Anatomy & Physiology
Unit 4 – Skeletal System
2004-2005
Lecture Notes
Unit 4 – Skeletal System (Ch. 6)
Slides 1-4
I. Bone Basics
A. Functions of the Skeletal System
1. Support – weight bearing (bone), flexible (cartilage),
holds bones together (ligament)
2. Protection – skull, vertebrae, rib cage
3. Movement – tendons, muscles, joints, smooth cartilage,
ligaments
4. Storage – minerals (calcium & phosphorus) and fat
(energy)
5. Blood cell production – bone marrow forms blood cells and
platelets
Slides 5-9
B. Composition of the Skeletal System (Connective Tissue)
1. bones, cartilage, tendons, ligaments
2. ECM: collagen (glue + producing), proteoglycans (protein
+ polysaccharide), other organic molecules, water,
minerals
a. Tendon/ligament ECM -  collagen (tough)
b. Cartilage (gristle) ECM – collagen + proteoglycans
(tough, smooth, & resilient)
c. Bone ECM – collagen & minerals
(hydroxyapatite – CaPO4) for
weight bearing strength; like
rebar in concrete
Slides 10-11
C. Types of Bone (based on shape)
1. Long bones – longer than wide,
limb bones Slide 12
2. Short bones – length = width;
wrist & ankle Slide 13
3. Flat bones – thin & flat; skull
bones, ribs, scapulae, sternum 14
4. Irregular bones – shapes don’t fit
in other categories; vertebrae,
facial bones Slide 15
Slides 16-18
Slide 19
D. Anatomical Terminology of Bones
1. diaphysis (growing between) – central
shaft
2. epiphysis (growing upon) – ends of
bone
3. articular cartilage (joint) – covers
epiphyses
Page 1 of 9
Anatomy & Physiology
Unit 4 – Skeletal System
2004-2005
Lecture Notes
4. epiphyseal plate (growth plate) – made of cartilage;
between epiphysis and diaphysis; growing long bone
5. epiphyseal line – bone replaces cartilage when growth
stops
6. medullary cavity – in diaphysis; filled with marrow (soft
tissue)
a. yellow marrow – mostly fat (higher in adults); in
diaphysis
b. red marrow – produces blood cells (higher in youth); in
spongy/cancellous bone; in adult axis bones and
proximal epiphyses of limbs
7. periosteum (around bone) – blood vessels, nerves;
covers bones
8. endosteum (inside bone) – line medullary cavity
(connective tissue)
Slides 20-22
Slides 23-24
9. osteoblasts (bone forming cells) – in both
periosteum and endosteum; bone formation, repair,
and remodeling
Slides 25-26
E. Bone Histology (study of bone tissue)
1. Compact Bone Slides 27-28
a. Compose the diaphysis of long bones and thinner
surfaces of
all other
bones
Slide 29
b. Osteon/haversian system – make up compact bone
i. Lamellae (plate) – thin sheets that make up bone,
formed in concentric circles (like tree rings)
ii. Lacunae (hollow) – in between lamellae, hold
osteocytes
iii. Osteocytes (bone cells) – inside lacunae between
lamellae
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Anatomy & Physiology
Unit 4 – Skeletal System
2004-2005
Lecture Notes
iv. Canaliculi (little canal) – provide communication
between osteocytes via blood vessels
v. Haversian/central canal – hollow canal inside
osteons housing blood vessels (nutrients, blood,
waste removal), lymph, and nerve fibers
 Blood vessels also connected to the blood vessels
in periosteum and endosteum
Slides 30-31
Slides 25-26
2. Cancellous Bone (spongy)
a. Epiphyses of long bones and interior of all bones
b. Trabeculae (beam) – thin bony spicules in sheets
arranged perpendicular to major force to bone
i. Get same strength and less weight
as if were solid (“I” beam vs.
solid beam)
ii. Spaces filled with marrow & blood
vessels
iii. No blood vessels or Haversian
canals in trabeculae
 Nutrients from blood vessels in
marrow diffuse through canaliculi
to osteocytes
iv. Spiculues of trabeculae composed
of osteons
Slides 31-32
Slide 33
F. Ossification (bone + to make) in fetus
1. Synthesis of organic matrix (collagen +
proteoglycans = osteoid) and
hydroxyapatite crystals
a. osteoblasts mineralized osteocytes (mature)
b. all bone growth is a result of bone deposition a
preexisting surface
c. Constant remodeling
Slide 34
2. Bone cells:
a. Osteoblasts – bone builder; make bone
b. Osteoclasts – bone dissolver, bone resorption;
multinucleate
c. Osteocytes – bone maintainer; regulatory function
Slide 35
3. Two types of ossification:
a. Intramembranous ossification (between membranes)(Fig.6.5)
i. Primarily in skull (frontals and parietals of
cranial vault) and some shoulder girdle
ii. For flat and irregular bone growth
Page 3 of 9
Anatomy & Physiology
Unit 4 – Skeletal System
2004-2005
Lecture Notes
Slide 36
iii. Ossification centers – osteoblasts retreat making
bone matrix by forming trabeculae (radiate out)
 fusion of ossification centers results in skull
bones
Slide 37
b. Endochondral ossification
 Most common (basicranium,
base of skull, rest of
body’s bones)
 Bone forms from cartilage
model
Slide 38
i. Perichondrium (around
cartilage) – surrounds
cartilage model
Slide 39
ii. Step #1: Chondrocytes (cartilage cells) – central
chondrocytes increase in number, hypertrophy ( in
size), & die forming lacunae which are calcified.
Blood vessels in perichondrium accumulate causing
formation of osteoblasts in perichondrium.
Slide 40
iii. Step #2: Osteoblasts form periosteum = bone collar.
Slide 41
iv. Step #3: Primary ossification center – center of
diaphysis where bone first appears
 Blood vessels invade calcified cartilage
 Osteoblasts invade spaces left by dying
chondrocytes forming trabeculae (cancellous)
 Osteoclasts remove some calcified cartilage forming
medullary cavity in center (fills with marrow)
Slide 42
v. Step #4: Secondary ossification centers – appear in
epiphyses (same process as above)
Page 4 of 9
Anatomy & Physiology
Unit 4 – Skeletal System
2004-2005
Lecture Notes
Slide 43
4. Bone Growth
a. Appositional growth – deposition of bone lamellae onto
existing bone or
connective tissue (adding
width)
i. Osteoclasts remove bone
endosteum while
Fig. 6.7
osteoblasts add bone
to periosteum,
increasing bone
diameter
b. Adding length – occurs at
epiphyseal plate
 Chondrocytes increase
in #, form lines,
elongating bone
 Chondrocytes mature,
hypertrophy, & die
 Cartilage matrix
around chondrocytes
calcifies.
Osteoclasts remove
cartilage matrix,
osteoblasts replace chondrocytes.
Page 5 of 9
Anatomy & Physiology
Unit 4 – Skeletal System
2004-2005
Lecture Notes
 Osteoblasts form bone (deposit lamellae on surface
of calcified cartilage) on diaphysis side of plate.
Slide 44
5. Bone Remodeling
a. Deposit new bone & remove bone
i. osteoclasts remove existing bone, osteoblasts add
bone
 cancellous → compact (conversion)
ii. medullary cavity increases in size as bone diameter
increases to avoid heavy bones
b. Occurs in all bone
c. Functions:
i. Changes in bone shape
ii. Adjustment to stress
iii. Bone repair
Slide 45
iv. Blood calcium regulation & storage (removal &
deposition via hormone control)
Slide 44
6. Bone Repair – when a bone is broken
Slide 46
a. clot formation – from vessel damage
b. callus formation – begins 2-3 days after injury. Blood
vessels and fibrous network of connective tissue
invade clot between bone fragments, filling gap
c. callus ossification – complete after 4-6 weeks.
Osteoblasts form cancellous bone (bone must be
immobile).
d. bone remodeling – several months. Cancellous → compact
+ cancellous (can result in stronger bone).
Show x-rays
Fig. 6.8
Page 6 of 9
Anatomy & Physiology
Unit 4 – Skeletal System
2004-2005
Lecture Notes
Slide 47
G. Bone and Calcium Homeostasis
1. bone stores calcium; deposition and removal of Ca2+ to
maintain appropriate blood calcium levels
a. needed for nervous & muscle system function
b. Ca2+ deposited during bone building (osteoblasts), if 
blood [Ca2+]
c. Ca2+ removed when bone broken down (osteoclasts via
enzymes), if  blood [Ca2+]
2. Parathyroid hormone (PTH) - ’s
blood [Ca2+] by ’g osteoclasts
activity (break down bone)
a. Also  Ca resorption from
urine in kidney
b. Stimulates vitamin D
formation by kidneys – needed
for intestinal Ca2+ absorption
c. PTH stimulated by  blood
[Ca2+]
d. Secreted from parathyroid
gland (on kidneys)
3. Calcitonin - ’s blood [Ca2+] by
’g osteoclasts activity (stores
Ca2+)
a. Calcitonin stimulated by 
blood [Ca2+]
Fig. 6.9
b. Secreted from thyroid gland
Slide 48
H. Skeletal Disorders
1. Growth & Developmental
a. Giantism – abnormally increased size, excessive
Endochondral growth @ epiphyseal plates
b. Dwarfism – person is abnormally small, improper growth
@ epiphyseal plates
c. Osteogenesis imperfecta (bone + production + imperfect)
– genetic disorders causing brittle bones with
insufficient collagen; easily fractured, especially in
fetus; poor healing/misalignment
d. Rickets (to twist) – bone growth retardation due to Ca,
P, or vitamin D deficiency (sunlight or dietary);
bones soft/weak, can twist and/or break
2. Bacterial infection
a. Osteomyelitis – bone marrow inflammation, can be caused
by Stapholococcus (type of bacterium) through wounds
or tuberculosis
3. Bone tumors
Page 7 of 9
Anatomy & Physiology
Unit 4 – Skeletal System
2004-2005
Lecture Notes
4. Decalcification
a. Osteomalacia (bone softness) – due to calcium depletion
from bones
i. Pregnancy or “Adult Rickets” from vitamin D
deficiency
b. Osteoporosis (bone-pore-condition) – general reduction
in bone quality
Slide 49
I. Bone Fractures
1. open/compound – skin perforated by bone
2. closed/simple – skin not perforated
3. complete – two bone fragments are separate
4. incomplete – two bone fragments are not separated
a. greenstick – partly broken and partly bent
5. comminuted - > 2 fragments
6. impacted – 1 fragment pushed into cancellous portion of
another fragment
7. linear – parallel to long axis of bone
8. transverse – perpendicular to long axis
9. oblique/spiral – at an angle other than perpendicular

Note: joint immobilization during mid-late bone
healing results in 3x decrease in strength
o Muscles lose mass (atrophy)
o Bone not subject to the stresses that helps it
form
 Solution = walking cast
Slide 50
J. Bone Features – common terms
1. 206 bones in human body (varies between people & age)
2. Major features:
a. body/shaft – main portion
b. head – enlarged (often rounded) end
c. neck – constricted end between head and body
d. condyle (knuckle) – smooth rounded end of bone forming
an articulation with another bone
Page 8 of 9
Anatomy & Physiology
Unit 4 – Skeletal System
2004-2005
Lecture Notes
e. facet – small, flattened articular surface
f. crest – prominent ridge
g. process – projection
h. tubercle/tuberosity – lump; often sites of muscle
attachment, can change in size with muscle usage
i. trochanter – large tuberosity found only on the
proximal femur
j. epicondyle – enlargement near or above a condyle
Slide 51
3. Openings or Depressions:
a. foramen/foramina (to pierce) – holes in bones for
nerves or blood vessels
b. canal/meatus (passage) – tunnel through bone
c. fissure – cleft
d. sinus – cavity
e. fossa – depression
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