Anatomy
1 questionsIn walking, gravity tends to tilt pelvis and trunk to the unsupported side, the major factor in preventing this unwanted movement is?
NEET-PG 2012 - Anatomy NEET-PG Practice Questions and MCQs
Question 321: 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.
Biochemistry
2 questionsTaurine is biosynthesized from which amino acid?
Enzymes of glycolysis are found in:
NEET-PG 2012 - Biochemistry NEET-PG Practice Questions and MCQs
Question 321: Taurine is biosynthesized from which amino acid?
- A. Cysteine (Correct Answer)
- B. Valine
- C. Arginine
- D. Leucine
Explanation: ***Cysteine*** - **Taurine** is primarily synthesized from the amino acid **cysteine** through a pathway involving **cysteine sulfinic acid** and **hypotaurine**. - This pathway utilizes enzymes like **cysteine dioxygenase** and **cysteine sulfinic acid decarboxylase**. - The biosynthetic pathway: Cysteine → Cysteine sulfinic acid → Hypotaurine → Taurine. *Arginine* - **Arginine** is a precursor for **nitric oxide**, **urea**, and **creatine**, not taurine. - It is involved in various metabolic pathways, including the **urea cycle** and protein synthesis. *Valine* - **Valine** is a **branched-chain amino acid (BCAA)** involved in protein synthesis and energy production. - It is not a direct precursor for taurine biosynthesis. *Leucine* - **Leucine** is also a **branched-chain amino acid (BCAA)** crucial for protein synthesis and muscle metabolism. - It does not participate in the synthesis of taurine.
Question 322: Enzymes of glycolysis are found in:
- A. Cytosol (Correct Answer)
- B. Cell membrane
- C. Mitochondria
- D. Ribosomes
Explanation: ***Cytosol*** - Glycolysis is a metabolic pathway that occurs in the **cytosol** of cells. - All the enzymes required for the conversion of glucose to pyruvate are freely dissolved in the **cytoplasm**. *Cell membrane* - The cell membrane is primarily involved in **regulating the passage of substances** into and out of the cell, as well as cell signaling. - Glycolytic enzymes are not associated with the cell membrane. *Mitochondria* - Mitochondria are the primary site of **oxidative phosphorylation** and the **citric acid cycle**, not glycolysis. - While pyruvate (the end product of glycolysis) moves into the mitochondria for further metabolism, the initial glycolytic steps do not occur there. *Ribosomes* - Ribosomes are responsible for **protein synthesis** (translation). - They do not contain enzymes for metabolic pathways like glycolysis.
Physiology
7 questionsWhat does Einthoven's law state regarding the relationship between the electrical potentials of the limb leads?
Which hormone primarily inhibits gastric acid secretion in response to acidic chyme?
What percentage of gastric secretion is attributed to the cephalic phase?
Growth hormone level is highest during
Wolff–Chaikoff effect is due to?
Insensible water loss per day is ?
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 321: What does Einthoven's law state regarding the relationship between the electrical potentials of the limb leads?
- A. I + III = II (Correct Answer)
- B. I - III = II
- C. I + II + III = 0
- D. I + III = avL
Explanation: ***I + III = II*** - Einthoven's law describes the relationship between the three **bipolar limb leads** (I, II, and III) in an **electrocardiogram (ECG)**. - It states that the electrical potential of Lead II is equal to the sum of the potentials of Lead I and Lead III (Lead II = Lead I + Lead III). - This can also be expressed as **I + III = II**, which is the **correct mathematical representation** of Einthoven's law. *I - III = II* - This equation is **incorrect** and does not represent Einthoven's law. - The correct relationship involves **addition** of Leads I and III, not subtraction. *I + II + III = 0* - This equation is **incorrect** as written with all positive signs. - Einthoven's law can be rearranged as **I + III - II = 0** (not I + II + III = 0). - The equation shown suggests adding all three leads to get zero, which is **mathematically inconsistent** with the correct formulation (I + III = II). *I + III = avL* - This equation is incorrect and does not relate to Einthoven's law. - **avL (augmented vector left)** is one of the augmented unipolar limb leads calculated as: avL = I - (II/2), not as a direct sum of Leads I and III.
Question 322: Which hormone primarily inhibits gastric acid secretion in response to acidic chyme?
- A. Secretin
- B. Somatostatin (Correct Answer)
- C. Insulin
- D. Gastrin
Explanation: ***Somatostatin*** - **Somatostatin** is the **primary hormone** that inhibits gastric acid secretion in response to acidic chyme. - Released by D cells in the stomach and duodenum when pH drops below 3.0. - **Direct inhibitory effects:** Inhibits parietal cells directly, suppresses gastrin release from G cells, and blocks histamine release from ECL cells. - Acts as the main **negative feedback mechanism** to prevent excessive gastric acidification. *Secretin* - **Secretin** is released by S cells in the duodenum in response to acidic chyme (pH < 4.5). - Its **primary function** is to stimulate pancreatic bicarbonate secretion to neutralize duodenal acid. - While it does have a **secondary effect** of inhibiting gastric acid secretion, this is not its primary role. *Gastrin* - **Gastrin** is a hormone that **stimulates** gastric acid secretion, not inhibits it. - Released by G cells in the gastric antrum in response to peptides, amino acids, and gastric distension. - Promotes acid secretion by stimulating parietal cells and ECL cells (which release histamine). *Insulin* - **Insulin** is a pancreatic hormone primarily involved in **glucose metabolism** and cellular glucose uptake. - It has **no significant role** in the regulation of gastric acid secretion.
Question 323: What percentage of gastric secretion is attributed to the cephalic phase?
- A. 20% (Correct Answer)
- B. 70%
- C. 10%
- D. 100%
Explanation: ***20%*** - The **cephalic phase** of gastric secretion is initiated by the sight, smell, taste, or even thought of food and accounts for approximately **20-30%** of total gastric acid secretion. - This phase is mediated by the **vagus nerve**, stimulating parietal cells (via acetylcholine) and G cells (via gastrin-releasing peptide) to release acid and gastrin, respectively. *70 %* - **70%** represents the approximate contribution of the **gastric phase** to total gastric secretion, which is the largest phase. - This phase is activated by the presence of food in the stomach, distension, and the presence of amino acids and peptides. *10%* - **10%** is a value that is too low for the cephalic phase; it typically accounts for a more significant portion of initial acid secretion. - This percentage is sometimes associated with the intestinal phase, which produces a smaller amount of acid secretion after chyme enters the duodenum. *100%* - **100%** is incorrect because gastric secretion is a complex process involving multiple phases (cephalic, gastric, intestinal), each contributing a portion of the total secretion. - Each phase has distinct stimuli and regulatory mechanisms, ensuring a coordinated digestive response.
Question 324: Growth hormone level is highest during
- A. Sleep (Correct Answer)
- B. Hypoglycemia
- C. Fasting
- D. Exercise
Explanation: ***Sleep*** - Growth hormone (GH) secretion is **pulsatile**, with the largest and most consistent pulses occurring during **slow-wave sleep** (deep sleep). - This nocturnal surge contributes significantly to the overall daily GH output and is crucial for growth and metabolic regulation. *Hypoglycemia* - While **hypoglycemia** is a potent stimulus for GH release, it is an acute stress response rather than a state where GH levels are consistently highest. - The body's primary response to hypoglycemia is to raise blood glucose, and while GH helps, it is not the peak physiological secretion time. *Fasting* - **Prolonged fasting** can increase GH secretion as a mechanism to mobilize fat stores and conserve glucose. - However, the peak levels due to fasting are generally less pronounced than the dramatic surge observed during deep sleep. *Exercise* - **Vigorous exercise** can acutely stimulate GH release, particularly with sustained effort. - This increase is typically transient and not as high or consistently cyclical as the secretion during nocturnal sleep.
Question 325: 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 326: 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 327: 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.