Skeletal Sx.

• Osteoclasts are cells that are designed to break
  down bone. Bone is living, changing tissue and
  is constantly being laid down and picked up by
  the body for various uses.
• Bone will continue to grow in length for so long
  as the epiphyseal plates remain in their
  cartilaginous state. Once they growth plate
  fuses shut and all chondrocytes are dead, the
  epiphyseal plate becomes the epiphyseal line and
  no further apical growth is possible.

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The Skeletal Sx.

• Bone grows in circumference by the action of
  osteoclasts and osteoblasts under the periosteum
  and endosteum. Osteoclasts under the endosteum
  pick up old bone and it is later laid back down
  on the existing framework via osteoblasts under
  the periosteum. Thus medullary cavity comes into
  existance.
• Note Blasts Build, Clasts Cleave

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The Skeletal Sx.

• Disorders of Bone
• Many factors ranging from genetics, to nutrition,
  to exercise, to external factors can play a role
  in bone health.
• Osteomalacia (Rickets in children) is a condition
  where calcium is poorly absorbed due to a lack of
  Vitamin D synthesis or in diet. The result is
  bone softening and deformity (saber shin
  deformity).

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The Skeletal Sx.

• A lack of Vitamins A or C will also lead to bone
  disorders. Vitamin A is necessary for
  osteoblastic and osteoclastic activity. Vitamin
  C is necessary for collagen synthesis. Scurvy is
  a vitamin C deficiency and can inhibit bone
  development as well as cause the teeth to fall
  out.
• A deficiency of sex hormones (the estrogens and
  testosterone) will inhibit bony growth.

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The Skeletal Sx.

• Growth Hormone, secreted by the anterior
  pituitary gland, is largely responsible for the
  division of the cartilage cells of the growth
  plate. A lack of this hormone in childhood is
  called Pituitary Dwarfism. An over abundance in
  childhood will lead to abnormal growth of the
  long bones and is called Gigantism. The same
  over abundance in adult life will lead to a
  disorder called Acromegaly. Acromegaly is
  characterized by growth in thickness in most
  bones, but is most visibly seen in the lower jaw
  bone, the brow ridge, and the hands.

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The Skeletal Sx.

• Osteoporosis is a condition associated with aging
  bone. The bone loses overall mass and mineral
  content. While both sexes can exhibit
  osteoporosis, post-menopausal female are much
  more at risk than their male counterparts. With
  the decline of the estrogens in middle to later
  life, women lose bone mass much more rapidly than
  men. Couple this with the fact that men start
  adulthood with more bone mass than women, and
  that men continue to synthesize sex hormone much
  later into life than women do and the idea
  becomes quite apparent why women suffer this
  condition much more than men. Some social and
  occupational factors can also play a role in this
  condition.

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The Skeletal Sx.

• Wolffs Law
• Physical stress on bones, or lack there of will
  cause bone to change in response.
• Put simply, the more weight bearing stress that
  is placed on bone, the thicker it will become.

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The Skeletal Sx.

• Fractures
• Bones can break in a variety of ways for several
  reasons. Following are some simple categories of
  fractures that may be encountered.
• Displaced the broken edges are abutted
• Non-displaced the broken edges are removed from
  each other
• Open the bone has pierced the skin and is
  exposed to the environment
• Closed the bone is still enclosed in the body
  (no exposure)
• Spiral a twisting fracture
• Comminuted the bone is burst into small pieces
• Transverse broken at a 90 degree angle
• Greenstick an incomplete fracture

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The Skeletal Sx.

• Bone Fxns
• Support bones give the framework for the body
• Protection bones protect many organs and
  important blood vessels
• Movement bones provide a site for muscle
  attachment and thus movement
• Hematopoiesis red marrow is responsible for all
  blood cell formation
• Mineral storage Calcium, phosphorus, potassium,
  magnesium and other minerals are stored in the
  skeletal system. These minerals are used for
  many physiological uses throughout the body.

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The Skeletal Sx.

• Skeletal Organization
• On average there are about 206 bones in the body.
  Remember that this is an average and is not a
  hard and fast rule.
• The skeleton has two major divisions, the Axial
  and Appendicular Skeletons. See figure 7.15
  p.207

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The Skeletal Sx.

• Axial Skeleton
• The axial skeleton consists of the skull, hyoid,
  vertebral column, ribs, and sternum.
• The skull consists of two parts, the cranium and
  the face. The following bones are a part of the
  cranium and form the cranial vault that encloses
  the brain

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The Skeletal Sx.

• Frontal bone forward most
• Parietal bone top most
• Temporal bone on either side of the orbitals
• Occipital bone rear most
• Sphenoid bone forms a major portion of the
  floor of the cranial vault and has a bat or
  butterfly shape
• Ethmoid bone deepest bone of the cranium which
  is riddled with sinuses
• The infantile skull has six different openings
  called fontanels. These openings allow for the
  skull to move during child birth, and allow the
  skull to grow as the brain grows.

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The Skeletal Sx.

• The bones of the face are rather small in
  contrast to those of the cranium. They give fine
  detail and aid in facial expression. Below are
  some of the bones of the face
• Maxilla central-most bone of the face, holds
  the upper teeth
• Palatine bones forms the roof of the mouth
• Zygomatic bones cheek bones
• Lacriminal bones have the lacriminal foramen
• Nasal bones at the bridge of the nose
• Vomer bones the bony portion of the nasal
  septum
• Mandible the lower jaw bone

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The Skeletal Sx.

• Vertebral Column
• The vertebral column is made up of 33 bones in
  four different regions. These vertebrae are
  separated by intervertebral discs made of
  fibrocartilage.
• The four regions are
• Cervical 7 vertebrae
• Thoracic 12 vertebrae
• Lumbar 5 vertebrae
• Sacral 9 vertebrae in 2 fused sections

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The Skeletal Sx.

• The bones of the spine begin very small in the
  cervical region and get progressively larger as
  you move down the spine, as do the IVDs. The
  reason for this is gravity. The bones on the
  bottom carry a larger load than the bones on top.
  
• The bone at the top of the spine (in the cervical
  region) is given the name Atlas (C1), and the
  bone beneath it is called Axis (C2). All other
  vertebrae are named by letter and number in
  accordance with their region and count within
  that region (i.e. C3, T6, L2).

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The Skeletal Sx.

• Atlas is the smallest bone in the spine, has no
  vertebral body, and no spinous process.
• Axis has a tooth like projection called the dens
  or odontoid process.
• Only cervical vertebrae have a transverse
  formina.

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The Skeletal Sx.

• Thoracic vertebrae articulate with a rib. They
  usually have a longer spinous process and longer
  transverse processes.
• Lumbar vertebrae have very large vertebral bodies
  and short flat spinous processes.

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The Skeletal Sx.

• Sacrum is a large triangular shaped bone composed
  of 5 fused segments. In a child these bones are
  separate and individual with fusion not taking
  place until late puberty.
• The sacroiliac joints are the joints made by the
  sacrum and the ilia (hip bones) on either side of
  the pelvis.
• The Coccyx is a small structure made up of four
  fused segments.

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The Skeletal Sx.

• The ribs are flat bones that enclose the thoracic
  cavity and protect the vital organs therein.
  There are a total of 24 ribs which are divided
  into three catagories
• True ribs pairs 1-7
• False ribs pairs 8-10
• Floating ribs pairs 11 12
• True ribs have a direct anterior articulation
  with the sternum, false ribs all connect to rib 7
  via costal cartilage, floating ribs have no
  anterior connection.

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The Skeletal Sx.

• The sternum is a flat bone on the anterior
  portion of the thorax that has articulations with
  the first seven pairs of ribs and the clavicles.
  It has three parts the manibrium (superiorly),
  the body (in the middle) and the xyphoid process
  (inferiorly). The Angle of Louis is found at the
  junction between the manubrium and the body of
  the sternum.
• The hyoid bone is a small U shaped bone found
  in the anterior throat at about the level of C3
  or so. It is an important site of muscular
  attachment. Notedly, it makes a joint with no
  other bone.

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The Skeletal Sx.

• Appendicular Skeleton
• Pectoral Girdle consists of the clavicle and
  the scapula and functions to hold the upper limb
  onto the torso. This structure is built for
  mobility of the limb.
• The clavicles are a structurally weak bone due to
  the double curve. They are fairly featureless
  other than having a sternal end and an acromial
  end. Due to the nature of their ossification,
  the clavicles are considered a flat bone.

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The Skeletal Sx.

• The scapulae are very busy bones. Each has 3
  angles and 3 sides. Also they have a glenoid
  fossa which is the site of articulation with the
  upper bone of the arm. The coracoid process sits
  beside the glenoid labrium. The anterior side of
  the scapula has a smooth subscapular fossa, and
  the posterior aspect has a supraspinous fossa as
  well as an infraspinous fossa. These two fossae
  are seperated by the spine of the scapula.

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The Skeletal Sx.

• The Humerus is the only bone in the upper arm.
  The humerus has a very pronounced head, and two
  necks one anatomical where the epiphyseal plate
  or line can be found, and a surgical neck which
  can be the site of fracture. It has numerous
  bony prominences and notedly has a large fossa on
  its posterior surface called the Olecranon Fossa.

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The Skeletal Sx.

• The Radius is the bone in the forearm located on
  the thumb side when the arm is in anatomical
  position. Proximally the radius has a disc like
  head followed by the radial tuberosity. The
  styloid process of the radius is at the distal
  most point.
• The Ulna is on the pinky side of the forearm when
  the arm is in anatomical position. Proximally it
  has the trochlear notch and olecranon process.
  Distally it displays a styloid process similar to
  that of the radius.

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The Skeletal Sx.

• The hand is made up of the wrist, palm, and
  fingers. The wrists consist of the carpal bones
  which are two rows of four bones each. The
  proximal row consists of the scaphoid, lunate,
  triquetrum, and pisiform. The distal row
  consists of the trapezoid, trapezium, capitate
  and hamate. The metacarpals reside in the
  webbing of the hand, and are numbered 1-5
  beginning with the pollex. The phalanges are
  numbered in the same fashion. Each consists of
  three bones each with the exception of the
  pollex, which has two.

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The Skeletal Sx.

• The Pelvic Girdle consists of three bones which
  are fused together. These are the ilium, the
  ischium, and the pubis. A fusion line of the
  three bones can be seen in the Acetabulum, a
  large cavity in the outside of the bone where
  the femur joins the pelvis. The obturator
  foramen is found in the inferior portion of this
  structure it is the largest foramen in the
  skeleton.

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The Skeletal Sx.

• The Femur is the longest strongest bone in the
  body. It has a very pronounced head and neck.
  The neck is a site of frequent fracture for
  people with osteoporois and usually calls for hip
  joint replacement.
• The Patella is the largest sesmoid bone in the
  body. It is a part of the knee joint and stops
  the knee from hyper-extending.
• The Tibia is also called the shin bone. It is
  the only weight bearing bone in the lower leg.

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The Skeletal Sx.

• The Fibula is the little lateral bone in the
  lower leg. It is non-weight bearing and aids in
  balance.
• The Foot consists of the ankle, the instep and
  the toes. The ankle contains the seven tarsels
  which are the calcaneus (the largest), the talus
  (top most), navicular, cuboid, and the lateral,
  intermediate and medial cuneiform bones. The
  five metatarsels are the bones in the webbing of
  the foot. They are numbered 1-5 beginning with
  the Hallux (great toe). The phalanges here are
  numbered the same as in the hand.