Ch 6 Answers to End-of-Chapter Questions
Multiple-Choice and Matching Question answers appear in Appendix H of the main text.
Short Answer Essay Questions
15. Cartilage has greater resilience than bone because its matrix lacks the bone salts found
in bone tissue. Regeneration is much faster and more complete in bone tissue because it
has a dense network of canaliculi throughout the matrix for nutrient delivery, compared
to cartilage, which only receives nutrients via diffusion from blood vessels that lie
external to the cartilage. (pp. 174, 181)
16. a. In endochondral ossification, a bony collar is laid down around the diaphysis of the
hyaline cartilage model.
b. Nutrient delivery to the cartilage in the center of the diaphysis is hindered, causing
calcification and deterioration of the cartilage matrix.
c. The periosteal bud invades the newly formed cavities in the cartilage, and spongy
bone forms.
d. Bone matrix deposition progresses outward from the ossification center: deterioration
of bone matrix in the center of the diaphysis forms a medullary cavity.
e. Secondary ossification centers form at the epiphyses, completing bone deposition
at the ends of the bone, leaving only articular cartilage and epiphyseal plates.
(pp. 183–184)
17. Peforating 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. 181)
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. (p. 187)
19. In an adult bone, new bone tissue is formed when osteoblasts deposit new bone matrix,
forming an osteoid seam, a layer of unmineralized bone matrix. A calcification front,
next to the older, mineralized bone, forms as new matrix becomes mineralized.
Important to this calcification are levels of calcium and phosphate, and functional
proteins that guide the process. (p. 187)
20. Two control loops regulate bone remodeling. A hormonal mechanism involving PTH
that maintains blood Ca2+ promotes increased breakdown of bone matrix, while
mechanical force acting on the skeleton promotes increased deposition of minerals in
bone matrix. Bones would tend to lose mass and density under the influence of PTH,
while they would gain mass and density if stress on the bone increased. (pp. 187–188)
21. a. Skeletal mass increases the most during the first decade of life, and begins to decline
during the fourth decade of life. (p. 193)
b. Elderly people usually experience bone loss, osteoporosis, and an increasing lack of
blood supply, resulting in bones that are more prone to fracture. (p. 194)
c. Greenstick fractures are more likely in children because their bones have
proportionally more organic matrix. This imparts the bone with more resilience, and
a tendency to break incompletely. (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. 181, 184)
Critical Thinking and Clinical Application Questions
1. A bony callus is tissue formed when the fibrocartilaginous callus is converted to a
callus containing trabeculae of spongy bone. (p. 191)
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 of the bones. 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. 192)
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. Considerably more fragile than compact bone, an outer layer of spongy bone
would be constantly damaged by the forces directed to bone. (pp. 181, 189)
4. The changes in bone development throughout adolescence are driven by changes in
levels of sex steroids, as well as stress associated with muscle growth. A lack of bone
remodeling during adolescence would keep bones in more of a preadolescent form.
Bones would remain thinner, and less dense. This would be especially noticeable in
areas that are under the greatest stress. (pp. 186–187)
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 paralyzed limbs will begin to
atrophy. (p. 189)
6. It is likely that he has suffered an epiphyseal fracture, in which the epiphyseal platebone 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. 190)
7. Paget’s disease, which results in irregular thickening of bone tissue and often affects the
skull and spine, causing pain and deformity. (p. 193)