Bone And Cartilage Histology Questions

A. Thyroxine, testosterone, and somatotropin stimulate cartilage growth and matrix formation (see Chapter 71A2).

B. Because calcium must be maintained at a constant level in the blood and the tissues, a diet deficient in calcium leads to calcium loss from the bones. As a result, the bones become fragile (see Chapter 7 II C 4 Clinical Considerations).

D. Hyaline cartilage is avascular, contains type II collagen, and grows both interstitially and ap- positionally. It is located at the articulating ends of long bones (see Chapter 7 I A).

D. Hydrocortisone inhibits cartilage growth and matrix formation (see Chapter 7 I A 2).

C. In the absence of vitamin D, epiphyseal chondrocytes continue to proliferate, but their ma- trix does not calcify, which leads to rickets (see Chapter 7 II I Clinical Considerations

B. Excessive growth hormone causes acromegaly. Excessive vitamin D causes bone resorption. Both an excess and a deficiency of vitamin A result in short stature (see Chapter 7 II J Clinical Considerations).

D. The inner layer of the periosteum possesses osteoprogenitor cells, whereas the outer layer of the periosteum is fibrous. The periosteum functions to distribute blood vessels to the bone; thus, appositional bone growth takes place here (see Chapter 7 II В

E. Osteoclasts are multinucleated cells that produce proteolytic enzymes and occupy Howship lacunae. They are not derived from osteoprogenitor cells but from monocyte precursors (see Chapter 7 II C 4).

C. Haversian canals run longitudinally, parallel to the long axis of bone. They are connected to one another by Volkmann canals that run perpendicular (or obliquely) to them (see Chapter 7 II E 1)

. A. Osteocytes communicate with each other via gap junctions on narrow cytoplasmic pro- cesses that extend through canaliculi. They are mature bone cells that occupy individual lacu- nae as mature resting bone cells (see Chapter 7 II C 3).

B. Hypervitaminosis A accelerates ossification of epiphyseal plates, whereas hypovitaminosis A reduces the width of the epiphyseal plates (see Chapter 7 II I).

E. Osteopetrosis is a genetic defect involving the osteoclasts. Persons with this defect possess osteoclasts without ruffled borders, which prohibit them from resorbing bone. Therefore, bone forms but is not resorbed. This leads to increased bone density, anemia, blindness, deafness, and cranial nerve involvement because the nerves are impinged upon as they exit the cranium via their foramina (see Chapter 7 II B Clinical Considerations).