Insight
When not to eat your spinach
Skeletal System
individual
bones
c.t.
marrow
I. Functions
1. support
2. protection
3. levers– movement
4. mineral storage Ca++ - 90%
PO4-5. hemopoiesis by red bone marrow
blood
make
II. Anatomy of a long bone
A. Know Fig. 6.1 – all terms & word roots
diaphysis
epiphysis
epiphyseal line
compact bone
spongy bone
marrow (medullary)cavity
red marrow
yellow marrow
articular cartilage
periosteum
endosteum
nutrient
foramen
nutrient
artery
B. Blood and nerve supply
1. nutrient artery (via nutrient foramen)  supplies diaphysis
2. epiphyseal & periosteal arteries provide alternate sources
3. veins accompany arteries
4. nerves accompany vessels = neurovascular bundle
- most sensory are in the periosteum
shin splints
fractures
III. Histology of bone
A. Components
1. Cells (Fig. 6.3)
 osteogenic cells
bone “stem cells”
deep to periosteum, endosteum, line central canals,
 mitosis
 osteoblasts
secrete matrix (fibers and salts)
 mature
 osteocytes
mature, resting cell
maintains bone
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osteoclasts
 “break”
develop from WBC
huge, multinucleated
resorb matrix
2. matrix
25% H2O
25% collagen fibers (organic component) – provide tensile strength
50% mineral salts (inorganic component) – provide hardness
 calcium phosphate = hydroxyapatite  85% of inorganic
 CaCO3, Mg, Fl, SO4
 Calcification – deposition of salts on collagen
 Matrix is not solid
holes
channels
B. Compact (dense) bone tissue
 location – external layer of all bones
– bulk of diaphysis
 structural unit is the osteon
 Know Fig. 6.4 (Note legends for c & d reversed)
osteon (haversian system)
central (haversian) canal
perforating (Volkmann) canals
concentric lamellae
circumferential lamellae
interstitial lamellae (ADD)
lacunae
canaliculi
C. Spongy (cancellous) bone tissue
 location – everywhere else
– bulk of epiphysis
 structural units are flat trabeculae = “little beams” and pointed spicules
 only site of red marrow in adults
IV. Bone formation: ossification
A. Overview
1. two pathways, both start with
fibrous c.t. membrane
intramembranous
bone
cartilage
endochondral
bone
2. both form spongy bone which is then remodeled to compact bone
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B. Intramembranous ossification (Fig. 6.7)
- flat bones of the skull and clavicle
-sketch:
fibrous membrane with mesenchymal cells
and blood vessels
 fetal c.t

mesenchymal cells surround blood vessels
& differentiate into osteogenic cells

become osteoblasts  deposit osteoid
(non-mineralized bone)
-sketch:
(Fig. 6.7)

Calcification converts osteoid into
fibrous membrane now a periosteum
bony spicules & trabeculae
w/trapped osteocytes
(Fig. 6.7  &  )

- result is multiple trabeculae separated by miniature marrow cavities filled with red
marrow & many blood vessels

Fig. 6.7  Osteoid deposition and bone formation continue; peripheral bone is remodeled into
compact bone, creating “sandwich” (Fig. 6.2)
C. Endochondral ossification (Fig. 6.9) Know Handout
- most bones are formed this way
1. mesenchymal cells become chondroblasts, which form a cartilage model of the
bone.
**Ossification will occur simultaneously  around shaft (like intramembranous)
 from the inside toward both ends
Steps 2-5 on Handout
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V. Bone growth
A. In length: interstitial growth (Fig. 6.10 & 6.11)
1. occurs at metaphysis  transition between epiphyseal plate & diaphyseal bone
Sketch  5 zones
2. mechanism
- division and enlargement in middle two zones pushes epiphysis away
from diaphysis
- zone 5 creates a region of spongy bone at end of marrow cavity
- rate of proliferation = rate of ossification, so plate remains same width until
teen years
3. growth is controlled by hormones, but stops when cartilage is replaced by bone:
epiphyseal plate becomes epiphyseal line.
B. In diameter: appositional growth
1. occurs under periosteum
-- osteoblasts deposit bone on outside, while
2. osteoclasts lining the endosteum resorb bone from the inside, widening marrow
cavity
VI. Remodeling
– osteoblast/ osteoclast balance continually altered
 rapidly adjusts plasma levels of Ca++ and PO4—
 allows response to applied stresses (Rule #1? = Wolff’s Law)
weight-bearing exercise 
increases bone mass
 allows quick fracture repair
VII. Aging and Osteoporosis (= “porous bone”)  Fig. 6.16
A. Loss of Ca++ and minerals
 bone mass (density)   compression fracture risk
- entire skeletal system affected
- females > males due to hormone loss at menopause
PREVENTION  Diet and Exercise
B. Decreased rate of protein synthesis
 collagen  loss of tensile strength  SNAP!  increase fracture risk
(brittle bones)
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