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Anatomy And Physiology > Skeletal System > Flashcards

Skeletal System Flashcards

1
Q

Functions of the skeletal system

A

• Support and protection
• Mineral storage
– Calcium and phosphorus
• Triglyceride storage
– Yellow bone marrow
• Blood cell production (hemopoiesis)
– Red bone marrow
• Movement
– With skeletal muscles

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2
Q

Typical long bone

A

• Diaphysis: long shaft
– Around medullary cavity with red or
yellow bone marrow (age dependent)
• Epiphysis: proximal and distal
• Metaphysis (also epiphysis in some texts)
– Epiphyseal (growth) plate: child -teen
• Hyaline cartilage
• Allows diaphysis growth in length
• Replaced by:
– Epiphyseal line: adult “scar”
• Bone replaces cartilage
• Bone stops growing
• Articular cartilage that remains:
– Hyaline cartilage at end of long bone
– Joints

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3
Q

Membranes of long bones

A

• Periosteum:
– Covers outside of bone except where
have articular cartilage
– Functions:
• Attach ligaments, tendons
• Anchors blood vessels/nerves
• Contain bone cells (osteo-blasts, -
clasts, -genic)
• Endosteum:
– Lines surfaces inside bone: canals,
medullary cavity, spongy bone
trabeculae
– Contains bone cells (osteo-blasts, -
clasts, -genic)

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4
Q

Microscopic anatomy of bone

A

• Cells: osteocytes, osteoblasts,
osteoclasts, osteoprogenitor cells
• Extracellular matrix: osteoid +
calcium salts
– Osteoid (organic): osteoblasts
make
• Collagen fibers: strength
(but alone = flexible)
• Ground substance
– Mineral (Ca2+) salt crystals
(inorganic): Hardness
• Hydroxyapatite crystals
– Ca2+ phosphate
– Ca2+ hydroxide
• Needed for calcification

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5
Q

Types of bone textures

A

• Compact bone with
osteons
• Spongy bone with
trabeculae

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6
Q

Compact bone

A

• Hard, dense, resists
bending
• Osteons: Structural units
– Parallel to diaphysis
– Central canal in middle
• Connected by
perforating canals
– Concentric lamellae
– Osteocytes in lacuna,
canaliculi
– Align parallel with lines
of stress, remodel
• Lamellae
– Concentric
– Circumferential: internal and external
• Periosteum
Compact bone

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7
Q

Spongy bone

A

• AKA trabecular bone
• Always covered with compact bone!
• Locations:
– Where bone not heavily stressed OR
stress arrives from many directions
• Short, flat, irregular bones
• Long bone:
– Around medullary cavity
– Epiphyses
• Benefits:
– Light, easily moved
– Helps bone resist stress
– Protects red bone marrow

• Trabeculae
• No osteons
– Contains lamella,
osteocytes in lacuna
– Endosteum covering
– Spaces between
trabeculae
• Red bone marrow:
blood cell formation
• Yellow bone marrow:
fat storage
– Canaliculi open onto
bone surface

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8
Q

Bone cells (the “O” cells) and origins

A

• Osteoprogenitor (osteogenic) cells: stem cells
• Osteoblasts: bone-building cells, secrete ECM
• Osteocytes: after osteoblasts become trapped, maintain bone
• Osteoclasts: bone-chewing cells, break down ECM
• Origins:
– Mesenchyme:
• Osteoprogenitor cells
• Osteoblasts
• Osteocytes
– Red bone marrow
• Osteoclast

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9
Q

Osteoprogenitor cells

A

• Originate from mesenchyme (embryo connective tissue)
– Mitotic stem cells
– Maintain osteoblast population
• Location:
– In endosteum
– Inner cellular periosteum

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10
Q

Osteoblasts

A

• Formed from osteoprogenitor
cells
• Bone-building cells:
responsible for bone
formation (ossification)
• Secrete matrix (osteoid): Bone
matrix w/out Ca2+ salts
– Make collagen, proteins
• Role in calcification: osteoid to
bone
– Hydroxyapatite formation
• Become trapped as osteocytes

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11
Q

Osteocytes

A

• Mature bone cells,
once osteoblasts
• Majority of cells,
connected
• Functions:
– Maintains bone
matrix
– Detect mechanical
stress on bone-
signal osteoblasts

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12
Q

Osteoclasts (pac-man)

A

• Large, multinucleated, phagocytic cells
– Fusion of many bone marrow cells =
many nuclei!
• Job: bone chewing resorption (osteolysis)
• Has ↑ contact with bone
– Releases HCl (acid) and enzymes
– Matrix products (including Ca2+) released
to blood
• Function:
– Regulate Ca2+ and phosphate in blood
– Normal bone remodeling: balance with
osteoblasts

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13
Q

The importance of balance

A

• Osteoblast > osteoclast activity: bone growth, stronger/more
massive
• Osteoclast > osteoblast activity: bone break down, weaken…(age,
osteoporosis)

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14
Q

Bone formation

A

• Process by which bone forms:
ossification or osteogenesis
– Replace other tissue with bone
– Center of ossification: location in
tissue where bone formation
begins
– Requires Calcification: deposit of
Ca2+ salt
• Why needed?
– Formation of bony skeleton in
embryo/fetus
– Growth of bone until adult
– Remodeling of bone
– Repair of bone (fractures)

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15
Q

Formation of bony skeleton:
embryonic/fetal ossification

A
  1. Endochondral ossification
    • Cartilage made from
    mesenchyme tissue
    • Mesenchyme replaced by
    cartilage
    • Cartilage replaced by bone
    • Most bones of body (i.e. long
    bones)
  2. Intramembranous ossification
    • Bone made directly from
    mesenchyme tissue membrane
    • No cartilage stage
    • Flatbones of skull, mandible,
    some facial bones, baby “soft
    spots”
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16
Q

Intramembranous ossification

A

• Start with mesenchyme connective tissue membrane
• Steps:
1. Formation of ossification center
• Mesenchymal cells become osteoprogenitor, which become
osteoblasts
• Ossification center established
Intramembranous ossification
2. Osteoid production and calcification:
– Osteoblasts make osteoid
– Calcium and mineral salts deposited = calcification
– Early bone forms and traps osteoblasts
– Trapped osteoblasts become osteocytes
3. Early spongy bone trabeculae with periosteum forms
– More bone produced and fuses to form trabeculae of immature
spongy bone
– Mesenchyme covering bone forms periosteum

  1. Compact bone
    formation/red bone
    marrow appears
    • Compact bone forms
    under periosteum
    • Spongy bone remains
    inside
    • Red bone marrow
    forms within spongy
    bone cavities
    • Continual remodeling
17
Q

Endochondral ossification
• Start with mesenchyme →replaced by
hyaline cartilage → replaced by bone
• Early embryo to adulthood
• Cartilage model developed
– Mesenchymal cells become cartilage
cells
– Cartilage cells form hyaline cartilage
model with perichondrium cover
• Note: chondroblasts, chondrocytes =
cartilage cells of different ages

A
  1. Periosteum and bone collar
    forms
    – Cells under perichondrium
    become osteoblasts
    – Make bone matrix and form
    bone collar (early compact
    bone)
    – Internal cartilage
  2. Inside diaphysis
    – Cartilage cells divide to
    make more
    – Make cartilage, cells grow
    bigger (hypertrophy),
    – Cartilage begins to calcify
    – Cartilage cells die leaving
    big holes
  3. Primary ossification center forms
    in diaphysis (~3 month fetus)
    – 1st center of bone formation
    – Blood vessels and osteoblasts
    invade calcified cartilage
    – Osteoblasts replace cartilage
    with spongy bone
    – Bone development spreads in
    both directions from primary
    ossification center towards
    epiphyses
    – Bone collar continues to grow
  4. Medullary cavity formed
    – Osteoclasts enter and form
    medullary cavity in diaphysis
    center
    – Medullary cavity fills with red
    bone marrow, surrounded by
    spongy bone and compact
    bone
    – Cartilage continues to form at
    epiphyseal plates, bone
    continues to replace cartilage =
    lengthening of bone called
    (interstitial growth
  5. Secondary ossification
    centers form in epiphyses
    – Cartilage replaced by
    spongy bone in epiphyses
    – Ossification moves out
    from center in all
    directions
    – BUT! No medullary cavity
    formed in epiphyses,
    spongy bone remains
  6. Replacement of all cartilage
    by bone continues until:
    Hyaline cartilage only present in
    2 places:
    – Articular cartilage:
    epiphyseal surface, joint
    area
    – Epiphyseal plate:
    • Allows for bone
    lengthening (interstitial
    growth) through
    adolescence
18
Q

Bone lengthening: interstitial growth

A

• Infants – adolescence bone lengthening: interstitial growth
• Epiphyseal growth plates: like endochondral ossification event!
– Chondrocytes divide (proliferate), produce cartilage
– Osteoblast replace cartilage with bone
– With continued cartilage production and ossification – bone grows

19
Q

Epiphyseal (growth) plate

A

• Children, adolescents bone formation > bone resorption
• Growth plate closes post-puberty leaving epiphyseal line
– Cartilage cells stop dividing and make less cartilage,
osteoblasts bone production completely replaces cartilage

20
Q

Bone widening: Appositional growth

A

• Osteoblasts under periosteum produce bone and widen bone

21
Q

Bone remodeling

A

• Bone remodeling: old bone
tissue replaced by new
– Bone resorption:
osteoclasts
– Bone deposition:
osteoblasts
– Continues even after
epiphyseal plate closure

Healthy adult (<40yo): total bone mass remains constant
– Bone formation = Bone resorption
• ~10% of bone mass removed and replaced/year
• Needed for fracture repair!
• Influenced by Ca 2+ homeostasis, mechanical stress, exercise, dietary
changes, sedentary lifestyle

22
Q

Factors affecting bone health:
growth and remodeling

A
  1. Nutrition: vitamins and minerals
  2. Hormones
    – Affects calcium and phosphate levels
  3. Weight-bearing exercises
23
Q

Nutrition and bone health

A

• Protein: collagen fibers
• Calcium: calcification to harden bone
• Vitamin C:
– Important in collagen synthesis, stimulates
osteoblasts
– Deficiency: Scurvy
• Vitamin D: activation to calcitriol
– Absorption of calcium in GI tract
– Deficiency: Rickets, osteomalacia

24
Q

Results of poor mineralization

A

• Rickets (children)/osteomalacia (adult)
– Can be result of lack of vitamin D, calcium or problem absorbing fats
– Collagen fibers present but ECM not hardened normally
– Growth plates affected in children: rickets
– Osteomalacia – “Adult rickets”, bones soft due to Ca2+ depletion

25
Q

Hormonal regulation of bone

A

• Hormones: chemicals released into blood by
a cell, affects other cells
• Growth hormone
– From anterior pituitary gland
– Critical for bone growth
• ↑ interstitial cartilage growth and
appositional bone growth

26
Q

Hormonal regulation of bone

A

• Sex hormones: Estrogen (primary female) and testosterone (primary male)
– ↑ cartilage growth, osteoblast activity in epiphyseal plates
– Growth spurt during puberty due to ↑ sex hormones, bone produced
faster than cartilage – plate eventually closes
Average gender height differences: males taller than females
– Estrogen ↑ bone formation rate even more and plate closes faster
– Females start puberty earlier – fewer years of slow growth
• Sex hormones in adulthood still important: bone remodeling, maintain
normal rate of bone production

27
Q

Importance of calcium balance

A

• Skeleton is a Ca2+ reserve!!: Hydroxyapatite crystals : Ca10(PO4)6(OH)2
• Calcium balance (9-11mg/dl)
– Blood Ca2+ is tightly controlled
– Calcium critical for many physiological processes
• Muscle contractions, blood clotting, neuron activity
– Maintained by hormones: calcitriol, parathyroid hormone, calcitonin

28
Q

Regulation of blood Ca2+ levels

A

• Calcitriol: helps to ↑ blood calcium when low
– Starts as vitamin D3 : from diet or skin makes
with sun exposure
– Vitamin D3 activated to calcitriol in kidney
– Results in:
• ↑ Ca2+ absorption in intestines→ to blood
• Can ↑ release of Ca2+ from bone →to blood
• ↑ kidneys reabsorption of Ca2+ → to blood

29
Q

Regulation of blood Ca2+ levels

A

• PTH (parathyroid hormone) from
parathyroid glands
– ↑ blood Ca2+ when Ca2+ is low
– Most important!
– Results in ↑ blood Ca2+ by:
• ↑ osteoclast activity, ↑ Ca2+
release from bone
• ↑ Ca2+ reabsorption by
kidneys, ↓ Ca2+ in urine
• ↑ calcitriol formation: ↑
Ca2+ absorption intestines

30
Q

Hypocalcemic response

A

• Hypocalcemia: decreased blood Ca2+ below normal
– Response: ↑ PTH and ↑/enhance calcitriol

31
Q

Regulation of blood Ca2+ levels

A

• Calcitonin from thyroid
gland: helps to ↓ blood Ca2+
when high
– Less important
– **At same time PTH
and calcitriol would ↓
Effect: ↓ blood Ca2+
– ↓ osteoclast activity:
Ca2+ locked up in bone
– ↓ Ca2+ reabsorption, ↑
Ca2+ elimination by
kidneys
– ↓ Ca2+ absorption by
intestines

32
Q

Hypercalcemic response

A

• Hypercalcemia:
increased Ca2+ blood
levels above normal
• Response:
– ↓ PTH, calcitriol
– Calcitonin secreted:
less Ca2+ enters and
more leaves blood

33
Q

Mechanical stress, exercise and bone

A

• Mechanical stress (muscle pull), gravity,
pressure: regulates bone remodeling
– Thicker and stronger when stressed,
pulled
– Thinner and weaker without stress
• Remodels in response to stress changes
• Weight bearing exercises important for normal bone structure and strength

34
Q

Osteoporosis

A

• Bones thinner, weaker as we age –
↓ bone density
• Osteoblasts slow down, osteoclast
continue normal speed
• Bone resorption > bone formation
• Females more susceptible, less
body weight and menopause (↓ in
estrogen needed for healthy bone)
• Spongy bone most affected
– Epiphysis, vertebrae, jaw
• Osteoporosis: bone loss is so
significant can increase risk of
fracture

35
Q

Heterotopic bone formation

A

Fibrodysplasia Ossificans Progressiva -“Stone man syndrome”

36
Q

Fracture and repair

A

• Simple fracture heals in 6-8 weeks
1. Fracture hematoma: forms hours
after injury
– Broken blood vessels!
– Swollen, painful with
inflammation
– Inflammation and removal of
dead bone cells by WBCs
2. Fibrocartilage (soft) callus forms
– Within days of break
– Fibroblasts and cartilage cells
enter area
• Fibroblasts make collagen
• Cartilage cells make hyaline
cartilage
– Mixture of collagen and hyaline
cartilage = fibrocartilage callus;
connects broken ends
3. Bony (hard) callus forms
– Osteoblasts replace fibrocartilaginous callus
with immature bony callus
– Continues for several weeks
4. Bone remodeling
– Bone callus remodeled
– Immature bone replaced by more mature
bone
– Medullary cavity made
– Excess external diaphysis removed
• Growth plate fracture: concern
– Could lead to bone length difference

Anatomy And Physiology (5 decks)

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