Chapter 7a by dfhdhdhdhjr


									 Chapter 7

Skeletal System
• The organs of the skeletal system include the
  bones and the structures that connect bones
  to other structures, including ligaments,
  tendons, and cartilages
• The hard matrix makes bone seem inert
  – Not true!
• Bone is a living, changing organ

               Bone Structure
• Bones are classified according to their shape
• Long bones consist of a shaft with two ends
  – Examples include:
     • thigh bone = femur
     • upper arm bone = humerus
• Short bones are cube-like
  – Examples include:
     • wrist bones = carpals
     • ankle bones = tarsals
          Bone Structure cont.
• Flat bones are thin and usually curved
  – Examples include:
    •   most skull bones
    •   breast bone = sternum
    •   shoulder blades = scapulae
    •   rib
         Bone Structure cont.
• Irregular bones are not long, short, or flat
  – Have irregular projections
  – Examples include:
     • vertebrae
     • auditory ossicles
• Sesamoid bones develop within a tendon.
  – The patella is a human sesamoid bone.
• Wormian bones (or sutural bones) are tiny
  bones within the skull that lie between major
  skull bones
                Bone shapes

•   Long
•   Flat
•   Short
•   Irregular
•   Sesamoid
•   Sutural
         Parts of a Long Bone
• Diaphysis = shaft
  – consists of a central medullary cavity (filled with
    yellow marrow)
  – surrounded by a thick collar of compact bone
• Epiphyses (pl) = expanded ends
  – consist mainly of spongy bone (red marrow)
  – surrounded by a thin layer of compact bone.
• Epiphyseal line = remnant of epiphyseal
  – cartilage at the junction of the diaphysis and
    epiphyses (growth plate)
             Long Bone cont.
• Periosteum = outer, fibrous, protective
  covering of diaphysis
  – richly supplied with blood & lymph vessels, nerves
     • Nutrient Foramen = perforating canal allowing blood
       vessels to enter and leave bone
  – Osteogenic layer contains osteoblasts (bone-
    forming cells) and osteoclasts (bone-destroying
  – serves as insertion for tendons and ligaments
            Long Bone cont.
• Endosteum = inner lining of medullary cavity
  – contains layer of osteoblasts & osteoclasts
• Articular cartilage = pad of hyaline cartilage
  on the epiphyses where long bones articulate
  or join
  – "shock absorber"
                Flat bones
• covered by periosteum-covered compact
• surrounding endosteum-covered spongy bone
• In a flat bone, the arrangement looks like a
  – spongy bone (meat), sandwiched between
  – two layers of compact bone (bread)
• Hematopoietic tissue (red marrow) is
  located in the spongy bone within the
  epiphyses of long bones and flat bones
  Chemical Composition of Bone
• Organic components (35%)
• osteoprogenitor cells
  – can undergo mitosis and become osteoblasts
• osteoblasts
  – form bone matrix by secreting collagen
  – cannot undergo mitosis
           Composition cont.
• osteocytes
  – mature bone cells derived from osteoblasts
  – principle bone cell
  – cannot undergo mitosis
  – maintain daily cellular activities
    • (i.e. exchange of nutrients & wastes with blood)
• osteoclasts
  – functions in bone resorption (i.e. destruction of
    bone matrix)
  – important in development, growth, maintenance &
    repair of bone
            Composition cont.
• Osteoid
  – Protien mixture secreted by ostioblasts
  – primarily collagen which
  – gives bone its high tensile strength.
  – Also contains glycolipids and glycoproteins
• Inorganic component (65%):
  – Hydroxyapatite (mineral salts)
  – which is primarily calcium phosphate
    • [Ca3(PO4)2.(OH)2]
Microscopic Structure of Compact
• Compact Bone is solid, dense, and smooth
• Structural unit = Haversian system or Osteon
• elongated cylinders cemented together to
  form the long axis of a bone
Components of Haversian system:
• osteocytes (spider-shaped bone cells that lie
  in "lacunae")
  – laid down a matrix of collagen and calcium salts
  – in concentric lamellae (layers)
  – around a central Haversian canal
     • containing blood vessels and nerves.
   Microscopic Structure cont.
• Communicating canals within compact bone:
  – Canaliculi
• Canaliculi connect the lacunae of osteocytes
• Volkmann's canals connect the blood &
  nerve supply of adjacent Haversian systems
  – run at right angles to and connects adjacent
    Haversian canals
                   central (Haversian)
(Volkmann) canal
 Microscopic Structure of Spongy
       (Cancellous) Bone
• consists of poorly organized trabeculae
  (small needle-like pieces of bone)
• with a lot of open space between them.
• nourished by diffusion from nearby Haversian
Bone Development And
• The "skeleton" of an embryo is composed of
  fibrous CT membranes
  – (formed from mesenchyme and hyaline cartilage)
  – loosely shaped like bones
• This "skeleton" provides supporting structures
  for ossification to begin
• At about 6-7 weeks gestation, ossification
  begins and continues throughout adulthood
• Ossification follows one of two patterns:
  – Both mechanisms involve the replacement of preexisting
    CT with bone.
• Intramembranous Ossification is when a bone
  forms on or within a fibrous CT membrane.
  – Flat bones are formed in this manner (i.e. skull bones,
• Endochondral Ossification occurs when a bone is
  formed from a hyaline cartilage model.
  – Most bones of the skeleton are formed in this manner.
  – Primary Ossification center hardens as fetus and infant.
  – Secondary Ossification centers develop in child and
    harden during adolescence and early adulthood.
     Intramembranous Ossification
1)Sheets of relatively        4) Osteoblasts become
   unspecialized                 osteocytes when bony
   connective tissue             matrix completely
   appear at the sites of        surrounds them.
   future bones
2)Partially specialized       5)Connective tissue on the
   connective tissue cells       surface of each
   collect around the            developing structure
   blood vessels in these        form a periosteum.
   tissues                    6) Osteoblasts on the inside
3)Connective tissue cells        of the periosteum deposit
   further differentiate into    compact bone over the
   osteoblasts, which            spongy bone.
   deposit spongy bone.
       Endochondral Ossification
1) Masses of hyaline          4) Osteoblasts form spongy
    cartilage form models        bone in the space
    of future bones.             occupied by cartilage.
2) Cartilage tissue calcifies 5) Osteoblasts become
    and beaks down.              osteocytes when bony
   -periosteum develops          matrix completely
3) Blood vessels and             surrounds them.
    differentiating           6) Osteoblasts beneath the
    osteoblasts from the         periosteum deposit
    periosteum invade the        compact bone around
    disintegrating tissue.       spongy bone.
  Endochondral Ossification cont.
a/b) hyaline cartilage model   e/f) epiphyseal plate
c) primary ossification        • osteoblasts vs.
   center                         osteoclasts
d) secondary ossification
                Bone Growth
• During infancy and
  childhood, long bones
  lengthen entirely by
  growth at the epiphyseal
  plates (called
  longitudinal growth) and
  all bones grow in
  thickness by a process
  called appositional
    Growth at the Epiphyseal Plate
First layer of cells
   • closest to the
   end of epiphysis
   • resting cells
   • anchors
   epiphyseal plate
   to epiphysis

Second layer of
   • many rows of
   young cells
   • undergoing
    Growth at the Epiphyseal Plate
Third layer of cells
  • older cells
  • left behind when
  new cells appear
  • cells enlarging
  and becoming

Fourth layer of
  • thin
  • dead cells
  • calcified
        Appositional Growth
• Along with increasing in length, bones
  increase in thickness or diameter
  – occurs in osteogenic layer of periosteum
  – Osteoblasts lay down matrix (compact bone) on
    outer surface.
  – This is accompanied by osteoclasts destroying
    the bone matrix at the endosteal surface
             Bone Function
• Support
  – The bones in legs and pelvis support the
  – The atlas (1st vertebra) supports the skull,
• Protection of underlying organs
  – The skull protects the brain
  – The rib cage protects the heart and lungs,
         Bone Function cont.
• Body Movement
  – Skeletal muscles attached to bones by tendons
    • serve as levers to move bones
• Hematopoiesis
  – Definition = Blood Cell Formation
  – All blood cells are formed in the red marrow of
    certain bones
        Bone Function cont.
• Inorganic Salt Storage
  – Bone stores many minerals
    • calcium,
    • phosphorus
    • others.
  – Also a means of calcium homeostasis
• Energy Storage
  – Yellow marrow in the shaft of long bones
  – serve as an important chemical energy
  Bone Remodeling And Repair
• Once a bone has been formed, it is
  continuously being remodeled throughout life.
  This process involves the action of
  osteoblasts and osteoclasts, two hormones
  (calcitonin & parathyroid hormone) and in turn
  affects blood calcium homeostasis.
Bone Remodeling And Repair cont.
• Rate of Remodeling Varies:
  – Distal femur is replaced every four months
  – Diaphysis may not be fully replaced during one's
• Osteoclasts are large multinucleated cells
  responsible for bone resorption
  – secretes lysosomal enzymes that digest the
    organic matrix
  – secrete acids that decompose calcium salts into
    Ca++ and PO4- ions, which can then enter blood
   Control of Bone Remodeling
• Calcium Homeostasis
• involves 2 hormones (negative feedback):
  – Parathyroid hormone (PTH), which is secreted by the
    parathyroid glands when blood calcium levels are low
  – stimulates osteoclast activity (resorption of bone occurs),
    which releases Ca++ into the blood
  – causes kidney tubules to reabsorb Ca ++ back into the
  – causes intestinal mucosa to increase dietary absorption of
    Ca ++ and therefore
  – causes an increase in blood calcium levels (back to
 Control of Bone Remodeling cont.
• Calcitonin, which is secreted by the thyroid
  gland when blood calcium levels are high:
  – inhibits bone resorption, increases osteoblast
    activity (i.e. causes a deposition of bone matrix)
  – causes the kidney tubules to secrete excess Ca       ++

    into the urine and therefore
  – results in a decrease in blood calcium levels
    (back to normal)
     Factors Affecting Bone
 Development, Growth and Repair
• Minerals needed for bone remodeling:
  – Calcium (component of hydroxyapatite matrix)
  – Phosphorus (component of hydroxyapatite)
  – Magnesium (needed for normal osteoblast
  – Boron (inhibits calcium loss)
  – Manganese (needed for new matrix)
• Exercise increases bone growth
                 Factors cont.
• Vitamins needed for bone growth,
  remodeling, repair
  – Vitamin D greatly increases intestinal absorption
    of dietary calcium & retards its urine loss
     • Deficiency causes rickets in children and osteomalacia
       in adults
  – Vitamin C helps maintain bone matrix (collagen
     • Deficiency causes scurvy
  – Vitamin A is required for bone resorption,
    controls the activity, distribution and coordination
    of osteoblasts & osteoclasts during
  – Vitamin B12 may play a role in osteoblast activity
Hormones needed for bone growth &
• Human Growth Hormone (hGH):
  – secreted by pituitary
  – responsible for the general growth of all tissues
  – Stimulates reproduction of cartilage cells at
    epiphyseal plate
• Sex hormones
  – estrogens & androgens (testosterone)
  – aid osteoblast activity (i.e. promote new bone
  – also degenerate cartilage cells in epiphyseal plate
    (i.e. close epiphyseal plate)
  – Estrogen effect is greater than androgen effect
             Hormones cont.
• Thyroid hormones (T3 and T4)
  – T3 = Triiodothyronine
  – T4 = Thyroxine
  – Stimulates replacement of cartilage by bone in
    epiphyseal plate.
• PTH & Calcitonin (discussed previously)
• The skeletal system consists of 206 bones
  and joints that allow for the many functions
  discussed above in the overview.
  – many bones contain holes that allow blood
    vessels and/or nerves to pass through (i.e.
  – many bones have distinct markings that allow for
    attachment of muscles and therefore movement.
• The skeleton is divided into two major
  divisions, an axial and appendicular portion
           Skeletal Organization
Axial Skeleton
   • head
   • neck
   • trunk

Appendicular Skeleton
   • upper limbs
   • lower limbs
   • pectoral girdle
   • pelvic girdle
 The Axial skeleton includes the bones of the
skull, hyoid bone, vertebral column and thoracic
Skull Structure
 The appendicular skeleton includes the limbs of the
upper and lower extremities, and the bones that attach
those limbs to the trunk (pectoral and pelvic girdles)
Types of Fractures
Hyoid Bone
• brain case or helmet
• The cranium is composed of eight bones
  including the frontal, occipital, sphenoid, and
  ethmoid bones, along with a pair of parietal
  and temporal bones
Frontal (1)
   • forehead
   • roof of nasal cavity
   • roofs of orbits
   • frontal sinuses
   • coronal suture
Parietal (2)
   • side walls of cranium
   • roof of cranium
   • sagittal suture
Occipital (1)
  • back of skull
  • base of cranium
  • foramen magnum
  •lambdoid suture
Temporal (2)
   • side walls of cranium
   • floor of cranium
   • floors and sides of orbits
   • squamous suture
   •zygomatic process
       •Zygomatic arch
Sphenoid (1)
   • base of cranium
   • sides of skull
   • floors and sides of orbits

Ethmoid (1)
   • roof and walls of nasal cavity
   • floor of cranium
   • wall of orbits
   •perpendicular plate
   • superior and middle nasal conchae
   • ethmoidal sinuses
   • crista galli
            Facial Skeleton
• The facial skeleton shapes the face and
  provides attachment for various muscles that
  move the jaw and control facial expressions
                 Facial Skeleton
Maxillary (2)
  • upper jaw
  • anterior roof of mouth
  • floors of orbits
  • sides of nasal cavity
  • floors of nasal cavity
  •maxillary sinuses
Facial Skeleton
                  Facial Skeleton
Palatine (2)
   • L shaped bones located
   behind the maxillae
   • posterior section of hard
   • floor of nasal cavity
   • lateral walls of nasal
                  Facial Skeleton
Zygomatic (2)
   • prominences of cheeks
   • lateral walls of orbits
   • floors of orbits
   • temporal process
        •Zygomatic arch
Lacrimal (2)
   • medial walls of
   • groove from orbit to
   nasal cavity

Nasal (2)
  • bridge of nose
                   Facial Skeleton
Vomer (1)                   Inferior Nasal Conchae (2)
  • inferior portion of         • extend from lateral
  nasal septum                  walls of nasal cavity
                Facial Skeleton
Mandible (1)
  • lower jaw
              Vertebral Column
• cervical vertebrae (7)
• thoracic vertebrae (12)
• lumbar vertebrae (5)
• sacrum
• coccyx
               Vertebral Column
•   cervical curvature
•   thoracic curvature
•   lumbar curvature
•   sacral curvature
•   rib facets
•   vertebra prominens
•   intervertebral discs
•   intervertebral foramina
                 Atlas and Axis
• Atlas– 1st; supports head
• Axis – 2nd; dens pivots to turn head
             Sacrum and Coccyx
•five fused vertebrae
• median sacral crest
• posterior sacral
• posterior wall of
pelvic cavity
• sacral promontory

• four fused vertebrae
                  Thoracic Cage
• Ribs
• Sternum
• Thoracic vertebrae
• Costal cartilages

•Supports shoulder
girdle and upper limbs
• Protects viscera
• Role in breathing
                 Thoracic Cage
• Ribs
  – True ribs (7)
  – False ribs (5)
     • floating (2)
• Sternum
  – Manubrium
  – Body
  – Xiphoid
             Pectoral Girdle
• The pectoral (shoulder) girdle connects the
  upper limbs to the rib cage and consists of
  two pairs of bones.
  – anterior clavicles (2) = collar bones
  – posterior scapulae (2) = shoulder blades
                Pectoral Girdle
• shoulder girdle
• clavicles
• scapulae
• supports upper limbs
            Pectoral Girdle cont.
•articulate with manubrium
• articulate with scapulae
(acromion process)

•acromion process
• coracoid process
• glenoid cavity
                Upper Limb
• Humerus
• Radius
• Ulna
• Carpals
• Metacarpals
• Phalanges
              Wrist and Hand
• Carpals (16)
• Metacarpals
• Phalanges (28)
  – proximal
  – middle
  – distal phalanx
           Pelvic (hip) Girdle
• connects lower limbs to the vertebral column
• Composed of a pair of coxal bones: coxae
• which articulate:
  – anteriorly at the symphysis pubis, posteriorly with
    the sacrum
  – Each coxal bone consists of 3 separate bones
    during childhood, but these bones are securely
    fused in adults
Pelvic Girdle
• Coxae (2)
• supports trunk of body
• protects viscera
• hip bones               • ischium                • pubis
    – acetabulum                                       – obturator foramen
                             – ischial spines
•   ilium                                              – symphysis pubis
                              – lesser sciatic notch
     – iliac crest                                     – pubic arch
                              – ischial tuberosity
    – iliac spines
    – greater sciatic notch
          Lower Limb

• Femur
• Patella
• Tibia
• Fibula
• Tarsals
• Metatarsals
• Phalanges
• kneecap
• anterior surface of
• flat sesamoid bone
located in a tendon
                 Ankle and Foot

• Tarsals (14)
  – calcaneus
  – talus
• Metatarsals (10)
• Phalanges (28)
  – proximal
  – middle
  – distal

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