lecture Chap 6 skeletal tissue

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julianne.elizabeth
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lecture Chap 6 skeletal tissue
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2012-03-01 21:35:54
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classifications Bones cartilage bone formation cells hormonal regulation growth repair fractures homeostatic imbalances
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lecture chapter 6 bone and skeletal tissue
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  1. Skeletal cartilages
    describe
    -avascular and no nerves

    -primarily water, accounts for its ability to spring back

    -Dense connective tissue girdle of perichondrium contains blood bessels for nutrient delivery to cartilage
  2. Skeletal Cartilages
    Types
    • 1. Hyaline Cartilage
    • -provides support, flexibility, and resilience (collagen fibers)
    • -most abundant type
    • -articular cartilage, costal cartilage, respiratory cartilage, nasal cartilage (bones form from this when little)

    • 2. Elastic Cartilage
    • -similar to hyaline, but contain elastic fibers (bendy)
    • -external ear and epiglottus

    • 3. Fibrocartilage
    • -collagen fibers: have great tensile strength
    • -intervertebral discs, menisci, and pubic symphysis
  3. Growth of cartilage
    • 1. Appositional
    • -cells secrete matrix against external face of existing cartilage

    • 2. Interstitial
    • -chondrocytes divide and secrete new matric, expanding cartilage from within

    • Calcification of cartilage occures during...
    • -normal bone growth
    • -old age

    calcified cartilage is not calcified bone
  4. Bones of the Skeleton
    206 named bones

    • 2 Main groups by location
    • 1. Axial
    • -bones of skull, vertebrak column, and ribs
    • -protect, support, and carry other body parts

    • 2. Appendicular skeleton
    • -upper and lower limbs
    • -pectoral and pelvic girdles
    • -locomation, manipulation of the enviornment
  5. Classification of bones by shape
    • Long bones
    • -longer than they are wide
    • -shaft and 2 ends
    • -femur, humerus, phalanges

    • Short Bones
    • -cube shaped bones (carpals and tarsals)
    • -Sesmoid bones: grow within tendons (patella)

    • Flat Bones
    • -thin, flat, slightly curved
    • -sternum, ribs, scapulae, cranium bones

    • Irregular Bones
    • -complicated shapes
    • -vertebrae, hip bones
  6. Functions of Bones
    • 1. Support
    • -for the body and the soft organs

    • 2. Protection
    • -for the brain, spinal cord, and vital organs

    • 3. Movement
    • -levers for muscle action
    • -design of joins determines the type of movement

    • 4. Storage
    • -minerals (calcium and phosphorus) and growth factors
    • - released into the bloodstream when needed for distribution to all parts of the body (continual)

    5. Blood cell formation (hematopoiesis) in marrow cavities

    6. Triglyceride (energy/fat) storage in bone cavities
  7. Bone Markings
    Functions
    • Bulges, depressions, and holes serve as...
    • -sites of attachment for muscles, ligaments, and tendons
    • -joint surfaces
    • -conduits for blood vessels and nerves
  8. Bone Markings: Projections
    Sites of muscle and ligament attachment
    Tuberosity: rounded projection

    Crest: narrow, prominent ridge

    Trochanter: large, blunt, irregular surface

    Line: Narrow ridge of bone

    Tuberacle: small rounded projection

    Epicondyle: raised area above the condyle

    Spine: Sharp, slender projection

    Process: any bony prominence
  9. Bone Markings: projections
    Projections that help form joints
    Head: bony expansion carroed on a narrow neck

    Facet: smooth, nearly flat articular surface

    Condyle: rounded articular projection

    Ramus: armlike bar
  10. Bone Markings: depressions and openings
    Meatus: canal-like passageway

    Sinus: cavity within the bone

    Fossa: Shallow, basin like depression

    Groove: furrow

    Fissure: narrow, slitlike opening

    Foramen: round or oval opening through a bone
  11. Bone textures
    1. Compact bone: dense outter layer

    • 2. Spongey (cancellous) bone
    • -honeycomb of trabeculae
    • -filled with red or yellow bone marrow
  12. Structure of a long bone
    • Diaphysis: shaft
    • -compact bone collar surrounds medullary (marrow cavity)
    • -medullary cavity in adults contains fat (yellow marrow)

    • Epiphysis: expanded ends
    • -compact bone exterior and spongey bone interior
    • -epiphyseal line (remnant of growth plate) between the diaphysis and each epiphysis
    • -articular (hyaline) cartilahe on joint surfaces has the function of cushioning
  13. Membranes of Bone
    Periosteum
    -covers entire external bone except where joint is (glistening white)

    • 2 Layers:
    • 1. outer fibrous layer (dense irregular connective tissue) of bone
    • 2. Inner osteogenic layer
    • *osteoblasts: bone forming cells
    • *osteoclasts: bone destroying cells
    • *osteogenic cells: stem cells that give rise to osteoblasts

    -nerve fibers, nutrient blood vessels, and lymphatic vessels enter the bone via nutrient foramina

    -secured to underlying bone by Sharpey's fibers (collagen fibers which are exceptionally dense at point of anchoring for ligaments and tendons)
  14. Membranes of Bone
    Endosteum
    • Delicate membrane on internal surfaces of bone
    • -covers the trabeculae of spongey bone and lines the canals that pass through the compact bone

    Also cntain osteoblasts and osteoclasts
  15. Structure of short, irregular, and flat bones
    No shaft or epiphysis

    Periosteum-covered compact bone on outside

    • Endosteum-covered spongey bone within
    • -called siploe in flat bones
    • -like a stiffened sandwhich

    -bone marrow between trabecular
  16. Location of hematopoietic Tissue (red marrow)
    • Red marrow cavities in adults
    • -trabecular caivites of the heads of femur and humerus
    • -trabecular cavities of the diploe of flat bones
    • *tend to be more cative in red marrow production, so samples are often drawn from here

    • Red Marrow cavities in newborn infants
    • -medullary cavities and all spaces of spongey bone
  17. Cells of the Bone
    Osteogenic (osteoprogenitor) cells: stem cells in periosteum and endosteum that give rise to osteoblasts

    Osteoblasts: bone forming cells

    Osteoclasts: break down or resorb matrix

    • Osteocytes: mature bone cells
    • -help to maintain bone matrix and act as stress sensors
  18. Label
  19. microscopic anatomy of bone: Compact/Lamellar Bone
    Structural Unit: Haversian System or Osteon

    • Lamella:
    • -weight bearin
    • -column like matrix tubes like rings on a tree
    • -collagen fibers in lamellae always go in the same direction, but the next one (ring) goes in a different direction
    • *this reinforces to prevent twisting

    • Central/haversian Canal:
    • -through the lamllae
    • -contains blood vessels and nerves

    • Perforating (Volkmann's) Canals
    • -Covered with endosteum
    • -at right angles to the central canal
    • -connects blood vessels and nerves of the periosteum and central canal

    • Lacunae:
    • -small cavities that contain oesteocytes (spider shaped)

    • Canaliculi:
    • -hairlike canals thatr connect lacunae to each other and the central canal
    • -allows bone to be nurished through connection of osteocytes
  20. Microscopic anatomy of bone: spongey bone
    • Trabeculae:
    • -align along lines of stress (Stress resistors)
    • -no osteons
    • -contain irrefularly arranged lamellae, osteocytes, and canaliculi
    • -cappillaries in endosteum supply nutrients (diffuses thru canaliculi)
  21. Chemical Composition of Bone: Organic
    • -Osteogenic cells, osteoblasts, osteocytes, osteoclasts
    • -Osteoid: organic bone matrix secreted by osteoblasts (1/3 of matrix)
    • *ground substance (proteoglycans, glycoprotiens)
    • *collagen fibers: provide tensile strength and flexibility
  22. Chemical Composition of Bone: Inorganic
    • Hydroxyapatites (mineral salts)
    • -65% of bone by mass
    • -mainly calcium phosphate crystals
    • -responsible for hardness and resistance to compression
    • -why bones remain hard after death
  23. Bone development
    Osteogenesis (ossification)-bone tissue formation

    • Stages:
    • -bone formation: begins 2nd month of development
    • -postnatal bone growth: until early childhood
    • -bone remodeling and repair: lifelong
  24. Two types of ossification
    • 1. Intramembranous ossification (from mesenchyme)
    • -membrane bone develops from fibrous membrane
    • -forms flat bones, e.g. clavicles and cranial bones

    • 2. Endochondral ossification
    • -cartilage (endochondral) bone forms by replacing hyaline cartilage
    • -forms most of the rest of the skeleton
  25. Intramembranous Ossification
    Steps
    • 1. Ossification center appears in the fibrous connective tissue membrane
    • -selected centrally located to mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center

    • 2. Bone matrix (osteoid) is secreted within the fibrous membrane and calcifies
    • -osteoblasts begin to secrete osteoid, which is calcified within a few days
    • -trapped ostepblasts become osteocytes

    • 3. Woven bone and periosteum form
    • -accumulating osteoid is laid down between embryonic blood vessels ina random manner. This creates a network of woven trabeculae

    • 4. Lamellar Bone replaces woven bone, just deep to the periosteum. Red marrow appears
    • -trabeculae jus deep to the periosteum thicken, and are later replaced with mature lamellar bone, forming compact bone plates
    • -spongey bone (diploe) consisting of distinct trabeculae persists internall and its vascular tissue becomes red marrow
  26. Intramembranous Ossification
    Label picture
  27. Endochondral ossification (of long bone)
    Steps
    1.Bone Collar forms around hyaline cartilage model (periosteal bone collar) (week 9 of development)

    • 2. Cartilage in the center of disaphysis calcified and then dvelops cavities
    • -chondrocytes within the shaft enlarge (hypertrophy) and signal surrounding cartilage to calcify
    • *these condrocytes die due to lack of nutrients so cavitiy forms
    • -elsewhere, cartilage remains healthy and grows for the catrilage model to enlongate

    • 3. The periosteal bud invades the internal cavities and spongey bone begins to form (month 3 of development)
    • -nutrient artery and vein, lymphatic vessels, nerve fibers, red marrow elements, osteoblasts, osteoclasts
    • -osteoclasts partially erode calcified cartilage and steoblasts secrete osteroid, beginning the creation of spongey bone

    • 4. The diaphysis elongates and a medullary cavitiy form as ossification continues. Secondary ossification center appears in epiphysis in prep for stage 5 (at birth)
    • -osteoclasts create the medullary cavoty and "chase" cartilahe formation along the shaft

    • 5. The epiphysises ossify. When completed, hyaline cartilage reamins only in the epiphyseal plates and articular cartilage
    • -stages 1-4 same at secondary epiphysis site until ossification is complete
  28. Endochondral ossification (of long bone)
    label picture
  29. Postnatal Bone Growth
    • Interstitial growth: length of long bones
    • -growth ends when bone of epiphysis and diaphysis fuse, around 18 for f and 23 for m

    Appositional growth: thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces throughout life
  30. Growth in Length in Long bones
    • Epiphyseal plate cartilage organizes into four important functional zones:
    • 1. Proliferation (Growth)
    • -cartilage abutting the plate on the diaphysis side is in the growth zone

    • 2. Hypertropic:
    • -older chondrocytes enlarge, leaving spaces

    • 3. Calcification:
    • -surrounding cartilage die and calcify

    • 4. Ossification (osteogenic)
    • -calcification leaves long spondle like spincules. Will be invaded with marrow elements from medullary cavity
  31. Growth in Length in Long bones
    Label picture
  32. Hormonal Regulation of Bone growth
    • Growth hormone stumulates epiphyseal plate activity
    • -released by anterior pituitary gland

    Thyroid hormone modulates activity of growth hormone

    • Testosterone and estrogens (at puberty)
    • -promote adolescent growth spurts as well as feminization/masculization
    • -end growth by epiphyseal plate closure
  33. Bone remodeling
    Spongey bone replaced every 3-5 years

    Compact bne replaced every 10 years

    • bone remodeling: bone deposit and bone resorbtion
    • *remodeling does not occur uniformly, some faster than others
  34. Bone deposit
    -Occues where bone is injured or added strength is needed

    -requires a diet rich in protien, vits A, C, and D, calcium, phosphorus, magnesium, and manganese

    • Sites of new matrix deposit are revealed by...
    • *Osteoid Seam
    • - Unmineralized band of the matrix
    • *calcification front
    • - the abrupt transition zone between the osteoid seam and the older mineralized bone
  35. Bone resorption
    • Osteoclasts secrete...
    • -Lysosomal enzymes: digest organic matrix
    • -Acids: convert calcium salts into soluable forms (hydrocloric acid)
    • -creates grooves in bone

    Dissolved matrix is transcytossed across osteoclast, enters interstitual fluid and then blood
  36. Control of Remodeling
    What controls the continual remodeling of bone?
    • Hormonal mechanisms that maintain calcium homeostasis in the blood
    • -negative feedback system
    • -determines whether and when

    • Mechanical and gravitational forces
    • -determines where
  37. Hormonal Control of Blood Calcium
    What is Ca 2+ necessary for?
    • Calcium is necessary for...
    • -transmission of nerve impulses
    • -muscle contraction
    • -blood coagulation
    • -secretion by glands and nerve cells
    • -cell division

    *99% of bodies calcium is found in bones
  38. Hormonal Control of Blood Calcium
    Label Negative feedback system
  39. Hormonal Control of Blood Calcium
    Levels down
    Primarily control by parathyroid hormone (PTH)

    Levels decline-->parathyroid gland releases PTH-->PTH stimulates osteoclasts to degrade bone matrix and release Calcium--> blood Ca2+ levels raise
  40. Hormonal Control of Blood Calcium
    levels up
    -May be affected to a lesser extent by calcitonin

    Levels up-->parafollicular cells of thyroid release calcitonin-->osteoblasts deposit calcium salts--> blood Ca2+ levels decrease

    *leptin has also been shown to influence bone density by inhibiting osteoblasts
  41. Response to mechanical stress
    Wolff's Law: a bone grows or remodels in response to forces or demands placed upon it

    • Observations supporting wolff's law:
    • -handedness (right or left) results in bone of one upper limb being thicker and stronger
    • -curved bones are thickest where they are most likely to buckle
    • -Trabeculae form along lines of stress
    • -large, boney projections occur where heavy, active muscles attach
  42. Classification of Bone fractures
    May be classfified by 4 "either/or" categories

    • 1. Position of bone ends after fracture
    • A. nondisplaced: ends retain normal position
    • B. Displaced: ends out of normal allignemnt

    • 2. Completeness of Break
    • A. Complete: broken all the way through
    • B. Incomplete: not broken all the way through

    • 3. Orientation of the break long the long axis of bone
    • A. Linear: Parallell to long axis of bone
    • B. Transverse: perpendicular to lone axis of the bone

    • 4. Whether or not ends penetrate skin
    • A. Compound (open)- bone ends pentrate
    • B. Simple (closed)- bone ends do not penetrate
  43. Common fractures
    All fractures can be described in terms of the location, external appearance, and nature of the break

  44. Stages in Healing of a bone fracture
    • 1. Hematoma forms
    • -torn blood vessels hemorage
    • -clot forms
    • -site becomes swollen, painful, and inflamed (bone cells starve and die)

    • 2. Fibrocartilaginous callus forms
    • -phagocytic cells clear debris
    • -osteoblasts behin forming spngey bone within 1 week
    • -fibroblasts secrete collagen fibers to connect bone ends
    • -mass of repair tissue now calls fibrocartilaginous callus (splints the broken bone)

    • 3. Bony Callus formation
    • -new trabeculae form a bony (hard) callus
    • -bony callus continues until firm union is formed (about 2 mo)

    • 4. Bone remodeling
    • -in response to mechanical stressors over several months
    • -final structure resembles original
  45. Stages in Healing of a bone fracture
    label picture
  46. Osteomalacia and Rickets
    Osetomalacia is adult form of rickets

    Almost non-existent in US except in certain situations

    • -Calcium salts not deposited
    • -Rickets (childhood disease) causes bowed legs and other born deformities

    Cause: Vit D deficience or dietary calcium deficience

    Symptoms: pain when weight on affected area

    Treatment: Vit D, Calcium, and Sun
  47. Osteoporosis
    Loss of bone mass: bone resoption outpaces deposit

    Bones become porous and light

    Spongey bone of spine and neck femur become most susceptible to fracture

    Risk factors: lack of estrogen, calcium or vit D, petite body form, immobility, low levels of TSH, diabetes mellitis
  48. Osteoporosis: treatment and prevention
    • Prevent:
    • -calcium, vit d, and flouride suppliments
    • -increase weight-bearing exercise throughout life

    • Treat:
    • -hormone (Estrogen) replacement therapy (HRT) slows bone loss, but is controversial due to side effects
    • -some drugs increase bone mineral density
  49. Paget's disease
    Excessive and haphazard bone formtion and breakdown, usually in spine, pelvis, femur, or skull

    Pegetic bone has very high ratio of spongey to compact bone and reduced mineralization

    Unknown cause (possibly viral)

    Treatment includes calcitonin and biosphonates
  50. Developmental Aspects of Bones
    Embyronic skeleton ossifies predictably so fetal age is easily determined from x-rays or sonograms

    At birth, most long bones are well ossified (except epiphyses)

    In children and adolescents, bone formation exceeds bone resorption

    • nearly all bones are completely ossified by age 25
    • Bone mass decreases with age beginning at 40 (except in skull)

    Rate of loss determined by genetics and enviornmental factos

    In old age, bone resoption predominates leading to fractures (that heal more slowly)

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