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Biology, Genetics & Bone Healing MCQs

Practice Set 56 of 212

This practice set contains high-yield board review questions covering key concepts in Biology, Genetics & Bone Healing. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 1101

Topic: Biology, Genetics & Bone Healing

Osteonecrosis of the large joints may develop in patients with which of the following conditions?

. Collagen I disease
. Antiphospholipid syndrome (APS)
. Hemochromatosis
. Achondroplasia
. Paget's disease

Correct Answer & Explanation

. Antiphospholipid syndrome (APS)

Explanation

Osteonecrosis of major joints can occur in patients exposed to corticosteroids, alcohol, and antiseizure medications, as well as patients with hemaglobulinopathy, such as sickle cell anemia. In addition, patients with primary APS who had not taken corticosteroids were also found to be at high risk for osteonecrosis of the hip. In one study of 30 patients with primary APS, asymptomatic osteonecrosis was evident in 20%. A recent article has also found a high association between idiopathic osteonecrosis of the hip and collagen II mutation. None of the other conditions has been shown to be associated with a higher risk of osteonecrosis. Tektonidou MG, Malagari K, Vlachoyiannopoulos PG, et al: Asymptomatic avascular necrosis in patients with primary antiphospholipid syndrome in the absence of corticosteroid use: A prospective study by magnetic resonance imaging. Arthritis Rheum 2003;48:732-736.

Question 1102

Topic: Biology, Genetics & Bone Healing

In the process of aseptic loosening due to particulate wear debris, macrophages phagocytose the particles and subsequently release cytokines that drive osteoclastogenesis. Which of the following cytokines is a primary mediator of this process?

. Interleukin-10 (IL-10)
. Tumor necrosis factor-alpha (TNF-alpha)
. Transforming growth factor-beta (TGF-beta)
. Interleukin-4 (IL-4)
. Osteoprotegerin (OPG)

Correct Answer & Explanation

. Tumor necrosis factor-alpha (TNF-alpha)

Explanation

TNF-alpha, IL-1, and IL-6 are the major pro-inflammatory cytokines secreted by macrophages in response to wear debris, leading to upregulation of RANKL and subsequent osteolysis.

Question 1103

Topic: Biology, Genetics & Bone Healing

Which of the following genetic mutations results in high bone mass due to decreased inhibition of the Wnt/beta-catenin signaling pathway?

. Loss-of-function mutation in SOST
. Gain-of-function mutation in FGFR3
. Loss-of-function mutation in RANK
. Gain-of-function mutation in COL1A1
. Loss-of-function mutation in LRP5

Correct Answer & Explanation

. Loss-of-function mutation in SOST

Explanation

Sclerostin (encoded by SOST) normally inhibits Wnt signaling by binding LRP5/6 receptors. Loss-of-function mutations in SOST lead to conditions like sclerosteosis, characterized by an uninhibited Wnt pathway and abnormally high bone mass.

Question 1104

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the mechanism of action of denosumab in the treatment of osteoporosis?

. Competitive inhibition of osteoclast proton pumps
. Monoclonal antibody binding directly to RANK ligand
. Stimulation of osteoblast proliferation via the Wnt pathway
. Selective estrogen receptor modulation
. Integration into the bone matrix resulting in osteoclast apoptosis

Correct Answer & Explanation

. Monoclonal antibody binding directly to RANK ligand

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL. This neutralizes RANKL, preventing it from activating RANK on osteoclasts, which profoundly inhibits osteoclast differentiation and bone resorption.

Question 1105

Topic: Biology, Genetics & Bone Healing

Intermittent administration of recombinant human parathyroid hormone (teriparatide) achieves its anabolic effect on bone primarily by preventing the apoptosis of which cell type?

. Osteoclasts
. Osteoblasts
. Osteocytes
. Chondrocytes
. Mesenchymal stem cells

Correct Answer & Explanation

. Osteoblasts

Explanation

Intermittent PTH administration (teriparatide) exerts a net anabolic effect primarily by stimulating osteoblast activity and prolonging their lifespan by inhibiting osteoblast apoptosis. Continuous PTH exposure, conversely, promotes net bone resorption.

Question 1106

Topic: Biology, Genetics & Bone Healing

The acidification of the resorption pit by osteoclasts requires the secretion of protons across the ruffled border. Which intracellular enzyme primarily generates these protons?

. Alkaline phosphatase
. Tartrate-resistant acid phosphatase
. Carbonic anhydrase II
. Cathepsin K
. Matrix metalloproteinase-9

Correct Answer & Explanation

. Carbonic anhydrase II

Explanation

Carbonic anhydrase II catalyzes the conversion of carbon dioxide and water into carbonic acid, which rapidly dissociates into protons and bicarbonate. The protons are then actively pumped into the resorption lacuna to dissolve bone mineral.

Question 1107

Topic: Biology, Genetics & Bone Healing

Recombinant human bone morphogenetic protein-2 (rhBMP-2) signals through transmembrane serine-threonine kinase receptors. Which intracellular signaling molecules are directly phosphorylated following this activation?

. Beta-catenin
. Smad 1/5/8
. JAK/STAT
. NF-kappaB
. Cyclic AMP

Correct Answer & Explanation

. Smad 1/5/8

Explanation

BMPs bind to specific serine-threonine kinase receptors that directly phosphorylate receptor-regulated Smads (Smads 1, 5, and 8). These phosphorylated Smads form a complex with Smad 4, translocate to the nucleus, and drive osteogenic gene transcription.

Question 1108

Topic: Biology, Genetics & Bone Healing

A patient presents with osteomalacia. Laboratory testing reveals low calcium, low phosphorus, and elevated parathyroid hormone (PTH) levels. Which of the following best explains the mechanism of low serum phosphorus in this patient?

. Decreased intestinal absorption of phosphorus
. PTH-mediated inhibition of renal phosphate reabsorption
. Decreased bone resorption of phosphorus
. Increased renal synthesis of 1,25-dihydroxyvitamin D
. Reduced FGF-23 secretion

Correct Answer & Explanation

. PTH-mediated inhibition of renal phosphate reabsorption

Explanation

In vitamin D deficiency (osteomalacia), secondary hyperparathyroidism develops to maintain serum calcium. The elevated PTH decreases phosphate reabsorption in the proximal renal tubule, causing phosphaturia and subsequent hypophosphatemia.

Question 1109

Topic: Biology, Genetics & Bone Healing

During endochondral ossification at the physis, in which histologic zone do chondrocytes undergo apoptosis as the extracellular matrix begins to calcify?

. Reserve zone
. Proliferative zone
. Zone of maturation
. Zone of hypertrophy
. Zone of provisional calcification

Correct Answer & Explanation

. Zone of provisional calcification

Explanation

In the zone of provisional calcification, the cartilage matrix undergoes calcification and the hypertrophic chondrocytes undergo apoptosis. This calcified matrix provides a temporary scaffold for osteoblasts to lay down primary woven bone.

Question 1110

Topic: Biology, Genetics & Bone Healing

Which cell is considered the primary mechanosensor in bone tissue, responsible for orchestrating the remodeling process in response to changes in mechanical loading?

. Osteoblast
. Osteoclast
. Osteocyte
. Bone lining cell
. Mesenchymal stem cell

Correct Answer & Explanation

. Osteocyte

Explanation

Osteocytes, embedded deep within the bone matrix, are the primary mechanosensors of bone. They sense fluid shear stress within their canalicular networks during mechanical loading and direct osteoblast and osteoclast activity accordingly.

Question 1111

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates, such as alendronate, inhibit bone resorption primarily by inhibiting which of the following enzymes?

. HMG-CoA reductase
. Farnesyl pyrophosphate (FPP) synthase
. Carbonic anhydrase II
. Cathepsin K
. Tyrosine kinase

Correct Answer & Explanation

. Farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates inhibit FPP synthase in the mevalonate pathway within osteoclasts. This prevents the prenylation of critical small GTP-binding proteins (e.g., Rab, Rho, Rac), leading to osteoclast apoptosis and loss of function.

Question 1112

Topic: Biology, Genetics & Bone Healing

Which of the following is the primary histological finding that distinguishes osteomalacia from osteoporosis?

. Decreased cortical thickness
. Increased unmineralized osteoid seams
. Presence of empty osteocyte lacunae
. Increased woven bone formation
. Multinucleated giant cells

Correct Answer & Explanation

. Increased unmineralized osteoid seams

Explanation

Osteomalacia is characterized by a defect in bone mineralization, resulting in a classic histological appearance of thickened, unmineralized osteoid seams. Osteoporosis, by contrast, shows normal mineralization but a quantitatively decreased total bone mass.

Question 1113

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the cellular mechanism of action of nitrogen-containing bisphosphonates (e.g., alendronate)?

. Inhibiting the farnesyl pyrophosphate synthase enzyme in the mevalonate pathway
. Acting as a decoy receptor for RANKL
. Inhibiting DNA gyrase within the osteoclast nucleus
. Stimulating osteoblast differentiation through Wnt signaling
. Binding to sclerostin to prevent its inhibitory effects

Correct Answer & Explanation

. Inhibiting the farnesyl pyrophosphate synthase enzyme in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents prenylation of small GTPase proteins (like Ras and Rho), ultimately leading to osteoclast apoptosis and decreased bone resorption.

Question 1114

Topic: Biology, Genetics & Bone Healing

Denosumab is a potent antiresorptive agent used in the treatment of osteoporosis and giant cell tumor of bone. What is its primary mechanism of action?

. Recombinant parathyroid hormone analog
. Monoclonal antibody against sclerostin
. Inhibitor of the mevalonate pathway
. Monoclonal antibody that binds to RANKL
. Selective estrogen receptor modulator (SERM)

Correct Answer & Explanation

. Monoclonal antibody that binds to RANKL

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding RANKL, it prevents interaction with the RANK receptor on osteoclasts, thus inhibiting osteoclast formation and function.

Question 1115

Topic: Biology, Genetics & Bone Healing
Which of the following combinations correctly identifies the predominant collagen type and its synthesizing cell in normal hyaline articular cartilage?
. Type I collagen synthesized by osteoblasts
. Type II collagen synthesized by chondrocytes
. Type III collagen synthesized by fibroblasts
. Type IV collagen synthesized by endothelial cells
. Type X collagen synthesized by hypertrophic chondrocytes

Correct Answer & Explanation

. Type II collagen synthesized by chondrocytes

Explanation

Normal hyaline articular cartilage is primarily composed of water and Type II collagen, which is synthesized exclusively by chondrocytes. Type X collagen is localized to the calcified zone and is produced by hypertrophic chondrocytes.

Question 1116

Topic: Biology, Genetics & Bone Healing

Teriparatide is an anabolic agent utilized for the treatment of severe osteoporosis. How does its administration lead to increased bone mineral density?

. Continuous exposure directly inhibits osteoclast apoptosis
. Intermittent administration stimulates osteoblastic bone formation
. Continuous exposure suppresses parathyroid hormone-related peptide
. Intermittent administration directly binds and inhibits RANKL
. Continuous administration decreases renal calcium reabsorption

Correct Answer & Explanation

. Intermittent administration stimulates osteoblastic bone formation

Explanation

Teriparatide is a recombinant human parathyroid hormone (PTH 1-34) analog. While continuous PTH exposure primarily drives osteoclast-mediated bone resorption, daily intermittent administration paradoxically stimulates robust osteoblastic bone formation.

Question 1117

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, primary bone healing (osteonal remodeling without callus formation) occurs only when the interfragmentary strain is maintained below what specific threshold?

. 2 percent
. 10 percent
. 25 percent
. 50 percent
. 100 percent

Correct Answer & Explanation

. 2 percent

Explanation

Perren's strain theory states that primary (absolute) bone healing occurs when interfragmentary strain is kept below 2%. Strains between 2% and 10% promote secondary bone healing via callus formation, while strains above 10% result in nonunion.

Question 1118

Topic: Biology, Genetics & Bone Healing

Osteoprotegerin (OPG) plays a critical regulatory role in bone remodeling. Which of the following accurately describes its cellular source and function?

. Secreted by osteoclasts to stimulate osteoblast proliferation
. Secreted by osteoblasts to act as a decoy receptor for RANKL
. Secreted by osteocytes to inhibit Wnt signaling
. Secreted by macrophages to directly induce osteoclast apoptosis
. Secreted by the parathyroid gland to increase serum calcium

Correct Answer & Explanation

. Secreted by osteoblasts to act as a decoy receptor for RANKL

Explanation

Osteoprotegerin (OPG) is a glycoprotein secreted primarily by osteoblasts. It acts as a decoy receptor that competitively binds RANKL, preventing RANKL from activating RANK on osteoclasts and thereby inhibiting bone resorption.

Question 1119

Topic: Biology, Genetics & Bone Healing

Which of the following cells is the primary source of receptor activator of nuclear factor kappa-B ligand (RANKL) in bone metabolism?

. Osteoclasts
. Osteoblasts
. Osteocytes
. Macrophages
. Chondrocytes

Correct Answer & Explanation

. Osteoblasts

Explanation

Osteoblasts and bone marrow stromal cells express RANKL on their surface in response to various stimuli. RANKL binds to RANK on osteoclast precursors, promoting their differentiation and activation.

Question 1120

Topic: Biology, Genetics & Bone Healing

A 65-year-old female is prescribed alendronate for osteoporosis. What is the specific cellular mechanism of action of this medication?

. Inhibits osteoclast proton pumps
. Binds to RANKL to prevent osteoclast activation
. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway
. Stimulates Wnt signaling by inhibiting sclerostin
. Acts as a selective estrogen receptor modulator

Correct Answer & Explanation

. Inhibits farnesyl pyrophosphate synthase in the mevalonate pathway

Explanation

Nitrogen-containing bisphosphonates like alendronate inhibit farnesyl pyrophosphate synthase (FPPS) in the mevalonate pathway. This prevents protein prenylation, leading to osteoclast apoptosis and decreased bone resorption.

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