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Skeletal system

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Fundamentals of Anatomy & Physiology

Eleventh Edition

Chapter 6

Bones and Bone Structure

Lecture Presentation by

Deborah A. Hutchinson

Seattle University

Learning Outcomes
6-1 Describe the major functions of the skeletal system.
6-2 Classify bones according to shape and structure, giving examples of each type, and explain the functional significance of each of the major types of bone markings.
6-3 Identify the cell types in bone, and list their major functions.
6-4 Compare the structures and functions of compact bone and spongy bone.
6-5 Compare the mechanisms of endochondral ossification and intramembranous ossification.
© 2018 Pearson Education, Inc.
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Learning Outcomes
6-6 Describe the remodeling and homeostatic mechanisms of the skeletal system.
6-7 Discuss the effects of exercise, nutrition, and hormones on bone development and on the skeletal system.
6-8 Explain the role of calcium as it relates to the skeletal system.
6-9 Describe the types of fractures, and explain how fractures heal.
6-10 Summarize the effects of the aging process on the skeletal system.
© 2018 Pearson Education, Inc.
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6-1 Functions of Skeletal System
Skeletal system includes
Bones of the skeleton
Cartilages, ligaments, and other connective tissues
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6-1 Functions of Skeletal System
Primary functions of the skeletal system
Support
Storage of minerals and lipids
Blood cell production
Protection
Leverage
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6-2 Classification of Bones
Bones are classified by their
Shape
Structure
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6-2 Classification of Bones
Bone shapes
Sutural
Irregular
Short
Flat
Long
Sesamoid
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Figure 6–1 A Classification of Bones by Shape.
© 2018 Pearson Education, Inc.
Sutural Bones
Sutural bone
Sutural bones, or
Wormian bones, are
small, flat, oddly
shaped bones found
between the flat bones
of the skull. They range
in size from a grain of
sand to a quarter. Their
borders are like pieces
of a jigsaw puzzle.
Posterior view
Flat Bones
Flat bones have thin, parallel surfaces. Flat
bones form the roof of the skull, the sternum
(breastbone), the ribs, and the scapulae
(shoulder blades). They provide protection for
underlying soft tissues and offer an extensive
surface area for the attachment
of skeletal muscles.
Parietal bone
Sectional
view
Irregular Bones
Irregular bones have
complex shapes with
short, flat, notched, or
ridged surfaces. The
vertebrae that form the
spinal column, the bones
of the pelvis, and several
bones in the skull are
examples of irregular bones.
Long Bones
Long bones are relatively
long and slender. They are
located in the arm and
forearm, thigh and leg,
palms, soles, fingers, and
toes. The femur, the long
bone of the thigh, is the
largest and heaviest bone in
the body.
Vertebra
Humerus
Short Bones
Short bones are
boxlike in
appearance.
Examples of short
bones include the
carpal bones (wrists)
and tarsal bones
(ankles).
Sesamoid Bones
Carpal
bones
Patella
Sesamoid bones are
usually small, round, and
flat. They are found near
joints of the knees, hands,
and feet. Few people have
sesamoid bones at every
possible location, but
everyone has sesamoid
patellae (pa-TEL-ē;
singular, patella, a small
shallow dish), or kneecaps.
Sutures
a
b
c
d
e
f

6-2 Classification of Bones
Sutural bones (Wormian bones)
Small, flat, irregularly shaped bones
Between flat bones of the skull
Number varies among individuals
Irregular bones
Have complex shapes
Examples: spinal vertebrae, pelvic bones
© 2018 Pearson Education, Inc.
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Figure 6–1a A Classification of Bones by Shape.
© 2018 Pearson Education, Inc.
Sutural Bones
Sutural bone
Sutural bones, or
Wormian bones, are
small, flat, oddly shaped
bones found between
the flat bones of the
skull. They range in size
from a grain of sand to a
quarter. Their borders
are like pieces of a
jigsaw puzzle.
Sutures
Posterior view
a

Figure 6–1b A Classification of Bones by Shape.
© 2018 Pearson Education, Inc.
Irregular Bones
Irregular bones have
complex shapes with
short, flat, notched, or
ridged surfaces. The
vertebrae that form the
spinal column, the bones
of the pelvis, and several
bones in the skull are
examples of irregular bones.
Vertebra
b
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6-2 Classification of Bones
Short bones
Boxy
Examples: carpal bones and tarsal bones
Flat bones
Thin with parallel surfaces
Examples: bones of skull roof, sternum, ribs, and scapulae
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Figure 6–1c A Classification of Bones by Shape.
© 2018 Pearson Education, Inc.
Short Bones
Short bones are
boxlike in
appearance.
Examples of short
bones include the
carpal bones
(wrists) and tarsal
bones (ankles).
Carpal
bones
c

Figure 6–1d A Classification of Bones by Shape.
© 2018 Pearson Education, Inc.
Flat Bones
Flat bones have thin, parallel surfaces. Flat bones
form the roof of the skull, the sternum (breastbone),
the ribs, and the scapulae (shoulder blades). They
provide protection for underlying soft tissues and
offer an extensive surface area for the attachment
of skeletal muscles.
Parietal bone
Sectional
view
d
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6-2 Classification of Bones
Long bones
Long and slender
Found in arms, legs, palms, soles, fingers, toes
Sesamoid bones
Usually small, round, and flat
Develop within tendons near joints of knees, hands, and feet
Location and number vary between individuals
Example: patellae
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Figure 6–1e A Classification of Bones by Shape.
© 2018 Pearson Education, Inc.
e
Long bones are relatively
long and slender. They are
located in the arm and
forearm, thigh and leg,
palms, soles, fingers, and
toes. The femur, the long
bone of the thigh, is the
largest and heaviest bone
in the body.
Humerus
Long Bones

Figure 6–1f A Classification of Bones by Shape.
© 2018 Pearson Education, Inc.
Sesamoid Bones
Patella
Sesamoid bones are
usually small, round, and
flat. They are found near
joints of the knees, hands,
and feet. Few people have
sesamoid bones at every
possible location, but
everyone has sesamoid
patellae (pa-TEL-ē;
singular, patella, a small
shallow dish), or kneecaps.
f

6-2 Classification of Bones
Bone markings (surface features)
Projections
Where muscles, tendons, and ligaments attach
At articulations with other bones
Openings and depressions
For passage of blood vessels and nerves
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Figure 6–2 An Introduction to Bone Markings (Part 1 of 2).
© 2018 Pearson Education, Inc.
Openings
Sinus:
Chamber within
a bone, normally
filled with air
Projections
Process:
Projection or
bump
Ramus:
Part of a bone
that forms an
angle with the
rest of the
structure
Skull, anterior view
Foramen:
Rounded
passageway for
blood vessels
and/or nerves
Fissure:
Deep furrow,
cleft, or slit
Meatus:
Passage or
channel,
especially the
opening of a canal
Canal:
Duct or channel
Skull, lateral view

Figure 6–2 An Introduction to Bone Markings (Part 2 of 2).
© 2018 Pearson Education, Inc.
Projections where
muscles, tendons, or
ligaments attach
Trochanter:
Crest:
Spine:
Head
Line:
Tubercle:
Pelvis
Neck
Prominent
ridge
Pointed
process
Low ridge
Small,
rounded
projection
Femur
Projections for forming joints
Head:
Expanded articular
end of an epiphysis,
often separated from
the shaft by a
narrower neck (see
Figure 6–3a)
Narrow connection
between the
epiphysis and
diaphysis (see
Figure 6–3a)
Neck:
Depressions
Sulcus:
Narrow
groove
Fossa:
Shallow
depression
Humerus
Tuberosity:
Rough
projection
Facet:
Small, flat
articular surface
Condyle:
Smooth, rounded
articular process
Condyle
Trochlea:
Smooth, grooved
articular process
shaped like a pulley

Large, rough
projection
20

6-2 Classification of Bones
Structure of a long bone
Diaphysis (shaft)
Wall of compact bone
Central space called medullary cavity (marrow cavity)
Epiphysis (wide part at each end)
Mostly spongy bone (trabecular bone)
Metaphysis
Where diaphysis and epiphysis meet
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Figure 6–3a Bone Structure.
© 2018 Pearson Education, Inc.
Epiphysis
Spongy
bone
Metaphysis
Compact
bone
Medullary
cavity
Diaphysis
(shaft)
Metaphysis
Epiphysis
The structure of a representative
long bone (the femur) in longitudinal
section
a

6-2 Classification of Bones
Structure of flat bones
For example, parietal bones of the skull
Consist of spongy bone between two layers of compact bone (cortex)
Within the cranium, the layer of spongy bone is called the diploë
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Figure 6–3b Bone Structure.
© 2018 Pearson Education, Inc.
Cortex
(compact bone)
Diploë
(spongy bone)
The structure of a flat bone (the parietal bone)
b

6-3 Bone Tissue
Bone tissue
Dense, supportive connective tissue
Contains specialized cells
Solid extracellular matrix with collagen fibers
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6-3 Bone Tissue
Characteristics of bone
Dense matrix due to deposits of calcium salts
Osteocytes (bone cells) within lacunae organized around blood vessels
Canaliculi
Narrow passageways that allow for exchange of nutrients, wastes, and gases
Periosteum
Covers outer surfaces of bones (except at joints)
Consists of outer fibrous and inner cellular layers
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6-3 Bone Tissue
Bone matrix
Calcium phosphate, Ca3(PO4)2 makes up almost two-thirds of bone mass
Interacts with calcium hydroxide, Ca(OH)2, to form crystals of hydroxyapatite, Ca10(PO4)6(OH)2
Incorporates other calcium salts such as calcium carbonate (CaCO3) and ions (e.g., magnesium)
A bone lacking a calcified matrix looks normal, but is very flexible
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Figure 6–4 Bone Lacking a Calcified Matrix.
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6-3 Bone Tissue
Bone matrix
Matrix proteins
About one-third of bone mass is collagen fibers
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6-3 Bone Tissue
Bone cells
Make up only 2 percent of bone mass
Four types
Osteogenic cells
Osteoblasts
Osteocytes
Osteoclasts
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Figure 6–5 Types of Bone Cells.
© 2018 Pearson Education, Inc.
Types of Bone Cells
Endosteum
Osteogenic
cell
Medullary
cavity
Osteogenic cell: Stem
cell whose divisions
produce osteoblasts
Osteoblast: Immature
bone cell that secretes
organic components of
matrix
Medullary
cavity
Ruffled
border
Osteoclast
Matrix
Osteoblast
Osteoid
Matrix
Matrix
Osteocyte
Canaliculi
Osteocyte: Mature bone
cell that maintains the bone
matrix
Osteoclast: Multinucleate
cell that secretes acids and
enzymes to dissolve bone
matrix
a
b
c
d

6-3 Bone Tissue
Osteogenic cells (osteoprogenitor cells)
Mesenchymal cells that divide to produce osteoblasts
Located in inner cellular layer of periosteum and in endosteum
Assist in fracture repair
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Figure 6–5a Types of Bone Cells.
© 2018 Pearson Education, Inc.
Endosteum
Osteogenic
cell
Medullary
cavity
Osteogenic cell: Stem
cell whose divisions
produce osteoblasts
a

6-3 Bone Tissue
Osteoblasts
Immature cells that produce new bone matrix during osteogenesis (ossification)
Osteoid—matrix produced by osteoblasts that has not yet become calcified
Osteoblasts surrounded by bone matrix become osteocytes
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Figure 6–5b Types of Bone Cells.
© 2018 Pearson Education, Inc.
b
Osteoblast
Osteoid
Matrix
Osteoblast: Immature
bone cell that secretes
organic components of
matrix

6-3 Bone Tissue
Osteocytes
Mature bone cells that do not divide
Live in lacunae between layers of matrix
Have cytoplasmic extensions that pass through canaliculi
Two major functions
Maintain protein and mineral content of matrix
Help repair damaged bone
© 2018 Pearson Education, Inc.
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Figure 6–5c Types of Bone Cells.
© 2018 Pearson Education, Inc.
c
Matrix
Osteocyte
Canaliculi
Osteocyte: Mature bone
cell that maintains the
bone matrix

6-3 Bone Tissue
Osteoclasts
Absorb and remove bone matrix
Large, multinucleate cells
Secrete acids and protein-digesting enzymes
Dissolve bone matrix and release stored minerals
This osteolysis is important in homeostasis
Derived from the same stem cells that produce monocytes and macrophages
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Figure 6–5d Types of Bone Cells.
© 2018 Pearson Education, Inc.
d
Medullary
cavity
Ruffled
border
Osteoclast
Matrix
Osteoclast: Multinucleate
cell that secretes acids and
enzymes to dissolve bone
matrix

6-4 Compact Bone and Spongy Bone
Osteon—functional unit of compact bone
Central canal contains blood vessel(s)
Perforating canals
Perpendicular to surface of bone
Carry blood vessels into deep bone and marrow
Lamellae—layers of bone matrix
Concentric lamellae surround central canal
Interstitial lamellae fill spaces between osteons
Circumferential lamellae are at outer and inner bone surfaces
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Figure 6–6 Osteons of Compact Bone.
© 2018 Pearson Education, Inc.
Osteon
Lacunae
Central canal
Lamellae
Osteons
SEM × 182

Figure 6–7a The Structure of Compact Bone.
© 2018 Pearson Education, Inc.
Venule
Capillary
Periosteum
Concentric
lamellae
Interstitial
lamellae
Circumferential
lamellae
Osteons
Perforating fibers
Endosteum
Central
canal
Concentric
lamellae
Trabeculae of
spongy bone
(see Figure 6–8)
The organization of osteons
and lamellae in compact bone
Perforating
canal
Central
canal
Arteriole
a

Vein
Artery
42

Figure 6–7b The Structure of Compact Bone.
© 2018 Pearson Education, Inc.
Collagen
fiber
orientation
The orientation of collagen
fibers in adjacent lamellae
of an osteon
b
43

6-4 Compact Bone and Spongy Bone
Spongy bone lacks osteons
Matrix forms an open network of trabeculae
Lacks capillaries and venules
Red bone marrow fills spaces between trabeculae
Forms blood cells
Contains blood vessels that supply nutrients to osteocytes by diffusion
Yellow bone marrow
Found in other sites of spongy bone
Stores fat
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Figure 6–8 The Structure of Spongy Bone.
© 2018 Pearson Education, Inc.
Trabeculae of
spongy bone
Canaliculi
opening
on surface
Lamellae
Endosteum

6-4 Compact Bone and Spongy Bone
Weight-bearing bones
Trabeculae in epiphysis of femur transfer forces from pelvis to compact bone of femoral shaft
Medial side of shaft compresses
Causing tension on the lateral side
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Figure 6–9 The Distribution of Forces on a Long Bone.
© 2018 Pearson Education, Inc.
Body weight (applied force)
Tension on lateral
side of shaft
Compression on
medial side of shaft
47

The femur, or thigh bone, has a diaphysis (shaft) with walls of compact bone and epiphyses filled with spongy bone. The body weight is transferred to the femur at the hip joint. Because the hip joint is off center relative to the axis of the shaft, the body weight is distributed along the bone in a way that compresses the medial (inner) portion of the shaft and stretches the lateral (outer) portion.
47

6-4 Compact Bone and Spongy Bone
Periosteum—membrane that covers outside of bones
Except within joint cavities
Outer, fibrous layer and inner, cellular layer
Fibers are interwoven with those of tendons
Perforating fibers—fibers that become incorporated into bone tissue
Increase strength of attachments
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6-4 Compact Bone and Spongy Bone
Functions of periosteum
Isolates bone from surrounding tissues
Provides a route for blood vessels and nerves
Participates in bone growth and repair
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Figure 6–10a The Periosteum and Endosteum.
© 2018 Pearson Education, Inc.
a
Circumferential
lamellae
Periosteum
Fibrous layer
Cellular layer
Canaliculi
Osteocyte
in lacuna
Perforating
fibers
The periosteum contains outer (fibrous) and
inner (cellular) layers. Collagen fibers of the
periosteum are continuous with those of the
bone, adjacent joint capsules, and attached
tendons and ligaments.

6-4 Compact Bone and Spongy Bone
Endosteum—incomplete cellular layer that lines medullary cavity
Active during bone growth, repair, and remodeling
Covers trabeculae of spongy bone
Lines central canals of compact bone
Consists of flattened layer of osteogenic cells
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Figure 6–10b The Periosteum and Endosteum.
© 2018 Pearson Education, Inc.
Endosteum
Osteoclast
Bone matrix
Osteocyte
Osteogenic
cell
Osteoid
Osteoblast
The endosteum is an incomplete
cellular layer containing osteoblasts,
osteogenic cells, and osteoclasts.
b

6-5 Bone Formation and Growth
Bone development
Ossification (osteogenesis)—bone formation
Calcification—deposition of calcium salts
Occurs during ossification
Two forms of ossification
Endochondral ossification
Intramembranous ossification
Some human bones grow until about age 25
© 2018 Pearson Education, Inc.
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6-5 Bone Formation and Growth
Endochondral ossification
How most bones form
Primary ossification center develops inside hyaline cartilage
Cartilage is gradually replaced by bone
Seven main steps
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SmartArt Video: Endochondral Ossification
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Figure 6–11 Endochondral Ossification (Part 1 of 7).
© 2018 Pearson Education, Inc.
1
As the cartilage
enlarges, chondro-
cytes near the center
of the shaft increase
greatly in size. The
matrix is reduced to
a series of small
struts that soon
begin to calcify. The
enlarged chondro-
cytes then die and
disintegrate, leaving
cavities within the
cartilage.
Enlarging
chondrocytes within
calcifying matrix
Hyaline
cartilage
Disintegrating
chondrocytes
of the cartilage
model

Figure 6–11 Endochondral Ossification (Part 2 of 7).
© 2018 Pearson Education, Inc.
2
Blood vessels grow
around the edges of
the cartilage, and the
cells of the perichon-
drium convert to
osteoblasts. The
shaft of the cartilage
then becomes
ensheathed in a
superficial layer of
bone.
Perichondrium
Epiphysis
Bone collar
Blood
vessel
Diaphysis
Periosteum
formed from
perichondrium

Figure 6–11 Endochondral Ossification (Part 3 of 7).
© 2018 Pearson Education, Inc.
3
Blood vessels penetrate the
cartilage and invade the
central region. Fibroblasts
migrating with the blood
vessels differentiate into
osteoblasts and begin
producing spongy bone at a
primary ossification center.
Bone formation then
spreads along the shaft
toward both ends of the
former cartilage model.
Medullary
cavity
Primary
ossification
center
Superficial
bone
Spongy
bone

Figure 6–11 Endochondral Ossification (Part 4 of 7).
© 2018 Pearson Education, Inc.
4
Remodeling occurs as
growth continues,
creating a medullary
cavity. The osseous
tissue of the shaft
becomes thicker, and the
cartilage near each
epiphysis is replaced by
shafts of bone. Further
growth involves increases
in length and diameter.
Medullary
cavity
Metaphysis

Figure 6–11 Endochondral Ossification (Part 5 of 7).
© 2018 Pearson Education, Inc.
5
Capillaries and osteoblasts
migrate into the epiphyses,
creating secondary
ossification centers.
Hyaline cartilage
Epiphysis
Metaphysis
Periosteum
Secondary
ossification
center
Compact
bone

Figure 6–11 Endochondral Ossification (Part 6 of 7).
© 2018 Pearson Education, Inc.
6
The epiphyses eventually become filled
with spongy bone. The metaphysis, a
relatively narrow cartilaginous region
called the epiphyseal cartilage, or
epiphyseal plate, now separates the
epiphysis from the diaphysis. On the
shaft side of the metaphysis,
osteoblasts continuously invade the
cartilage and replace it with bone. New
cartilage is produced at the same rate on
the epiphyseal side.
Articular cartilage
Spongy
bone
Epiphyseal
cartilage
Diaphysis
Within the epiphyseal cartilage, the
chondrocytes are organized into zones.
Chondrocytes at the
epiphyseal side of the
cartilage continue to
divide and enlarge.
Chondrocytes degenerate
at the diaphyseal side.
Osteoblasts migrate
upward from the diaphysis
and cartilage is gradually
replaced by bone.

Figure 6–11 Endochondral Ossification (Part 7 of 7).
© 2018 Pearson Education, Inc.
7
At puberty, the rate of epiphyseal cartilage
production slows and the rate of osteoblast
activity accelerates. As a result, the
epiphyseal cartilage gets narrower and
narrower, until it ultimately disappears.
This event is called epiphyseal closure.
The former location of the epiphyseal
cartilage becomes a distinct epiphyseal
line that remains after epiphyseal growth
has ended.
Articular cartilage
Epiphyseal line
Spongy
bone
Medullary
cavity
A thin cap of the original cartilage
model remains exposed to the joint
cavity as the articular cartilage.
This cartilage prevents damaging
the joint from bone-to-bone
contact.

Figure 6–11 Endochondral Ossification.
© 2018 Pearson Education, Inc.
63

6-5 Bone Formation and Growth
Interstitial growth—growth in length
Secondary ossification centers develop
Epiphyseal closure—completion of epiphyseal growth
Width of epiphyseal cartilages reveals timing of endochondral ossification
Former location of epiphyseal cartilage is visible on
x-rays as an epiphyseal line
Remains after epiphyseal closure
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Figure 6–12a Bone Growth at Epiphyseal Cartilages.
© 2018 Pearson Education, Inc.
An x-ray of growing epiphyseal cartilages (arrows)
a
65

Figure 6–12b Bone Growth at Epiphyseal Cartilages.
© 2018 Pearson Education, Inc.
Epiphyseal lines in an adult (arrows)
b
66

6-5 Bone Formation and Growth
Appositional growth—growth in width
Thickens and strengthens long bones
Layers of circumferential lamellae are added at outer surface
Deepest layers become replaced by osteons
During this process, osteoclasts slowly remove bone matrix at inner surface of bone
Enlarging medullary cavity
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6-5 Bone Formation and Growth
Intramembranous ossification
Also called dermal ossification
Because it occurs in the dermis
Produces dermal bones such as mandible (lower jaw) and clavicles (collarbones)
Five main steps
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68

Figure 6–13 Intramembranous Ossification (Part 1 of 5).
© 2018 Pearson Education, Inc.
1
Parietal bone
Frontal
bone
Occipital bone
Mesenchymal cells clus-
ter together, differentiate
into osteoblasts, and
start to secrete the
organic components of
the matrix. The resulting
osteoid then becomes
mineralized with calcium
salts forming bone
matrix.
Bone matrix
Osteoid
Mesenchymal cell
Ossification center
Blood vessel
Osteoblast
Mandible
Intramembranous ossification
starts about the eighth week of
embryonic development. This
type of ossification occurs in
the deeper layers of the dermis,
forming dermal bones.

Figure 6–13 Intramembranous Ossification (Part 2 of 5).
© 2018 Pearson Education, Inc.
2
As ossification proceeds,
some osteoblasts are
trapped inside bony pockets
where they differentiate into
osteocytes. The developing
bone grows outward from the
ossification center in small
struts called spicules.
Spicules
Osteocyte

Figure 6–13 Intramembranous Ossification (Part 3 of 5).
© 2018 Pearson Education, Inc.
3
Blood vessels begin to
branch within the region
and grow between the
spicules. The rate of bone
growth accelerates with
oxygen and a reliable
supply of nutrients. As
spicules interconnect,
they trap blood vessels
within the bone.
Blood vessel
trapped
within bone
matrix
71

Figure 6–13 Intramembranous Ossification (Part 4 of 5).
© 2018 Pearson Education, Inc.
4
Continued deposition of bone
by osteoblasts located close
to blood vessels results in a
plate of spongy bone with
blood vessels weaving
throughout.
72

Figure 6–13 Intramembranous Ossification (Part 5 of 5).
© 2018 Pearson Education, Inc.
5
Areas of spongy bone are
remodeled forming the
diploë and a thin covering
of compact bone.
Subsequent remodeling
around blood vessels
produces osteons typical
of compact bone.
Osteoblasts on the bone
surface along with
connective tissue around
the bone become the
periosteum.
Fibrous periosteum
Compact bone
Blood vessels
trapped within
bone matrix
Spongy bone
Compact bone
Cellular periosteum

6-5 Bone Formation and Growth
Blood supply to bones
Nutrient artery and vein
Most bones have one of each (some have more)
Pass through nutrient foramina in diaphysis
Metaphyseal vessels
Supply blood to epiphyseal cartilages
Where bone growth occurs
Periosteal vessels
Supply blood to superficial osteons
And to secondary ossification centers
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Figure 6–14 The Blood Supply to a Mature Bone.
© 2018 Pearson Education, Inc.
Vessels in Bone
Epiphyseal
artery and vein
Metaphyseal
artery and vein
Articular
cartilage
Branches of
nutrient artery
and vein
Nutrient artery
and vein
Periosteal
arteries and veins
Periosteum
Periosteum
Compact
bone
Medullary
cavity
Nutrient
foramen
Artery and vein in
perforating canal
Metaphyseal
artery and vein
Metaphysis
Epiphyseal
line

6-5 Bone Formation and Growth
Periosteum also contains
Network of lymphatic vessels
Sensory nerves
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6-6 Bone Remodeling
Bone remodeling
Occurs throughout life
Functions in bone maintenance
By recycling and renewing bone matrix
Involves osteocytes, osteoblasts, and osteoclasts
Normally, activities are balanced
If removal is faster than replacement, bones weaken
If deposition predominates, bones strengthen
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77

6-7 Exercise, Nutrition, and Hormones
Effects of exercise on bone
Mineral recycling allows bones to adapt to stress
Heavily stressed bones become thicker and stronger
Exercise, particularly weight-bearing exercise, stimulates osteoblasts
Bone degeneration
Bone degenerates quickly
Up to one-third of bone mass can be lost in a few weeks of inactivity
© 2018 Pearson Education, Inc.
78

6-7 Exercise, Nutrition, and Hormones
Nutritional and hormonal effects on bone
Minerals
Calcium and phosphorus are required in the diet
Plus small amounts of magnesium, fluoride, iron, and manganese
Calcitriol and vitamin D3
Calcitriol is made in the kidneys
Essential for normal calcium and phosphate ion absorption in digestive tract
Synthesized from vitamin D3 (cholecalciferol)
© 2018 Pearson Education, Inc.
79

6-7 Exercise, Nutrition, and Hormones
Nutritional and hormonal effects on bone
Vitamin C is required for collagen synthesis
And it stimulates osteoblast differentiation
Vitamin A stimulates osteoblast activity
Vitamins K and B12 are required for synthesis of bone proteins
© 2018 Pearson Education, Inc.
80

6-7 Exercise, Nutrition, and Hormones
Nutritional and hormonal effects on bone
Growth hormone and thyroxine stimulate bone growth
Sex hormones
Estrogen and testosterone stimulate osteoblasts
Parathyroid hormone and calcitonin maintain calcium ion homeostasis
© 2018 Pearson Education, Inc.
81

SmartArt Video: The Hormones Regulating Calcium Ion Metabolism
© 2018 Pearson Education, Inc.
82

6-8 Calcium Homeostasis
The skeleton as a calcium reserve
Bones store 99 percent of the body’s calcium
In addition to other minerals
Calcium is the most abundant mineral in the body
Calcium ions are vital to many physiological processes
© 2018 Pearson Education, Inc.
83

Figure 6–15 A Chemical Analysis of Bone.
© 2018 Pearson Education, Inc.
Organic
compounds
(mostly collagen)
33%
Total inorganic
components
67%
Composition of Bone
Bone Contains

Calcium 39%
Potassium 0.2%
Sodium 0.7%
Magnesium 0.4%
Carbonate 9.7%
Phosphate 17%
99% of the body’s phosphate
80% of the body’s carbonate
50% of the body’s magnesium
35% of the body’s sodium
4% of the body’s potassium
99% of the body’s calcium
84

6-8 Calcium Homeostasis
Hormones and calcium ion balance
Calcium ion concentrations in body fluids must be closely regulated
Parathyroid hormone and calcitonin affect storage, absorption, and excretion of calcium ions in
Bones (storage)
Digestive tract (absorption)
Kidneys (excretion)
© 2018 Pearson Education, Inc.
85

6-8 Calcium Homeostasis
Parathyroid hormone (PTH)
Produced by parathyroid glands in neck
Increases blood calcium ion levels by
Stimulating osteoclast activity (indirectly)
Increasing intestinal absorption of calcium by enhancing calcitriol secretion by kidneys
Decreasing calcium excretion by kidneys
© 2018 Pearson Education, Inc.
86

6-8 Calcium Homeostasis
Calcitonin
Secreted by C cells in thyroid
Decreases blood calcium ion levels by
Inhibiting osteoclast activity
Increasing calcium excretion and reducing calcitriol secretion by kidneys
Decreasing intestinal absorption of calcium
© 2018 Pearson Education, Inc.
87

Figure 6–16 Factors That Increase the Blood Calcium Ion Level.
© 2018 Pearson Education, Inc.
Factors That Increase Blood Calcium Ion Level
These responses are triggered
when blood calcium ion level
decreases below 8.5 mg/dL.
Low Calcium Ion Level in Blood
(below 8.5 mg/dL)
Parathyroid Gland Response
Low calcium level causes the
parathyroid glands to secrete
parathyroid hormone (PTH).
PTH
Bone Response
Osteoclasts stimulated to
release stored calcium
ions from bone
Osteoclast
Bone
Intestinal Response
Intestinal
absorption
of calcium
increases
Kidney Response
Kidneys absorb
calcium ions
more
calcitriol
Factors That Decrease Blood Calcium Ion Level
Intestinal and kidney
responses are triggered when
blood calcium ion level rises
above 11 mg/dL.
High Calcium Ion Level in Blood
(above 11 mg/dL)
Thyroid Gland Response
C cells in the thyroid
gland secrete calcitonin.
Calcitonin
Bone Response
Osteoclast activity
decreases; osteoblast
activity unaffected
Osteoclast
Bone
Intestinal Response
Intestinal
absorption
of calcium
decreases
Kidney Response
Kidneys
excrete
calcium ions
less
calcitriol
Calcium released
Calcium absorbed
Calcium conserved
Calcium release slowed
Calcium absorbed slowly
Calcium excreted
Ca2+
level in
blood
increases
Decreased calcium
loss in urine
Ca2+
level in
blood
decreases
Increased calcium
loss in urine
b
a

Figure 6–16a Factors That Increase the Blood Calcium Ion Level.
© 2018 Pearson Education, Inc.
Factors That Increase Blood Calcium Ion Level
These responses are triggered
when blood calcium ion level
decreases below 8.5 mg/dL.
Low Calcium Ion Level in Blood
(below 8.5 mg/dL)
Parathyroid Gland Response
Low calcium level causes the
parathyroid glands to secrete
parathyroid hormone (PTH).
PTH
Bone Response
Osteoclasts stimulated to
release stored calcium ions
from bone
Osteoclast
Bone
Intestinal Response
Intestinal
absorption
of calcium
increases
Kidney Response
Kidneys
absorb
calcium ions
more
calcitriol
Calcium released
Calcium absorbed
Calcium conserved
Ca2+
level in
blood
increases
Decreased calcium
loss in urine
a
89

Figure 6–16b Factors That Increase the Blood Calcium Ion Level.
© 2018 Pearson Education, Inc.
Factors That Decrease Blood Calcium Ion Level
Intestinal and kidney
responses are triggered when
blood calcium ion level rises
above 11 mg/dL.
High Calcium Ion Level in Blood
(above 11 mg/dL)
Thyroid Gland Response
C cells in the thyroid
gland secrete calcitonin.
Calcitonin
Bone Response
Osteoclast activity
decreases; osteoblast
activity unaffected
Osteoclast
Bone
Intestinal Response
Intestinal
absorption
of calcium
decreases
Kidney Response
Kidneys
excrete
calcium ions
less
calcitriol
Calcium release slowed
Calcium absorbed slowly
Calcium excreted
Ca2+
level in
blood
decreases
Increased calcium
loss in urine
b
90

6-9 Fractures
Fractures
Cracks or breaks in bones due to physical stress
Open (compound) or closed (simple)
Major types of fractures
Transverse, displaced, compression, spiral, epiphyseal, comminuted, greenstick, Colles, Pott’s
© 2018 Pearson Education, Inc.
91

Figure 6–17 Types of Fractures and Steps in Repair.
© 2018 Pearson Education, Inc.
Epiphyseal
fracture
Transverse fracture
Greenstick fracture
Comminuted
fracture
Displaced fracture
Compression
fracture
Colles fracture
Spiral fracture
Pott’s fracture
92

Figure 6–17 Types of Fractures and Steps in Repair (Part 1 of 9).
© 2018 Pearson Education, Inc.
Transverse fracture
93

Figure 6–17 Types of Fractures and Steps in Repair (Part 2 of 9).
© 2018 Pearson Education, Inc.
Displaced fracture
94

Figure 6–17 Types of Fractures and Steps in Repair (Part 3 of 9).
© 2018 Pearson Education, Inc.
Compression
fracture
95

Figure 6–17 Types of Fractures and Steps in Repair (Part 4 of 9).
© 2018 Pearson Education, Inc.
Spiral fracture
96

Figure 6–17 Types of Fractures and Steps in Repair (Part 5 of 9).
© 2018 Pearson Education, Inc.
Epiphyseal
fracture
97

Figure 6–17 Types of Fractures and Steps in Repair (Part 6 of 9).
© 2018 Pearson Education, Inc.
Comminuted
fracture
98

6-9 Fractures
Fractures are repaired in four steps
Fracture hematoma formation
Callus formation
Spongy bone formation
Compact bone formation
© 2018 Pearson Education, Inc.
102

6-9 Fractures
Fracture hematoma formation
Production of a large blood clot
Establishes a fibrous network
Bone cells in the area die
Callus formation
Cells of endosteum and periosteum divide and migrate into fracture zone
Calluses stabilize the break
Internal callus develops in medullary cavity
External callus of cartilage and bone surrounds break
© 2018 Pearson Education, Inc.
103

Figure 6–17 Types of Fractures and Steps in Repair (Part 1 of 4).
© 2018 Pearson Education, Inc.
Fracture
hematoma
Dead bone
Bone fragments
Fracture hematoma
formation.
Fracture
hematoma
1

104

Figure 6–17 Types of Fractures and Steps in Repair (Part 2 of 4).
© 2018 Pearson Education, Inc.
Spongy bone of
internal callus
Cartilage of
external callus
Spongy bone of
external callus
2
Periosteum
Callus formation.

105

6-9 Fractures
Spongy bone formation
Osteoblasts replace central cartilage of external callus with spongy bone
Compact bone formation
Repaired bone may be slightly thicker and stronger than normal
© 2018 Pearson Education, Inc.
106

Figure 6–17 Types of Fractures and Steps in Repair (Part 3 of 4).
© 2018 Pearson Education, Inc.
Internal callus
External callus
Spongy bone formation.
3

107

Figure 6–17 Types of Fractures and Steps in Repair (Part 4 of 4).
© 2018 Pearson Education, Inc.
External
callus
Compact bone
formation.
4

108

6-10 Effects of Aging on Skeletal System
Bones become thinner and weaker with age
Osteopenia—inadequate ossification (reduction of bone mass)
Begins between ages 30 and 40
Women lose 8 percent of bone mass per decade
Men lose 3 percent
Epiphyses, vertebrae, and jaws are most affected
Results in fragile limbs, reduced height, and tooth loss
© 2018 Pearson Education, Inc.
109

6-10 Effects of Aging on Skeletal System
Osteoporosis—severe loss of bone mass
Compromises normal function
Over age 45, occurs in
29 percent of women
18 percent of men
Hormones and bone loss
Sex hormones help maintain bone mass
In women, osteoporosis accelerates after menopause
© 2018 Pearson Education, Inc.
110

Figure 6–18 The Effects of Osteoporosis on Spongy Bone.
© 2018 Pearson Education, Inc.
Spongy bone in osteoporosis
SEM × 21
Normal spongy bone
SEM × 25
111

6-10 Effects of Aging on Skeletal System
Cancer and bone loss
Cancerous tissues release osteoclast-activating factor
Stimulates osteoclasts
Produces severe osteoporosis
© 2018 Pearson Education, Inc.
112

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