chapter 6 7 the skeletal system
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Chapter 6 & 7: The Skeletal System

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Chapter 6 & 7: The Skeletal System. 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

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skeletal cartilages structures types locations
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 @ movable joints), costal (connects ribs to sternum), respiratory (larynx & reinforce passageways), and nasal (external nose) cartilages.
    • Provide support & flexibility (due to collagen fibers)
skeletal cartilages cont
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
growth of cartilage
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
classifications of bones
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
shape
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)
shape cont
Shape cont.
  • Flat bones –
    • Thin, flattened, and often curved bones
    • Include –
      • Skull bones, sternum, scapulae, and ribs
  • Irregular bones –
    • Complicated shapes
    • Don’t fit into any other class
    • Include –
      • Vertebrae
      • Hip bones & coxae
functions
Functions
  • 5 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
bone structure gross anatomy
Bone structure: gross anatomy
  • Bone markings –
    • Projections;
      • Muscle attach to and pull
      • Modified for where bones meet (joints)
      • E.g. heads, trochanters, spines
    • Depressions and openings;
      • Allows passages of nerves and blood vessels
      • E.g. fossae, sinuses, foramina, grooves
    • Table 6.1 pg. 179
bone textures
Bone Textures
  • External layer = compact bone
  • Internal layer = spongy bone
    • Made of trabeculae
long bones cont
Long bones cont.
  • Diaphysis –
    • The bone shaft
    • Contains cavity with yellow marrow
  • 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)
long bones cont1
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 – Sharpey’s 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
short flat irregular bones
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 = diploë
hematopoietic tissue
Hematopoietic tissue
  • Hematopoietictissue = red bone marrow
  • Located within trabecular cavities of the spongy bone, in diploëof flat bones & epiphysis of long bones
  • Infants – all areas of spongy bone contain red marrow
  • Adults – epiphysis of long bones – diaphysis – yellow marrow
gross anat cont
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 –
        • Deep to the periosteum
        • Superficial to endosteum
        • Resist twisting of long bones
microscopic anatomy
Microscopic anatomy
  • Compact bone – dense and solid
    • Structural unit = osteon
    • Contains lamellae, Haversian canal, & blood vessels and nerves
    • Volkmann’s 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
gross anat cont1
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
chemical composition of bone
Chemical Composition of Bone
  • Organic components
    • Cells (osteogenic cells, osteoblasts, osteocytes, and osteoclasts)
    • Osteoid – ground substance and collagen fibers
    • Contribute to bone’s structure and flexibility
  • Inorganic components
    • 65% mineral salts (calcium phosphates)
    • Tightly packed crystals around collagen fibers
    • Contribute to bone’s hardness – resists compression
formation of the bony skeleton
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
postnatal bone growth
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
postnatal bone growth1
Postnatal Bone Growth
  • Hormonal regulation
    • Infancy and childhood – growth hormone stimulates epiphyseal plate activity
      • Released by anterior pituitary gland
    • Thyroid hormones regulate the activity of growth hormone ensuring proper bone proportions
    • Testosterone and estrogens are released in increasing amounts at puberty
      • Initially – growth spurt, later induce epiphyseal plate closure
bone homeostasis
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)
      • Bone Modeling & Remodeling
    • Control of bone remodeling –
      • Hormones – maintain blood calcium homeostasis
      • Mechanical stress & gravity – affect bone growth & allow bone to withstand stresses
bone remodeling
Bone Remodeling
  • Response to mechanical stress
    • Wolff’s Law: a bone grows or remodels in response to the demands placed on it
      • Long bones are thickest midway along the diaphysis (where bending stresses are greatest)
      • Curved bones are thickest where they are most likely to buckle
      • Trabeculae of spongy bone form trusses or struts along lines of compression
      • Large, bony projections occur where heavy, active muscles attach
bone repair
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 don’t penetrate the skin
bone repair1
Bone repair
  • Fractures are treated by reduction –
    • Closed (external) reduction
      • Bone ends coaxed into position by physician’s 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)
bone repair cont
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
homeostatic imbalances
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)
  • Paget’s Disease
    • Excessive and haphazard bone deposit and resorption
    • High ratio of spongy to compact -> spotty weakening
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