6: Bones and Skeletal Tissues
Objectives
Skeletal Cartilages
1. Describe the functional properties of the three types of cartilage tissue.
 Hyaline
 Elastic
 Fibro2. Locate the major cartilages of the adult skeleton as well as the type and reason for the type
of cartilage for each site.
 Auricular
 Nasal
 Articular
 Costal
 Intervertebral
 Pubic symphysis
3. Explain how cartilage grows. (see interstitial bone growth)
Classification of Bones
4. Name the major regions of the skeleton and describe their relative functions.
 Axial
 Appendicular
5. Compare and contrast the structure of the four bone classes and provide examples of each
class.
 Long
 Short
 Flat
 Irregular
Functions of Bones
6. List and describe the important functions of bones.
Bone Structure
7. Indicate the functional importance of bone markings.
8. Describe the gross anatomy of a typical long bone and flat bone.
 Indicate the locations and functions of the diaphysis, epiphysis, epiphyseal growth
line/plate, nutrient foramen/artery, compact and spongy bone, red and yellow marrow,
articular cartilage, periosteum, and endosteum.
 Label the regions of a long bone as demonstrated in class.
9. Describe the histology of compact and spongy bone.
 Label compact and spongy bone illustrations as demonstrated in class.
 What are Diploë, its function, and location?
 Location of red and yellow marrow in adults and children
 Describe the shift in blood formation from the embryo to adulthood.
10. Discuss the chemical composition of bone and the advantages conferred by the organic and
inorganic components.
 Osteoid
 Ground substance
 Collagen fibers
 Hydroxyapatite / calcium phosphate
Bone Development
11. Osteogenesis (ossification): compare and contrast intramembranous ossification and
endochondral ossification.
 Know the steps in each
 Know the difference in origins
o
Mesenchyme vs. hyaline cartilage
o
Primary and secondary ossification centers
12. Describe the process of long bone growth that occurs at the epiphyseal plates.
 Interstitial bone growth vs. appositional bone growth
 Epiphyseal growth plate
o
Proliferation
o
Hypertrophy
o
Calcification
o
Ossification
Microscopic Anatomy of Bone
13. Cells of bone
 Compare the locations and remodeling functions of the osteoblasts, osteocytes, and
osteoclasts.
 Know functions and characteristics of each:
o
Osteogenic stem cell
o
Osteoblast
o
Osteocytes
o
Osteoclasts
o
Chondroblasts
o
Chondrocytes
o
Mesenchymal stem cell
o
Mesenchyme
 Compact bone
o
Osteon
o
Lamellae
o
Central canal
o
Collagen fibers, their orientation and contribution to bone strength
o
Perforating canals
o
Lacunae
o
Canaliculi
 Spongy bone
o
Trabeculae
o
Alignment
o
Lamellar vs. woven bone
 Homeostasis: Remodeling and Repair
o
Hormonal mechanisms
o
Mechanical and gravitational forces
o
Wolff’s law
 Calcium functions
o
Transmission of nerve impulses
o
Muscle contraction
o
Blood coagulation
o
Secretion of glands and neurons
o
Cell division
14. Explain how hormones and physical stress regulate bone remodeling.
 Growth hormone
 Thyroid hormone
 Estrogen and testosterone
 Parathyroid hormone and calcitonin
o
How they affect calcium metabolism
15. Describe the steps of fracture repair.
 Hematoma
 Fibrocartilaginous callus
 Bony callus
 Remodeling
Homeostatic Imbalances of Bone
16. Contrast the disorders of bone remodeling seen in
 Osteomalacia and rickets
 Osteoporosis

o
What is the physiologic mechanism?
o
Risk factors
o
Most susceptible individuals and areas
o
Know the potential complications of osteoporosis.
o
Know ways to avert and treat osteoporosis.
Developmental aspects of bones
 Nearly all bones completely ossified by age 25
 Bone mass decreases with age beginning in 4th decade
 Rate of loss determined by genetics and environmental factors
 In old age, bone resorption predominates
Suggested Lecture Outline
I. Skeletal Cartilages (p. 173; Fig. 6.1)
A. Basic Structure, Types, and Locations (p. 173; Fig. 6.1)
1.
Skeletal cartilages are made from cartilage, surrounded by a layer of dense irregular
connective tissue called the perichondrium.
2.
Hyaline cartilage is the most abundant skeletal cartilage, and includes the articular,
costal, respiratory, and nasal cartilages.
3.
Elastic cartilages are more flexible than hyaline, and are located only in the external
ear and the epiglottis of the larynx.
4.
Fibrocartilage is located in areas that must withstand a great deal of pressure or
stretch, such as the cartilages of the knee and the intervertebral discs.
B. Growth of Cartilage (p. 173)
1.
Appositional growth results in outward expansion due to the production of cartilage
matrix on the outside of the tissue.
2.
Interstitial growth results in expansion from within the cartilage matrix due to
division of lacunae-bound chondrocytes and secretion of matrix.
II. Classification of Bones (pp. 173–175; Figs. 6.1–6.2)
A. There are two main divisions of the bones of the skeleton: the axial skeleton, consisting of
the skull, vertebral column, and rib cage; and the appendicular skeleton, consisting of the
bones of the upper and lower limbs, and the girdles that attach them to the axial skeleton
(pp. 173–174; Fig. 6.1).
B. Shape (pp. 174–175; Fig. 6.2)
1.
Long bones are longer than they are wide, have a definite shaft and two ends, and
consist of all limb bones except patellas, carpals, and tarsals.
2.
Short bones are somewhat cube shaped and include the carpals and tarsals.
3.
Flat bones are thin, flattened, often curved bones that include most skull bones, the
sternum, scapulae, and ribs.
4.
Irregular bones have complicated shapes that do not fit in any other class, such as the
vertebrae and coxae.
III. Functions of Bones (pp. 175–176)
A. Bones support the body and cradle the soft organs, protect vital organs, allow
movement, store minerals such as calcium and phosphate, and house hematopoietic
tissue in specific marrow cavities (pp. 175–176).
IV. Bone Structure (pp. 176–182; Figs. 6.3–6.7; Table 6.1)
A. Gross Anatomy (pp. 176–178; Figs. 6.3, 6.5; Table 6.1)
1.
Bone markings are projections, depressions, and openings found on the surface of
bones that function as sites of muscle, ligament, and tendon attachment, as joint
surfaces, and as openings for the passage of blood vessels and nerves.
2.
Bone Textures: Compact and Spongy Bone
a. All bone has a dense outer layer consisting of compact bone that appears smooth
and solid.
b. Internal to compact bone is spongy bone, which consists of honeycomb, needlelike, or flat pieces, called trabeculae.
3.
Structure of a Typical Long Bone
a. Long bones have a tubular bone shaft, consisting of a bone collar surrounding a
hollow medullary cavity, which is filled with yellow bone marrow in adults.
b. Epiphyses are at the ends of the bone, and consist of internal spongy bone covered
by an outer layer of compact bone.
c. The epiphyseal line is located between the epiphyses and diaphysis, and is a
remnant of the epiphyseal plate.
d. The external surface of the bone is covered by the periosteum.
e. The internal surface of the bone is lined by a connective tissue membrane called
the endosteum.
4.
Structure of Short, Flat, and Irregular Bones
a. Short, flat, and irregular bones consist of thin plates of periosteum-covered
compact bone on the outside, and endosteum-covered spongy bone inside, which
houses bone marrow between the trabeculae.
5.
Location of Hematopoietic Tissue in Bones
a. Hematopoietic tissue of bones, red bone marrow, is located within the trabecular
cavities of the spongy bone in flat bones, and in the epiphyses of long bones.
b. Red bone marrow is found in all flat bones, epiphyses, and medullary cavities
of infants, but in adults, distribution is restricted to flat bones and the proximal
epiphyses of the humerus and femur.
B. Microscopic Anatomy of Bone (pp. 179–180; Figs. 6.3–6.7)
1.
The structural unit of compact bone is the osteon, or Haversian system, which
consists of concentric tubes of bone matrix (the lamellae) surrounding a central
Haversian canal that serves as a passageway for blood vessels and nerves.
a. Perforating, or Volkmann’s, canals lie at right angles to the long axis of the bone,
and connect the blood and nerve supply of the periosteum to that of the central
canals and medullary cavity.
b. Osteocytes occupy lacunae at the junctions of the lamellae, and are connected to
each other and the central canal via a series of hairlike channels, canaliculi.
c. Circumferential lamellae are located just beneath the periosteum, extending
around the entire circumference of the bone, while interstitial lamellae lie between
intact osteons, filling the spaces in between.
2.
Spongy bone lacks osteons but has trabeculae that align along lines of stress, which
contain irregular lamellae.
C. Chemical Composition of Bone (p. 180)
1.
Organic components of bone include cells (osteoblasts, osteocytes, and osteoclasts)
and osteoid (ground substance and collagen fibers), which contribute to the
flexibility and tensile strength of bone.
2.
Inorganic components make up 65% of bone by mass, and consist of hydroxyapatite,
a mineral salt that is largely calcium phosphate, which accounts for the hardness and
compression resistance of bone.
V. Bone Development (pp. 182–185; Figs. 6.8–6.11)
A. Formation of the Bony Skeleton (pp. 182–184; Figs. 6.8–6.9)
1.
Intramembranous ossification forms membrane bone from fibrous connective tissue
membranes, and results in the cranial bones and clavicles.
2.
In endochondral ossification bone tissue replaces hyaline cartilage, forming all
bones below the skull except for the clavicles.
a. Initially, osteoblasts secrete osteoid, creating a bone collar around the diaphysis of
the hyaline cartilage model.
b. Cartilage in the center of the diaphysis calcifies and deteriorates, forming cavities.
c. The periosteal bud invades the internal cavities and spongy bone forms around
the remaining fragments of hyaline cartilage.
d. The diaphysis elongates as the cartilage in the epiphyses continues to lengthen
and a medullary cavity forms through the action of osteoclasts within the center of
the diaphysis.
e. The epiphyses ossify shortly after birth through the development of secondary
ossification centers.
B. Postnatal Bone Growth (pp. 184–185; Figs. 6.10–6.11)
1.
Growth in length of long bones occurs at the ossification zone through the rapid
division of the upper cells in the columns of chondrocytes, calcification and
deterioration of cartilage at the bottom of the columns, and subsequent
replacement by bone tissue.
2.
Growth in width, or thickness, occurs through appositional growth due to
deposition of bone matrix by osteoblasts beneath the periosteum.
3.
Hormonal Regulation of Bone Growth
a. During infancy and childhood, the most important stimulus of epiphyseal plate
activity is growth hormone from the anterior pituitary, whose effects are
modulated by thyroid hormone.
b. At puberty, testosterone and estrogen promote a growth spurt, but ultimately
induct the closure of the epiphyseal plate.
VI. Bone Homeostasis: Remodeling and Repair (pp. 185–190; Figs. 6.11–6.15; Table 6.2)
A. Bone Remodeling (pp. 185–188; Figs. 6.11–6.13)
1.
In adult skeletons, bone remodeling is balanced bone deposit and removal; bone
deposit occurs at a greater rate when bone is injured; and bone resorption allows
minerals of degraded bone matrix to move into the blood.
2.
Control of Remodeling
a. The hormonal mechanism is mostly used to maintain blood calcium
homeostasis, and balances activity of parathyroid hormone and calcitonin.
b. In response to mechanical stress and gravity, bone grows or remodels in ways
that allow it to withstand the stresses it experiences.
B. Bone Repair (pp. 188–190; Fig. 6.15; Table 6.2)
1.
Fractures are breaks in bones, and are classified by: the position of the bone ends
after fracture, completeness of break, orientation of the break relative to the long axis
of the bone, and whether the bone ends penetrate the skin.
2.
Repair of fractures involves four major stages: hematoma formation,
fibrocartilaginous callus formation, bony callus formation, and remodeling of the
bony callus.
VII.
Homeostatic Imbalances of Bone (pp. 189–191, 194; Fig. 6.16)
A. Osteomalacia and Rickets (p. 189)
1.
Osteomalacia includes a number of disorders in adults in which the bone is
inadequately mineralized.
2.
Rickets is inadequate mineralization of bones in children caused by insufficient
calcium or vitamin D deficiency.
B. Osteoporosis refers to a group of disorders in which the rate of bone resorption exceeds
the rate of formation (pp. 189–191, Fig. 6.16).
1.
Bones have normal bone matrix, but bone mass is reduced and the bones become
more porous and lighter, increasing the likelihood of fractures.
2.
Older women are especially vulnerable to osteoporosis, due to the decline in
estrogen after menopause.
3.
Other factors that contribute to osteoporosis include a petite body form, insufficient
exercise or immobility, a diet poor in calcium and vitamin D, abnormal vitamin D
receptors, smoking, and certain hormone-related conditions.
C. Paget’s disease is characterized by excessive bone deposition and resorption, with the
resulting bone abnormally high in spongy bone. It is a localized condition that results in
deformation of the affected bone (pp. 191, 194).
VIII. Developmental Aspects of Bones: Timing of Events (p. 194; Fig. 6.17)
A. The skeleton derives from embryonic mesenchymal cells, with ossification occurring at
precise times. Most long bones have obvious primary ossification centers by 12 weeks
gestation (p. 194).
B. At birth, most bones are well ossified, except for the epiphyses, which form secondary
ossification centers (p. 194).
C. Throughout childhood, bone growth exceeds bone resorption; in young adults, these
processes are in balance; in old age, resorption exceeds formation (p. 194).
Cross References
Additional information on topics covered in Chapter 6 can be found in the chapters listed below.
1. Chapter 2: Calcium salts
2. Chapter 4: Bone (osseous tissue); chondroblasts; collagen fibers; fibroblasts; fibrocartilage;
hyaline cartilage; proteoglycans
3. Chapter 7: Individual bones that make up the skeleton; identifying marks of individual bones
4. Chapter 8: Articular cartilage and joint structure
5. Chapter 16: Gigantism and dwarfism as related to bone growth and length; effects of
parathyroid hormone and calcitonin on bone homeostasis
6.Chapter 17: Hematopoietic tissue
Online Resources for Students
myA&P™
www.myaandp.com
The following shows the organization of the Chapter Guide page in myA&P™. The Chapter Guide
organizes all the chapter-specific online media resources for Chapter 6 in one convenient location, with ebook links to each section of the textbook. Students can also access A&P Flix animations, MP3 Tutor
Sessions, Interactive Physiology® 10-System Suite, Practice Anatomy Lab™ 2.0, PhysioEx™ 8.0,
and much more.
Objectives
Section 6.1 Skeletal Cartilages (p. 173)
Section 6.2 Classification of Bones (pp. 173–175)
Section 6.3 Functions of Bones (pp. 175–176)
Section 6.4 Bone Structure (pp. 176–182)
Art Labeling: Structure of a Long Bone (Fig. 6.3, p. 176)
Art Labeling: Microscopic Anatomy of Compact Bone (Fig. 6.7, p. 181)
Memory Game: The Architecture of Bone
Memory Game: Cartilage and Bone Structure
Section 6.5 Bone Development (pp. 181–185)
Section 6.6 Bone Homeostasis: Remodeling and Repair (pp. 185–190)
MP3 Tutor Session: Calcium Regulation
MP3 Tutor Session: How Bones React to Stress
Section 6.7 Homeostatic Imbalances of Bone (pp. 189–191)
Section 6.8 Developmental Aspects of Bones: Timing of Events (p. 194)
Chapter Summary
Crossword Puzzle 6.1
Crossword Puzzle 6.2
Web Links
Chapter Quizzes
Art Labeling Quiz
Matching Quiz
Multiple-Choice Quiz
True-False Quiz
Chapter Practice Test
Study Tools
Histology Atlas
myeBook
Flashcards
Glossary
Answers to End-of-Chapter Questions
Multiple Choice and Matching Question answers appear in Appendix G of the main text.
Short Answer Essay Questions
15. Cartilage has greater resilience because its matrix lacks bone salts, but its cells receive
nutrients via diffusion from blood vessels that lie external to the cartilage. By contrast, bone
has a beautifully engineered system of canaliculi for nutrient delivery, and for that reason its
regeneration is much faster and more complete. (pp. 173, 179–180)
16. a. A bone collar is laid down around the diaphysis of the hyaline cartilage model.
b. Cartilage in the center of the diaphysis calcifies and then develops cavities.
c. The periosteal bud invades the internal cavities and spongy bone forms.
d. The diaphysis elongates and a medullary cavity forms.
e. The epiphyses ossify. (pp. 183–184)
17. Volkmann’s canals radiate throughout the bone matrix, linking the central canal, periosteum,
and all lamellae. Canaliculi interconnect all lacunae, allowing transfer of nutrients and wastes
between the blood and osteocytes. (p. 179)
18. The increase in thickness of compact bone on its superficial face is counteracted by the
resorption of bone by osteoclasts on its internal surface. (pp. 185–186)
19. An osteoid seam is an unmineralized band of bony matrix that is about 10–12 micrometers
wide. Between this seam and older bone is an abrupt transition called a calcification front.
The osteoid seam always stays the same width, indicating that osteoid tissue must mature
before it can be calcified. This area then changes quickly from an unmineralized matrix to a
mineralized matrix. (p. 186)
20. Two control loops regulate bone remodeling. One is a negative feedback hormonal
mechanism that maintains blood Ca2+, and the other involves mechanical and gravitational
forces acting on the skeleton. (p. 186)
21. a. First decade is fastest; fourth decade is slowest. (p. 194)
b. Elderly people usually experience bone loss, osteoporosis, and an increasing lack of blood
supply. (p. 191)
c. Children have proportionally more organic matrix. (p. 190)
22. This bone section is taken from the diaphysis of the specimen. The presence of an osteon, the
concentric layers surrounding a central cavity, indicates compact bone found in the
diaphysis. The epiphyseal plate, the site of active bone growth, lacks osteons. (pp. 179, 181)
Critical Thinking and Clinical Application Questions
1. A bony callus represents the conversion of the fibrocartilaginous callus to a callus containing
trabeculae of spongy bone. (p. 189)
2. Rickets. Milk provides dietary calcium and vitamin D. Vitamin D is needed for its uptake by
intestinal cells; the sun helps the skin synthesize vitamin D. Thick epiphyseal plates indicate
poor calcification of the growing area. Because of this lack of sufficient calcium, the bones
will be more pliable, and weight-bearing bones, like those in the leg, will bend. (p. 189)
3. The compact lamellar structure of dense bone produces structural units designed to resist
twisting and other mechanical stresses placed on bones. In contrast, spongy bone is made up
of trabeculae only a few cell layers thick containing irregularly arranged lamellae. (p. 187)
4. Because the changes throughout adolescence involve changes in stress associated with
muscle growth, and sex steroids that, in part, affect bone deposition, a lack of bone
remodeling during adolescence would keep bones in more of a preadolescent form. Bones
would retain a thinner, less dense appearance than would usually be expected, especially in
areas that are under the greatest stress. (pp. 185–187)
5. According to Wolff’s law, bone growth and remodeling occur in response to stress placed on
such bones. With disuse, the bones in the limbs not being used will begin to atrophy. (p. 187)
6. Presumably the epiphyseal plate-bone junction has separated. The same would not happen to
the boy’s 23-year-old sister because by this age, epiphyseal plates have been replaced by bone
and are no longer present. (p. 185)
7. Paget’s disease, which results in irregular thickening of bone tissue and often affects the skull
and spine, causing pain and deformity. (p. 191)