Chapter 6

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Chapter 6 7 The Skeletal System
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Skeletal Cartilages structures, types
locations

• Skeletal cartilage
• Made from cartilage
• Consists primarily of water
• Allows for resilience
• No nerves or blood vessels
• Surrounded by a layer of dense irregular
  connective tissue perichondrium
• Resists outward expansion when compressed
• Source of blood vessels feeds the matrix
  chondrocytes
• Hyaline cartilage
• Hyaline cartilage is the most abundant skeletal
  cartilage, and includes the articular (cover bone
  ends _at_ movable joints), costal (connects ribs to
  sternum), respiratory (larynx reinforce
  passageways), and nasal (external nose)
  cartilages.
• Provide support flexibility (due to collagen
  fibers)

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Skeletal cartilages cont.

• Elastic cartilage
• More flexible than hyaline
• Contains more elastic fibers
• Located in the external ear epiglottis
• Fibrocartilage
• Located in areas that need to withstand a great
  deal of pressure stretch
• Chondrocytes collagen fibers
• Knee intervertebral discs

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Growth of cartilage

• Appositional
• growth from the outside
• Outward expansion due to production of cartilage
  matrix on the outside of tissue
• Secrete new matrix against the external surface
  of the existing cartilage
• Occurs in the shafts of long bones
• Interstitial
• growth from the inside
• Expansion within the cartilage matrix due to
  divisions of lacunae-bound chondrocytes
  secretions of the matrix
• Occurs in the ends of bone

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Classifications of bones

• 206 bones in the body
• 2 divisions
• Axial
• Consists of
• The skull, vertebral column, rib cage
• Involved in protection, support, or carrying
  other body parts
• Appendicular
• Consists of
• The bones of the upper lower limbs the
  girdles (shoulder hip bones) that attach them
  to the axial skeleton

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Shape

• Long bones
• Longer than they are wide
• Have a definite shaft two ends
• Consist of all limb bones except
• Patellas, carpals, tarsals
• Named for their shape not size (fingers are long
  bones even though they are small)
• Short bones
• Somewhat cube-shaped
• Include
• the carpals tarsals
• Sesamoid bones that form with in tendons
  (patella)

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Shape cont.

• Flat bones
• Thin, flattened, and often curved bones
• Include
• Skull bones, sternum, scapulae, and ribs
• Irregular bones
• Complicated shapes
• Dont fit into any other class
• Include
• Vertebrae
• Hip bones coxae

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Functions

• 4 main functions
• Support
• Support body
• Cradle soft organs
• Protection
• Protect vital organs
• Movement
• Allow movement
• Muscles attach to bones acting as levers for
  movement
• Mineral storage
• Store calcium phosphate
• Released into the blood stream as ions for
  distribution to the body
• Blood cell formation
• House hematopoietic tissue

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Bone structure gross anatomy

• Bone markings
• Projections, depressions, openings found on the
  surface of bones that function as sites of
  muscle, ligament, and tendon attachment
• And as joint surfaces, and openings for the
  passage of blood vessels and nerves

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Gross anat. cont.

• 2 types of bone texture
• Compact
• Appears dense, smooth solid
• Contains passageways for blood vessels nerves
• Osteon
• structural unit of bones
• tiny weight bearing pillars
• arranged like tree rings
• Each matrix tube lamella
• Collagen fibers run in same direction in
  opposing lamella they run in opposing directions
  allow extra strength
• Haversian canal
• Center of osteon
• Contain blood vessels nerves
• Lacunae
• Contain osteocytes mature bone cells
• Canaliculi connect lacunae to each other and
  the central canals
• Interstitial lamellae
• Incomplete lamellae between osteons
• Circumferential lamellae

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Compact Bone
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Gross anat. cont.

• Spongy
• Internal to compact bone
• Honeycomb, needle-like, flat pieces trabeculae
• Align along the lines of stress
• Help the bone to resist stress
• Contain irregularly arranged lamellae
  osteocytes connected by canaliculi
• No osteons present
• Nutrients diffused from canaliculi from
  capillaries in the endosteum

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Structure of long bones

• Long bones have a tubular bone shaft, consisting
  of a bone collar surrounding a hollow medullary
  cavity, which is filled with yellow (in adults)
  and red (in children) bone marrow.

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Long bones cont.

• Epiphysis
• Ends of long bones
• Typically wider than diaphysis (shaft)
• Consist of internal spongy bone outer layer of
  compact bone
• Ends are covered with hyaline (protects bone ends
  where they meet at the joint)
• Epiphyseal line/plate
• Between epiphysis diaphysis
• Line remnant of plate (hyaline cartilage disc
  in young adults that lengthens bone)
• Diaphysis
• The bone shaft

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Long bones cont.

• The external surface of bone is covered by the
  periosteum
• Double layered membrane
• Covers all bones except joint surfaces
• Contains osteoblasts osteoclasts
• Richly supplied w/ blood, nerve fibers,
  lymphatic vessels enter bone shaft via nutrient
  foramen
• Secured to bone shaft by Sharpeys fibers
  tufts of collagen fibers
• Provides insertion points for tendons and
  ligaments
• The internal surface of bone is lined by a
  connective tissue membrane called the endosteum
• Covers trabeculae of spongy bone
• Lines canals that run through compact bone
• Also contains osteoblasts osteoclasts

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Short, flat, irregular bones

• Short, flat, irregular bones consist of thin
  plates of periosteum-covering compact bone on the
  outside, and endosteum-covered spongy bone
  inside, which houses bone marrow between the
  trabeculae
• No shaft or epiphyses
• Flat bones internal layer of spongy bone
  diploe

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Hematopoietic tissue

• Hematopoietic red bone marrow
• Located within trabecular cavities of the spongy
  bone, in diploe of flat bones epiphysis of long
  bones
• Infants all areas of spongy bone contain red
  marrow
• Adults epiphysis of long bones diaphysis
  yellow marrow

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Microscopic anatomy

• Compact bone dense and solid
• Structural unit osteon
• Contains lamellae, Haversian canal, blood
  vessels and nerves
• Volkmanns canals
• Lie at right angles to the long bone axis
• Connect blood nerve supplies of the periosteum
  to the central canals medullary cavity
• Osteocytes
• Occupy lacunae lamella junctions
• Connected by canaliculi
• Lamellae
• Circumferential
• Beneath periosteum
• Interstitial
• Between osteons

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Microscopic anatomy cont.

• Spongy bone lacks osteons but has trabeculae that
  align along lines of stress, which contain
  irregular lamellae

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Formation of the Bony Skeleton

• Ossification or osteogenesis process of bone
  formation
• Before week 8, skeleton made up of fibrous
  membranes and hyaline cartilage
• Flexible and resilient, can accommodate mitosis
• Intramembranous ossification
• Formation of cranial bones of the skull and
  clavicles
• Endochondral ossification
• All bones below base of the skull (except
  clavicles)
• Hyaline cartilage broken down as ossification
  proceeds

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Postnatal bone growth

• During youth bones lengthen entirely by
  interstitial growth from the epiphyseal plates
• Growth in length
• The cartilage cells at the top of the epiphyseal
  plate (closest to the epiphysis) push the
  epiphysis away from the diaphysis causing the
  bone to grow
• Old chondrocytes (closer to the diaphysis)
  calcify replace the cartilage with bone tissue
• Growth in width
• Occurs through appositional growth
• Bone growth due to deposition of bone matrix by
  osteoblasts beneath the periosteum

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Bone homeostasis

• Bone remodeling
• Weekly recycle 5-7 of bone mass
• Spongy bone replaced every 3-4 yrs
• Compact bone replaced every 10 yrs
• Adults
• Balanced due to deposit removal
• Bone deposit occurs at a greater rate when bone
  is injured
• Bone resorption allows minerals to be absorbed
  into the blood
• Vit C (collagen synthesis), Vit D (absorption of
  dietary calcium), Vit A (needed for balance
  between deposit removal of bone)
• Control of bone remodeling http//www.youtube.co
  m/watch?vBrI7Ra5FTus
• Hormones maintain blood calcium homeostasis
• Mechanical stress gravity affect bone growth
  allow bone to withstand stresses

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Bone repair

• Classification of fractures
• Position of bone ends after fracture
• Nondisplaced fractures bone ends retain normal
  position
• Displaced fracture bone ends out of normal
  alignment
• Completeness of break
• Complete fracture bone broken through
• Incomplete not broken all the way through
• Orientation of break relative to the long axis of
  bone
• Linear parallels the long axis
• Transverse perpendicular to the bones long axis
  
• Whether the bone ends penetrate the skin
• Open/compound bone ends penetrate the skin
• Closed/simple bone ends dont penetrate the
  skin

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Bone repair

• Fractures are treated by reduction
• Closed (external) reduction
• Bone ends coaxed into position by physicians
  hands
• Open (internal) reduction
• Bone ends secured together surgically with pins
  or wires
• Check out Fig 6.2 on pg. 192 for other types
• Comminuted common in elderly (brittle bones)
• Compression common in porous bones
• Spiral common sports fracture
• Epiphyseal
• Depressed typical skull fracture
• Greenstick common in children (more organic
  matter)

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Spiral fractures
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Comminuted
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Compression
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Dislocations open fractures

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Bone repair cont.

• 4 stages of fracture repair
• 1. Hematoma formation
• Blood vessels are torn during the break, blood
  clot forms
• Nearby bone cells deprived of nutrition and die
• 2. Fibroncartilaginous callus formation
• Vessels begin to form
• Phagocytic cells clean up debris
• Fibroblasts (produce collagen fibers that
  reconnect the bone) osteoblasts (begin forming
  spongy bone) begin to reform the bone
• 3. Bony callus formation
• Bone trabeculae convert callus into bone
• Begins 3-4 weeks after injury
• Continues for about 2-3 months
• 4. Remodeling of bony callus
• Excess material removed
• Compact bone is laid down

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Homeostatic Imbalances

• Osteomalacia Rickets (in children)
• Bones inadequately mineralized
• Caused by insufficient calcium or vitamin D
  deficiency
• Osteoporosis
• Bone resorption outpaces bone deposit, bone mass
  reduced
• Spongy bone of spine most vulnerable and neck of
  femur (broken hip)
• Caucasian women most susceptible group
• Estrogen helps restrain osteoclast activity
• GET ENOUGH CALCIUM WHILE BONES STILL INCREASING
  IN DENSITY! (Also, drink fluoridated water)
• Pagets Disease
• Excessive and haphazard bone deposit and
  resorption
• High ratio of spongy to compact -gt spotty
  weakening