BONE

1
BONE

• 206 bones in adult
• 270 bones at birth
• organization
• axial skeleton- 80 bones
• skull- 29 bones
• vertebral column- 26 bones
• thorax (ribs and sternum)- 25 bones
• appendicular skeleton- 126 bones
• pectoral girdle- 4 bones
• upper limbs- 60 bones
• pelvic girdle- 2 bones
• lower limbs- 60 bones

2
BONE FUNCTIONS

• support - attaches to most skeletal muscles
• movement - needs articulations
• protection - brain, heart, lungs, blood forming
  tissue, bladder
• mineral reserve - Ca, P, Na, K
• blood cell production
• red marrow
• storage of energy
• yellow marrow

3
BONE FUNCTIONS

• acid-base balance
• absorb or release alkaline salts
• detoxification
• removes heavy metals and other foreign elements
  from the blood

4
Bone Problem

• Ann is a 55 year old white woman who is
  postmenopausal and who has done little exercise
  in her life
• Ann has experienced a fracture of the hip and is
  concerned about possible osteoporosis
• Ann does not understand the cause or treatment of
  osteoporosis
• she decided to have a bone density test

5
BONE TYPES

• 1. Compact or dense bone
• 2. Spongy or cancellous bone

6
EXTERNAL ANATOMY OF LONG BONE

• diaphysis -- shaft
• epiphysis with proximal and distal ends
• medullary or marrow cavity
• center of ________________
• fat storage- yellow marrow
• gelatinous bone marrow -- reddish jelly that
  replaces yellow marrow in old age
• endosteum
• thin layer
• lines ___________ cavity
• dense irregular connective tissue
• contains _______________ cells

7
EXTERNAL ANATOMY OF LONG BONE

• periosteum
• double layer of dense irregular connective tissue
• outer fibrous layer
• inner osteogenic layer
• elastic fibers, blood vessels, bone cells
• lines outside of bone
• sharpeys fibers
• ______________ fibers that penetrate into bone
  matrix
• no periosteum at ends- ___________ cartilage

8
EXTERNAL ANATOMY OF LONG BONE

• Compact bone
• outer surface of bone
• Spongy bone or _________________
• central regions of flat bone
• within epiphyses of long bones
• reduces weight of bone
• forms along lines of stress
• contains _________ marrow

9
RED BONE MARROW

• Major areas
• Ribs
• Sternum
• Vertebrae
• Innominate bones
• Head of femur
• Head of humerus

10
HISTOLOGY OF COMPACT BONE

• Haversian systems or osteons
• Haverisan canals - contains blood vessels
  nerves
• Volkmann's canals - perpendicular to HC
• connect HC to outside blood vessels
• 1/2 liter of blood per minute
• lamellae - ring of hard calcified intercellular
  substance
• concentric
• interstitial
• circumferential
• lacunae - spaces that contain _______________
• canaliculi - connect osteocytes
• connected by __________ junctions

11
CELLS IN BONE

• a. osteogenic cells
• - found in cellular layer of periosteum,
• endosteum and Haversian canals
• - ________ cells --gt osteoblasts

12
CELLS IN BONE

• b. osteoblasts
• - produce bone matrix
• - before calcium salts are deposited --
  __________
• - promotes deposition of calcium in the matrix
• - osteoblasts become surrounded by bone and are
• now called ___________
• - not mitotic

13
OSTEOBLAST FORMING BONE
14
CELLS IN BONE

• c. Osteocytes
• - cannot divide
• - two functions
• 1. maintain and monitor protein and mineral
  content of matrix
• 2. participate in repair of damaged bone
• - if released from lacunae can form ___________
  or ______________cells

15
CELLS IN BONE

• d. osteoclasts in Howship's lacunae
• - multinuclear- up to 50 nuclei
• - derived from _____________
• - sends out projections toward bone and secrete
  
• two substances
• 1. ___________ enzymes
• - acid phosphatase
• - from lysosomes and digest collagen
• 2. acids- _______ and ___________ acids
• - dissolve bone salts

16
HISTOLOGY OF SPONGY BONE

• no haversian systems
• thin plates called ____________
• osteocytes in lacunae
• canaliculi but link to surrounding red bone
  marrow

17
MATRIX OF BONE

• 1. inorganic salts- 67
• hydroxyapatite- Ca10 (PO4)6(OH)2
• other salts
• Mg, Na, K, CO3- not in crystal form
• strontium, uranium, plutonium, lead, gold
• 9 of 14 of the major radioactive products from
  hydrogen bomb
• function
• allows bone to withstand __________
• calcination
• remove organic material by __________

18
MATRIX OF BONE

• 2. organic framework or osteoid -- 33
• collagenous fibers and chondrin
• function
• provide bone with great _________ strength
• ability to resist stretching and twisting
• acid treatment
• remove inorganic salts with acid
• leaves the protein

19
OSSIFICATION

• begins 6th week of embryo
• continues until about age of 25
• types
• Intramembranous ossification
• flat bones of skull, mandible and clavicle
• called dermal bones
• Endochondral ossification
• most of the bones in the body
• formed from hyaline cartilage

20
INTRAMEMBRANOUS OSSIFICATION

• 1. Mesenchyme cells --gt osteoblasts --gt
  osteocytes
• osteoblasts secrete ___________ matrix
• osteoid becomes mineralized thru crystallization
  of Ca salts -- using enzyme __________________
• called ossification center
• 2. Blood vessels begin to grow
• spicules meet and fuse together

21
INTRAMEMBRANOUS OSSIFICATION

• 3. Spongy bone gives rise to compact bone on the
  outside
• 4. Ossification is incomplete at birth
• dense irregular CT left are called fontanels
• _______________ at birth
• most close by 12 months, all close by 24 months

22
ENDOCHONDRAL OSSIFICATION

• 1. Hyaline cartilage (step 1)
• perichondrium
• 2. Bony collar (step 2)
• osteoblasts gather on inner surface of
  perichondrium -- begin laying down bone called
  the bony collar
• in the center, cartilage cells enlarging and dying

23
ENDOCHONDRAL OSSIFICATION

• 3. Primary ossification center (steps 3 and 4)
• cartilage cells dying and calcified matrix begins
  to degenerate
• blood vessels enter matrix carrying
• ______________ to form bone
• ______________ to dissolve bone forming marrow
  cavity
• 3rd month of fetal life

24
ENDOCHONDRAL OSSIFICATION

• 4. Secondary ossification center (step 5)
• shortly after birth in the proximal epiphysis, a
  secondary ossification center forms
• no marrow cavity forms
• at two years old secondary ossification center
  forms at the distal epiphysis
• two areas of cartilage left after 2 years old
• a. ___________ cartilage - on ends
• b. ___________ plate - between primary and
• secondary ossification centers

25
ENDOCHONDRAL OSSIFICATION

• 5. End of endochondral ossification (step 6)
• for most bone, stops by ages of ________
• epiphyseal plate ossifies to form the epiphyseal
  line
• articular cartilage only remaining cartilage
• found at the ends of the bone

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PRIMARY OSSIFICATION CENTERMETAPHYSIS

• Zone of reserve cartilage
• Zone of cell proliferation
• chondrocytes multiply and become arranged into
  longitudinal columns of flattened lacunae
• Zone of hypertrophy
• chondrocytres cease to divide and hypertrophy

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PRIMARY OSSIFICATION CENTERMETAPHYSIS

• 4. Zone of calcification
• minerals (Ca) are deposited in matrix
• 5. Zone of bone deposition
• chondrocytes die
• osteoblasts invade and lay down trabeculae
• osteoclasts erode bone away and leave marrow
  cavity
• osteoblasts continue to lay down compact bone on
  the bony collar

28
BONE GROWTH - LENGTH

• on epiphyseal side
• chondrocytes continually reproduce by _________
• on diaphyseal side
• chondrocytes swell and become surrounded by
  calcified matrix
• chondrocytes die, bone replaces chondrocytes
• bone is eroded away by osteoclasts, marrow cavity
  forms
• epiphyseal plate remains constant ______________
• epiphyseal plate becomes ossified- _____________
• 18 years in females
• 20 years in males

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BONE GROWTH - DIAMETER

• compact bone remains constant _____________
• marrow cavity increases in diameter
• balance between osteoblasts and osteoclasts not
  always same

30
PIEZOELECTRIC EFFECT

• bone is deposited in proportion to compressional
  load
• compression causes a ________ potential at the
  site
• remainder of bone has a _________ potential

31
REQUIREMENTS FOR BONE GROWTH

• 1. Salts
• Ca P
• calcium is the most abundant mineral in body
• stores 99 of calcium in bone
• plasma - Ca
• stores 85-90 of P in bone
• plasma - HPO4-2 and H2PO4-1
• Mg, F, Fe, and Mn

32
REQUIREMENTS FOR BONE GROWTH

• 2. Vitamins
• Vit. A -- stimulates chondroitin sulfate
  synthesis
• Vit. K and B12 -- synthesis of proteins
• Vit. C -- collagen synthesis and stimulates
  osteoblast differentiation
• Vit. D3 -- forms calcitriol which causes
  increased absorption of Ca and P from intestine

33
REQUIREMENTS FOR BONE GROWTH

• 3. Hormones
• calcitriol -- Ca P absorption from small
  intestine
• other hormones
• Growth hormone
• Thyroid hormones
• Glucocorticoids
• Insulin
• sex hormones (estrogen and testosterone)
• stimulates osteoblast activity and closure of
  epiphyseal plate
• Estrogen has a stronger effect so growth starts
  and stops earlier than with testosterone
• anabolic steroids (testosterone) and prematurely
  close epiphyseal plate

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REQUIREMENTS FOR BONE GROWTH

• 3. Hormones (continued)
• Parathyroid hormone
• from parathyroid gland
• increases blood calcium - 10 fluctuation is
  normal
• increase blood Ca by 30 --gt neurons and muscles
  are unresponsive
• decrease blood Ca by 35 --gt neurons excite and
  may cause convulsions
• works on three levels
• a. Bone
• increases number activity of osteoclasts
• decreases activity of osteoblasts

35
REQUIREMENTS FOR BONE GROWTH

• 3. Hormones (continued)
• Parathyroid hormone
• b. Kidney
• increases reabsorption of Ca
• increases excretion of P
• c. Intestine
• activate vitamin D3 to calcitriol
• cholesterol --gt (UV light) --gt Vit. D3 --gt
  calcidiol (liver) --gt calcitriol (kidney, PTH)
• increases absorption of Ca and P from intestine

36
REQUIREMENTS FOR BONE GROWTH

• 3. Hormones (continued)
• Parathyroid
• Hyperparathyroidism
• _________ PTH
• depresses nervous system
• brittle bones, kidney stones
• Hypoparathyroidism
• _________ PTH
• increased excitability of nervous system
• respiratory paralysis

37
REQUIREMENTS FOR BONE GROWTH

• 3. Hormones (continued)
• Calcitonin
• from parafollicular cells or C cells of the
  _________
• decreases blood Ca
• acts mainly on bone
• decrease activity of osteoclasts
• increases activity number of osteoblasts
• infants - _____________
• adults - ______________
• accounts for movement of 0.8 grams of Ca per day

38
Problem - OsteoporosisTreatments

• Hormone Replacement Therapy (HRT)
• types
• estrogen (ERT)
• estrogen progestin (HRT)
• side effects
• nausea, bloating, breast tenderness, high blood
  pressure and blood clots
• issue of a relationship between breast cancer and
  estrogen use is still to be determined.

39
Problem - OsteoporosisTreatments

• Alendronate Sodium and Risedronate Sodium
• biphosphonates (bind to hydroxyapetites)
• reduces bone loss, increased bone density, and
  reduces risk of spine fractures and hip fractures
• side effects rare - abdominal pain, nausea,
  heartburn, irritation of esophagus
• Raloxifene
• selective estrogen receptor modulators (SERMs)
• produces increase in bone mass
• side effects rare - hot flashes and deep vein
  thrombosis
• Calcitonin
• side effect - may cause allergic reaction-
  flushing of face and hands, urinary frequency,
  nausea and a skin rash

40
Problem - OsteoporosisPrevention

• calcium
• 1000 - 1300 mg per day
• vitamin D
• fortified dairy products, egg yolks, saltwater
  fish and liver
• exercise
• weight-bearing
• bone mineral tests