Anatomy
2 questionsWhich of the following is NOT a surface marking of the oblique fissure of the lung?
Nucleus gracilis and nucleus cuneatus are seen in?
NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs
Question 251: Which of the following is NOT a surface marking of the oblique fissure of the lung?
- A. 6th costal cartilage
- B. T3
- C. 5th rib
- D. 7th rib (Correct Answer)
Explanation: ***7th rib*** - The **oblique fissure** typically extends from the spine at approximately the **T3 vertebral level** anteriorly to the **6th costal cartilage**. [1] - The **7th rib** is generally inferior to the typical anterior termination point of the oblique fissure. [1] *T3* - The **oblique fissure** begins posteriorly at the level of the **spinous process of T3**. [1] - This marks the superior-posterior extent of the fissure on the surface. *5th rib* - The **oblique fissure** crosses the **5th intercostal space** on the lateral chest wall. [1] - This point helps map the fissure's path between its posterior and anterior endpoints. *6th costal cartilage* - The **oblique fissure** terminates anteriorly near the **6th costal cartilage** in the midclavicular line. [1] - This represents the inferior-anterior most point of the fissure on the chest wall.
Question 252: Nucleus gracilis and nucleus cuneatus are seen in?
- A. Medulla (Correct Answer)
- B. Temporal lobe
- C. Midbrain
- D. Pons
Explanation: ***Medulla*** - The **nucleus gracilis** and **nucleus cuneatus** are located in the **dorsal medulla** and are crucial for processing **conscious proprioception**, **vibration**, and **fine touch**. - These nuclei receive input from the fasciculus gracilis and fasciculus cuneatus (dorsal column tracts) and are part of the dorsal column-medial lemniscus pathway. - They give rise to the **internal arcuate fibers** which decussate and form the **medial lemniscus**. *Pons* - The pons contains several important nuclei, including the **pontine nuclei** (involved in motor coordination), nuclei of cranial nerves V, VI, VII, and VIII, and the **locus coeruleus**. - The dorsal column nuclei are not located in the pons. *Temporal lobe* - The **temporal lobe** is part of the cerebral cortex and is primarily involved in **auditory processing**, memory formation, and language comprehension. - It contains structures like the hippocampus and amygdala, but not the dorsal column nuclei. *Midbrain* - The **midbrain** contains nuclei such as the **red nucleus**, **substantia nigra**, and nuclei of cranial nerves III and IV, involved in motor control and eye movements. - The nucleus gracilis and nucleus cuneatus are not found in the midbrain.
Biochemistry
4 questionsPyridoxine deficiency leads to altered metabolism of?
In which stage of cell division is chromosomal study best carried out?
Acute intermittent porphyria is due to deficiency of?
What is the primary metal ion found in myoglobin?
NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs
Question 251: Pyridoxine deficiency leads to altered metabolism of?
- A. Phenylalanine
- B. Methionine
- C. Tyrosine
- D. Tryptophan (Correct Answer)
Explanation: ***Tryptophan*** - **Pyridoxine (vitamin B6)** is a critical coenzyme in the metabolism of **tryptophan**, particularly in its conversion to **niacin** and serotonin. - A deficiency leads to an accumulation of abnormal tryptophan metabolites, such as **xanthurenic acid**, which can be excreted in the urine. *Phenylalanine* - The metabolism of phenylalanine involves its conversion to tyrosine, a process catalyzed by **phenylalanine hydroxylase**, which does not directly require pyridoxine. - Deficiencies in phenylalanine metabolism often point to issues like **phenylketonuria**. *Methionine* - Methionine metabolism involves a cycle that generates **S-adenosylmethionine (SAM)** and then homocysteine. - While vitamin B6 is involved in the transsulfuration pathway (converting homocysteine to cysteine), its primary direct impact on methionine metabolism itself is less pronounced than on tryptophan. *Tyrosine* - Tyrosine is synthesized from phenylalanine and is a precursor for **catecholamines** and thyroid hormones. - Its metabolism does not directly rely on pyridoxine as a coenzyme in the main initial steps.
Question 252: In which stage of cell division is chromosomal study best carried out?
- A. Metaphase (Correct Answer)
- B. Telophase
- C. Anaphase
- D. Prophase
Explanation: ***Metaphase*** - During **metaphase**, chromosomes are maximally condensed and align at the cell's equatorial plate, making them easily visible and distinguishable under a microscope. - This arrangement allows for clear visualization of **chromosome number**, **size**, and **morphology**, which is crucial for genetic analysis. *Prophase* - In **prophase**, chromosomes begin to condense, but they are still diffuse and not fully compact, making detailed study difficult. - The nuclear envelope is also still present for most of prophase, obstructing a clear view of the chromosomes. *Telophase* - During **telophase**, chromosomes decondense and arrive at opposite poles, becoming less distinct and harder to analyze individually. - New nuclear envelopes form around the separated chromosomes, further obscuring their view for detailed study. *Anaphase* - In **anaphase**, sister chromatids separate and move towards opposite poles, but they are in motion and not aligned, making them difficult to capture and analyze individually. - The separated chromatids are also stretched and elongated, which makes their morphological assessment challenging.
Question 253: Acute intermittent porphyria is due to deficiency of?
- A. Porphobilinogen deaminase (Correct Answer)
- B. Uroporphyrinogen III synthase
- C. Ferrochelatase
- D. ALA synthase
Explanation: ***Porphobilinogen deaminase*** - **Acute intermittent porphyria (AIP)** results from a deficiency in **porphobilinogen deaminase** (also known as hydroxymethylbilane synthase). - This enzyme deficiency leads to the accumulation of **aminolevulinic acid (ALA)** and **porphobilinogen (PBG)**, which are neurotoxic and cause the characteristic symptoms of AIP. *Uroporphyrinogen III synthase* - A deficiency in **uroporphyrinogen III synthase** causes **congenital erythropoietic porphyria (Günther disease)**, which is characterized by severe photosensitivity and hemolytic anemia. - This enzyme defect leads to the accumulation of uroporphyrinogen I and coproporphyrinogen I, not the ALA and PBG associated with AIP. *Ferrochelatase* - Deficiency in **ferrochelatase** causes **erythropoietic protoporphyria (EPP)**, which presents with photosensitivity and chronic liver disease due to the accumulation of **protoporphyrin**. - This condition does not cause the acute neurological attacks seen in AIP. *ALA synthase* - **ALA synthase** is the **rate-limiting enzyme** in heme synthesis; while its activity is crucial, a congenital *deficiency* is not the cause of AIP. - Instead, the *upregulation* of ALA synthase activity in AIP (due to the PBG deaminase block) contributes to the accumulation of ALA and PBG.
Question 254: What is the primary metal ion found in myoglobin?
- A. Iron (Correct Answer)
- B. Copper
- C. Selenium
- D. Zinc
Explanation: ***Iron*** - **Iron** is the central metal ion in the **heme group** of myoglobin. - It is responsible for **binding oxygen** reversibly, which is myoglobin's primary function in muscle tissue. *Copper* - **Copper** is a component of several enzymes, such as **cytochrome c oxidase** and **superoxide dismutase**, but not myoglobin. - It plays a role in **electron transport** and connective tissue formation. *Selenium* - **Selenium** is an essential trace element that functions as a component of **glutathione peroxidase**, an antioxidant enzyme. - It is not found in the structure of myoglobin. *Zinc* - **Zinc** is a critical component of many enzymes, including **carbonic anhydrase** and **DNA polymerase**. - It is involved in **immune function** and wound healing, but not in oxygen transport by myoglobin.
Pathology
1 questionsWhat is the most important prognostic factor of Wilms tumour?
NEET-PG 2012 - Pathology NEET-PG Practice Questions and MCQs
Question 251: What is the most important prognostic factor of Wilms tumour?
- A. Mutation of WT1 gene
- B. Histopathology (Correct Answer)
- C. Ploidy of cells
- D. Age < 1 yr
Explanation: ***Histopathology*** - The presence of **anaplastic histology**, particularly diffuse anaplasia, is the most significant adverse prognostic factor in Wilms tumor. - Tumors with favorable histology (triphasic, blastemal, stromal, or epithelial predominant) have an excellent prognosis, while those with anaplastic features have significantly worse outcomes [1]. *Ploidy of cells* - While **aneuploidy** (specifically, **hyperdiploidy**) has been associated with improved prognosis in some childhood cancers, its role as an independent prognostic factor in Wilms tumor is less significant than histology [2]. - It is not the most important factor in determining the overall outcome. *Age < 1 yr* - **Younger age** (typically less than 1 year) at diagnosis is generally associated with a **more favorable prognosis** in Wilms tumor. - This is because these tumors are often smaller, less aggressive, and more likely to have favorable histology. *Mutation of WT1 gene* - **WT1 gene mutations** are implicated in the development of Wilms tumor, particularly in syndromes like WAGR (Wilms tumor, aniridia, genitourinary anomalies, intellectual disability). - While critical for pathogenesis, the mere presence of a WT1 mutation is **not the primary determinant** of prognosis compared to tumor histology. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 488-490. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of Infancy and Childhood, pp. 486-487.
Physiology
3 questionsWhich of the following has the lowest Respiratory Quotient (RQ)?
What is a key difference between smooth muscle and skeletal muscle physiology?
What is the process by which water moves from the extracellular space to the intracellular space?
NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs
Question 251: Which of the following has the lowest Respiratory Quotient (RQ)?
- A. Heart
- B. Brain
- C. RBC
- D. Adipose (Correct Answer)
Explanation: ***Adipose*** - **Adipose tissue** primarily metabolizes **fatty acids** for energy, which have the lowest theoretical RQ of approximately **0.7**. - A lower RQ indicates that less carbon dioxide is produced relative to the oxygen consumed during metabolic fuel oxidation. - Among tissues that perform aerobic respiration, adipose tissue has the lowest RQ. *Brain* - The brain primarily uses **glucose** as its energy source under normal conditions, which has an RQ of approximately **1.0**. - During prolonged fasting, the brain can adapt to use **ketone bodies** (RQ ≈ 0.89), but glucose remains the primary fuel. - Higher RQ than adipose tissue. *RBC* - **Red blood cells (RBCs)** lack mitochondria and rely exclusively on **anaerobic glycolysis** for energy, metabolizing glucose to lactate. - RBCs **do not consume oxygen** for energy metabolism and therefore **do not have a meaningful RQ value** (RQ = CO₂ produced / O₂ consumed in aerobic respiration). - This makes RBC an inappropriate answer to a question about "lowest RQ" since RQ is undefined for anaerobic metabolism. *Heart* - The heart is a highly metabolic organ that can utilize various substrates, including **fatty acids**, **glucose**, **lactate**, and **ketone bodies**. - While it has a high capacity for fatty acid oxidation, it also significantly uses glucose and lactate, leading to an overall RQ typically between **0.7-0.9**. - Higher average RQ than adipose tissue due to mixed substrate utilization.
Question 252: What is a key difference between smooth muscle and skeletal muscle physiology?
- A. Calcium is required for contraction.
- B. Troponin is absent in smooth muscle. (Correct Answer)
- C. Myosin is essential for contraction.
- D. Potassium is required for contraction.
Explanation: ***Troponin is absent in smooth muscle.*** * Smooth muscle contraction is regulated by **calcium-calmodulin complex** and subsequent activation of **myosin light chain kinase (MLCK)**, in contrast to skeletal muscle's reliance on the troponin-tropomyosin system. * **Troponin** is a calcium-binding protein found in skeletal and cardiac muscle, which plays a critical role in regulating muscle contraction by initiating the movement of tropomyosin, thereby exposing myosin-binding sites on actin. *Calcium is required for contraction.* * While calcium is indeed required for contraction in both smooth and skeletal muscle, the **mechanism of its action** differs, making this statement insufficiently discriminative as a *key difference*. * In both muscle types, an increase in intracellular **calcium** initiates the contractile process, but the downstream signaling pathways diverge significantly. *Myosin is essential for contraction.* * **Myosin** is a fundamental motor protein essential for contraction in *all* muscle types, including skeletal, cardiac, and smooth muscle. * This statement highlights a similarity, not a key difference, as **actin-myosin cross-bridge cycling** is the basis of force generation in all muscle tissues. *Potassium is required for contraction.* * **Potassium ions** are crucial for maintaining the resting membrane potential and for repolarization following an action potential, which is necessary for muscle excitability, but they do not directly trigger muscle contraction. * The influx of calcium (or release from intracellular stores) is the direct trigger for contraction, not potassium.
Question 253: What is the process by which water moves from the extracellular space to the intracellular space?
- A. Osmosis (Correct Answer)
- B. Diffusion
- C. Filtration
- D. Active transport
Explanation: ***Osmosis*** - **Osmosis** is the movement of water across a **semipermeable membrane** from an area of higher water concentration (lower solute concentration) to an area of lower water concentration (higher solute concentration). - In the context of fluid shifts, if the **extracellular fluid** becomes hypotonic relative to the **intracellular fluid**, water will move into the cells to equalize the solute concentration. *Diffusion* - **Diffusion** refers to the net movement of particles from an area of higher concentration to an area of lower concentration, down their **concentration gradient**. - While water molecules can diffuse, **osmosis** specifically describes the net movement of water across a membrane due to **solute concentration differences**, which is the precise mechanism for water moving between fluid compartments. *Filtration* - **Filtration** is the process by which water and solutes move across a membrane due to a **pressure gradient**, typically a **hydrostatic pressure gradient**. - This process is crucial in the kidneys for forming filtrate, but it is not the primary mechanism for water movement between the intra- and extracellular spaces based on solute concentration. *Active transport* - **Active transport** involves the movement of molecules across a membrane against their **concentration gradient**, requiring **energy expenditure** (e.g., ATP). - Water movement between fluid compartments is generally a passive process, relying on **osmotic gradients** rather than direct energy input to pump water molecules.