DEXA Anatomy & Physiology of Bone Structure 5 — Questions and Answers
Question 1: The metaphysis of a long bone is best described as the region:
- Central medullary canal filled with marrow
- Flared zone between the epiphysis and diaphysis containing the former growth plate (Correct answer)
- Articular surface covered by hyaline cartilage
- Outer periosteal layer of compact bone
Correct answer: Flared zone between the epiphysis and diaphysis containing the former growth plate
The metaphysis is the wider transitional region between the epiphysis and the diaphysis, encompassing the area of the former growth plate in skeletally mature individuals.
Question 2: Mechanotransduction in bone refers to:
- Hormonal signaling between osteoblasts and osteoclasts
- The process by which mechanical loads are converted to cellular biochemical signals that regulate bone remodeling (Correct answer)
- Electrical conduction through Haversian canals
- Nutrient transport across the periosteum
Correct answer: The process by which mechanical loads are converted to cellular biochemical signals that regulate bone remodeling
Mechanotransduction describes how osteocytes sense mechanical strain and translate it into biochemical signals (e.g., nitric oxide, prostaglandins) that regulate bone formation and resorption.
Question 3: Vitamin D's principal role in bone physiology is to:
- Directly stimulate osteoclast differentiation
- Enhance intestinal absorption of calcium and phosphate to support mineralization (Correct answer)
- Inhibit parathyroid hormone secretion at all serum calcium levels
- Increase urinary calcium excretion
Correct answer: Enhance intestinal absorption of calcium and phosphate to support mineralization
Active vitamin D (1,25-dihydroxyvitamin D) promotes intestinal absorption of calcium and phosphate, providing the mineral substrate needed for bone mineralization.
Question 4: The lacunocanalicular system in bone primarily serves to:
- Provide structural support to trabeculae
- Allow osteocytes to communicate and receive nutrients via fluid-filled channels (Correct answer)
- House hematopoietic stem cells
- Facilitate osteoclast attachment to bone surface
Correct answer: Allow osteocytes to communicate and receive nutrients via fluid-filled channels
The lacunocanalicular network consists of lacunae (osteocyte cell bodies) connected by canaliculi (tiny channels) through which nutrients, waste, and signaling molecules diffuse.
Question 5: Degenerative changes such as osteophytes and aortic calcification can artificially _______ lumbar spine BMD measurements on DEXA.
- Decrease
- Increase (Correct answer)
- Have no effect on
- Randomize
Correct answer: Increase
Osteophytes, vertebral fractures, and overlying aortic calcifications increase X-ray attenuation in the scan field, falsely elevating apparent lumbar BMD values.
Question 6: Red (hematopoietic) bone marrow in adults is found predominantly in which skeletal locations?
- Shafts of long bones in the limbs
- Flat bones (sternum, ilium, ribs, vertebrae) and proximal long bone epiphyses (Correct answer)
- Subchondral bone beneath articular cartilage
- Cortical bone of the femoral diaphysis
Correct answer: Flat bones (sternum, ilium, ribs, vertebrae) and proximal long bone epiphyses
In adults, active red marrow is concentrated in flat bones and the proximal epiphyses of long bones, while the shafts contain yellow (fatty) marrow.
Question 7: The RANK/RANKL/OPG signaling axis regulates bone remodeling primarily by controlling:
- Osteoblast proliferation and collagen synthesis
- Osteoclast differentiation, activation, and survival (Correct answer)
- Calcium transport across the intestinal epithelium
- Growth plate chondrocyte hypertrophy
Correct answer: Osteoclast differentiation, activation, and survival
RANKL (from osteoblasts/stromal cells) binds RANK on osteoclast precursors to promote their differentiation; OPG acts as a decoy receptor blocking RANKL, inhibiting osteoclastogenesis.
DEXA Anatomy & Physiology of Bone Structure 5
The metaphysis of a long bone is best described as the region: