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1. General Principles & Basic Science MCQs

Practice Set 503 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 10041

Topic: 1. General Principles & Basic Science

In the context of articular cartilage mechanotransduction, chondrocytes primarily sense mechanical stimuli through which of the following cellular structures or pathways?

. Voltage-gated calcium channels responsive to fluid flow.
. Primary cilia that deform under compressive and shear forces.
. Integrin-mediated interactions with the extracellular matrix (ECM).
. Piezo channels activated by membrane stretch.
. All of the above play significant, interconnected roles.

Correct Answer & Explanation

. All of the above play significant, interconnected roles.

Explanation

Chondrocytes are highly mechanosensitive cells, and their ability to detect and respond to mechanical stimuli is critical for maintaining articular cartilage homeostasis. Mechanotransduction in chondrocytes is a complex process involving multiple interconnected pathways. Primary cilia act as mechanosensors, detecting fluid flow and shear. Integrins connect the cell to the ECM, mediating force transmission. Stretch-activated ion channels (e.g., Piezo channels) and voltage-gated calcium channels are also involved, responding to membrane deformation and changes in ionic environment. Therefore, all listed options (A, B, C, D) represent valid and significant mechanisms by which chondrocytes sense mechanical stimuli, making Option E the most comprehensive and correct answer.

Question 10042

Topic: Biology, Genetics & Bone Healing
In the context of bone fracture healing, secondary fracture healing (endochondral ossification) is initiated by the formation of a soft callus. Which of the following conditions is most crucial for the successful progression from soft callus to hard callus via endochondral ossification?
. Absolute rigidity and complete absence of micromotion at the fracture site.
. Adequate vascularization of the hypertrophic chondrocytes within the callus.
. High oxygen tension and a pH below 7.0 within the soft callus.
. The absence of inflammatory cytokines such as TNF-α and IL-6.
. Dominance of intramembranous ossification in the periosteal regions.

Correct Answer & Explanation

. Adequate vascularization of the hypertrophic chondrocytes within the callus.

Explanation

For secondary fracture healing (endochondral ossification) to progress from a soft callus (cartilaginous) to a hard callus (bony), the hypertrophic chondrocytes within the cartilage template must undergo apoptosis and be replaced by invading blood vessels and osteoblasts, a process known as chondroclastic resorption and vascular invasion. This vascularization is absolutely crucial for bringing in osteoprogenitor cells and nutrients, and for establishing the oxygen gradient necessary for bone formation. Option B is correct. Option A is incorrect; some controlled micromotion (interfragmentary strain) is beneficial for secondary healing, unlike primary healing which requires absolute rigidity. Option C is incorrect; cartilage is typically maintained in relatively low oxygen tension, and the progression to bone requires an increase in oxygenation associated with vascularization. Option D is incorrect; inflammatory cytokines play an essential role in the initial phases of fracture healing. Option E is incorrect; while intramembranous ossification occurs in the periosteal regions, the question specifically asks about the progression of the soft callus via endochondral ossification.

Question 10043

Topic: 1. General Principles & Basic Science

A researcher is studying the potential of induced pluripotent stem cells (iPSCs) for orthopedic tissue regeneration. A key advantage of using iPSCs over adult mesenchymal stem cells (MSCs) for certain applications is that iPSCs:

. Exhibit greater immunomodulatory properties, reducing host immune response.
. Have a lower risk of teratoma formation after transplantation.
. Possess unlimited self-renewal capacity and broader differentiation potential.
. Are more easily isolated from patient tissues in large quantities.
. Require less complex culture conditions and growth factor cocktails.

Correct Answer & Explanation

. Possess unlimited self-renewal capacity and broader differentiation potential.

Explanation

Induced pluripotent stem cells (iPSCs) are similar to embryonic stem cells in their ability to self-renew indefinitely and differentiate into virtually any cell type in the body (pluripotency). This broad differentiation potential and unlimited self-renewal capacity are major advantages for regenerative medicine compared to adult mesenchymal stem cells (MSCs), which have more limited differentiation potential and replicative lifespan. Option C is correct. Option A is incorrect; MSCs are well-known for their immunomodulatory properties, whereas iPSCs and their derivatives can still elicit immune responses, though patient-specific iPSCs can avoid allogeneic rejection. Option B is incorrect; a significant concern with iPSCs is their propensity for teratoma formation if undifferentiated cells are transplanted. Option D is incorrect; iPSCs are generated through reprogramming somatic cells, which is a complex process, not simply isolated. MSCs are relatively easier to isolate. Option E is incorrect; iPSC culture is typically more complex and demanding than MSC culture, often requiring specific feeder layers or defined media and careful handling to maintain pluripotency.

Question 10044

Topic: Biomechanics & Biomaterials

Regarding the biomechanical properties of bone, the phenomenon of 'creep' refers to:

. The progressive deformation of a material under constant stress over time.
. The decrease in stress over time when a material is held at a constant strain.
. The ability of a material to absorb energy before fracturing.
. The load at which a material begins to undergo plastic deformation.
. The anisotropic behavior of bone under different loading directions.

Correct Answer & Explanation

. The progressive deformation of a material under constant stress over time.

Explanation

Creep and stress relaxation are two important viscoelastic phenomena. Creep is defined as the progressive deformation (increase in strain) of a material over time when it is subjected to a constant applied load or stress. Option A accurately describes creep. Option B describes stress relaxation, where the stress decreases over time while the material is held at a constant strain. Option C describes toughness. Option D describes the yield point. Option E describes anisotropy, which is a characteristic of bone but not the definition of creep.

Question 10045

Topic: Biology, Genetics & Bone Healing

Osteocytes, embedded within the bone matrix, are considered master regulators of bone remodeling. They communicate with surface osteoblasts and osteoclasts through various mechanisms. Which of the following is the most established primary mode of long-range communication for osteocytes to coordinate remodeling events across significant distances within bone?

. Direct cell-to-cell contact via gap junctions within the lacunar-canalicular network.
. Secretion of systemic hormones like PTH and calcitonin.
. Release of soluble factors such as sclerostin and FGF23.
. Neural innervation signaling directly to osteocytes.
. Direct sensing of systemic cytokine levels in the interstitial fluid.

Correct Answer & Explanation

. Release of soluble factors such as sclerostin and FGF23.

Explanation

While osteocytes communicate extensively via gap junctions within the lacunar-canalicular network (Option A), this is primarily for local, short-range signaling. For coordinating remodeling events across significant distances, osteocytes act as endocrine-like cells, releasing soluble factors that can act on distant osteoblasts, osteoclasts, or other cells. Key examples include sclerostin (a Wnt pathway inhibitor, discussed in Q1) which regulates bone formation, and FGF23 (fibroblast growth factor 23) which regulates phosphate homeostasis. These soluble factors allow for long-range communication and coordination. Option C is correct. Option B is incorrect; osteocytes respond to systemic hormones but do not primarily secrete them to regulate remodeling. Option D is incorrect; while bone has neural innervation, it's not the primary long-range communication method for osteocytes. Option E is part of their mechanosensing environment but not their primary long-range communication output.

Question 10046

Topic: Infection, Pharmacology & VTE

Biofilm formation on orthopedic implants is a major cause of periprosthetic joint infection (PJI). A critical component that allows bacteria to evade host immunity and antibiotic penetration within a biofilm is the:

. Activation of efflux pumps by planktonic bacteria.
. Production of exotoxins that neutralize host phagocytes.
. Expression of specific adhesion proteins like fibronectin-binding proteins.
. Extracellular polymeric substance (EPS) matrix.
. Rapid mutation rates within the bacterial population.

Correct Answer & Explanation

. Extracellular polymeric substance (EPS) matrix.

Explanation

The extracellular polymeric substance (EPS) matrix is the hallmark of a bacterial biofilm. This self-produced matrix, composed of polysaccharides, proteins, and extracellular DNA, encases the bacteria, providing structural integrity, protecting them from host immune responses (e.g., phagocytosis), and creating a diffusion barrier that significantly impairs antibiotic penetration. This makes the bacteria within biofilms up to 1000 times more resistant to antibiotics than their planktonic counterparts. Option D is correct. Option A (efflux pumps) and B (exotoxins) are bacterial virulence mechanisms but are not specific to the biofilm structure itself. Option C (adhesion proteins) are important for initial attachment but are part of the bacteria, not the protective matrix. Option E (mutation rates) can contribute to resistance over time but is not the immediate structural component that causes evasion within the established biofilm.

Question 10047

Topic: Biology, Genetics & Bone Healing
The growth plate (physis) is a critical structure for longitudinal bone growth. The transition of chondrocytes from proliferation to hypertrophy and subsequent apoptosis is tightly regulated. Which of the following signaling pathways primarily maintains the balance between chondrocyte proliferation and hypertrophy by negatively regulating hypertrophy and promoting proliferation?
. Wnt/β-catenin signaling pathway.
. Indian Hedgehog (IHH) and Parathyroid Hormone-related Protein (PTHrP) feedback loop.
. Bone Morphogenetic Protein (BMP) signaling pathway.
. Fibroblast Growth Factor (FGF) receptor signaling.
. Transforming Growth Factor-beta (TGF-β) signaling pathway.

Correct Answer & Explanation

. Indian Hedgehog (IHH) and Parathyroid Hormone-related Protein (PTHrP) feedback loop.

Explanation

The Indian Hedgehog (IHH) and Parathyroid Hormone-related Protein (PTHrP) feedback loop is a central regulator of chondrocyte differentiation and the rate of endochondral ossification in the growth plate. Chondrocytes in the prehypertrophic zone produce IHH, which diffuses to the perichondrium, inducing PTHrP expression. PTHrP then acts on receptors on proliferating chondrocytes, preventing their premature differentiation into hypertrophic chondrocytes and promoting their proliferation. As chondrocytes move away from the PTHrP source, PTHrP levels drop, allowing them to differentiate into hypertrophic chondrocytes. This finely tuned feedback loop maintains the correct proportions of the proliferating and hypertrophic zones. Option B is correct. Wnt, BMP, FGF, and TGF-β all play roles in skeletal development but the IHH/PTHrP loop is the most specific and primary pathway for this particular balance in the growth plate.

Question 10048

Topic: Biology, Genetics & Bone Healing

When considering the long-term success of an orthopedic implant designed for osseointegration, the most critical factor at the cellular level is the direct interaction between osteoblasts and the implant surface. This interaction is primarily mediated by:

. The overall bulk modulus and stiffness of the implant material.
. The electrical conductivity of the implant surface.
. Specific adsorbed proteins from host fluids, like fibronectin and vitronectin.
. The macroscopic surface roughness and geometry of the implant.
. The rate of release of growth factors from the implant's core.

Correct Answer & Explanation

. Specific adsorbed proteins from host fluids, like fibronectin and vitronectin.

Explanation

Osseointegration is a complex biological process, and while many factors contribute, the initial and most critical cellular event is the adsorption of host proteins onto the implant surface. Within minutes to hours of implantation, proteins from blood and interstitial fluid, such as fibronectin, vitronectin, collagen, and albumin, rapidly adsorb to the implant surface. These adsorbed proteins form a 'conditioning film' that then dictates how host cells, particularly osteoblasts and osteoprogenitor cells, will interact with the surface. Integrins on the cell membrane bind to specific recognition sequences within these adsorbed proteins, mediating cell adhesion, spreading, and subsequent differentiation and matrix production. Option C is correct. While bulk modulus (Option A), surface roughness (Option D), and even electrical properties (Option B) influence osseointegration, they do so indirectly by affecting protein adsorption and subsequent cellular responses, not by direct interaction between the cell and the 'naked' implant. Option E is less about the surface interaction itself, but more about drug delivery.

Question 10049

Topic: 1. General Principles & Basic Science

Muscles can exhibit plasticity in response to various stimuli. Which of the following statements most accurately describes the primary role of satellite cells in adult skeletal muscle?

. They are terminally differentiated cells responsible for muscle contraction.
. They function as mechanosensors, initiating gene expression changes in response to stretch.
. They are quiescent stem cells that activate, proliferate, and differentiate to repair and grow muscle fibers.
. They primarily produce extracellular matrix components to maintain muscle integrity.
. They regulate neuromuscular junction formation and maintenance.

Correct Answer & Explanation

. They are quiescent stem cells that activate, proliferate, and differentiate to repair and grow muscle fibers.

Explanation

Satellite cells are quiescent, normally dormant stem cells located beneath the basal lamina of muscle fibers. Upon muscle injury or in response to exercise-induced stress, they activate, proliferate, migrate to the injury site, and differentiate into myoblasts. These myoblasts then fuse with existing damaged muscle fibers to repair them, or fuse with each other to form new muscle fibers. This makes them crucial for muscle regeneration, hypertrophy, and adaptation. Option C is correct. Option A describes muscle fibers themselves. Option B describes roles of other cells or intracellular components. Option D describes the role of fibroblasts. Option E describes the role of Schwann cells and components of the muscle fiber itself in forming the NMJ.

Question 10050

Topic: 1. General Principles & Basic Science

In the context of peripheral nerve regeneration following injury, the role of Schwann cells is paramount. After axonal degeneration, Schwann cells in the distal stump undergo significant changes, including:

. Becoming quiescent and migrating away from the injury site to prevent scar tissue formation.
. Dedifferentiating and forming 'Bungner bands' which guide regenerating axons.
. Producing myelin at an accelerated rate to speed up initial nerve impulse conduction.
. Undergoing rapid apoptosis to clear debris and reduce inflammation.
. Transforming into fibroblasts to contribute to epineurial scar tissue.

Correct Answer & Explanation

. Dedifferentiating and forming 'Bungner bands' which guide regenerating axons.

Explanation

Following peripheral nerve injury (e.g., axotomy), the distal axon segment degenerates (Wallerian degeneration). In the distal stump, Schwann cells dedifferentiate, proliferate, and align themselves to form organized cellular conduits known as 'Bungner bands.' These bands provide a crucial scaffold and secrete neurotrophic factors (e.g., NGF, BDNF) that guide the regenerating axonal sprouts from the proximal stump towards their target. Option B is correct. Option A is incorrect; they actively participate in regeneration. Option C is incorrect; myelin production is halted, and remyelination occurs much later during the regeneration process. Option D is incorrect; they proliferate and participate in debris clearance, not undergo rapid apoptosis themselves. Option E is incorrect; while fibroblasts contribute to scar, Schwann cells have a distinct regenerative role.

Question 10051

Topic: 1. General Principles & Basic Science

The maintenance of articular cartilage health is crucial for joint function. Which of the following components of the articular cartilage extracellular matrix (ECM) is primarily responsible for its ability to resist compressive loads and return to its original shape?

. Type II collagen fibers, providing tensile strength.
. Elastin fibers, allowing for extensive stretch and recoil.
. Aggrecan and other proteoglycans, attracting water to create osmotic swelling pressure.
. Chondronectin, mediating chondrocyte adhesion to collagen.
. Hyaluronic acid, reducing friction at the articular surface.

Correct Answer & Explanation

. Aggrecan and other proteoglycans, attracting water to create osmotic swelling pressure.

Explanation

Articular cartilage's remarkable ability to withstand compressive loads is primarily due to its unique ECM composition. Aggrecan, a large proteoglycan, aggregates with hyaluronic acid and link protein to form large macromolecular complexes. The glycosaminoglycan (GAG) chains of aggrecan are highly negatively charged and hydrophilic, attracting large amounts of water into the matrix. This creates a high osmotic swelling pressure within the collagen network. When a compressive load is applied, water is squeezed out, but the negative charges of the GAGs repel each other, creating a repulsive force that resists compression. Upon release of the load, water is re-imbibed, and the cartilage returns to its original shape. Option C is correct. Type II collagen (Option A) provides tensile strength, containing the swelling pressure, but doesn't directly resist compression by itself. Elastin (Option B) is minimal in articular cartilage. Chondronectin (Option D) is an adhesion protein. Hyaluronic acid (Option E) is a component of synovial fluid and also contributes to the aggrecan aggregate, but it's the osmotic properties of the GAGs on aggrecan that drive the compressive resistance.

Question 10052

Topic: Biology, Genetics & Bone Healing

A biopsy from a patient with a rare bone disorder shows abnormally increased activity of cathepsin K. Cathepsin K is a cysteine protease primarily associated with:

. Osteoblast differentiation and collagen synthesis.
. Osteoclast-mediated bone matrix degradation.
. Chondrocyte proliferation in the growth plate.
. Myoblast fusion and muscle repair.
. Tendon fibroblast collagen cross-linking.

Correct Answer & Explanation

. Osteoclast-mediated bone matrix degradation.

Explanation

Cathepsin K is a potent lysosomal cysteine protease that is highly expressed by osteoclasts. It plays a critical role in the degradation of organic components of the bone matrix, particularly type I collagen, within the acidified resorption lacuna. Inhibitors of cathepsin K have been investigated as potential treatments for osteoporosis due to their specific targeting of osteoclast activity without affecting osteoblast function. Option B is correct. Options A, C, D, and E describe processes associated with other cell types or different enzymatic activities.

Question 10053

Topic: Physiology & Rehabilitation
The cellular response to hypoxia is crucial in various orthopedic conditions, from fracture healing to avascular necrosis. Hypoxia-inducible factor-1 alpha (HIF-1α) is a master regulator of the cellular response to low oxygen. Under hypoxic conditions, HIF-1α:
. Is rapidly degraded by proteasomes, preventing gene transcription.
. Is hydroxylated, marking it for ubiquitination and degradation.
. Stabilizes and translocates to the nucleus to induce target gene expression.
. Inhibits the transcription of genes involved in angiogenesis and glycolysis.
. Promotes the formation of reactive oxygen species, leading to cell damage.

Correct Answer & Explanation

. Stabilizes and translocates to the nucleus to induce target gene expression.

Explanation

Under normoxic conditions, HIF-1α is rapidly hydroxylated by prolyl hydroxylase enzymes, leading to its ubiquitination and proteasomal degradation. However, under hypoxic conditions, these hydroxylases are inhibited due to the lack of oxygen. This prevents HIF-1α degradation, allowing it to stabilize, accumulate, and translocate to the nucleus. In the nucleus, HIF-1α heterodimerizes with HIF-1β and binds to hypoxia-responsive elements (HREs) in the promoters of target genes. This induces the transcription of genes involved in adapting to low oxygen, such as those promoting angiogenesis (e.g., VEGF), glycolysis, and erythropoiesis. Option C is correct. Option A and B describe its fate under normoxia. Option D is incorrect; it induces, not inhibits, these genes. Option E is a consequence of severe hypoxia, but not HIF-1α's direct regulatory role.

Question 10054

Topic: Biology, Genetics & Bone Healing

In the process of bone remodeling, activation of bone multicellular units (BMUs) involves a highly coordinated sequence of cellular events. The initial signal for BMU activation and the recruitment of osteoclast precursors often originates from:

. Direct sensing of microcracks and fatigue damage by osteoclasts.
. Osteocytes releasing RANKL and other signaling molecules in response to mechanical changes.
. Parathyroid hormone (PTH) directly stimulating osteoclast differentiation.
. Mesenchymal stem cells differentiating directly into osteoclasts.
. Systemic calcitonin acting to suppress initial osteoclast activation.

Correct Answer & Explanation

. Osteocytes releasing RANKL and other signaling molecules in response to mechanical changes.

Explanation

Osteocytes, embedded within the bone matrix, are considered the primary mechanosensors and orchestrators of bone remodeling. In response to microdamage (microcracks) or changes in mechanical loading, osteocytes undergo apoptosis or release signaling molecules (e.g., RANKL, sclerostin, FGF23). Specifically, osteocytes can increase RANKL expression (or reduce OPG expression) and other pro-resorptive factors, which signals to osteoblasts and stromal cells to recruit and activate osteoclast precursors, thereby initiating the remodeling cycle. Option B is correct. Option A is incorrect; osteoclasts resorb bone but are not the primary sensors of microcracks. Option C is incorrect; PTH primarily acts on osteoblasts to induce RANKL expression, which then stimulates osteoclast activity, not directly on osteoclasts themselves. Option D is incorrect; osteoclasts derive from hematopoietic stem cells, not mesenchymal stem cells. Option E describes calcitonin's role in inhibiting osteoclasts, which is a counter-regulatory mechanism, not an activating signal.

Question 10055

Topic: 1. General Principles & Basic Science

The synovial membrane plays a critical role in joint homeostasis. Its 'intima' layer, which directly faces the joint cavity, is primarily composed of two main cell types, type A and type B synoviocytes. Type B synoviocytes are characterized by their primary function as:

. Phagocytic cells, clearing debris and foreign material from the joint fluid.
. Connective tissue cells, providing structural support to the synovial lining.
. Fibroblast-like cells, responsible for synthesizing hyaluronic acid and other ECM components.
. Chondrocyte-like cells, producing cartilage matrix for repair.
. Neurosecretory cells, regulating joint pain perception.

Correct Answer & Explanation

. Fibroblast-like cells, responsible for synthesizing hyaluronic acid and other ECM components.

Explanation

The synovial intima contains two main cell types: Type A synoviocytes and Type B synoviocytes. Type A synoviocytes are macrophage-like cells, primarily involved in phagocytosis and antigen presentation (Option A). Type B synoviocytes are fibroblast-like cells that are crucial for the production of synovial fluid components, most notably hyaluronic acid (which lubricates the joint and contributes to synovial fluid viscosity) and other extracellular matrix components. Option C is correct. Option D is incorrect; chondrocytes are cartilage cells, not synovial cells. Option E is incorrect; neurosecretory functions are not the primary role of Type B synoviocytes.

Question 10056

Topic: Biomechanics & Biomaterials

In cartilage tissue engineering, the ideal scaffold should mimic the native extracellular matrix (ECM) properties. A key challenge is replicating the anisotropic and zonal organization of articular cartilage. Which of the following ECM components contributes most significantly to the tensile strength and organization of collagen fibrils within articular cartilage?

. Aggrecan aggregates.
. Decorin and other small leucine-rich proteoglycans (SLRPs).
. Hyaluronic acid.
. Link protein.
. Chondroitin sulfate.

Correct Answer & Explanation

. Decorin and other small leucine-rich proteoglycans (SLRPs).

Explanation

While aggrecan provides compressive resistance and hyaluronic acid is a backbone for aggrecan aggregates, Small Leucine-Rich Proteoglycans (SLRPs) like decorin, biglycan, and fibromodulin play crucial roles in regulating collagen fibrillogenesis, organization, and stability. Decorin, in particular, binds to collagen fibrils, influencing their diameter, spacing, and mechanical properties. It helps to maintain the hierarchical organization of the collagen network, which is vital for the tensile strength and overall integrity of the cartilage. Option B is correct. Option A and E primarily contribute to compressive properties. Option C is a backbone for aggrecan aggregates. Option D stabilizes aggrecan-hyaluronic acid interactions.

Question 10057

Topic: Biology, Genetics & Bone Healing
Which of the following non-collagenous proteins in bone matrix is primarily known for inhibiting osteoblast differentiation and promoting osteoclastogenesis via the canonical Wnt/β-catenin pathway?
. Osteocalcin
. Osteopontin
. Sclerostin
. Bone Sialoprotein
. Matrix Gla Protein

Correct Answer & Explanation

. Sclerostin

Explanation

Sclerostin (SOST) is a glycoprotein produced by osteocytes that acts as a negative regulator of bone formation by binding to LRP5/6 co-receptors, thereby inhibiting the canonical Wnt/β-catenin signaling pathway. This inhibition reduces osteoblast differentiation and activity, and indirectly promotes osteoclastogenesis. Osteocalcin and Bone Sialoprotein are involved in mineralization. Osteopontin is involved in cell attachment and crystal formation. Matrix Gla Protein inhibits ectopic calcification.

Question 10058

Topic: 1. General Principles & Basic Science
In the context of the growth plate, which factor is primarily responsible for regulating chondrocyte proliferation and hypertrophy by signaling through a feedback loop with Parathyroid Hormone-related Protein (PTHrP)?
. Fibroblast Growth Factor 2 (FGF-2)
. Vascular Endothelial Growth Factor (VEGF)
. Transforming Growth Factor-beta (TGF-β)
. Insulin-like Growth Factor 1 (IGF-1)
. Indian Hedgehog (Ihh)

Correct Answer & Explanation

. Indian Hedgehog (Ihh)

Explanation

Indian Hedgehog (Ihh) is produced by pre-hypertrophic chondrocytes and diffuses to the resting and proliferative zones, promoting chondrocyte proliferation and inducing PTHrP expression in the perichondrium. PTHrP, in turn, inhibits chondrocyte hypertrophy and proliferation. This Ihh-PTHrP feedback loop is crucial for maintaining the proper balance of chondrocyte proliferation and differentiation within the growth plate. VEGF is involved in vascular invasion, while FGF-2, TGF-β, and IGF-1 have broader roles in growth plate regulation but not the primary feedback with PTHrP.

Question 10059

Topic: 1. General Principles & Basic Science

A patient with early-stage osteoarthritis is found to have increased levels of cartilage oligomeric matrix protein (COMP) fragments in their synovial fluid. Which of the following best describes the structural component of COMP and its role in healthy cartilage?

. A proteoglycan that aggregates with hyaluronan to form large complexes.
. A fibrillar collagen primarily responsible for tensile strength.
. A non-collagenous protein involved in chondrocyte adhesion and matrix assembly.
. An enzyme that degrades aggrecan, indicating cartilage breakdown.
. A lubricating glycoprotein reducing friction between joint surfaces.

Correct Answer & Explanation

. A non-collagenous protein involved in chondrocyte adhesion and matrix assembly.

Explanation

Cartilage oligomeric matrix protein (COMP) is a non-collagenous protein of the thrombospondin family. It plays a significant role in cartilage extracellular matrix assembly, particularly in organizing the collagen network, and in chondrocyte adhesion. Increased fragmentation of COMP indicates early cartilage degradation. Proteoglycans (like aggrecan) aggregate with hyaluronan. Fibrillar collagens (e.g., Type II) provide tensile strength. COMP is not an enzyme, nor is it primarily a lubricating glycoprotein (that's hyaluronan or lubricin).

Question 10060

Topic: 1. General Principles & Basic Science

In the context of tendon mechanotransduction, which cell-surface receptor complex is critically involved in sensing mechanical load and translating it into intracellular biochemical signals, leading to gene expression changes in tenocytes?

. Toll-like receptors (TLRs)
. Receptor tyrosine kinases (RTKs)
. G protein-coupled receptors (GPCRs)
. Integrin-focal adhesion kinase (FAK) complexes
. C-type lectin receptors (CLRs)

Correct Answer & Explanation

. Integrin-focal adhesion kinase (FAK) complexes

Explanation

Integrin-focal adhesion kinase (FAK) complexes are crucial for mechanotransduction in tenocytes. Integrins link the extracellular matrix to the cytoskeleton, and when activated by mechanical forces, they initiate intracellular signaling cascades through proteins like FAK, leading to gene expression changes that regulate matrix synthesis and remodeling. TLRs, RTKs, GPCRs, and CLRs are involved in various cellular processes (e.g., immunity, growth factor signaling, general cell signaling, pathogen recognition), but integrins are the primary mechanosensors at the cell-matrix interface in tendons.

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