Chapter 7
Skeletal System
Functions of Skeletal
System:
1. Support
2. Protection
3. Produces blood cells
4. Stores inorganic materials
Classification – bones
classified by shape:





1.
2.
3.
4.
5.
Long
Short
Flat
Irregular
Sesamoid
Structure of Long Bone
Epiphysis- expanded portion at end, forms
joint.
Epiphyseal disk (line)-growth plate
Diaphysis- shaft of bone
Medullary cavity-hollow chamber in center
Spongy bone- cancellous bone, found
mainly in epiphysis
Compact bone-tightly packed tissue
Periosteum-tough, vascular covering
Endosteum- membrane of bone forming
cells
Articular cartilage-layer of hyaline
cartilage on epiphysis of bone
Structure of a Long
Bone
• Red marrow- formation of red blood cells,
white blood cells and platelets.
– Found in flat bones and epiphysis
• Yellow marrow- stores
fats, no blood cell
production.
– Found in diaphysis
Compact vs. Spongy Bone
• Perforating(Volkmann’s)
canal- Connects central
canals
• Trabeculae-bony plates
of spongy bone
• Canaliculi- canals btwn
osteocytes
• Osteocyte-Bone cells
• Lacunae- space in bone
containing osteocytes
Compact vs. Spongy Bone
Bone Structure Animation
• structure of bone animation
Osteoblast vs. Osteoclast
• Osteoblast- bone forming cells which
deposit Calcium and Phosphorous into the
dense collagen framework.
• Osteoclast- Large multinucleated cells
formed from fusing white blood cells.
– Secrete an acid which breaks down the bony
matrix
• Both work together over a person’s lifetime
to remodel bone and allow for resorption
on minerals.
Osteoblast vs osteoclast
• osteoblast osteoclast animation
Homeostasis of Bone Tissue
Bone Development – 2 Types:
1. Intramembranous ossification
(changing cartilage to bone) (ex. - skull)
•
•
•
•
layers of undifferentiated connective tissue
appear at sites of future bone
connective tissue cells differentiate into
osteoblasts (cells that build bone) around
blood vessels
osteoblasts become osteocytes (mature bone
cells) when completely surrounded by a bony
matrix
Connective tissue on surface forms the
periosteum
Intramembranous Ossification
Intramembranous Ossifiction
2. Endochondral ossification
(remainder of skeleton)
•
•
•
•
Hyaline cartilage models form
at sites of future bone
Cartilage cells degenerate
over time
osteoblasts form bone over
cartilage
osteoblasts become
osteocytes when completely
surrounded by a bony matrix
Ossification Animation
• Ossification animation
Endochondral Ossification
Bone Development
•
•
•
In a long bone, hyaline cartilage is
replaced by bony tissue in the center of
the diaphysis first (primary ossification
center)
Bone develops from this point towards
the end of the bone
Secondary ossification centers appear
in the epiphysis last.
Bone Development
Growth of Bones
• Epiphyseal disk – area of
growth; separates epiphysis
from diaphysis; 4 layers:
1. Resting cells – closest to
end; do not add length but
act as anchor
2. Reproducing cells as they reproduce, they
lengthen the bone
1.
Growth of Bones
3. Mature cells – growing
and accumulating Ca
4. Degenerating cells &
osteoblasts depositing
bony tissue
Epiphyseal Plate Video
• http://www.youtube.com/watch?v=RTxZ0a9wvM
Epiphyseal disk
• Bones continue to
lengthen until epi. disks
are ossified (approx. 21
yrs. of age)
• Bones thicken throughout life as compact bone
is added under periosteum
• Hyaline cartilage on ends remains
Bone Growth Video
• http://app.discoveryeducation.com/player/
view/assetGuid/39B53919-B11C-4D2CA92C-E030DF639351
Epiphyseal disk
1. Radial growth plate→
2. Fracture – distal
end of radius →
Digital growth
plate (in fingers)
(2 ½ yr. old)→
Fractures
• Greenstick- incomplete
break in convex surface
• Fissured- incomplete
longitudinal break
• Comminuted-complete,
fragments bone
• Transverse- complete
break at right angle
• Oblique- complete at angle
other than right angle
• Spiral- complete, caused
by twisting of bone
Fracture Repair
• 4 stages
– Blood escapes from blood
vessels and from
hematoma.
– Spongy bone forms near
blood vessels, fibrocartilage
forms in distant regions
(within days to weeks)
– Bony callus forms from
cartilaginous callus similar
to bone formation
– Osteoclasts remove excess
bone to restore to original
Bone Fracture Video
• https://www.youtube.com/watch?v=MNkI6
Of2PRs
Factors Affecting Bone Growth
(Nutrients)
Deficiency
Effect
Vit D (for Ca absorption)
dehydrocholesterol
soft bones
(rickets/osteomalacia)
Vit A (for osteoblast &
slow bone development
osteoclast activity)
Vit C (for collagen
synthesis)
fragile bones
Rickets/Osteomalacia
Factors Affecting Bone Growth
(Hormones)
Deficiency
Pituitary growth
hormone
(stimulates cell division
in the epi. disks)
Thyroid hormone
(stimulates cartilage
replacement in disk)
Effect
Pituitary dwarfism
(excess – pituitary
gigantism/acromegaly)
premature disk
ossification-growth
stunted
Pituitary dwarfism
Acromegaly
Yao Defen is
34 yrs. old &
The world’s tallest
female at 7ft. 8 in!!
Factors Affecting Bone Growth
(Hormones & Exercise)
Deficiency
Sex hormones
(cause growth of
long bones; estrogen
stronger than androgen)
Physical stress
(stimulates bone width;
hypertrophy)
Effect
stimulate ossification of disks;
stop bone length
bone thins & weakens; atrophy
2 divisions of skeleton:
1. Axial –
skull, vertebrae, sternum, ribs (thorax),
hyoid bone
2. Appendicular –
pectoral & pelvic girdles, upper & lower
limbs
Human Skeleton – composed of 206 bones
(extra – sutural)
Axial vs. Appendicular
Skeleton
Surface Markings on Bone
• Surface of bones have various structural
features for specific functions
• Depressions & Openings:
Foramen
Meatus
Sinus
Foramen
Opening for b.v., nerves, ligaments (ex.foramen magnum)
Meatus
Tubelike passageway (ex.-external auditory
meatus)
Sinus
Cavity within a bone
(ex.-frontal sinus)
Surface Markings on Bone
• Processes that Form Joints:
Condyle
Head
Facet
Condyle
Rounded process for
articulation w/another
bone (ex. – mandibular
condyle)
Head
An enlargement at the end of a bone (ex.head of femur)
Facet
Small, nearly flat surface where 2 bones
articulate (ex.-vertebral facet)
Surface Markings on Bone
• Processes that Connective Tissue
Attaches To:
Tuberosity
Spine
Trochanter
Crest
Process
Tuberosity
Knoblike process (ex.-ischial tuberosity)
Spine
Thornlike ridge or projection (ex.-spine of
scapula)
Trochanter
Large process or projection (ex.-trochanter
of femur)
Crest
Ridgelike projection (ex.-iliac crest)
Process
Prominent projection on a bone
(ex.-spinous process)
Surface Markings – Misc.
Suture - Interlocking lines where bones
meet (ex.-coronal suture)