Chapter 6- Bones
What do bones do for you other than make up
18% of your weight?
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•
•
•
1. Support- muscles
2. Protection- organs
3. Movement- with muscles
4. Mineral storage- calcium (99% of body's),
phosphorus,
• 45% of bone weight
• 5. Hemopoiesis- Blood cell production, in the Red
bone marrow
• 6. Fat storage- Yellow bone marrow
Figure 6-1
A Classification of Bones by Shape
Flat Bones
Sutural Bones
Sutures
External table
Parietal bone
Sutural
bone
Internal Diploë
table (spongy
bone)
Irregular Bones
Long Bones
Vertebra
Humerus
Short Bones
Carpal
bones
Sesamoid Bones
Patella
Structure of Bone(pg 173)
• 1. Diaphysis- shaft
• 2. Epiphyses- ends
• 3. Metaphyses- b/w 1 & 2, includes the
epiphyseal plate (cartilage)
- cartilage replaced by bone when done
growing = epiphyseal line
• 4. Articular cartilage- reduces friction
• 5. Periosteum-covering for protection &
nourishment
• 6. Medullary cavity/ Marrow cavityyellow marrow
• 7. Endosteum- lines the marrow cavity
6-3 Bone (Osseous) Tissue
• Matrix composed of:
– Minerals:
• Hydroxyapatite (Calcium)
• Function: Hard, brittle and can withstand
compression
– Protein Fibers:
• Collagen
• Function: Tensile strength, tolerates
twisting/bending
Bone Cells
Maintain matrix, help
repair damage bone
Secrete new matrix
(osteoid), become
osteocytes
Resorption- breakdown of
bone *every 7 years you make
a new skeleton
Produce osteoblasts,
repair fractures
Remove/recycle matrix by
dissolving with
acids/enzymes (osteolysis)
Bone Tissue
• 1. Compact- 80% of bone, few spaces
–
Haversian canals (bld vessels), Lamellae (layers),
Lacunae(pockets with osteocytes)
* All bone tissue has a rich supply of blood
2. Spongy- 20% of bone, found in
the epiphyses
• No osteons
• Matrix = trabeculae
(lattice structures), appears to
have holes
stores red marrow
– Open network of fibers w/
no blood vessels
6-4 Compact Bone and Spongy Bone
• Periosteum:
– Outer membrane
covering compact
bone
– fibrous and cellular
layer
– Functions:
– Isolates bone
– Route for blood
vessels/nerves
– Bone growth/repair
6-4 Compact Bone and Spongy Bone
• Endosteum
– incomplete cellular layer
lining the medullary
cavity
– Contains osteoblasts,
osteoprogenitor cells
and osteoclasts
– Functions:
– Covers trabeculae
– Lines central canals
– bone growth and repair
6-5 Bone Formation and Growth
• Ossification
• The process of replacing other tissues with bone
• Includes calcification: deposition of Ca salts
• Two Main forms of ossification:
• Endochondral Ossification and Intramembranous
Ossification
Endochondral Ossification
• Ossifies bones that originated as hyaline
cartilage
• Step 1:
• Chondrocytes increase in size
• Matrix begins to calcify
• Enlarged chondrocytes die
Endochondral Ossification
• Step 2:
• BVs grow into perichondrium
• Cells of perichondrium
convert to osteoblasts and
produce thin layer of
superficial bone
Endochondral Ossification
• Step 3:
• BVs penetrate cartilage
• Fibroblasts migrate and
differentiate into osteoblasts
• Form primary ossification
center, cartilage replaced with
spongy bone
Endochondral Ossification
• Step 4:
• Remodeling occurs
• Osseous tissue becomes thicker
• Cartilage near epiphysis
replaced by bone
• Osteoclasts erode spongy bone
and form medullary cavity
Endochondral Ossification
• Step 5:
• Capillaries and osteoblasts
migrate into epiphyses
• Secondary ossification
centers form
Endochondral Ossification
• Step 6:
• Epiphyses fill with spongy bone
• Articular cartilage remains
• Metaphysis: epiphyseal cartilage
separates epiphysis from
diaphysis
• Epiphyseal cartilage lost after
puberty
complete females 23, males 25
when complete-no epiphyseal disks
Figure 6-11a Bone Growth at an Epiphyseal Cartilage
An x-ray of growing epiphyseal
cartilages (arrows)
Epiphyseal lines in an
adult (arrows)
Intramembranous (Dermal)
Ossification
Bone Formation Video
6-6 Bone Remodeling
• The adult skeleton:
• Maintains itself
• Replaces mineral reserves
• Recycles and renews bone matrix
6-7 Exercise, Hormones, and
Nutrition
• Exercise
– Mineral recycling allows bones to adapt to stress
– Heavily stressed bones become thicker and
stronger
• Bone Degeneration
– Bone degenerates quickly
– Up to one third of bone mass can be lost in a few
weeks of inactivity
6-7 Exercise, Hormones, and
Nutrition
• Nutrition
– Diet must include calcium and phosphate salts,
plus small amounts of magnesium, fluoride, iron,
and manganese
– Calcitriol
• Vitamin C required for collagen synthesis and
stimulation of osteoblast differentiation
• Vitamin A stimulates osteoblast activity
• Vitamins K and B12 help synthesize bone proteins
6-7 Exercise, Hormones, and
Nutrition
• Hormones
– Growth hormone and thyroxine stimulate
bone growth
– Estrogens and androgens stimulate
osteoblasts
– Calcitonin and parathyroid hormone regulate
calcium levels
Figure 6-16b Factors That Alter the Concentration of Calcium Ions in Body Fluids
Factors That Decrease Blood Calcium Levels
These responses are
triggered when plasma
calcium ion concentrations
rise above 11 mg/dL.
HIgh Calcium Ion Levels in Plasma
(above 11 mg/dL)
Thyroid Gland Response
Parafollicular cells (C cells) in the
thryoid gland secrete calcitonin.
Calcitonin
Bone Response
Osteoclasts inhibited while
osteoblasts continue to lock
calcium ions in bone matrix
Intestinal Response
Kidney Response
Rate of intestinal
absorption
decreases
Kidneys allow
calcium loss
less
Bone
calcitriol
Calcium absorbed slowly
Calcium excreted
Calcium stored
↓Ca2+
levels in
bloodstream
Increased calcium
loss in urine
Figure 6-16a Factors That Alter the Concentration of Calcium Ions in Body Fluids
Factors That Increase Blood Calcium Levels
These responses are
triggered when plasma
calcium ion concentrations
fall below 8.5 mg/dL.
Low Calcium Ion Levels in Plasma
(below 8.5 mg/dL)
Parathyroid Gland Response
Low calcium plasma levels cause
the parathyroid glands to secrete
parathyroid hormone (PTH).
PTH
Bone Response
Osteoclasts stimulated to
release stored calcium ions
from bone
Osteoclast
Intestinal Response
Kidney Response
Rate of
intestinal
absorption
increases
Kidneys retain
calcium ions
more
Bone
Calcium released
calcitriol
Calcium absorbed quickly
↑Ca2+
levels in
bloodstream
Calcium conserved
Decreased calcium
loss in urine
Cracks/breaks in bones
Caused by physical
stress
Repaired in four steps
Figure 6-17 Types of Fractures and Steps in Repair
REPAIR OF A
FRACTURE
Fracture
hematoma
Dead
bone
Bone
fragments
Immediately after the
fracture, extensive
bleeding occurs. Over a
period of several hours, a
large blood clot, or fracture
hematoma, develops.
Spongy bone of
external callus
Periosteum
An internal callus forms as a
network of spongy bone
unites the inner edges, and an
external callus of cartilage and bone
stabilizes the outer edges.
Figure 6-17 Types of Fractures and Steps in Repair
External
callus
Internal
callus
External
callus
The cartilage of the external
callus has been replaced by
bone, and struts of spongy bone now
united the broken ends. Fragments of
dead bone and the areas of bone
closest to the break have been
removed and replaced.
A swelling initially
marks the location of
the fracture. Over time, this
region will be remodeled,
and little evidence of the
fracture will remain.
Fractures
•
•
•
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1. Open/Compound- through the skin
2. Closed/ Simple- not through the skin
3. Comminuted- smaller fragments
4. Greenstick- only children, 1 side broken, 1 side
bends
• 5. Impacted- bone through bone
• Stress fracture- microscopic , repeated stress
• can withstand 24,000 lbs/sq in, 4x greater
than steel
Transverse- break along shaft
Spiral- from twisting
Displaced- produces
abnormal bone
alignment
6-10 Effects of Aging on the Skeletal
System
• Bones become thinner and weaker with age
• Osteopenia begins between 30 - 40
• Inadequate ossification/osteoblast activity
declines = loss of bone mass
• Women lose 8% of bone mass/decade, men
3%
• The epiphyses, vertebrae, jaws most affected
• Result = fragile limbs, reduction in height,
tooth loss
• Osteoporosis
• Severe bone loss
• Affects normal
function/increases possibility of
fracture
Normal spongy bone
SEM  25
Causes:
• inadequate intake of calcium and
vitamin D
• lack of weight-bearing exercise
• lack of certain hormones, particularly
estrogen in women (menopausal
women are at higher risk)
• Cigarette smoking
• eating disorders such as anorexia
nervosa or bulimia
Spongy bone in osteoporosis SEM  21
Abnormal Development of Bone
Pituitary dwarfism =inadequate production
of growth hormone resulting in short bones
Gigantism= overproduction of HGH
Robert Wadlow (Alton) 8ft, 11in
Marfan’s syndrome =
excess cartilage at
epiphyseal plates