Menu

Biology, Genetics & Bone Healing MCQs

Practice Set 76 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 1501

Topic: Biology, Genetics & Bone Healing

According to Wolff's Law, bone undergoes remodeling in response to mechanical stress. Which cellular mechanism directly senses fluid shear stress within the bone matrix?

. Osteoblast differentiation
. Osteoclast resorption
. Osteocyte mechanotransduction
. Chondrocyte hypertrophy
. Macrophage activation

Correct Answer & Explanation

. Osteoblast differentiation

Explanation

Osteocytes are the primary mechanosensory cells in bone. Fluid flow through the lacunocanalicular network resulting from mechanical loading creates shear stress, which is sensed by osteocyte dendritic processes to regulate bone remodeling.

Question 1502

Topic: Biology, Genetics & Bone Healing

The normal human intervertebral disc exhibits distinct collagen distributions to resist different biomechanical loads. What is the predominant collagen type found in the nucleus pulposus?

. Type I collagen
. Type II collagen
. Type III collagen
. Type IX collagen
. Type X collagen

Correct Answer & Explanation

. Type I collagen

Explanation

The nucleus pulposus is rich in proteoglycans and Type II collagen, which gives it a gel-like consistency to resist compressive forces. In contrast, the annulus fibrosus is composed primarily of Type I collagen to resist tensile and torsional forces.

Question 1503

Topic: Biology, Genetics & Bone Healing

A novel osteoporosis medication targets sclerostin. What is the primary mechanism by which this medication increases bone mass?

. Stimulation of the Wnt/beta-catenin signaling pathway
. Inhibition of RANKL binding to RANK
. Direct activation of osteoclast apoptosis
. Stimulation of PTH receptors on osteoblasts
. Inhibition of cathepsin K activity

Correct Answer & Explanation

. Stimulation of the Wnt/beta-catenin signaling pathway

Explanation

Sclerostin is produced by osteocytes and inhibits the Wnt/beta-catenin pathway, which normally stimulates osteoblastogenesis. Monoclonal antibodies against sclerostin block this inhibition, thereby directly increasing bone formation.

Question 1504

Topic: Biology, Genetics & Bone Healing

Rigid internal fixation of a transverse diaphyseal radius fracture with absolute stability and no fracture gap promotes bone healing primarily through which of the following cellular processes?

. Intramembranous ossification from the periosteum
. Direct osteonal remodeling via cutting cones
. Endochondral ossification
. Formation of a soft cartilaginous callus
. Chondrocyte hypertrophy and apoptosis

Correct Answer & Explanation

. Intramembranous ossification from the periosteum

Explanation

Rigid internal fixation with absolute stability results in primary bone healing. This occurs via direct osteonal remodeling, where cutting cones cross the fracture site without an intermediate cartilaginous stage or macroscopic callus.

Question 1505

Topic: Biology, Genetics & Bone Healing

Which of the following enzymes is primarily responsible for the degradation of the organic bone matrix within the Howship lacuna during osteoclastic bone resorption?

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

Correct Answer & Explanation

. Matrix metalloproteinase-9

Explanation

Osteoclasts dissolve inorganic minerals using hydrogen ions and degrade the organic matrix (primarily Type I collagen) through the secretion of Cathepsin K. Carbonic anhydrase II is essential for generating the protons used to dissolve the mineral phase.

Question 1506

Topic: Biology, Genetics & Bone Healing

Sclerostin plays a critical role in the regulation of bone mass by osteocytes. What is the primary mechanism by which sclerostin exerts its inhibitory effect on bone formation?

. Binding to RANKL to prevent osteoclast activation
. Inhibiting Cathepsin K secretion
. Binding to LRP5/6 to antagonize Wnt signaling
. Activating the BMP signaling pathway
. Downregulating osteoprotegerin (OPG) expression

Correct Answer & Explanation

. Binding to RANKL to prevent osteoclast activation

Explanation

Sclerostin, secreted by osteocytes, inhibits osteoblastic bone formation by competitively binding to LRP5/6 receptors. This action antagonizes the canonical Wnt/beta-catenin signaling pathway.

Question 1507

Topic: Biology, Genetics & Bone Healing

Recombinant human parathyroid hormone (teriparatide) is utilized in the treatment of severe osteoporosis. What is the underlying mechanism by which it exerts an anabolic effect on bone?

. Direct inhibition of osteoclast apoptosis
. Intermittent administration stimulates osteoblast survival and bone formation
. Continuous administration suppresses RANKL expression
. Direct binding to osteoclasts to inhibit acid secretion
. Stimulation of sclerostin release from osteocytes

Correct Answer & Explanation

. Direct inhibition of osteoclast apoptosis

Explanation

While continuous PTH exposure upregulates RANKL and causes net bone resorption, intermittent administration of PTH (teriparatide) stimulates osteoblast proliferation and survival, resulting in net bone formation.

Question 1508

Topic: Biology, Genetics & Bone Healing

Which of the following transcription factors is essential for the commitment of mesenchymal stem cells to the osteoblast lineage?

. Sox9
. Runx2 (Cbfa1)
. PPAR-gamma
. MyoD
. HIF-1 alpha

Correct Answer & Explanation

. Sox9

Explanation

Runx2 (also known as Cbfa1) is the master transcription factor required for osteoblast differentiation. Sox9 drives chondrogenesis, while PPAR-gamma drives adipogenesis.

Question 1509

Topic: Biology, Genetics & Bone Healing

Commercially prepared demineralized bone matrix (DBM) is best described as possessing which of the following biological properties?

. Osteogenic only
. Osteoconductive and osteoinductive
. Osteogenic and osteoinductive
. Osteoinductive only
. Osteoconductive, osteoinductive, and osteogenic

Correct Answer & Explanation

. Osteogenic only

Explanation

DBM provides a collagenous scaffold (osteoconductive) and contains viable bone morphogenetic proteins (BMPs) (osteoinductive). Because it lacks living cells, it is not osteogenic.

Question 1510

Topic: Biology, Genetics & Bone Healing

Primary (strain-free) bone healing relies on absolute stability and achieves union via which of the following mechanisms?

. Endochondral ossification
. Intramembranous ossification
. Haversian remodeling with cutting cones
. Chondrocyte hypertrophy and apoptosis
. Callus formation and mineralization

Correct Answer & Explanation

. Endochondral ossification

Explanation

Primary bone healing occurs without a cartilaginous callus when absolute stability (e.g., compression plating) is achieved. It proceeds directly via osteoclastic cutting cones followed by osteoblastic bone deposition (Haversian remodeling).

Question 1511

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) stimulates bone resorption primarily by binding to receptors on the surface of which cell type?

. Osteoclast precursors
. Mature osteoclasts
. Osteoblasts
. Macrophages
. Chondrocytes

Correct Answer & Explanation

. Osteoclast precursors

Explanation

PTH binds to the PTH1R receptor on osteoblasts. This stimulates osteoblasts to upregulate RANKL and downregulate OPG, indirectly driving osteoclast differentiation and bone resorption.

Question 1512

Topic: Biology, Genetics & Bone Healing

What is the most abundant structural protein in the extracellular matrix of bone, constituting roughly 90% of its organic matrix?

. Osteocalcin
. Type II collagen
. Type I collagen
. Aggrecan
. Osteopontin

Correct Answer & Explanation

. Osteocalcin

Explanation

Type I collagen forms a triple helix and makes up about 90% of the organic matrix of bone, providing significant tensile strength. Osteocalcin and osteopontin are noncollagenous proteins involved in mineralization.

Question 1513

Topic: Biology, Genetics & Bone Healing

Which of the following molecules acts as a decoy receptor to bind RANKL, thereby inhibiting osteoclast differentiation and bone resorption?

. Macrophage colony-stimulating factor (M-CSF)
. Osteoprotegerin (OPG)
. Interleukin-1 (IL-1)
. Transforming growth factor-beta (TGF-beta)
. Calcitonin

Correct Answer & Explanation

. Macrophage colony-stimulating factor (M-CSF)

Explanation

Osteoprotegerin (OPG) is produced by osteoblasts and binds to RANKL as a decoy receptor. This interaction prevents RANKL from binding to RANK on osteoclast precursors, effectively inhibiting osteoclastogenesis and bone resorption.

Question 1514

Topic: Biology, Genetics & Bone Healing

Rigid plate fixation of a transverse radial shaft fracture with absolute stability primarily heals through which of the following processes?

. Endochondral ossification
. Intramembranous ossification
. Primary bone healing via cutting cones
. Secondary healing with hard callus formation
. Chondrogenesis followed by osteogenesis

Correct Answer & Explanation

. Endochondral ossification

Explanation

Absolute stability achieved through rigid internal fixation prevents micromotion and leads to primary (direct) bone healing. This process bypasses callus formation and relies on Haversian remodeling via cutting cones traversing the fracture site.

Question 1515

Topic: Biology, Genetics & Bone Healing

Parathyroid hormone (PTH) helps regulate serum calcium levels. Which of the following mechanisms is NOT a direct action of PTH?

. Increasing osteoclast activity via RANKL stimulation
. Increasing renal tubular reabsorption of calcium
. Decreasing renal tubular reabsorption of phosphate
. Stimulating 1-alpha-hydroxylase activity in the kidney
. Directly stimulating intestinal absorption of calcium

Correct Answer & Explanation

. Increasing osteoclast activity via RANKL stimulation

Explanation

PTH does not directly stimulate the intestinal absorption of calcium. Instead, it promotes intestinal calcium absorption indirectly by upregulating 1-alpha-hydroxylase in the kidneys, which converts 25-hydroxyvitamin D to its active form, 1,25-dihydroxyvitamin D.

Question 1516

Topic: Biology, Genetics & Bone Healing

Which of the following markers is essential for the differentiation of macrophages into osteoclasts?

. Runx2
. SOX9
. RANKL
. Osteoprotegerin
. Sclerostin

Correct Answer & Explanation

. Runx2

Explanation

RANKL binds to the RANK receptor on osteoclast precursors to stimulate their differentiation into mature osteoclasts. Runx2 is a transcription factor for osteoblasts, while SOX9 is essential for chondrocytes.

Question 1517

Topic: Biology, Genetics & Bone Healing

Which type of bone healing is primarily characterized by the formation of a fracture callus and occurs under conditions of relative stability?

. Intramembranous ossification
. Primary bone healing
. Endochondral ossification
. Cutting cone remodeling
. Appositional bone growth

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Secondary bone healing via a fracture callus primarily involves endochondral ossification, where a cartilage intermediate forms before being replaced by bone. This process occurs when relative stability (some micromotion) is present.

Question 1518

Topic: Biology, Genetics & Bone Healing

Which bone morphogenetic protein (BMP) is an FDA-approved osteoinductive agent commonly utilized in specific spinal fusion surgeries?

. BMP-2
. BMP-3
. BMP-4
. BMP-6
. BMP-9

Correct Answer & Explanation

. BMP-2

Explanation

Recombinant human BMP-2 (rhBMP-2) is an FDA-approved osteoinductive agent used in anterior lumbar interbody fusions and open tibial shaft fractures. BMP-7 (OP-1) was previously used but had a humanitarian device exemption.

Question 1519

Topic: Biology, Genetics & Bone Healing

According to Wolff's Law, bone remodels in response to mechanical stress. The mechanotransduction signal is primarily sensed by which resident cell type?

. Osteoblast
. Osteoclast
. Osteocyte
. Chondrocyte
. Macrophage

Correct Answer & Explanation

. Osteoblast

Explanation

Osteocytes act as the primary mechanosensory cells in bone. They detect mechanical strain and fluid flow through the canalicular network, coordinating osteoblast and osteoclast activity.

Question 1520

Topic: Biology, Genetics & Bone Healing

When utilizing a plate for absolute stability (compression plating) in a transverse midshaft radius fracture, the primary goal is to achieve:

. Secondary bone healing with robust callus formation
. Primary bone healing through Haversian remodeling
. Endochondral ossification
. Increased interfragmentary strain
. Controlled micromotion at the fracture site

Correct Answer & Explanation

. Secondary bone healing with robust callus formation

Explanation

Absolute stability eliminates micromotion and interfragmentary strain, bypassing callus formation. This results in primary (direct) bone healing via cutting cones and Haversian remodeling.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page