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Biology, Genetics & Bone Healing MCQs

Practice Set 74 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 1461

Topic: Biology, Genetics & Bone Healing

A patient with chronic kidney disease presents with renal osteodystrophy. Laboratory analysis reveals elevated parathyroid hormone (PTH). What is the direct mechanism by which persistently elevated PTH drives bone resorption?

. Direct binding to RANK receptors on osteoclasts
. Stimulation of osteoblasts to increase RANKL and decrease OPG expression
. Inhibition of M-CSF production by mesenchymal stem cells
. Direct stimulation of osteoclast ruffled border formation
. Upregulation of osteoprotegerin (OPG) secretion by osteocytes

Correct Answer & Explanation

. Direct binding to RANK receptors on osteoclasts

Explanation

Osteoclasts do not possess PTH receptors. PTH binds to receptors on osteoblasts, stimulating them to upregulate RANKL and downregulate OPG expression, which secondarily stimulates osteoclast differentiation and activation.

Question 1462

Topic: Biology, Genetics & Bone Healing

Which of the following bone morphogenetic proteins (BMPs) utilizes an absorbable collagen sponge carrier and is FDA-approved for the treatment of acute, open tibial shaft fractures?

. BMP-2
. BMP-3
. BMP-4
. BMP-7
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for use in acute, open tibial shaft fractures treated with an intramedullary nail, as well as anterior lumbar interbody fusions. It is applied using an absorbable collagen sponge.

Question 1463

Topic: Biology, Genetics & Bone Healing

Osteocalcin is the most abundant non-collagenous protein found in the bone matrix and is frequently used as a serum marker. What is its primary physiological role within the matrix?

. Providing tensile strength to the osteon
. Initiating collagen fibril cross-linking
. Regulating osteoclast apoptosis
. Binding extracellular calcium to regulate mineralization
. Serving as a structural template for proteoglycans

Correct Answer & Explanation

. Providing tensile strength to the osteon

Explanation

Osteocalcin is secreted by mature osteoblasts and contains gamma-carboxyglutamic acid residues (Vitamin K dependent) that tightly bind calcium. Its primary role is regulating bone mineralization and density.

Question 1464

Topic: Biology, Genetics & Bone Healing

Intermittent administration of low-dose parathyroid hormone (e.g., Teriparatide) is used clinically for its profound anabolic effect on bone. This anabolic action is primarily mediated by:

. Inhibition of osteoclast ruffled border formation
. Direct stimulation of osteoblast survival, proliferation, and differentiation
. Upregulation of sclerostin production by osteocytes
. Increased secretion of OPG by circulating macrophages
. Downregulation of Runx2 in mesenchymal stem cells

Correct Answer & Explanation

. Inhibition of osteoclast ruffled border formation

Explanation

While continuous elevated PTH causes bone resorption, intermittent administration has an anabolic effect. It directly stimulates osteoblast proliferation and differentiation while preventing osteoblast apoptosis, leading to net bone formation.

Question 1465

Topic: Biology, Genetics & Bone Healing

A patient with osteoporosis is started on denosumab. This medication acts by binding to which of the following targets, thereby mimicking the action of what endogenous molecule?

. Binds to RANKL, mimicking osteoprotegerin (OPG)
. Binds to RANK receptor, mimicking osteoprotegerin (OPG)
. Binds to RANKL, mimicking parathyroid hormone (PTH)
. Binds to osteoblasts, mimicking bisphosphonates
. Binds to sclerostin, mimicking Wnt signaling

Correct Answer & Explanation

. Binds to RANKL, mimicking osteoprotegerin (OPG)

Explanation

Denosumab is a fully human monoclonal antibody that binds to RANKL, preventing it from interacting with the RANK receptor on osteoclasts. This mechanism directly mimics the function of the endogenous decoy receptor osteoprotegerin (OPG).

Question 1466

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) regulates serum calcium levels through multiple mechanisms. Which of the following is a direct physiologic effect of continuous, high-dose PTH exposure on bone cellular activity?

. Stimulation of osteoprotegerin (OPG) release
. Direct binding to osteoclasts to increase bone resorption
. Upregulation of RANKL expression on osteoblasts
. Inhibition of 1-alpha-hydroxylase in the kidney
. Decreased calcium reabsorption in the distal tubule

Correct Answer & Explanation

. Stimulation of osteoprotegerin (OPG) release

Explanation

Continuous PTH exposure binds to receptors on osteoblasts, stimulating them to upregulate RANKL expression. RANKL then binds to RANK on osteoclast precursors, driving osteoclastogenesis and increasing bone resorption.

Question 1467

Topic: Biology, Genetics & Bone Healing

The compressive stiffness of articular cartilage is primarily provided by the interaction between interstitial fluid and which of the following extracellular matrix components?

. Type I collagen
. Type II collagen
. Proteoglycans (e.g., aggrecan)
. Hyaluronic acid
. Fibronectin

Correct Answer & Explanation

. Type I collagen

Explanation

Proteoglycans, primarily aggrecan, possess highly negatively charged glycosaminoglycan (GAG) side chains that repel each other and draw in water via the Donnan osmotic effect. This creates a swelling pressure that is resisted by the collagen network, providing compressive stiffness.

Question 1468

Topic: Biology, Genetics & Bone Healing

Primary (strain-free) bone healing, such as that achieved with rigid absolute stability, is characterized microscopically by which of the following processes?

. Formation of a soft cartilaginous callus
. Endochondral ossification
. Direct osteonal remodeling via cutting cones across the fracture site
. Intramembranous ossification originating from the periosteum
. Rapid woven bone formation leading to a hard external callus

Correct Answer & Explanation

. Formation of a soft cartilaginous callus

Explanation

Primary bone healing occurs without callus formation under conditions of absolute stability. It is characterized by direct Haversian remodeling, where osteoclastic cutting cones traverse the fracture site, followed by osteoblasts laying down lamellar bone.

Question 1469

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates (e.g., alendronate) inhibit osteoclast function primarily by interfering with which of the following intracellular pathways?

. Inhibition of RANKL binding to its receptor
. Disruption of the mevalonate pathway by inhibiting farnesyl pyrophosphate synthase
. Direct competitive inhibition of cathepsin K
. Downregulation of sclerostin production by osteocytes
. Activation of the Wnt/beta-catenin signaling pathway

Correct Answer & Explanation

. Inhibition of RANKL binding to its receptor

Explanation

Nitrogen-containing bisphosphonates act by inhibiting the enzyme farnesyl pyrophosphate synthase within the mevalonate pathway. This prevents the prenylation of small GTPase proteins essential for osteoclast survival and cytoskeletal function.

Question 1470

Topic: Biology, Genetics & Bone Healing

Denosumab is a monoclonal antibody used in the treatment of osteoporosis and giant cell tumors of bone. It functions by binding to which of the following targets to inhibit osteoclastogenesis?

. Osteoprotegerin (OPG)
. Receptor Activator of Nuclear factor Kappa B (RANK)
. RANK Ligand (RANKL)
. Sclerostin
. Cathepsin K

Correct Answer & Explanation

. Osteoprotegerin (OPG)

Explanation

Denosumab mimics the natural decoy receptor osteoprotegerin (OPG) by binding to RANKL. This prevents RANKL from interacting with RANK on osteoclast precursors, thereby inhibiting osteoclast maturation and survival.

Question 1471

Topic: Biology, Genetics & Bone Healing

Romosozumab increases bone mineral density primarily through the inhibition of sclerostin. Sclerostin normally inhibits bone formation by directly blocking which of the following intracellular signaling pathways?

. Wnt/beta-catenin pathway
. RANK/RANKL pathway
. BMP/Smad pathway
. Notch signaling pathway
. Hedgehog signaling pathway

Correct Answer & Explanation

. Wnt/beta-catenin pathway

Explanation

Sclerostin is a glycoprotein secreted by osteocytes that acts as an antagonist to the Wnt/beta-catenin signaling pathway. Inhibiting sclerostin allows Wnt signaling to proceed, which is essential for osteoblast differentiation and bone formation.

Question 1472

Topic: Biology, Genetics & Bone Healing

Teriparatide is an anabolic agent used for severe osteoporosis. Its mechanism of action requires which of the following administration profiles to stimulate bone formation rather than resorption?

. Continuous high dose
. Intermittent daily administration
. Monthly intravenous infusion
. Single annual infusion
. Weekly oral dosing

Correct Answer & Explanation

. Continuous high dose

Explanation

Intermittent daily administration of parathyroid hormone (PTH) analogs like teriparatide preferentially stimulates osteoblast-mediated bone formation. Continuous PTH exposure leads to net bone resorption by upregulating RANKL.

Question 1473

Topic: Biology, Genetics & Bone Healing

Osteoclasts degrade the organic matrix of bone primarily through the secretion of which of the following enzymes into the resorption pit?

. Alkaline phosphatase
. Cathepsin K
. Matrix metalloproteinase-3
. Tartrate-resistant acid phosphatase
. Carbonic anhydrase II

Correct Answer & Explanation

. Alkaline phosphatase

Explanation

Cathepsin K is the primary lysosomal protease secreted by osteoclasts to degrade the type I collagen-rich organic matrix of bone. It operates optimally in the acidic environment of the resorption pit.

Question 1474

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what dictates the type of tissue that forms during fracture healing if the interfragmentary strain is maintained between 2% and 10%?

. Healing occurs via primary cortical bone formation
. Healing occurs via lamellar bone without callus formation
. Healing occurs via secondary bone healing (callus formation)
. Granulation tissue persists leading to nonunion
. Fibrous tissue forms and prevents union

Correct Answer & Explanation

. Healing occurs via primary cortical bone formation

Explanation

Perren's theory states that strain levels dictate tissue formation. Primary bone healing occurs at <2% strain, while secondary healing with endochondral ossification (callus) occurs at moderate strains between 2% and 10%.

Question 1475

Topic: Biology, Genetics & Bone Healing

A 65-year-old patient presents with diffuse bone pain and a history of gastric bypass surgery. Laboratory workup reveals low serum calcium, low phosphorus, high alkaline phosphatase, and elevated PTH. What is the most likely underlying basic science pathology?

. Uncoupled remodeling favoring osteoclastic overactivity
. Defective mineralization of newly formed osteoid
. Hyperactive osteoblasts depositing disorganized woven bone
. Autonomous parathyroid adenoma secreting excess hormone
. Inability of the kidney to excrete phosphate

Correct Answer & Explanation

. Uncoupled remodeling favoring osteoclastic overactivity

Explanation

The clinical history and labs are classic for osteomalacia due to vitamin D malabsorption. Osteomalacia is characterized histologically by the defective mineralization of newly formed osteoid, leading to widened osteoid seams.

Question 1476

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the biological process of "creeping substitution" during the incorporation of a massive cortical structural allograft?

. Rapid vascularization followed by immediate woven bone formation
. Simultaneous osteoclastic resorption and osteoblastic bone formation advancing along Haversian canals
. Initial cartilage formation followed by endochondral ossification
. Direct differentiation of circulating stem cells into mature osteocytes
. Complete resorption of the graft by macrophages before new bone is formed

Correct Answer & Explanation

. Rapid vascularization followed by immediate woven bone formation

Explanation

Creeping substitution is a slow, sequential process where osteoclasts create cutting cones into the dead allograft bone, followed closely by osteoblasts laying down new lamellar bone within the Haversian systems.

Question 1477

Topic: Biology, Genetics & Bone Healing

A 12-year-old child presents with recurrent fractures and diffuse osteosclerosis. A mutation in the gene encoding Carbonic Anhydrase II is identified. This mutation prevents osteoclasts from performing which essential step in bone resorption?

. Attaching to the bone matrix via alphav-beta3 integrins
. Synthesizing the protease cathepsin K
. Generating protons to acidify the extracellular resorption pit
. Expressing RANK receptors on their cell surface
. Undergoing apoptosis after the completion of the resorption cycle

Correct Answer & Explanation

. Attaching to the bone matrix via alphav-beta3 integrins

Explanation

Carbonic anhydrase II catalyzes the formation of protons and bicarbonate from water and carbon dioxide. A deficiency impairs the osteoclast's ability to secrete protons and acidify the resorption pit, leading to osteopetrosis.

Question 1478

Topic: Biology, Genetics & Bone Healing

A 65-year-old woman is prescribed alendronate for osteoporosis. Which of the following describes the primary mechanism of action of this medication at the cellular level?

. Binding directly to the RANK receptor to prevent activation
. Inhibiting the enzyme farnesyl pyrophosphate synthase
. Stimulating osteoblast differentiation via Wnt signaling
. Blocking the action of cathepsin K
. Reducing the secretion of osteoprotegerin (OPG)

Correct Answer & Explanation

. Binding directly to the RANK receptor to prevent activation

Explanation

Nitrogen-containing bisphosphonates like alendronate inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This disrupts GTPase protein prenylation, leading to osteoclast apoptosis and loss of ruffled border function.

Question 1479

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum interfragmentary strain tolerated by the tissue required for primary bone healing to occur?

. <2%
. 2-10%
. 10-30%
. 30-50%
. >100%

Correct Answer & Explanation

. <2%

Explanation

Primary bone healing (direct Haversian remodeling) occurs only under conditions of absolute stability when interfragmentary strain is less than 2%. Strains between 2% and 10% promote secondary bone healing with callus formation.

Question 1480

Topic: Biology, Genetics & Bone Healing

Which of the following factors is directly secreted by osteocytes to inhibit osteoblast-mediated bone formation in response to mechanical unloading?

. Osteocalcin
. Sclerostin
. Osteoprotegerin (OPG)
. Macrophage colony-stimulating factor (M-CSF)
. Bone morphogenetic protein-2 (BMP-2)

Correct Answer & Explanation

. Osteocalcin

Explanation

Sclerostin is a glycoprotein secreted primarily by osteocytes, especially in states of mechanical unloading. It acts by binding to LRP5/6 receptors on osteoblasts, thereby inhibiting the Wnt/beta-catenin signaling pathway and decreasing bone formation.

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