Bone Metabolism and Turnover Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Bone Metabolism and Turnover. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Bone Metabolism and Turnover Indian Medical PG Question 1: Osteoclasts have all of the following functions except -
- A. Receptor for parathormone (Correct Answer)
- B. Ruffled border
- C. Bone resorption
- D. RANK ligand production
Bone Metabolism and Turnover Explanation: ***Receptor for parathormone***
- **Osteoclasts** do not directly have receptors for **parathormone (PTH)**; instead, **osteoblasts** have PTH receptors.
- When PTH binds to osteoblasts, they release factors (like **RANKL**) that stimulate osteoclast activity, thus indirectly regulating bone resorption.
*Bone resorption*
- **Osteoclasts** are specialized cells primarily responsible for **resorbing bone matrix**, a critical process in bone remodeling.
- They secrete **acids and enzymes** to break down the mineral and organic components of bone.
*Ruffled border*
- The **ruffled border** is a characteristic morphological feature of active osteoclasts, representing a highly folded plasma membrane.
- This specialized structure increases the surface area for the secretion of **protons and lysosomal enzymes** into the bone-resorbing compartment.
*RANK ligand production*
- **Osteoclasts** do not produce **RANK ligand (RANKL)**; rather, they have **RANK receptors** that bind to RANKL produced by **osteoblasts and stromal cells**.
- The binding of RANKL to RANK is essential for the **differentiation, activation, and survival** of osteoclasts.
Bone Metabolism and Turnover Indian Medical PG Question 2: Estrogen administration in a menopausal woman increases the:
- A. Bone mass (Correct Answer)
- B. Gonadotropin secretion
- C. Muscle mass
- D. LDL cholesterol
Bone Metabolism and Turnover Explanation: ***Bone mass***
- Estrogen plays a crucial role in maintaining **bone density** by inhibiting osteoclast activity and promoting osteoblast function.
- In menopausal women, estrogen administration counteracts bone loss and thus **increases bone mass**, reducing the risk of osteoporosis.
*Gonadotropin secretion*
- In menopausal women, **gonadotropin-releasing hormone (GnRH)** and subsequent **FSH and LH levels are elevated** due to the absence of ovarian estrogen feedback.
- Estrogen administration would exert a **negative feedback** on the hypothalamus and pituitary, thereby **decreasing**, not increasing, gonadotropin secretion.
*Muscle mass*
- While estrogen has some anabolic effects, **androgens** (like testosterone) are the primary hormones responsible for significantly increasing muscle mass.
- Estrogen administration to menopausal women is not a primary intervention for increasing muscle mass; its effects on this parameter are generally **modest or negligible**.
*LDL cholesterol*
- Estrogen generally has a **favorable effect on lipid profiles**, typically leading to a **decrease in LDL cholesterol** and an increase in HDL cholesterol.
- Therefore, estrogen administration would generally **reduce**, not increase, LDL cholesterol levels.
Bone Metabolism and Turnover Indian Medical PG Question 3: What is the primary organic component of bone?
- A. 10% collagen
- B. 10% noncollagenous protein
- C. 20% noncollagenous protein
- D. 90% collagen protein (Correct Answer)
Bone Metabolism and Turnover Explanation: ***90% collagen protein***
- **Type I collagen** constitutes around 90% of the organic matrix of bone, providing its tensile strength and flexibility [1].
- This extensive collagen network forms the framework upon which **mineral crystals** (hydroxyapatite) are deposited [1].
*10% collagen*
- This percentage is significantly lower than the actual proportion of collagen in the organic matrix of bone.
- If collagen only represented 10%, bone would lack its characteristic **tensile strength** and elasticity [2].
*10% noncollagenous protein*
- While noncollagenous proteins like **osteocalcin** and **osteonectin** are important for bone mineralization and cell signaling, they only constitute about 10% of the *organic matrix*, not the entire bone, and are not the *primary organic component* [1].
- The dominant organic component is collagen, which provides the structural scaffold [1].
*20% noncollagenous protein*
- This percentage is inaccurate; **noncollagenous proteins** typically make up about 10% of the bone's organic matrix [1].
- A higher proportion of noncollagenous proteins would alter the bone's mechanical properties, potentially making it more brittle.
Bone Metabolism and Turnover Indian Medical PG Question 4: The most important regulator of serum 1,25(OH)2 vitamin D concentration is:
- A. Calcium levels in serum
- B. Magnesium levels in serum
- C. Parathyroid hormone (Correct Answer)
- D. 25-hydroxyvitamin D in serum
Bone Metabolism and Turnover Explanation: ***Parathyroid hormone***
- **Parathyroid hormone (PTH)** directly stimulates the **kidney's 1-alpha hydroxylase** enzyme, which converts **25(OH)D** to its active form, **1,25(OH)2D (calcitriol)**.
- This regulation is critical for maintaining **calcium and phosphate homeostasis**, with PTH levels increasing when serum calcium is low, thereby boosting 1,25(OH)2D production.
*Calcium levels in serum*
- While **low serum calcium** indirectly stimulates **PTH** release, which then regulates 1,25(OH)2 vitamin D, calcium itself is not the direct or most important regulator.
- The direct regulatory action on the conversion enzyme is mediated by PTH.
*Magnesium levels in serum*
- **Magnesium** plays a cofactor role in various enzymatic reactions, including those involving vitamin D metabolism, but it is not a direct or primary regulator of **1,25(OH)2 vitamin D concentration**.
- Severe **hypomagnesemia** can sometimes impair PTH secretion and action, indirectly affecting vitamin D, but this is a secondary effect.
*25-hydroxyvitamin D in serum*
- **25-hydroxyvitamin D** is the precursor to **1,25(OH)2 vitamin D**, and its availability limits the maximum potential production of the active form.
- However, the *rate* of conversion into the active form and thus the *concentration* of 1,25(OH)2D is primarily dictated by PTH, not the precursor itself.
Bone Metabolism and Turnover Indian Medical PG Question 5: A patient is on a low calcium diet for 8 weeks. Which of the following increases to maintain serum calcium levels?
- A. Active 24,25 dihydroxy cholecalciferol
- B. PTH (Correct Answer)
- C. Serum phosphate level
- D. Calcitonin
Bone Metabolism and Turnover Explanation: ***PTH***
- **Parathyroid hormone (PTH)** is the primary regulator of calcium homeostasis and the key hormone that **increases in response to hypocalcemia** (low serum calcium).
- In a patient on a low calcium diet for 8 weeks, **PTH secretion increases** to maintain normal serum calcium levels.
- PTH acts through three main mechanisms: increasing **bone resorption** (releasing calcium from bone), enhancing renal **calcium reabsorption** in the distal tubule, and stimulating the production of **active vitamin D (1,25-dihydroxycholecalciferol)** which increases intestinal calcium absorption.
*Active 24,25 dihydroxy cholecalciferol*
- **24,25-dihydroxycholecalciferol** is a relatively **inactive metabolite** of vitamin D and represents a pathway of vitamin D catabolism, not activation.
- The **active form** of vitamin D that increases calcium absorption is **1,25-dihydroxycholecalciferol (calcitriol)**, whose production is stimulated by PTH.
- This metabolite does **not increase** in response to hypocalcemia as a compensatory mechanism.
*Serum phosphate level*
- A low calcium diet would **not directly lead to an increase in serum phosphate levels**.
- In fact, PTH (which increases in response to low calcium) typically causes a **decrease in serum phosphate** by promoting renal phosphate excretion (phosphaturic effect).
- High phosphate levels can actually exacerbate hypocalcemia by forming insoluble calcium-phosphate complexes.
*Calcitonin*
- **Calcitonin** is released from the thyroid parafollicular cells (C cells) in response to **high serum calcium levels** (hypercalcemia).
- It acts to **lower** calcium by inhibiting osteoclast activity and reducing renal calcium reabsorption.
- In hypocalcemia (low calcium diet), calcitonin secretion would **decrease, not increase**, making this the opposite of what occurs to maintain calcium homeostasis.
Bone Metabolism and Turnover Indian Medical PG Question 6: Most metabolically active part in bone is
- A. Endosteal surface
- B. Cortical bone
- C. Cancellous bone (Correct Answer)
- D. Periosteal surface
Bone Metabolism and Turnover Explanation: ***Cancellous bone***
- **Cancellous bone** (trabecular/spongy bone) is the **most metabolically active** part of bone due to its **large surface area-to-volume ratio** (approximately 10 times greater than cortical bone).
- It has a **high rate of bone turnover** and remodeling, being 8-10 times more active than cortical bone.
- Contains abundant **osteoblasts** and **osteoclasts** on trabecular surfaces, making it the primary site for **calcium homeostasis** and rapid response to metabolic demands.
- Metabolic bone diseases like **osteoporosis** and **hyperparathyroidism** predominantly affect cancellous bone first due to its high metabolic activity.
*Endosteal surface*
- The **endosteal surface** (inner lining of cortical bone and trabecular surfaces) is metabolically active with osteoblasts and osteoclasts.
- While technically the trabecular surfaces are endosteal surfaces, in clinical teaching, **cancellous bone as a whole** is recognized as the most metabolically active component.
- This option represents an anatomical subdivision rather than the structural answer expected in standard physiology.
*Cortical bone*
- **Cortical bone** (compact bone) is dense and provides structural strength but has **lower metabolic activity** due to its compact structure and smaller surface area.
- Remodeling rate is significantly slower (about 1/10th) compared to cancellous bone.
- Makes up 80% of skeletal mass but contributes less to metabolic bone turnover.
*Periosteal surface*
- The **periosteal surface** (outer bone covering) is involved in bone growth in width and fracture repair.
- Has osteoblasts and osteoclasts but accounts for a **smaller proportion** of total bone remodeling compared to the extensive trabecular surfaces.
- Less metabolically active than cancellous bone overall.
Bone Metabolism and Turnover Indian Medical PG Question 7: The success of estrogen and estrogen-like drugs in combating osteoporosis in postmenopausal women may indicate that estrogen:
- A. Increases the activity of bone-resorbing cells
- B. Decreases the activity of bone-resorbing cells (Correct Answer)
- C. Prevents the mineralization of bone during turnover
- D. Reduces the activity of bone-forming cells
Bone Metabolism and Turnover Explanation: ***Decreases the activity of bone-resorbing cells***
- **Estrogen** plays a crucial role in maintaining **bone density** by inhibiting the activity of **osteoclasts**, which are the cells responsible for **bone resorption**.
- In postmenopausal women, the decline in estrogen levels leads to increased osteoclast activity and accelerated **bone loss**, hence the effectiveness of estrogen therapy.
*Increases the activity of bone-resorbing cells*
- An increase in **bone-resorbing cell** (osteoclast) activity would lead to further **bone loss** and exacerbate osteoporosis, contrary to the observed therapeutic effect of estrogen.
- Estrogen's protective role in **bone health** is primarily through its inhibitory effect on osteoclasts.
*Prevents the mineralization of bone during turnover*
- This option describes a process that would lead to **osteomalacia** or **rickets**, where new bone matrix fails to mineralize adequately.
- Estrogen's action is not primarily on mineralization but on the **balance between bone formation and resorption**.
*Reduces the activity of bone-forming cells*
- Reducing the activity of **bone-forming cells** (osteoblasts) would also lead to reduced bone density and worsen osteoporosis.
- While estrogen has complex effects, its main therapeutic benefit in osteoporosis is to **slow down bone breakdown**, not to reduce bone formation.
Bone Metabolism and Turnover Indian Medical PG Question 8: The X-ray shows plating done for a fracture. How does this fracture heal?
- A. Primary healing (Correct Answer)
- B. Secondary healing
- C. Tertiary healing
- D. Distraction histiogenesis
Bone Metabolism and Turnover Explanation: **Primary healing**
- **Plating of a fracture** aims to achieve **absolute stability** at the fracture site, which facilitates primary bone healing.
- In primary healing, there is **direct bone formation** across the fracture gap without the formation of a significant callus.
*Secondary healing*
- Secondary healing involves the formation of a **callus** (fibrous tissue, cartilage, and immature bone) to bridge the fracture gap.
- This type of healing occurs in situations with **relative stability** and some micromotion at the fracture site, such as with casting or intramedullary nailing.
*Tertiary healing*
- **Tertiary healing** is not a recognized term in the context of fracture healing.
- Bone healing typically involves either primary or secondary mechanisms depending on the stability achieved.
*Distraction histiogenesis*
- **Distraction histiogenesis** is the process by which new bone is formed between bone surfaces that are gradually pulled apart using an external fixator (**distraction osteogenesis**).
- This is used in procedures like **limb lengthening** and is distinct from the direct healing of a fracture fixed with a plate.
Bone Metabolism and Turnover Indian Medical PG Question 9: The compression fracture is commonest in
- A. Upper thoracic spine
- B. Cervical spine
- C. Lumbosacral region
- D. Lower thoracic spine (Correct Answer)
Bone Metabolism and Turnover Explanation: ***Lower thoracic spine***
- The **thoracolumbar junction (T11-L2)** is the most common site for compression fractures due to its high biomechanical stress, transitioning from stiff thoracic spine to more flexible lumbar spine.
- This area is particularly vulnerable to axial loading and flexion injuries because it's a zone of increased mobility and stress concentration.
*Upper thoracic spine*
- The upper thoracic spine has **rib cage support** and less mobility, making fractures here less common without significant traumatic force.
- Fractures in this region often indicate a **high-energy injury** due to its inherent stability.
*Cervical spine*
- While cervical fractures can be serious, they typically result from **high-energy trauma** and are less commonly simple compression fractures compared to the thoracolumbar region.
- The **cervical spine** is more prone to **burst fractures** or **dislocations** from flexion-distraction or extension injuries.
*Lumbosacral region*
- The **sacrum and coccyx** are relatively stable bone structures and are less prone to common compression fractures unless there is severe trauma or significant bone weakening (e.g., severe osteoporosis).
- While lumbar compression fractures do occur, the **junctional region** between the thoracic and lumbar spine (lower thoracic/upper lumbar) is statistically more frequent.
Bone Metabolism and Turnover Indian Medical PG Question 10: Fracture at which site affects the longitudinal growth of a bone?
- A. Epiphyseal plate (Correct Answer)
- B. Diaphysis
- C. Epiphysis
- D. Metaphysis
Bone Metabolism and Turnover Explanation: ***Epiphyseal plate***
- The **epiphyseal plate**, also known as the **growth plate**, is a cartilaginous disc responsible for the **longitudinal growth** of long bones.
- A fracture in this region can damage the **chondrocytes** and disrupt the normal ossification process, potentially leading to **growth arrest** or limb length discrepancies.
*Diaphysis*
- The **diaphysis** is the **shaft** or central part of a long bone.
- While a fracture here can cause pain and instability, it typically does not directly affect the **longitudinal growth** potential of the bone.
*Epiphysis*
- The **epiphysis** is the end part of a long bone, initially separated from the main bone by cartilage but later fused with it.
- Although it contains the epiphyseal plate in growing individuals, a fracture to the epiphysis itself (excluding the growth plate) primarily affects the **joint surface** and stability, rather than longitudinal growth directly.
*Metaphysis*
- The **metaphysis** is the transitional zone between the diaphysis and the epiphysis, adjacent to the growth plate.
- While fractures in this area can be close to the growth plate, a metaphyseal fracture generally does not directly damage the **growth plate cartilage** to the same extent as a fracture through the plate itself, making its impact on longitudinal growth less direct or severe.
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