• support
• protection
• movement
• electrolyte balance
• acid/base balance
• blood formation

• CT w/ a matrix hardened by minerals (calcium phosphate)
• individual bones consist of bone tissue, marrow, blood, cartilage, and periosteum
• continually remodels itself

• shapes of bones
  • long bones

• levers acted upon by muscles

• shapes of bones
  • short bones

• glide across one another in multiple directions

• shapes of bones
  • flat bones

• protect soft organs

• "shaft"
• cylinder of compact bone
• marrow cavity (medullary cavity) lined with endosteum (osteogenic cells & reticular CT)

• enlarged ends
• spongy bone covered by compact bone
• enlarged to strengthen joint and attach ligaments

• compact & spongy bone
• marrow cavity
• articular cartilage
• periosteum

• joint surface covered w/ articular cartilage
• shaft covered w/ periosteum
  • outer fibrous layer of collagen
  • inner osteogenic layer of bone forming cells
• epiphyseal plate (growth plate)
• compact bone
  • osteons
• spongy bone
  • trabeculae & lamellae but no osteons

• external & internal surfaces composed of compact bone
• middle layer is spongy bone & bone marrow
• skull fracture may leave inner layer of compact bone unharmed

• cells of osseous tissue
  • osteogenic cells

• in endosteum, periosteum, or central canals give rise to new osteoblasts
  • arise from embryonic fibroblasts
  • multiply continuously

• cells of osseous tissue
  • osteoblasts

• mineralize organic matter of matrix

• cells of osseous tissue
  • osteocytes

• osteoblasts trapped in the matrix they formed
• cells in lacunae connected by gap junctions inside canaliculi

• cells of osseous tissue
  • osteoclasts

• develop in bone marrow by fusion of 3-50 stem cells
• reside in pits that they ate into the bone

matrix of osseous tissue

• dry weight= 1/3 organic & 2/3 inorganic matter
• combination provides for strength & resilience
  • minerals resist compression; collagen resists tension
  • bone adapts by varying proportions

• matrix of osseous tissue

  • organic matter

• collagen, glycosaminoglycans, proteoglycans, & glycoproteins

• matrix of osseous tissue

  • inorganic matter

• 85% hydroxyapatite
• 10% calcium carbonate
• other minerals (fluoride, potassium, magnesium)

• osteogenesis imperfecta
  • easily breakable bones (like shattering glass)
• histology of compact bone
• needs inorganic minerals such as calcium

• osteon=basic structural unit
  • cylinders formed from layers (lamellae) of matrix around central canal (osteonic canal)
    • collagen fibers alternate b/w right & left handed helices from lamella to lamella
  • osteocytes connected to each other & their blood supply by tiny cell processes in canaliculi
• perforating canals or Volkmann canals
  • vascular canals perpendicularly joining central canals

• spongelike appearance formed by plates of bone called trabeculae
  • spaces filled w/ red bone marrow
• trabeculae have few osteons or central canals
  • no osteocyte is far from blood of bone marrow
• provides strength w/ little weight
  • trabeculae develop along bone's lines of stress

• like thick blood
• reticular fibers & immature cells
• hemopoietic (produces blood cells)
• in vertebra, ribs, sternum, pelvic girdle, & proximal heads of femur & humerus in adults

• in people of old age
• yellow marrow replaced w/ reddish jelly

1. intramembraneous ossification (takes place in flat fibrous membrane; flat bones of skull & clavicle)
2. endochondral ossification (form from preexisting hyaline cartilage; most bones)

intramembranous ossification

(*bone is directly formed!)

1. condensation of mesenchyme into trabeculae
2. osteoblasts on trabeculae lay down osteoid tissue (uncalcified bone)
3. calcium phosphate is deposited in the matrix forming spicules that unite to form bony trabeculae of spongy bone
4. osteoclasts create marrow cavity
5. surface mesenchyme produces periosteum by remaining uncalcified & increasing #'s of fibers
6. osteoblasts form compact bone at surface

• bone develops from pre-existing model
  • perichondrium & hyaline cartilage
• most bones develop this process

1. formation of primary ossification center & marrow cavity in shaft of model
   1. bony collar developed by osteoblasts
   2. areas in cartilage start to calcify
   3. chondrocytes swell & die
   4. stem cells give rise to osteoblasts & clasts
   5. bone laid down & marrow cavity created

• secondary ossification centers & marrow cavities form in ends of bone
  • same process
• cartilage remains as articular cartilage & epiphyseal (growth) plates
  • growth plates provide for increase in length of bone during childhood & adolescence
  • by early 20's, growth plates are gone & primary & secondary marrow cavities united

• zone of reserve cartilage
  • hyaline cartilage
• zone of proliferation
  • chondrocytes multiply forming columns of flat lacunae
• zone of hypertrophy
  • cell enlargement
• zone of calcification
  • mineralization of matrix
• zone of bone deposition
  • chondrocytes die & columns fill w/ osteoblasts
  • osteons formed & spongy bone is created

• bones increase in length
  • interstitial growth of epiphyseal plate
  • epiphyseal line is left behind when cartilage gone
• bones increase in width
  • "appositional growth"
  • osteoblasts lay down matrix in layers on outer surface & osteoclasts dissolve bone on inner surface
• bones remodeled throughout life
  • Wolff's law of bone=architecture of bone determined by mechanical stresses
    • action of osteoblasts & osteoclasts
  • greater density & mass of bone in athletes or manual worker is an adaptation to stress

• dwarfism
  • achondroplastic

• long bones stop growing in childhood
  • normal torso, short limbs
• spontaneous mutation during DNA replication
• failure of cartilage growth

• dwarfism
  • pituitary

• lack of growth hormone
• normal proportions w/ short stature

• mineralization is crystallization process
  • osteoblasts produce collagen fibers spiraled the length of the osteon
  • minerals cover the fibers & harden the matrix
    • ions (calcium & phosphate & from blood plasma) are deposited along the fibers
    • ion concentration must reach the solubility product for crystal formation to occur
• abnormal calcification (ectopic)
  • may occur in lungs, brain, eyes, muscles, tendons, or arteries (arteriosclerosis)

• bone dissolved & minerals released into the blood
  • performed by osteoclasts "ruffled border"
  • hydrogen pumps in membrane secrete hydrogen into space b/w the osteoclast & bone surface
  • chloride ions follow by electrical attraction
  • hydrochloric acid (pH 4) dissolves bone minerals
  • enzyme (acid phosphatase) digests the collagen
• dental braces reposition teeth & remodel bone
  • create more pressure on one side of the tooth
  • stimulates osteoclasts to remove bone
  • decreased pressure stimulates osteoblasts

• component of DNA, RNA, ATP, phospholipids, & pH buffers
  • ~750 g in adult skeleton
  • plasma concentration is ~4.0 mg/dL
    • 2 plasma forms: HPO₄^-2 & H₂PO₄^-

• needed in neurons, muscle contraction, blood clotting, & exocytosis
  • ~1100g in adult skeleton
  • plasma concentration is ~10 mg/dL

• ion imbalances
  • changes in phosphate levels

• ion imbalances
  • changes in calcium

• can be serious
• hypocalcemia
• hypercalcemia
• calcium phosphate homeostasis depends on calcitriol, calcitonin, & PTH hormone regulation

• ion imbalances
  • hypocalcemia

• deficiency of blood calcium
  • causes excitability of nervous system if too low
    • muscle spasms, tremors or tetany ~6mg/dL
    • laryngospasm & suffocation ~4mg/dL
  • w/ less calcium, sodium channels open more easily, sodium enters cell & excites neuron

• ion imbalances
  • hypercalcemia

• excess of blood calcium
  • binding to cell surface makes sodium channels less likely to open, depressing nervous system
    • muscle weakness & sluggish reflexes, cardiac arrest ~12mg/dL

• calcitriol (activated Vitamin D)
  • produced by the following process:

• UV radiation & epidermal keratinocytes convert steroid derivative to cholecalciferol - D3
• liver converts it to calcidiol
• kidney converts that to calcitriol (vitamin D)

• calcitriol
  • behaves as a hormone that raises blood calcium concentration

• increases intestinal absorption & absorption from the skeleton
• increases stem cell differentiation into osteoclasts
• promotes urinary reabsorption of calcium ions

• calcitriol
  • diseases

• rickets
  • abnormal softness in children
• osteomalacia
  • in adults w/out vitamin D

• secreted (C cells of thyroid gland) when calcium concentration rises too high
• functions
  • reduces osteoclast activity as much as 70%
  • increases the number & activity of osteoblasts
• important in children, little effect in adults
  • osteoclasts more active in children
  • deficiency does not cause disease in adults
• reduces bone loss in osteoporosis

picture...

• negative feedback

• glands on posterior surface of thyroid
• released w/ low calcium blood levels
• function: raise calcium blood level
  • causes osteoblasts to release osteoclast-stimulating factor (RANKL) increasing osteoclast population
  • promotes calcium resorption by the kidneys
  • promotes calcitriol synthesis in the kidneys
  • inhibits collagen synthesis & bone deposition by osteoblasts
• sporatic injection of low levels of PTH causes bone deposition

• hormones, vitamins, & growth factors
• growth rapid at puberty
  • hormones stimulate osteogenic cells, chondrocytes & matrix deposition in growth plate
  • girls grow faster than boys & reach full height earlier (estrogen stronger effect)
  • males grow for a longer time & taller
• growth stops (epiphyseal plate "closes")
  • teenage use of anabolic steroids = premature closure of growth plate & short adult stature

• fractures & their repair
  • classification

• fractures classified by structural char.
  • break in the skin
  • multiple pieces

• fractures & their repair
  • stress fracture

• caused by trauma
  • car accident, fall, athletics, etc.

• fractures & their repair
  • pathological fracture

• in bone weakened by disease
  • bone cancer or osteoporosis

• normally 8-12 weeks (longer in elderly)
• stages
  1. fracture hematoma: clot forms, then osteogenic cells form granulation tissue
  2. soft callus: fibroblasts produce fibers & fibrocartilage
  3. hard callus: osteoblasts produce a bony collar in 6 weeks
  4. remodeling (in 3 to 4 months): spongy bone replaced by compact bone

• closed reduction
  • fragments are aligned w/ manipulation & casted
• open reduction
  • surgical exposure & repair w/ plates & screws
• traction: risks long term confinement to bed
• electrical stimulation used on fractures
  • if 2 months necessary for healing
• orthopedics = prevention & correction of injuries & disorders of the bones, joints & muscles

• bones lose mass & become brittle (loss of organic matrix & minerals)
  • risk of fracture of hip, wrist, & vertebral column
  • complications (pneumonia & blood clotting)
• postmenopausal white women at greatest risk
  • by age 70, average loss is 30% of bone mass
  • black women rarely suffer symptoms

• estrogen maintains density in both sexes (inhibits resorption)
  • testes & adrenals produce estrogen in men
  • rapid loss after menopause, if body fat too low or w/ disuse during immobilization
• treatment
  • ERT slows bone resorption, but increases risk breast cancer, stroke & heart disease
  • PTH slows bone loss if given daily injection
    • Forteo increases density by 10% in 1 year
    • may promote bone cancer
  • best treatment is prevention: exercise & calcium intake (1000 mg/day) b/w ages 25 & 40

• joint classification
  • structural

• type of binding material
  • fibrous
  • cartilaginous
  • synovial

• joint classification
  • functional

• movement allowed
  • synarthroses--none
  • amphiarthroses--some
  • diarthroses--free

• fibrous CT connection; no joint cavity, mostly immovable
• types
  • sutures
  • syndesmoses
  • gomphoses

• cartilage connection; no joint cavity; no to some movement
• types
  • synchondroses
  • symphyses

• articular cartilage
  • cover bone ends for cushioning
• joint cavity
  • space surrounding joint filled w/ synovial fluid
• articular capsule
  • 2 layer "wall" forming above
  • fibrous capsule--outer wall; dense irregular CT; tough, continuous w/ bone periosteum; connection b/w jointed bones
  • synovial membrane--inner wall; loose CT (areolar)

• fat pads
• additional fibrocartilage (menisci) to help
• bursae-extra sacs of synovial fluid
• tendon sheath-bursa wrapped around tendon

• articular surfaces-shape/fit
• ligaments-usually more is better, but once they stretch--not so good!
• muscle tone-tendons help shore up joints; constant slight contraction of muscles keep them taut
  • some joints like knee also helped by muscle mass itself

• osteoarthritis-wear and tear
• rheumatoid arthritis-autoimmune
• Gout-uric acid crystals (disease of kings)
  • uric acid in red meats & red wine

• movement
  • respiration, digestion, birth
• body opening
  • light, food, waste
• stability
  • joints, posture
• communication
  • smiles, frowns, writing, speech
• heat production

• muscle cell (fiber): endomysium (areolar)
• visible fibers bundles (fasicles): perimysium
• multiple fasicles bundled (muscle): epimysium

• epimysium grades smoothly into CT sheets called fasciae
• fasciae connect muscles to each other (no fat) & to the skin above (hypodermis = superficial fasciae)

• epimysium can flow directly into periosteum of bone = DIRECT ATTACHMENT (ex: intercostal muscles)
• epimysium can flow into tendons before these attach to periosteum of bone = INDIRECT ATTACHMENT