CHAPTER 6
Answers to “What Did You Learn?”
1.
The three types of cartilage are hyaline cartilage, fibrocartilage, and elastic
cartilage. Hyaline cartilage attaches the ribs to the sternum, forms the apex of the
nasal septum, and supports the air passageways in the respiratory system.
Fibrocartilage is located in areas of high stress, such as the pubic symphysis and
within the intervertebral discs. Elastic cartilage is a component of the external
ear, where it can return to normal shape after deformation.
2.
Interstitial growth occurs from within the cartilage itself, whereas appositional
growth occurs around the periphery of the cartilage. Appositional growth
predominates in older cartilage.
3.
Bone functions include support and protection, movement, hemopoiesis, and
storage of minerals and energy.
4.
The four types of bones are long bones, short bones, flat bones, and irregular
bones. The os coxae is an irregular bone.
5.
The diaphysis is the shaft of a long bone, and contains the medullary cavity (filled
with yellow bone marrow in adults). Epiphyses are the ends of the long bone, and
are composed of spongy bone surrounded by an outer layer of compact bone.
6.
Organic bone components include bone cells, collagen fibers, and ground
substance. Inorganic components include calcium phosphate and calcium
hydroxide, which together form hydroxyapatite.
7.
When deposition of bone matrix is greater than resorption of bone matrix, the
mass of the bone increases.
8.
The central canal is the cylindrical space in the center of the osteon that houses
blood vessels and nerves. The canaliculi are small channels within bone tissue
that house the osteocyte cytoplasmic projections. It is through the canaliculi that
nutrients, minerals, gases, and wastes are exchanged between osteocytes and the
vessels in the central canal. Lacunae are the spaces within the bone that house
osteocytes.
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9.
Intramembranous ossification is the formation of bone within a thickened region
of mesenchyme. Bones produced by this process include flat bones of the skull,
some facial bones (zygomatic bone, maxilla), the mandible, and the central part of
the clavicle.
10.
The primary ossification center forms within the diaphysis of a hyaline cartilage
model of bone; a secondary ossification center forms within each epiphysis.
11.
A radiograph should show the presence of epiphyseal plates and/or epiphyseal
lines. If there are no epiphyseal plates present (and only epiphyseal lines present),
that would indicate growth is complete and the person has reached full height.
12.
The five zones in the epiphyseal plate are: Zone 1: zone of resting cartilage
(normal looking chondrocytes), Zone 2: Zone of proliferating Cartilage (cartilage
cells enlarge slightly, undergo mitotic cell division, and appear stacked), Zone 3:
Zone of hypertrophic cartilage (mitotic cell division ceases and chondrocytes
enlarge greatly), Zone 4: Zone of calcified cartilage (matrix undergoes
calcification and kills the cells, the matrix appears opaque), and Zone 5: Zone of
ossification (bone tissue replaces calcified cartilage).
13.
Growth hormone stimulates the production of somatomedin in the liver.
Somatomedin acts on the cartilage at the epiphyseal plate to increase bone growth
and, subsequently, bone mass. Parathyroid hormone activates osteoclasts to cause
bone resorption, resulting in reductions in bone mass.
14.
Vitamins A, C, and D help regulate bone growth.
15.
compound
16.
A narrow, slit like opening through a bone is called a fissure.
Answers to “Content Review”
1.
Hyaline cartilage has a “glassy” extracellular matrix with no visible protein
fibers. Fibrocartilage has an extracellular matrix that displays numerous thick
collagen fibers. Elastic carilage exhibits extensively branched elastic fibers
within its extracellular matrix.
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2.
The periosteum is a tough dense irregular connective tissue covering around the
outer surface of the bone, except where articular cartilage is present. It protects
bone from surrounding tissues, anchors blood vessels and nerves to the surface
of the bone, and provides bone stem cells (osteoprogenitor cells and osteoblasts)
for bone width growth and fracture repair.
3.
Articular cartilage is located on the epiphyses of long bones. It is composed of
hyaline cartilage and allows for easy articulation and movement between bones.
The medullary cavity is the space inside the diaphysis. In the adult, it is lined
with endosteum and filled with yellow bone marrow. Endosteum is a thin,
incomplete cellular layer that lines the medullary cavity and covers the
trabeculae of spongy bone. It contains bone cells that can produce or break
down bone matrix.
4.
Compact bone is organized into cylindrical structures called osteons. Osteons
run parallel to the shaft of the bone. In cross-section, the center of the osteon is
the central canal (which houses blood vessels and nerves), the rings of bone
surrounding the osteon are the concentric lamellae, osteocytes (mature bone
cells) rest in lacunae between the lamellae, and canaliculi are tiny channels that
connect osteocytes between lacunae. Also within compact bone are perforating
canals (canals that run perpendicular to the shaft of the bone and connect two or
more osteons), circumferential lamellae, and interstitial lamellae (incomplete
remnants of osteons).
5.
Trabeculae of spongy bone form a meshwork pattern of criss-crossing bony
bars. This structure provides great strength against stresses applied in many
directions without requiring a large mass of bone, by distributing the stress
throughout the entire framework.
6.
Ossification is the formation of and development of bone connective tissue.
Intramembranous ossification is where bone develops from a condensed layer of
mesenchyme. In contrast, endochondral ossification is where bone arises from a
hyaline cartilage model.
7.
The steps of endochondral ossification are: development and growth of a hyaline
cartilage model of bone; calcification of cartilage and formation of a periosteal
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bone collar around the diaphysis; primary ossification center formation in the
diaphysis; secondary ossification center formations in the epiphyses,
replacement of cartilage in most areas of bone, except for the epiphyseal plates
and articular cartilage, and; ossification of the epiphyseal plates (which form
epiphyseal lines).
8.
Long bones are supplied by four types of arteries. A nutrient artery supplies the
diaphysis of the long bone, while metaphyseal arteries supply the diaphyseal end
of the epiphyseal plate. Epiphyseal arteries supply the epiphyses, while the
periosteal arteries supply the periosteum, external circumferential lamellae, and
the osteons close to the external edge of the bone.
9.
In response to mechanical stress, bone is able to increase its strength and mass
somewhat. Usually, applications of stress strengthen bone tissue and increase
bone mass over a period of time by increasing the amounts of mineral salts
deposited and collagen fibers produced. Stress in the form of exercise also
increases the production of the hormone calcitonin, which encourages bone
deposition.
10.
The four steps in fracture repair are: (1) formation of a fracture hematoma; (2)
formation of a fibrocartilagecallus; (3) formation of a hard bony callus; and (4)
remodeling of bone.
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