Ossicles of middle ear are responsible for which of the following ?
Which of the following is responsible for localization of sound ?
Which immunoglobulin is primarily secreted by the intestine?
Result of liquorice ingestion
Which of the following is the principal mode of heat exchange in an infant incubator?
Coronary steal phenomenon caused due to
Which of the following is markedly decreased in restrictive lung disease?
What is the expected Transtubular Potassium Gradient (TTKG) in a patient with hypokalemia due to extrarenal losses?
At what age do the proportions of intracellular fluid (ICF) and extracellular fluid (ECF) in a child approximate those of an adult?
The Doppler effect in medical ultrasound is caused by:
NEET-PG 2013 - Physiology NEET-PG Practice Questions and MCQs
Question 81: Ossicles of middle ear are responsible for which of the following ?
- A. Amplification of sound intensity
- B. Reduction of sound intensity
- C. Protecting the inner ear
- D. Reduction of impedance for sound transmission (Correct Answer)
Explanation: ***Reduction of impedance for sound transmission*** - The ossicles (malleus, incus, and stapes) act as a **lever system** to match the impedance between the air-filled outer ear and the fluid-filled inner ear. - This impedance matching ensures that maximum sound energy is transferred to the cochlea, preventing significant **sound reflection**. *Amplification of sound intensity* - While the ossicles do slightly amplify the sound pressure, their primary role is not extensive amplification but rather **impedance matching**. - The amplification achieved is a byproduct of efficient energy transfer, rather than a direct goal of increasing sound intensity for its own sake. *Reduction of sound intensity* - This function is primarily attributed to the **acoustic reflex**, where the middle ear muscles contract to stiffen the ossicular chain in response to loud sounds. - The primary function of the ossicles themselves is to transmit sound efficiently, not to reduce intensity under normal conditions. *Protecting the inner ear* - While the **acoustic reflex** (involving middle ear muscles attached to the ossicles) offers some protection against very loud sounds by stiffening the ossicular chain, this is a separate, reflexive mechanism. - The intrinsic structure and primary mechanical function of the ossicles are centered on efficient sound transmission, not direct physical protection of the inner ear.
Question 82: Which of the following is responsible for localization of sound ?
- A. Cochlear nerve
- B. Cochlea
- C. Superior olivary nucleus (Correct Answer)
- D. Cochlear nuclei
Explanation: ***Superior olivary nucleus*** - The **superior olivary nucleus** is the first site in the auditory pathway where binaural (two-ear) input is integrated, which is crucial for **sound localization**. - It processes **interaural time differences (ITDs)** and **interaural level differences (ILDs)** to determine the horizontal position of a sound source. *Cochlear nerve* - The **cochlear nerve** transmits auditory information from the cochlea to the brainstem but does not perform the initial processing for sound localization. - It carries impulses for both ears independently, which are then integrated at higher centers. *Cochlea* - The **cochlea** is responsible for converting sound vibrations into electrical signals (transduction), encoding properties like pitch and loudness, but not directly for sound localization. - It acts as a mechanical analyzer, separating sound into its frequency components. *Cochlear nuclei* - The **cochlear nuclei** receive input solely from the ipsilateral cochlear nerve and primarily process monaural (one-ear) auditory information. - While they are a crucial relay in the auditory pathway, they do not integrate binaural cues for sound localization.
Question 83: Which immunoglobulin is primarily secreted by the intestine?
- A. IgG
- B. IgM
- C. IgA (Correct Answer)
- D. IgD
Explanation: **IgA** - **Secretory IgA** is the dominant immunoglobulin in mucosal secretions, including those of the intestine. - It plays a crucial role in providing **local immunity** by preventing microbial adherence and neutralizing toxins on mucosal surfaces. *IgG* - **IgG** is the most abundant immunoglobulin in serum and plays a major role in systemic immunity, including opsonization and complement activation. - While some IgG is found in secretions, it is not the primary immunoglobulin secreted by the intestine. *IgM* - **IgM** is a pentameric immunoglobulin, primarily found in blood and lymph, where it is very effective in activating the complement system and agglutinating antigens. - Although it can be found at mucosal surfaces in small amounts, it is not the principal secreted antibody in the intestine. *IgD* - **IgD** is primarily found on the surface of naive B lymphocytes, where it functions as a B cell receptor. - Its role in secreted form is minimal, and it is not significantly secreted into the intestine or other bodily fluids.
Question 84: Result of liquorice ingestion
- A. Hyperkalemic alkalosis
- B. Hypokalemic acidosis
- C. Hypernatremic acidosis
- D. Hypokalemic alkalosis (Correct Answer)
Explanation: ***Hypokalemic alkalosis*** - **Licorice** contains **glycyrrhizic acid**, which inhibits **11β-hydroxysteroid dehydrogenase** in the kidneys, preventing the conversion of cortisol to inactive cortisone. - This leads to increased cortisol acting on **mineralocorticoid receptors**, mimicking **aldosterone excess**, resulting in **sodium reabsorption**, **potassium excretion** (hypokalemia), and **hydrogen ion excretion** (metabolic alkalosis). *Hyperkalemic alkalosis* - This option is incorrect because licorice ingestion leads to **hypokalemia** due to increased potassium excretion, not hyperkalemia. - While it does cause alkalosis, the associated potassium imbalance is the opposite of this choice. *Hypokalemic acidosis* - This option is incorrect because licorice ingestion causes a **metabolic alkalosis** due to increased hydrogen ion excretion, not acidosis. - Although it correctly identifies hypokalemia, the acid-base disturbance is wrong. *Hypernatremic acidosis* - This option is incorrect as licorice ingestion initially causes **sodium and water retention** (which can lead to hypernatremia in severe cases, but is not the primary driver of the acid-base), but primarily leads to **metabolic alkalosis**, not acidosis. - The combination of hypernatremia and acidosis is not characteristic of licorice toxicity.
Question 85: Which of the following is the principal mode of heat exchange in an infant incubator?
- A. Radiation
- B. Evaporation
- C. Convection (Correct Answer)
- D. Conduction
Explanation: ***Convection*** - In an infant incubator, **convection** is the primary method of heat transfer where a fan circulates warm air around the infant. - This controlled circulation of warm air helps maintain a stable thermal environment for the neonate. *Radiation* - **Radiation** involves heat transfer through electromagnetic waves, and while it occurs, it's not the primary mode in a typical closed incubator, which aims to minimize radiant heat loss to cooler surfaces. - Radiant warmers, used for open care, primarily rely on radiation, but these are distinct from closed incubators. *Evaporation* - **Evaporation** is the loss of heat through the conversion of liquid (sweat or insensible water loss) to vapor, but incubators aim to minimize this by maintaining optimal humidity. - Excessive evaporative heat loss can be significant in premature infants, but it is a mode of *heat loss*, not the principal *mode of heat exchange* for maintaining warmth in an incubator. *Conduction* - **Conduction** is direct heat transfer through physical contact, such as between the infant's skin and the mattress. - While incubators have warm mattresses to prevent conductive heat loss, the circulating warm air (convection) is the main mechanism for overall temperature control.
Question 86: Coronary steal phenomenon caused due to
- A. Preferential vasodilation of normal coronary vessels over stenotic vessels (Correct Answer)
- B. Dilation of large coronary arteries
- C. Dilation of epicardial coronary vessels
- D. Dilation of capacitance vessels
Explanation: ***Preferential vasodilation of normal coronary vessels over stenotic vessels*** - In a coronary steal phenomenon, **vasodilator drugs** or agents cause **normal coronary arteries** to dilate significantly. - This increased flow in normal areas *diverts blood away* from areas supplied by **stenotic vessels**, leading to **ischemia** in the compromised regions. *Dilation of large coronary arteries* - While large coronary arteries can dilate, this alone does not fully explain the steal phenomenon. The critical factor is the *unbalanced dilation* between healthy and stenotic regions. - Most pharmacological agents used to induce steal, like **dipyridamole** or **adenosine**, primarily affect the **resistance arterioles**. *Dilation of epicardial coronary vessels* - **Epicardial coronary vessels** are the larger conductive arteries, and their dilation does not directly cause the steal phenomenon. - The steal occurs at the level of the **microvasculature**, where resistance is regulated and blood flow away from ischemic areas is diverted. *Dilation of capacitance vessels* - **Capacitance vessels** (mainly veins) store blood but do not play a significant direct role in regulating coronary blood flow or causing the coronary steal phenomenon. - The phenomenon is driven by changes in **arteriolar resistance** and distribution of flow.
Question 87: Which of the following is markedly decreased in restrictive lung disease?
- A. FVC (Correct Answer)
- B. RV
- C. FEV1/FVC
- D. FEV1
Explanation: ***FVC*** - In **restrictive lung disease**, there is a reduction in lung volume due to various causes, leading to a markedly decreased **Forced Vital Capacity (FVC)**. - **FVC** directly measures the total amount of air a person can exhale after a maximal inhalation, which is inherently limited in restrictive conditions. - This is the **hallmark finding** in restrictive lung disease and the most clinically significant decrease. *FEV1* - While **FEV1** (Forced Expiratory Volume in 1 second) is also decreased in restrictive lung disease, its decrease is proportional to the FVC decrease. - A decrease in FEV1 alone is less specific, as it could also indicate obstructive lung disease. - The key is that both FEV1 and FVC decrease together, maintaining a normal or increased ratio. *FEV1/FVC* - The **FEV1/FVC ratio** is typically **normal or even increased** in restrictive lung disease, as both FEV1 and FVC decrease proportionally or FEV1 decreases slightly less. - A decreased FEV1/FVC ratio is characteristic of **obstructive lung disease**, not restrictive. *RV* - **Residual Volume (RV)** is also **decreased** in restrictive lung disease, along with all other lung volumes (TLC, VC, FRC). - However, RV is not measured by standard spirometry and requires body plethysmography or gas dilution techniques. - While RV does decrease, **FVC** is the more clinically significant and readily measurable parameter that is "markedly decreased" and defines restrictive disease on routine pulmonary function testing.
Question 88: What is the expected Transtubular Potassium Gradient (TTKG) in a patient with hypokalemia due to extrarenal losses?
- A. < 3-4 (Correct Answer)
- B. 3-4
- C. > 4-5
- D. > 5-6
Explanation: ***< 3-4*** - A **Transtubular Potassium Gradient (TTKG)** of less than 3-4 indicates appropriate renal potassium conservation in response to hypokalemia. - This suggests that the hypokalemia is likely due to **extrarenal losses**, such as gastrointestinal losses (diarrhea, vomiting) or inadequate dietary intake, as the kidneys are working to retain potassium. *3-4* - A TTKG value in this range is typically considered indeterminate but could still point towards appropriate renal conservation if other clinical signs of extrarenal losses are present. - However, it does not as strongly confirm appropriate renal conservation as a value clearly below 3. *> 4-5* - A TTKG greater than 4-5 suggests **inappropriate renal potassium excretion** for a patient with hypokalemia. - This would indicate that the kidneys are complicit in the potassium loss, pointing towards renal causes of hypokalemia, such as **mineralocorticoid excess** or **diuretic use**. *> 5-6* - A TTKG greater than 5-6 strongly indicates significant **renal potassium wasting**. - This would be seen in conditions where the kidneys are actively secreting potassium despite hypokalemia, thereby contributing to the low potassium levels rather than conserving it.
Question 89: At what age do the proportions of intracellular fluid (ICF) and extracellular fluid (ECF) in a child approximate those of an adult?
- A. 3 years
- B. 4 years
- C. 1 year
- D. 2 years (Correct Answer)
Explanation: ***2 years*** - By the age of **2 years**, the relative proportions of intracellular fluid (ICF) and extracellular fluid (ECF) in a child reach levels comparable to those found in adults. - Infants have a significantly higher percentage of ECF, which gradually decreases as they grow and mature. - This represents the key transition point where adult fluid compartment ratios are first approximated. *1 year* - At **1 year of age**, the ECF proportion is still relatively higher than in adults, though it has decreased from neonatal levels. - The shift towards adult fluid proportions is ongoing and not yet complete. *3 years* - By **3 years of age**, the fluid proportions are already well-established at adult levels, as this milestone is reached by age 2. - This age comes after the initial approximation point, so it is not the earliest age when adult proportions are reached. *4 years* - At **4 years of age**, the child's fluid distribution is well within adult proportions. - The main transition period for fluid compartment ratios is usually completed by age 2, making this age too late to represent the approximation point.
Question 90: The Doppler effect in medical ultrasound is caused by:
- A. Change in direction of sound
- B. Change in amplitude of sound
- C. None of the options
- D. Change in frequency of sound (Correct Answer)
Explanation: ***Change in frequency of sound*** - The **Doppler effect** in medical ultrasound is fundamentally based on **frequency changes** that occur when sound waves reflect off moving structures like blood cells or tissues. - When ultrasound waves encounter moving objects, the frequency of reflected waves **shifts upward** (if moving toward transducer) or **shifts downward** (if moving away), enabling detection and measurement of blood flow and tissue movement. *Change in direction of sound* - While sound waves do change direction through **reflection** at tissue interfaces, this directional change doesn't explain the **frequency shift** characteristic of the Doppler effect. - Direction changes are related to **acoustic impedance** differences between tissues, not the motion-dependent frequency variations used in Doppler imaging. *Change in amplitude of sound* - Changes in **amplitude** relate to the **intensity** or strength of the sound waves, affected by factors like **attenuation** and **scattering**. - Amplitude variations don't create the **frequency shift** that allows Doppler ultrasound to detect moving structures and measure velocities. *None of the options* - This is incorrect because **frequency change** is indeed the correct mechanism underlying the Doppler effect in medical ultrasound. - The frequency shift phenomenon is what enables **color Doppler**, **pulsed-wave Doppler**, and **continuous-wave Doppler** imaging techniques to function.