Menu

Biology, Genetics & Bone Healing MCQs

Practice Set 123 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 2441

Topic: Biology, Genetics & Bone Healing
During the process of secondary fracture healing, a cartilaginous soft callus forms to bridge the fracture gap. Which type of collagen is the predominant structural component of this early soft callus phase?
. Type I collagen
. Type II collagen
. Type III collagen
. Type IV collagen
. Type X collagen

Correct Answer & Explanation

. Type II collagen

Explanation

Secondary fracture healing proceeds through hematoma formation, fibrocartilaginous (soft) callus, bony (hard) callus, and remodeling. The soft callus is primarily composed of cartilage, which is rich in Type II collagen. As endochondral ossification progresses, Type X collagen is expressed by hypertrophic chondrocytes, followed by the deposition of Type I collagen as woven bone is formed.

Question 2442

Topic: Biology, Genetics & Bone Healing

A 70-year-old woman is started on denosumab for the treatment of severe osteoporosis. What is the specific mechanism of action of this medication?

. Directly induces osteoclast apoptosis
. Binds to RANKL, preventing it from interacting with the RANK receptor
. Binds directly to the RANK receptor, antagonizing its activation
. Increases the endogenous production of osteoprotegerin (OPG)
. Inhibits the osteoclast ruffled border by targeting carbonic anhydrase II

Correct Answer & Explanation

. Binds to RANKL, preventing it from interacting with the RANK receptor

Explanation

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

Question 2443

Topic: Biology, Genetics & Bone Healing

A 65-year-old man presents with dull, aching bone pain, increasing head size, and progressive hearing loss. A biopsy of his affected bone is shown below.

If the histology demonstrates haphazardly arranged cement lines creating a 'mosaic' pattern, what is the most likely diagnosis?

. Osteomalacia
. Paget's disease of bone
. Osteogenesis imperfecta
. Fibrous dysplasia
. Primary hyperparathyroidism

Correct Answer & Explanation

. Paget's disease of bone

Explanation

Paget's disease of bone (osteitis deformans) is characterized by a focal increase in bone remodeling. In the late (osteosclerotic) phase, disorganized woven and lamellar bone is laid down, creating a classic 'mosaic' pattern with prominent, haphazard cement lines. Clinical features include bone pain, bowing deformities, increasing skull size, and cranial nerve impingement (e.g., hearing loss).

Question 2444

Topic: Biology, Genetics & Bone Healing

Vitamin C deficiency (scurvy) results in weakened connective tissue, bone pain, and mucosal bleeding. At a cellular level, Vitamin C acts as an essential cofactor for which of the following steps in collagen synthesis?

. Hydroxylation of proline and lysine residues
. Cleavage of registration peptides from procollagen
. Cross-linking of tropocollagen by lysyl oxidase
. Glycosylation of hydroxylysine residues
. Formation of the triple helix structure

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues

Explanation

Vitamin C (ascorbic acid) is a crucial cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase, which add hydroxyl groups to proline and lysine residues on the preprocollagen chains. This hydroxylation is required for the subsequent stable formation of the collagen triple helix.

Question 2445

Topic: Biology, Genetics & Bone Healing

A 68-year-old woman sustains a distal radius fracture after a low-energy fall. DEXA scanning reveals a T-score of -2.8 at the femoral neck. In primary osteoporosis, which of the following best describes the typical serum laboratory profile for calcium, phosphate, and alkaline phosphatase (ALP)?

. Normal Calcium, Normal Phosphate, Normal ALP
. High Calcium, Low Phosphate, High ALP
. Low Calcium, Low Phosphate, High ALP
. Normal Calcium, Normal Phosphate, High ALP
. High Calcium, Normal Phosphate, Normal ALP

Correct Answer & Explanation

. Normal Calcium, Normal Phosphate, Normal ALP

Explanation

Primary osteoporosis is characterized by low bone mass and microarchitectural deterioration, but routine serum chemistries (Calcium, Phosphate, Alkaline Phosphatase) are classically within normal limits. Abnormalities in these labs should prompt investigation for secondary causes such as osteomalacia, hyperparathyroidism, or Paget's disease.

Question 2446

Topic: Biology, Genetics & Bone Healing

What is the primary role of vitamin D in bone health?

. Directly stimulates osteoblast activity.
. Enhances calcium absorption from the gut.
. Increases phosphorus excretion by the kidneys.
. Inhibits parathyroid hormone (PTH) secretion.
. Promotes collagen synthesis in bone matrix.

Correct Answer & Explanation

. Enhances calcium absorption from the gut.

Explanation

The primary role of vitamin D in bone health is to enhance the absorption of calcium and phosphate from the gastrointestinal tract. This ensures adequate mineral availability for bone mineralization. While it has some indirect effects on osteoblasts and parathyroid hormone, its most direct and significant action is on intestinal absorption. Collagen synthesis is a role of vitamin C and other factors, not directly vitamin D.

Question 2447

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism of action of parathyroid hormone (PTH) on bone?

. Directly stimulates osteoblast activity, increasing bone formation.
. Directly inhibits osteoclast activity, decreasing bone resorption.
. Increases calcium absorption in the gut and renal calcium reabsorption.
. Indirectly stimulates osteoclast activity via osteoblasts, leading to bone resorption.
. Decreases phosphate reabsorption in the kidney.

Correct Answer & Explanation

. Indirectly stimulates osteoclast activity via osteoblasts, leading to bone resorption.

Explanation

Parathyroid hormone (PTH) primarily acts to increase serum calcium levels. It does this by several mechanisms: 1) indirectly stimulating osteoclast activity (via osteoblasts secreting RANKL) to promote bone resorption, 2) increasing calcium reabsorption in the renal tubules, and 3) stimulating the synthesis of calcitriol (active vitamin D), which in turn increases calcium absorption from the gut. While PTH causes bone resorption (answer 3 is incomplete), the most comprehensive answer regarding its primary physiological effect on calcium homeostasis, including gut and renal actions, is option C. However, option 3 focuses on specific bone action. Revisiting this: The question is 'on bone'. So the effect should be bone-specific. PTH primarily acts on osteoblasts, which then signal osteoclasts to resorb bone. Therefore, indirectly stimulating osteoclast activity via osteoblasts is the most accurate description of its action on bone. Let's reconsider. 'Increases calcium absorption in the gut and renal calcium reabsorption' are systemic effects on calcium, not directly on bone, although they contribute to overall calcium homeostasis. 'Directly stimulates osteoblast activity' is incorrect as it favors resorption in chronic exposure. 'Directly inhibits osteoclast activity' is incorrect. 'Decreases phosphate reabsorption in the kidney' is true but not its primary action on bone. Therefore, 'Indirectly stimulates osteoclast activity via osteoblasts, leading to bone resorption' is the most accurate description of its bone action.

Question 2448

Topic: Biology, Genetics & Bone Healing

What is the primary role of vitamin D in bone metabolism?

. Directly stimulates bone formation by osteoblasts.
. Increases calcium absorption from the gut.
. Decreases phosphate reabsorption in the kidney.
. Inhibits osteoclast activity.
. Regulates parathyroid hormone secretion.

Correct Answer & Explanation

. Increases calcium absorption from the gut.

Explanation

The primary role of active vitamin D (calcitriol) in bone metabolism is to increase calcium absorption from the gut. It also directly promotes bone mineralization and works synergistically with PTH to maintain calcium and phosphate homeostasis. While it has some effects on osteoblasts and osteoclasts, its most prominent and direct role in calcium homeostasis relevant to bone is intestinal calcium absorption.

Question 2449

Topic: Biology, Genetics & Bone Healing

Regarding avascular necrosis (AVN) of the femoral head, which of the following statements is most accurate?

. Corticosteroid use is the most common idiopathic cause.
. The earliest radiographic sign is typically subchondral collapse (crescent sign).
. Core decompression is primarily indicated for patients with Ficat Stage IV disease.
. Bisphosphonates have been shown to be universally effective in preventing disease progression.
. MRI is the most sensitive imaging modality for early diagnosis.

Correct Answer & Explanation

. MRI is the most sensitive imaging modality for early diagnosis.

Explanation

MRI is the most sensitive and specific imaging modality for early diagnosis of AVN, capable of detecting changes before they are visible on plain radiographs. Corticosteroid use is a commonacquiredrisk factor, but the most common cause is often considered idiopathic. The earliest radiographic signs are typically subtle changes in bone density, while the crescent sign (subchondral collapse) represents a later, pre-collapse stage. Core decompression is indicated for Ficat Stage I or II disease (pre-collapse) to halt progression, not Stage IV (end-stage arthritis). Bisphosphonates have shown promise in some studies, but are not universally effective and their role is still evolving.

Question 2450

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy presents with progressive genu varum. Radiographs show irregular metaphyses, flaring, and cupping of the distal femurs and proximal tibias. His vitamin D levels are normal, and he has a normal calcium-phosphate product. What is the most likely diagnosis?

. Physiologic genu varum
. Blount's disease
. Hypophosphatemic rickets
. Renal osteodystrophy
. Metaphyseal chondrodysplasia

Correct Answer & Explanation

. Hypophosphatemic rickets

Explanation

The radiographic findings of irregular, flared, and cupped metaphyses are classic signs of rickets. Given the progressive genu varum and normal vitamin D and calcium-phosphate product, hypophosphatemic rickets (e.g., X-linked hypophosphatemia) is the most likely diagnosis. This condition is characterized by renal phosphate wasting despite normal vitamin D levels. Physiologic genu varum usually resolves by age 2. Blount's disease primarily affects the medial proximal tibia. Renal osteodystrophy would have abnormal calcium/phosphate levels. Metaphyseal chondrodysplasia is a broader category, but hypophosphatemic rickets fits the specific laboratory findings.

Question 2451

Topic: Biology, Genetics & Bone Healing

What is the primary mechanism of action of bisphosphonates in the treatment of osteoporosis?

. Stimulate osteoblast activity and bone formation
. Inhibit osteoclast activity and bone resorption
. Increase calcium absorption in the gut
. Enhance renal calcium reabsorption
. Modulate estrogen receptors to improve bone density

Correct Answer & Explanation

. Inhibit osteoclast activity and bone resorption

Explanation

Bisphosphonates are the most commonly prescribed class of drugs for osteoporosis. Their primary mechanism of action is to inhibit osteoclast activity, thereby decreasing bone resorption and slowing down bone loss, which helps to increase bone mineral density over time. They do not directly stimulate osteoblast activity, increase gut calcium absorption, enhance renal calcium reabsorption, or modulate estrogen receptors (that's the role of SERMs).

Question 2452

Topic: Biology, Genetics & Bone Healing

What biomechanical strain environment is required to achieve primary (direct) bone healing without the formation of a fracture callus?

. Strain less than 2%
. Strain between 2% and 10%
. Strain between 10% and 20%
. Strain greater than 20%
. Strain between 5% and 15%

Correct Answer & Explanation

. Strain less than 2%

Explanation

According to Perren's strain theory, primary bone healing requires absolute stability with a strain environment of less than 2%. Secondary bone healing, which involves callus formation, occurs in environments of relative stability with a strain between 2% and 10%.

Question 2453

Topic: Biology, Genetics & Bone Healing

Denosumab is highly effective in the medical management of Giant Cell Tumor of bone. What is its exact mechanism of action?

. Binds directly to the RANK receptor on osteoclasts
. Binds directly to RANKL to prevent receptor activation
. Acts as a recombinant Osteoprotegerin (OPG) analog
. Inhibits Macrophage colony-stimulating factor (M-CSF)
. Directly induces apoptosis in neoplastic stromal cells

Correct Answer & Explanation

. Binds directly to RANKL to prevent receptor activation

Explanation

Denosumab is a fully human monoclonal antibody that binds directly to RANKL (Receptor Activator of Nuclear factor Kappa-B Ligand). This prevents RANKL from binding to the RANK receptor on osteoclast precursors, thereby profoundly inhibiting osteoclastogenesis and osteoclast function.

Question 2454

Topic: Biology, Genetics & Bone Healing

What is the primary cellular target and mechanism of action of Denosumab in the treatment of giant cell tumors of bone?

. Inhibits osteoclast H+/K+ ATPase directly
. Binds directly to the RANK receptor on osteoclast precursors
. Binds to RANKL, preventing its interaction with the RANK receptor
. Stimulates Osteoprotegerin (OPG) production by osteoblasts
. Induces apoptosis of neoplastic spindle cells in the tumor stroma

Correct Answer & Explanation

. Binds to RANKL, preventing its interaction with the RANK receptor

Explanation

Denosumab is a fully human monoclonal antibody that specifically binds to the Receptor Activator of Nuclear factor Kappa-B Ligand (RANKL). By binding to RANKL, it prevents RANKL from interacting with the RANK receptor on osteoclast precursors and mature osteoclasts, thereby inhibiting osteoclastogenesis and function. This is highly effective in Giant Cell Tumors of bone, which are rich in RANKL-expressing stromal cells that recruit RANK-expressing osteoclast-like giant cells.

Question 2455

Topic: Biology, Genetics & Bone Healing

Vitamin C (ascorbic acid) deficiency results in scurvy, which is characterized by bone pain, bleeding gums, and poor wound healing. Vitamin C serves as an essential cofactor for which of the following specific processes in bone and cartilage synthesis?

. Hydroxylation of proline and lysine residues in procollagen
. Glycosylation of hydroxylysine residues
. Cleavage of procollagen C-terminal and N-terminal propeptides
. Cross-linking of tropocollagen molecules by lysyl oxidase
. Translation of alpha chains on the rough endoplasmic reticulum

Correct Answer & Explanation

. Hydroxylation of proline and lysine residues in procollagen

Explanation

Vitamin C is a necessary cofactor for the enzymes prolyl hydroxylase and lysyl hydroxylase. These enzymes catalyze the hydroxylation of proline and lysine residues on the forming procollagen chains. This hydroxylation is critical for the subsequent formation of the stable triple-helix structure of collagen. Without it, collagen is structurally weak, leading to the clinical manifestations of scurvy.

Question 2456

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory of fracture healing, what is the maximum amount of interfragmentary tissue strain that permits the formation and survival of primary lamellar bone?

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

Correct Answer & Explanation

. < 2%

Explanation

Perren's strain theory states that the type of tissue that forms in a fracture gap depends on the interfragmentary strain. Lamellar bone can only form under very low strain conditions (< 2%). Woven bone can tolerate strain up to 10%, cartilage up to 30%, and granulation tissue can tolerate up to 100% strain. Absolute stability (e.g., lag screw and compression plate) aims for < 2% strain to allow direct (primary) bone healing.

Question 2457

Topic: Biology, Genetics & Bone Healing

During the initial active (lytic) phase of Paget's disease of bone, the primary pathological process is driven by abnormal cells that characteristically exhibit which of the following histological features?

. Spindle-shaped morphology actively producing disordered osteoid
. Mononuclear cells with abundant clear cytoplasm and distinct cell borders
. Small round blue cells with scant cytoplasm and prominent nucleoli
. Bizarre, atypical nuclei with frequent atypical mitoses
. Extremely large size with an increased number of nuclei (up to 100) and viral-like inclusions

Correct Answer & Explanation

. Extremely large size with an increased number of nuclei (up to 100) and viral-like inclusions

Explanation

Paget's disease of bone begins with an intensely osteolytic phase driven by abnormal osteoclasts. These osteoclasts are pathologically large and multinucleated, often containing up to 100 nuclei per cell (normal is 3-10). Ultrastructurally, they may contain viral-like inclusion bodies, which has led to theories of a paramyxovirus etiology. The subsequent mixed and sclerotic phases are characterized by chaotic osteoblast activity.

Question 2458

Topic: Biology, Genetics & Bone Healing

A radiograph of an infant presenting with multiple fractures and cranial nerve palsies demonstrates diffusely dense, 'marble-like' bones with an absence of normal medullary cavities. The most common malignant autosomal recessive form of this disease is fundamentally caused by a defect in which of the following?

. Type I collagen synthesis and assembly
. Fibroblast growth factor receptor 3 (FGFR3) regulation
. Runx2 transcription factor activity
. Carbonic anhydrase II leading to defective osteoclast ruffled border
. Lysosomal storage enzyme beta-galactosidase

Correct Answer & Explanation

. Carbonic anhydrase II leading to defective osteoclast ruffled border

Explanation

The disease is Osteopetrosis (Marble Bone Disease), characterized by dense but brittle bones due to failure of osteoclast resorptive function. The malignant autosomal recessive (infantile) form is most commonly associated with mutations in the TCIRG1 gene (vacuolar proton pump) or Carbonic Anhydrase II. These defects prevent the osteoclast from acidifying the resorption pit, manifested ultrastructurally by an absent or defective ruffled border.

Question 2459

Topic: Biology, Genetics & Bone Healing

Demineralized bone matrix (DBM) is commonly used as a bone graft substitute. Its osteoinductive capability is primarily mediated by the presence of which of the following components preserved during the demineralization process?

. Bone Morphogenetic Proteins (BMPs)
. Viable osteoprogenitor cells
. Living mesenchymal stem cells
. Calcium hydroxyapatite scaffolding
. Platelet-derived growth factor (PDGF)

Correct Answer & Explanation

. Bone Morphogenetic Proteins (BMPs)

Explanation

Demineralized bone matrix (DBM) is produced by acid-extracting minerals from allograft bone. This process destroys viable cells (meaning it is NOT osteogenic) and removes the mineral structure, but it exposes and preserves the non-collagenous proteins, particularly Bone Morphogenetic Proteins (BMPs). These BMPs provide DBM with its osteoinductive properties, allowing it to stimulate the differentiation of host mesenchymal cells into osteoblasts.

Question 2460

Topic: Biology, Genetics & Bone Healing

During a posterolateral lumbar fusion, a surgeon utilizes recombinant human Bone Morphogenetic Protein-2 (rhBMP-2). This biologic agent promotes bone formation strictly through which of the following properties?

. Osteogenesis
. Osteoconduction
. Osteoinduction
. Creeping substitution
. Contact guidance

Correct Answer & Explanation

. Osteoinduction

Explanation

rhBMP-2 acts purely via osteoinduction, meaning it stimulates the differentiation of host mesenchymal stem cells into bone-forming osteoblasts. It does not provide a structural scaffold (osteoconduction) nor does it contain live cells (osteogenesis).

Test Yourself

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

On this Page