Bone Biology and Growth — MCQs
The function of which of the following is increased by an elevated parathyroid hormone concentration:
Epiphyseal dysgenesis is a feature of
Osteochondroma arises from which part of the bone?
Functional matrix theory suggests that the primary determinants of growth of skeletal tissues reside in:
A middle aged man noticed that he can no longer fit in his shoes and that his jaw was protruding and phalanges were enlarged. These effects are likely to be mediated by
All of the following statements regarding bone remodeling are TRUE EXCEPT
Systemic factor which is responsible for bone remodeling :
The first primary ossification centre to appear of the carpal bones is
The bone matrix has the following crystals -
Which of the following cause low serum calcium?
Bone Biology and Growth Indian Medical PG Practice Questions and MCQs
Question 1: The function of which of the following is increased by an elevated parathyroid hormone concentration:
- A. Action of osteoblasts only
- B. Osteoclasts (Correct Answer)
- C. Phosphate reabsorptive pathways in the renal tubules
- D. Hepatic formation of 25-hydroxycholecalciferol
Explanation: ***Osteoclasts*** - **Parathyroid hormone (PTH)** primarily acts to increase serum calcium levels by stimulating **osteoclasts**, leading to bone resorption and release of calcium and phosphate into the bloodstream. - While PTH does not directly act on osteoclasts, it binds to receptors on osteoblasts, which then release factors that activate osteoclasts. *Action of osteoblasts only* - PTH indirectly affects **osteoblasts** by binding to their receptors, but this action primarily leads to **RANKL expression**, which then stimulates osteoclast activity, not a direct increase in osteoblastic bone formation. - Chronic elevation of PTH, as seen in primary hyperparathyroidism, can paradoxically lead to a net loss of bone mass due to increased osteoclastic activity. *Phosphate reabsorptive pathways in the renal tubules* - PTH actually **decreases reabsorption of phosphate** in the renal tubules, leading to phosphaturia. This helps to prevent calcium-phosphate precipitation by lowering serum phosphate levels while raising calcium. - This is a key mechanism by which PTH increases serum calcium—by both mobilizing it from bone and reducing its renal excretion, while simultaneously promoting renal phosphate excretion. *Hepatic formation of 25-hydroxycholecalciferol* - The **liver** is responsible for the hydroxylation of vitamin D3 (cholecalciferol) to **25-hydroxycholecalciferol (calcidiol)**, a process that is not directly regulated by PTH. - PTH primarily stimulates the **kidneys** to convert 25-hydroxycholecalciferol to its active form, **1,25-dihydroxyvitamin D (calcitriol)**, which then enhances intestinal calcium absorption.
Question 2: Epiphyseal dysgenesis is a feature of
- A. Hypoparathyroidism
- B. Hyperparathyroidism
- C. Hypothyroidism (Correct Answer)
- D. Hyperthyroidism
Explanation: ***Hypothyroidism*** - **Epiphyseal dysgenesis** (dysplastic or stippled epiphyses) is a classic radiographic feature of **congenital hypothyroidism**, particularly in infants and children [2]. - Reduced thyroid hormone levels impair normal bone development, leading to delayed bone maturation and abnormal epiphyseal ossification [2]. *Hypoparathyroidism* - This condition involves insufficient **parathyroid hormone (PTH)**, leading to **hypocalcemia** and **hyperphosphatemia** [1]. - Its effects on bone primarily involve increased bone density and sometimes basal ganglia calcification, not epiphyseal dysgenesis [1]. *Hyperparathyroidism* - Characterized by excessive **PTH**, which causes **hypercalcemia** and bone resorption. - Bone features include **osteitis fibrosa cystica** (brown tumors, subperiosteal resorption), which is distinct from epiphyseal dysgenesis. *Hyperthyroidism* - This condition is marked by excessive thyroid hormone, which can lead to **accelerated bone turnover** and increased risk of osteoporosis. - Unlike hypothyroidism, it does not cause epiphyseal dysgenesis; instead, it can lead to premature skeletal maturation.
Question 3: Osteochondroma arises from which part of the bone?
- A. Medullary cavity
- B. Diaphysis
- C. Metaphysis (Correct Answer)
- D. Epiphysis
Explanation: ***Metaphysis*** - **Osteochondromas** are outgrowths of bone and cartilage that typically arise from the **metaphyseal regions** of long bones, such as the distal femur, proximal tibia, and proximal humerus. - This region is characterized by active **endochondral ossification**, which is the process interrupted in the formation of ostecochondromas. *Medullary cavity* - The **medullary cavity** contains bone marrow and is not the primary site of origin for osteochondromas, which are exophytic lesions. - While some tumors can extend into the medullary cavity, their origin is generally from the outer bone surfaces rather than the central cavity. *Diaphysis* - The **diaphysis** is the main or mid-section of a long bone (the shaft), and it is primarily composed of compact bone, with less active growth than the metaphysis. - Though osteochondromas can occur in the diaphysis, they are far less common than in the metaphysis, which is the site of rapid bone growth. *Epiphysis* - The **epiphysis** is the end part of a long bone, initially separated from the main bone by cartilage but later fusing with it. - While it's a site of growth, osteochondromas are very rarely found in the epiphysis, as their growth mechanism is more closely linked to the **physeal plate** located in the metaphysis.
Question 4: Functional matrix theory suggests that the primary determinants of growth of skeletal tissues reside in:
- A. Cartilages
- B. Sutures
- C. Skeletal
- D. Non-skeletal tissues (Correct Answer)
Explanation: ***Non-skeletal tissues*** - The **functional matrix theory** posits that the growth and development of skeletal tissues, particularly in the craniofacial region, are primarily determined by the surrounding soft tissues and their functions. [1] - These **non-skeletal tissues**, such as muscles, nerves, blood vessels, and fat, exert forces and provide stimuli that dictate the growth and remodeling of adjacent bones. *Cartilages* - While **cartilage** (e.g., condylar cartilage of the mandible) is a significant growth center, the functional matrix theory suggests its growth is still influenced by surrounding functional demands, not solely intrinsic factors. - Cartilage growth alone does not entirely explain the comprehensive craniofacial growth patterns according to this theory. *Sutures* - **Sutures** are important growth sites in the cranium and maxilla, contributing to bone apposition and separation. [1] - However, the functional matrix theory views sutural growth as a secondary event, responding to the expansive forces generated by the growth of underlying soft tissues and functional spaces. *Skeletal* - The functional matrix theory explicitly argues against the idea that **skeletal tissues** themselves (bones and cartilage) are the primary determinants of their own growth. - Instead, it emphasizes that skeletal growth is adaptive and reactive to the influences of the associated non-skeletal tissues and their functions.
Question 5: A middle aged man noticed that he can no longer fit in his shoes and that his jaw was protruding and phalanges were enlarged. These effects are likely to be mediated by
- A. TRH
- B. ACTH
- C. TGF Beta
- D. IGF-1 (Correct Answer)
Explanation: ***IGF-1*** - The described symptoms (increased shoe size, jaw protrusion, enlarged phalanges) are characteristic of **acromegaly**, a condition caused by excessive growth hormone (GH) secretion in adults. - **Insulin-like Growth Factor 1 (IGF-1)** is primarily responsible for mediating the growth-promoting effects of GH on various tissues, leading to the clinical manifestations seen in this patient. *TRH* - **Thyrotropin-releasing hormone (TRH)** stimulates the release of thyroid-stimulating hormone (TSH) from the pituitary, which in turn regulates thyroid hormone production. - Excess TRH would lead to hyperthyroidism symptoms like weight loss, heat intolerance, and tachycardia, not acromegalic features. *ACTH* - **Adrenocorticotropic hormone (ACTH)** stimulates the adrenal glands to produce cortisol. - Excessive ACTH causes **Cushing's syndrome**, characterized by central obesity, moon facies, striae, and muscle weakness, which are different from the presented symptoms. *TGF Beta* - **Transforming growth factor beta (TGF-beta)** is a pleiotropic cytokine involved in cell growth, differentiation, apoptosis, and immune regulation. - While it plays a role in tissue remodeling and fibrosis, it is not the direct mediator of the generalized growth and skeletal changes seen in acromegaly.
Question 6: All of the following statements regarding bone remodeling are TRUE EXCEPT
- A. young children have a greater capacity for remodeling than adults
- B. Remodeling is related to the degree of angulation
- C. angulation in the natural plane of the joint motion will remodel more successfully than angulation outside the plane of joint motion
- D. Injuries involving the epiphyseal plate are more likely to remodel successfully (Correct Answer)
Explanation: ***Injuries involving the epiphyseal plate are more likely to remodel successfully*** - This statement is **FALSE**. Injuries involving the **epiphyseal plate** in children can disrupt normal growth and are **less likely to remodel successfully** compared to metaphyseal fractures, often leading to growth disturbances or angular deformities. - Damage to the growth plate interferes with the physiological process of bone elongation and shaping, making complete restoration of bone architecture via remodeling less probable. *young children have a greater capacity for remodeling than adults* - Young children have a **greater capacity for bone remodeling** due to their active growth plates and higher metabolic bone turnover rates. - This enhanced remodeling allows for significant correction of fracture deformities through growth. *Remodeling is related to the degree of angulation* - The success and extent of bone remodeling in fractures are **directly related to the degree of initial angulation**. Less severe angulation generally remodels more completely than severe angulation. - Significant angulation beyond certain limits may not fully remodel, potentially leading to persistent deformity. *angulation in the natural plane of the joint motion will remodel more successfully than angulation outside the plane of joint motion* - Fractures with **angulation in the plane of joint motion** (e.g., knee angulation in the sagittal plane) tend to remodel more effectively and functionally, as the forces through the joint continue to align the bone. - Angulation **outside the plane of joint motion** (e.g., varus/valgus deformity at the knee) imposes abnormal mechanical stresses and is less likely to remodel to a functional alignment.
Question 7: Systemic factor which is responsible for bone remodeling :
- A. Cytokines (e.g., IL-1, IL-6)
- B. Prostaglandin E2 (PGE2)
- C. PTH (Correct Answer)
- D. Transforming Growth Factor-beta (TGF-β)
Explanation: ***PTH*** - **Parathyroid hormone (PTH)** is a major systemic regulator of bone remodeling, primarily influencing **calcium and phosphate homeostasis**. - High levels of PTH, particularly prolonged or continuous elevation, stimulate **osteoclasts** directly or indirectly, leading to increased **bone resorption**. *Cytokines (e.g., IL-1, IL-6)* - These are primarily **local humoral factors** that regulate bone remodeling in a specific area, often in response to inflammation or injury. - While they can influence bone metabolism, their action is generally more localized, unlike the widespread systemic effects of PTH. *Prostaglandin E2 (PGE2)* - **PGE2** is another **local mediator** involved in bone remodeling, produced by various cells including osteoblasts and osteocytes. - It plays a role in both bone formation and resorption depending on concentration and context, but its effects are typically paracrine or autocrine rather than systemic endocrine control. *Transforming Growth Factor-beta (TGF-β)* - **TGF-β** is a potent **local growth factor** stored within the bone matrix and released during bone resorption. - It regulates proliferation and differentiation of osteoblasts and osteoclasts, primarily acting as a local regulator of bone formation and repair rather than a systemic hormone.
Question 8: The first primary ossification centre to appear of the carpal bones is
- A. Capitate (Correct Answer)
- B. Pisiform
- C. Triquetral
- D. Scaphoid
Explanation: The first primary ossification centre to appear of the carpal bones is ***Capitate*** - The **capitate** is the first carpal bone to show an ossification center, typically appearing around **1-3 months of age**. [1] - This early ossification is an important marker in assessing **bone age** in children. *Scaphoid* - The **scaphoid** ossifies later than the capitate, usually between **4 and 6 years of age**. - Its ossification center is often **bi-lobed** and can be confused with a fracture on X-ray if not recognized. *Triquetral* - The **triquetral** ossification center generally appears between **2 and 4 years of age**. - This makes it a mid-range ossifier among the carpal bones, not the first. *Pisiform* - The **pisiform** is typically the last carpal bone to ossify, with its center appearing between **8 and 12 years of age**. - Its delayed ossification makes it a useful indicator for assessing **skeletal maturity** in older children and adolescents.
Question 9: The bone matrix has the following crystals -
- A. Calcium pyrophosphate
- B. Calcium hydroxyapatite (Correct Answer)
- C. Calcium phosphate
- D. Calcium sulphate
Explanation: ***Calcium hydroxyapatite*** - The primary mineral component of bone matrix is **calcium hydroxyapatite**, which gives bone its rigidity and strength [1]. - These crystals are formed from **calcium and phosphate ions** arranged in a specific crystalline structure within the collagen fibers [1]. *Calcium pyrophosphate* - **Calcium pyrophosphate dihydrate (CPPD)** crystals are associated with **pseudogout**, a condition causing joint inflammation, not the normal bone matrix [1]. - They are found in articular cartilage and synovial fluid, not as a structural component of healthy bone. *Calcium phosphate* - While hydroxyapatite is a form of **calcium phosphate**, simply "calcium phosphate" is too general and does not specify the exact crystalline structure found in bone [1]. - Many calcium phosphate compounds exist, but **hydroxyapatite** is the specific and most abundant one in bone [1]. *Calcium sulphate* - **Calcium sulfate** is not a naturally occurring mineral component of the bone matrix in vertebrates. - It is sometimes used in medical applications as a **bone graft substitute** or a drug delivery system, but not as an endogenous component.
Question 10: Which of the following cause low serum calcium?
- A. GH
- B. Vit D deficiency (Correct Answer)
- C. Hypoparathyroidism
- D. Glucocorticoids
Explanation: ***Vit D deficiency*** - **Vitamin D** is crucial for **intestinal absorption of calcium**; its deficiency leads to reduced calcium uptake from the diet. - Low vitamin D levels stimulate **parathyroid hormone (PTH) release**, which initially maintains serum calcium by bone resorption, but chronic deficiency eventually results in **hypocalcemia**. - In the context of nutritional causes of hypocalcemia, **Vitamin D deficiency** is the **most common dietary/nutritional cause** tested in biochemistry. *GH* - **Growth hormone (GH)** primarily influences **bone growth** and protein synthesis, but is not directly responsible for regulating serum calcium levels. - While GH can indirectly affect calcium metabolism through IGF-1, it does **not cause hypocalcemia**. *Hypoparathyroidism* - **Hypoparathyroidism** is characterized by **insufficient parathyroid hormone (PTH)** production, leading to **low serum calcium**. - Without adequate PTH, **calcium reabsorption** from bones and kidneys is impaired, and **vitamin D activation** is reduced, resulting in hypocalcemia. - **Note**: While hypoparathyroidism does cause hypocalcemia, in a **biochemistry/nutrition context**, Vitamin D deficiency is the focus as a nutritional/metabolic cause, whereas hypoparathyroidism is more of an endocrine disorder. *Glucocorticoids* - **Glucocorticoids**, particularly at high doses and with long-term use, **reduce intestinal calcium absorption** and increase **bone resorption**. - Despite their impact on bone, they typically cause **hypercalciuria** (increased urinary calcium excretion) and can lead to **osteoporosis**, but do not directly cause **hypocalcemia** due to compensatory mechanisms.
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