NEET-PG 2012

1213 Questions — Page 13 of 122

Anatomy

2 questions

Q121

In walking, gravity tends to tilt pelvis and trunk to the unsupported side, the major factor in preventing this unwanted movement is?

Q122

Cricoid cartilage lies at which vertebral level?

NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs

Question 121: In walking, gravity tends to tilt pelvis and trunk to the unsupported side, the major factor in preventing this unwanted movement is?

A. Adductor muscles
B. Quadriceps
C. Gluteus medius and minimus (Correct Answer)
D. Gluteus maximus

Explanation: ***Gluteus medius and minimus*** - The **gluteus medius** and **gluteus minimus** are essential **abductors** of the hip, primarily responsible for stabilizing the pelvis during the **single-limb support phase of gait**. - When one leg is lifted during walking, these muscles on the **stance leg side** contract to prevent the pelvis from tilting downwards on the unsupported swing leg side. *Adductor muscles* - **Adductor muscles** (adductor longus, brevis, magnus, pectineus, gracilis) primarily function to bring the thigh toward the midline of the body. - While they play a role in gait stability, their main action is not to prevent the lateral pelvic tilt described. *Quadriceps* - The quadriceps femoris group (rectus femoris, vastus lateralis, medialis, intermedius) are powerful **extensors of the knee**. - They are crucial for weight acceptance and propulsion during walking but do not directly prevent lateral pelvic tilt [1]. *Gluteus maximus* - The **gluteus maximus** is the largest and most powerful muscle of the hip, primarily responsible for **hip extension** and **external rotation**. - It is crucial for activities like climbing stairs or running, but its main role in normal walking is not to prevent lateral pelvic tilt; that function is more specific to the gluteus medius and minimus.

Question 122: Cricoid cartilage lies at which vertebral level?

A. C3
B. C6 (Correct Answer)
C. T1
D. T4

Explanation: **C6** - The **cricoid cartilage** is an important anatomical landmark, as it signifies the transition from the **laryngopharynx** to the **esophagus** and the start of the **trachea**. - Its location at **C6 vertebral level** is significant for procedures like tracheostomy and in identifying the narrowest part of the adult airway. *C3* - The C3 vertebral level is typically associated with the **hyoid bone**, which is superior to the cricoid cartilage. - The **epiglottis** and the superior aspect of the larynx are more commonly found at C3-C4. *T1* - The T1 vertebral level is in the **thoracic spine**, well below the neck, and is associated with the **apex of the lung** and the **first rib**. - The airway structures at this level are primarily the **trachea** as it enters the thorax. *T4* - The T4 vertebral level is significant as it marks the approximate location of the **carina**, where the trachea bifurcates into the main bronchi. - This level is much lower than the larynx and cricoid cartilage.

Biochemistry

4 questions

Q121

Which enzyme in the TCA cycle catalyzes the step where substrate-level phosphorylation occurs?

Q122

All are activated by insulin except?

Q123

What coenzyme is required by gulonate dehydrogenase for its activity?

Q124

Which of the following enzymes uses citrate in fatty acid synthesis?

NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs

Question 121: Which enzyme in the TCA cycle catalyzes the step where substrate-level phosphorylation occurs?

A. Isocitrate dehydrogenase
B. Malate dehydrogenase
C. Aconitase
D. Succinate thiokinase (Correct Answer)

Explanation: ***Succinate thiokinase*** - This enzyme (also known as **succinyl-CoA synthetase**) catalyzes the conversion of **succinyl-CoA** to **succinate**. - During this reaction, the energy released from breaking the **thioester bond** in succinyl-CoA is directly used to synthesize **GTP** (or ATP in some organisms) from GDP (or ADP) and inorganic phosphate, which is a classic example of **substrate-level phosphorylation**. *Isocitrate dehydrogenase* - This enzyme catalyzes the **oxidative decarboxylation** of isocitrate to $\alpha$-ketoglutarate. - This step produces **NADH** and **CO2** but does not involve substrate-level phosphorylation. *Malate dehydrogenase* - This enzyme catalyzes the oxidation of **L-malate** to **oxaloacetate** in the final step of the TCA cycle. - It produces **NADH** but does not involve the direct synthesis of ATP or GTP. *Aconitase* - This enzyme catalyzes the **isomerization** of **citrate** to **isocitrate** via an aconitate intermediate. - No energy is generated or consumed in the form of ATP/GTP during this rearrangement.

Question 122: All are activated by insulin except?

A. Lipoprotein lipase
B. Pyruvate kinase
C. Acetyl-CoA carboxylase
D. Hormone sensitive lipase (Correct Answer)

Explanation: ***Hormone sensitive lipase*** - **Insulin** is an **anabolic hormone** that promotes energy storage; it **inhibits** hormone-sensitive lipase (HSL) activity which is responsible for **fat breakdown (lipolysis)**. - When insulin levels are high, the body stores fat rather than breaks it down, thus **decreasing** HSL activity. *Lipoprotein lipase* - **Insulin activates lipoprotein lipase (LPL)**, an enzyme that breaks down triglycerides in **chylomicrons** and **VLDL** into fatty acids for storage in adipose tissue. - This activation promotes the uptake of fatty acids into fat cells, aligning with insulin's role in **energy storage**. *Pyruvate kinase* - **Insulin activates pyruvate kinase** in glycolysis, promoting the conversion of **phosphoenolpyruvate to pyruvate**. - This enzyme's activation enhances glucose utilization and energy production following a meal when insulin levels are high. *Acetyl-CoA carboxylase* - **Insulin activates acetyl-CoA carboxylase (ACC)**, the **rate-limiting enzyme in fatty acid synthesis**. - Activation of ACC leads to the production of **malonyl-CoA**, which commits acetyl-CoA to fatty acid synthesis, storing excess energy as fat.

Question 123: What coenzyme is required by gulonate dehydrogenase for its activity?

A. FAD
B. FMN
C. NADP
D. NAD (Correct Answer)

Explanation: ***NAD*** - **Gulonate dehydrogenase** is an enzyme involved in the **uronic acid pathway**, specifically in the conversion of **L-gulonate to D-xylulose**. - This reaction is an **NAD-dependent oxidation**, meaning **NAD** acts as the electron acceptor, being reduced to **NADH**. *NADP* - **NADP** (nicotinamide adenine dinucleotide phosphate) is primarily involved in **anabolic pathways** like **fatty acid synthesis** and the **pentose phosphate pathway**, often in reduction reactions where it is converted to **NADPH**. - While structurally similar to NAD, it is generally not the direct coenzyme for gulonate dehydrogenase. *FAD* - **FAD** (flavin adenine dinucleotide) is a coenzyme derived from **riboflavin** (vitamin B2) and is typically involved in **redox reactions** where it repeatedly accepts and donates electrons, often in dehydrogenase reactions involving **carbon-carbon double bonds**. - Enzymes like **succinate dehydrogenase** (in the citric acid cycle) or acyl-CoA dehydrogenase (in fatty acid oxidation) utilize FAD, but not gulonate dehydrogenase. *FMN* - **FMN** (flavin mononucleotide) is another coenzyme derived from **riboflavin** and serves as a prosthetic group in various **flavoproteins**, often facilitating **single-electron transfers**. - It is frequently found in complexes like **NADH dehydrogenase** (Complex I of the electron transport chain) but is not the required coenzyme for gulonate dehydrogenase activity.

Question 124: Which of the following enzymes uses citrate in fatty acid synthesis?

A. Aconitase
B. ATP citrate lyase (Correct Answer)
C. Malic enzyme
D. Citrate synthase

Explanation: ***ATP citrate lyase*** - This enzyme is crucial for fatty acid synthesis, as it cleaves **citrate** in the cytoplasm to generate **acetyl-CoA** and oxaloacetate. - The acetyl-CoA produced is then used as the primary building block for **fatty acid synthesis**. *Aconitase* - This enzyme isomerizes **citrate** to isocitrate within the **Krebs cycle** (TCA cycle) in the mitochondria. - It does not directly participate in the cytosolic pathway of fatty acid synthesis. *Citrate synthase* - This enzyme synthesizes **citrate** from acetyl-CoA and oxaloacetate, initiating the **Krebs cycle** in the mitochondrial matrix. - It is involved in citrate formation, not its utilization for fatty acid synthesis in the cytoplasm. *Malic enzyme* - This enzyme converts **malate** to pyruvate, generating **NADPH** in the cytoplasm. - While NADPH is essential for fatty acid synthesis, malic enzyme does not directly use citrate.

Orthopaedics

1 questions

Q121

Which of the following conditions can cause locking of the knee joint?

Physiology

3 questions

Q121

Wolff–Chaikoff effect is due to?

Q122

Insensible water loss per day is ?

Q123

Which of the following factors increases the rate of particle diffusion across the cell membrane?

NEET-PG 2012 - Physiology NEET-PG Practice Questions and MCQs

Question 121: Wolff–Chaikoff effect is due to?

A. Decreased iodination of MIT
B. Excess iodine intake (Correct Answer)
C. Suppression of TSH secretion
D. Decreased conversion of T4 to T3

Explanation: ***Excess iodine intake*** - The **Wolff-Chaikoff effect** is a phenomenon where a high intake of iodine acutely **inhibits thyroid hormone synthesis** and release. - This effect protects the body from excessive thyroid hormone production during periods of very high iodine availability. *Decreased iodination of MIT* - While the Wolff-Chaikoff effect does inhibit **iodination**, the direct cause is the excessive iodine itself, which triggers an autoregulatory shutdown. - Decreased iodination is a *consequence* of the high iodine leading to inhibition of thyroid peroxidase activity, but not the primary cause of the effect. *Suppression of TSH secretion* - **TSH (Thyroid Stimulating Hormone)** secretion is primarily regulated by negative feedback from thyroid hormones (T3 and T4) and TRH from the hypothalamus. - The Wolff-Chaikoff effect directly involves the thyroid gland's response to iodine and is not primarily mediated by TSH suppression. *Decreased conversion of T4 to T3* - The **conversion of T4 to T3** primarily occurs in peripheral tissues, mediated by deiodinase enzymes. - The Wolff-Chaikoff effect focuses on the inhibition of **iodine organification** and hormone release within the thyroid gland itself, not peripheral conversion.

Question 122: Insensible water loss per day is ?

A. 100 ml
B. 1000 ml (Correct Answer)
C. 700 ml
D. 300 ml

Explanation: ***1000 ml*** - **Insensible water loss** occurs through the skin (evaporation) and respiratory tract (exhalation) without conscious perception. - The typical daily insensible water loss in an adult is approximately **800-1000 ml/day**. - **Breakdown**: Skin evaporation (~400-500 ml) + Respiratory tract (~300-400 ml) = **~900-1000 ml total**. - **1000 ml** is the standard value cited in major physiology textbooks (Guyton & Hall, Ganong) and is the most commonly accepted answer for NEET PG examinations. *100 ml* - This value is significantly **lower** than the actual insensible water loss, which occurs continuously throughout the day. - Such a low volume would imply negligible evaporation and respiratory loss, which is not physiologically accurate. *300 ml* - While greater than 100 ml, 300 ml is still **far below** the typical range for daily insensible water loss. - This amount represents only about one-third of the actual insensible losses from the skin and respiratory system combined. *700 ml* - Although this value is sometimes mentioned in literature, it is at the **lower end** of the physiological range. - The more widely accepted standard value for insensible water loss in a healthy adult under normal conditions is **900-1000 ml/day**. - 700 ml would underestimate the normal daily insensible losses.

Question 123: Which of the following factors increases the rate of particle diffusion across the cell membrane?

A. Decreasing the lipid solubility of the substance
B. Increasing the size of the opening in the cell membrane
C. Maintaining a concentration gradient across the membrane (Correct Answer)
D. Increasing the size of the particle

Explanation: ***Maintaining a concentration gradient across the membrane*** - **Diffusion** is the net movement of particles from an area of higher concentration to an area of lower concentration, driven by the **concentration gradient**. - A steeper gradient means a larger difference in concentration, leading to a faster rate of net diffusion until equilibrium is reached. - According to **Fick's Law**, the rate of diffusion is directly proportional to the concentration gradient across the membrane. *Decreasing the lipid solubility of the substance* - The cell membrane is primarily composed of a **lipid bilayer**, meaning that substances with **higher lipid solubility** can more easily pass through it via simple diffusion. - Decreasing lipid solubility would **hinder** the substance's ability to cross the membrane, thus slowing down or preventing diffusion. *Increasing the size of the opening in the cell membrane* - While increasing channel or pore diameter can increase diffusion rate for **channel-mediated transport**, this option is less comprehensive than maintaining a concentration gradient. - The concentration gradient is the **primary driving force** for diffusion across all types of membrane transport (simple diffusion through lipid bilayer, channel-mediated, and carrier-mediated). - Channel size is relevant only for specific facilitated diffusion pathways, not for general particle diffusion. *Increasing the size of the particle* - **Smaller particles** generally diffuse faster than larger particles because they have higher diffusion coefficients and can more easily navigate through the membrane. - According to the **Stokes-Einstein equation**, diffusion rate is inversely proportional to particle size. - Increasing particle size would therefore **decrease** the rate of diffusion.