chp 6

osteoclasts accomplish bone resorption by secreting __ and __

hydrogen ions and enzymes

ligament is __ to __ attachment

bone to bone

bone marrow types and function

• red bone marrow

  • inside medullar cavity

  • red marrow contains the stem cells that produce mature blood cells and is inside spongy bone

  • found in larger quantities in children

• yellow bone marrow

  • inside medullar cavity

  • contains lipids

  • found more in adults

Matrix of bone contains

• mineral salts - gives hardness

• collagen fibers - gives tensile strength

Osteolysis (resorption)

release of stored minerals and calcium by osteoclasts

Osteogenesis

• production of new bone

• osteoblasts form bone matrix

• matrix is known as osteoid and gets calcified

___ → __ → Osteoblasts → Osteocytes

Mesenchymal cells → Osteogenic cells → Osteoblasts → Osteocytes

osteocytes

-trapped osteoblasts and help in bone maintenance

Heterotopic bone formation

–– when bone forms where it should not. Osteoblasts develop where they should not.

endochondral ossification.

• preset shape

• frame is already set and inside is filled up

• formation of bone within a hyaline cartilage model

• has primary and secondary ossification center

intramembranous ossification

• no preset shape

• build and keep adding to core and shape into the shape you want

WOLFF'S LAW

bone in a healthy person or animal will adapt to the loads under which it is placed.

(exercise promotes bone mineral accumulation)

Vitamin D and bone growth

• Vitamin D is converted to calcidiol by the liver

• calcidiol is converted to active form calcitriol by kidney

• calcitriol is essential for absorption and utilization of calcium and phosphate from digestive tract

hormonal regulations of bone growth (hormones and such related to bone growth)

• Human Growth Hormone HGH

• Insulin

• thyroid and parathyroid hormones

• estrogen

  • seems to induce epiphyseal closure faster than testosterone (androgens) which results in women being shorter

• vitamin D

Thyroid and bone growth

• thyroid produces these hormones

  • Calcitonin

    • lowers the blood level of calcium and phosphate

    • not essential compared to parathyroid

thyroid:

high blood calcium (>10.4 mg/dl of blood) → secretion of calcitonin by the thyroid → decreases to normal blood calcium

Parathyroid and bone growth

• low blood calcium (< 8.7 mg/dl of blood) → secretion of PTH → increases to normal blood calcium

  -PTH has the opposite action of calcitonin

Normal calcium levels in the blood:

8.7 to 10.4 mg/dL

hypocalcemia

calcium < 8.7 mg/dL

low calcium = permeability in neuron = more sodium(positive charge) enters = neuron depolarizes = nervous system becomes hyperexcitable

(extreme case of this tetany which is sustained contraction of repiratory muscles which leads to asphyxiation)

what’s going on:

• normally calcium ions bind to negative charged surface of cell which contributes to the cell’s charge →

• hypocalcemia →

• less calcium ions to bind to cell surface →

• less charge difference between both sides of cell →

• sodium channels in plasma membrane are affected →

• difference is diminished →

• sodium channels open easily and stay open longer

interstitial growth vs appositional growth

interstitial grows in length

appositional grows in thickness

METAPHYSIS and 5 zones

metaphysis is in between epiphysis and diaphysis

• epiphysis are the ends of the bones

• diaphysis is the middle inside of the bone

metaphysis has 5 zones

• zones

  • reserve cartilage

    • only hyaline cartilage

  
  

  • proliferating

    • dividing chondrocytes (secrete the matrix of cartilage)

  
  

  • hypertrophic

    • chondrocytes mature, no more mitosis

  
  

  • calcified

    • mineral deposition, cartilage calcification

  
  

  • bone deposition

    • dead chondrocytes, because the matrix surrounding them is calcified. Osteoclasts absorb the matrix and the area is invaded by osteoblasts.

Normal phosphorus levels in the blood:

3.5 to 4.0 mg/dL

Hypercalcemia

calcium > 10.4

• hyper calcium = depression of NS and cardiac arrest

• sodium gates stay closed longer

calcitonin function

• decreases calcium levels

Fracture repair

1. blood clot forms (called fracture hematoma)

2. procallus forms (granulation tissue which is actively growing connective tissue)

3. procallus transformed into fibrocartilaginous-soft-callus by fibroblast and osteogenic cells

4. osteoblast converts fibrocartilaginous-callus into spongy bone

5. remodel callus to nearly original form

EXOGENOUS (ARTIFICIAL) STIMULATION OF BONE REPAIR

• surgical bone grafting

  • dead bone, bone fragments, living bone from another site or from cadavers can be inserted within the fracture to provide a bony model for the repair process

• Pulsating electromagnetic fields

  • electrical fields help osteoblasts

  • pulsating, low-frequency electromagnetic fields give to patients in a therapy mattress with coils

OSTEOPENIA

mild form of osteoporosis

AROMATASE

converts testosterone to estrogen

OSTEOPOROSIS DETECTION:

detect with a bone density scan called a dual-energy X-ray absorptiometry

(DXA)

causes of osteoporosis

• lack of estrogen

  • causes increase in osteoclasts

• Glucocorticoids

  • antagonize the actions of vitamin D, which in turn leads to calcium

    deficiency

• immobilization

  • bone not being used weakens bone (like when bone is in a cause after injury)

• weightless space travel

  • lack of weight-bearing activity by their muscles and bones leads to

    osteoporosis

• Other factors not well understood

  • persons with lean build, smokers, excessive consumption of alcohol, caffeine. Caffeine seems to decrease calcium absorption.

Osteoporosis treatment

• hormone replacement therapy

  • more estrogen but this has consequence of breast cancer years down the line

• calcium intake

  • increase intake is good for bones

• other drugs

  • BISPHOSPHONATES - reduces activity of osteoclasts

  • raloxifene

    • is selective estrogen receptor modulator = SERM

    • acts like estrogen only on bones

  • calcitonin

  • exercise

Abnormal bone formations

• Osteogenesis imperfecta (OI)

  • (usually inherited disease but can result from mutation)

  • genetic disorder where there is too little type 1 collagen or poor quality which causes bone to break

• marfan syndrome

  • too much cartilage at epiphyseal plates causes long and slender limbs

Abnormal Growth Hormones

• Dwarfism

  • too little HGH (human growth hormone)

  • stop growing during childhood

• Gigantism

  • too much HGH

  • excess growth and tall

  • can lead to diabetes

• Acromegaly

  • after puberty, hands-feet-lower part of face respond to too much HGH resulting overgrowth in those areas

  • can lead to diabetes

paget’s disease

• massive osteoclastic resorption and extensive bone formation

• bones become fragile and misshapened

Rickets in children and Osteomalacia in adults

• bone too flexible due to calcium deficiency and vitamin D deficiency

Osteogenic sarcoma

- BONE CANCER that primarily affects the osteoblasts.

Osteomyelitis

- inflammation of a bone especially the marrow caused by a pathogenic organism.