Specialized Connective Tissues: Bone and Cartilage Answers 207hypertrophy, and the cells synthesize alkaline phosphatase, which calcifies
the cartilage matrix. This secretion results in the eventual death of these cells
that depend on diffusion to obtain oxygen and nutrients from the matrix.
During development of the long bones of the body, specific zones are estab-
lished, as a cartilage model of a long bone is converted to mature bone. The
zones from the epiphysis toward the center of the shaft (diaphysis) are as fol-
lows: resting zone, proliferative zone, hypertrophy zone, and zone of calci-
fied cartilage that is used as the scaffolding for the deposition of bone. The
periosteal bud represents the ingrowth of blood vessels (angiogenesis) bring-
ing, bone marrow precursors and osteoprogenitor cells into the diaphysis.
Angiogenesis is required for bone formation. Bone is formed by the action of
osteoblasts forming type I collagen, noncollagenous proteins (e.g., osteocal-
cin, osteopontin, and osteonectin), and alkaline phosphatase, which plays an
essential role in mineralization of the osteoid. Cyclins are synthesized by cells
passing through the cell cycle, cells in the proliferative zone (answer a);acid
phosphatase(answer b)is synthesized by osteoclasts; and type I collagen
and osteocalcin (answers d and e)are synthesized by osteoblasts.
108.The answer is e.(Alberts, pp 1304–1308. Kumar, pp 1281–1283.
Guyton, pp 904–910. Greenspan, pp 274, 278–279, 286–287. Junqueira, pp 136,
- High-Yield Facts, p 20.)The patient in the vignette is suffering from
type II autosomal dominant osteopetrosis (type II ADO), also known as
Albers-Schönberg disease with a characteristic radiological image of “sand-
wich vertebrae.” The targets in this disease are the osteoclasts which are
indicated in the micrographs. Osteoclast function is altered in osteopetro-
sis. Osteoclasts function by release of lytic enzymes and protons (derived
from carbonic acid) into the calcified matrix beneath the ruffled border and
not through a grinding action (answer a).The bone compartment around
the ruffled border of the osteoclast is, therefore, analogous to a secondary
lysosome in function, albeit extracellular. Osteoclasts use protons derived
from carbonic acid, catalyzed by carbonic anydrase, in similar fashion to
parietal cells of the stomach. Alkaline phosphatase is synthesized by
osteoblasts(answer b); PTH and Vitamin D receptors are found on
osteoblasts(answers c and d), notosteoclasts.
The electron micrograph illustrates the typical ultrastructure of an
osteoclast with its distinctive ruffled border. The light micrograph illustrates
the position of the osteoclasts (multinucleate cells) in small depressions in
the bone (Howship’s lacunae). The arrowhead in the electron micrograph