Chapter 17. Final Examination
A mother brought her 10-year-old son to the physician's office for his annual physical examination. While examining the boy, the physician discovered that the child had grown very little since his last visit. An MRI shows that the boy's epiphyseal growth plates are beginning to close prematurely. To slow the closure of the growth plate and to promote continued growth of his long bones, the physician prescribes somatotropin (growth hormone) as a treatment. What effect will this hormone have on the child's bone development?
A. Stimulate the deposition of hydroxyapatite (calcium phosphate crystals) in the osteoid at the growth plate
B. Stimulate the deposition of osteoid at the growth plate
C. Stimulate the hypertrophy of chondrocytes in the growth plate
D. Stimulate the maturation of osteoblasts to osteocytes
E. Stimulate proliferation of chondrocytes in the growth plate
The answer is E: The growth and development of epiphyseal cartilage in the growth plate is influenced by various signaling molecules, including somatotropin. Somatotropin stimulates the liver to produce insulin-like growth factors (primarily IGF-1 or somatomedin C), which stimulate mitosis of chondrocytes in the epiphyseal growth plate, thereby promoting long-bone growth. Somatotropin levels (and hence IGF-1 levels) decrease at puberty, which contributes to closure of the epiphyseal plate.
Asthma is a reactive airway disease resulting in intermittent reversible obstruction to airflow in the lungs due to hyperactivity and inflammation. A problem that occurs during an asthma attack is the constriction of the bronchioles inhibiting the flow of air into and out of the lungs. What histologic feature do the trachea and bronchi both possess that most likely prevents collapse during an asthma attack?
D. Simple columnar epithelial cells
The answer is B: The C-shaped hyaline cartilage rings (trachea) and cartilage plates (bronchi) physically keep the lumen of their airways open during an asthma attack and during exhalation. The bronchioles lack this cartilage support and, therefore, close during an asthma attack because there is no physical support to keep the lumen open.
Nuclear extrusion is part of the normal process of producing human red blood cells. What is another process that normally involves the extrusion of the nucleus of a cell?