General Physiology — MCQs

General Physiology Indian Medical PG Practice Questions and MCQs

Question 441: Which of the following is NOT a component of Virchow's triad?

A. Endothelial injury
B. Stasis
C. Hypercoagulability
D. Hypotension (Correct Answer)

Explanation: ***Hypotension*** - **Hypotension** (low blood pressure) is not a component of Virchow's triad for thrombosis - While hypotension can affect blood flow, it is not one of the classic three factors described by Rudolf Virchow - Virchow's triad specifically consists of: endothelial injury, stasis/abnormal blood flow, and hypercoagulability *Endothelial injury* - Damage to the **blood vessel wall lining** is a key component of Virchow's triad - Causes include trauma, surgery, inflammation, atherosclerosis, and medical devices (catheters, stents) - Exposed subendothelial collagen triggers platelet adhesion and activation of the coagulation cascade *Stasis* - **Abnormal or stagnant blood flow** is the second component of Virchow's triad - Occurs in prolonged immobility, atrial fibrillation, venous obstruction, or varicose veins - Slow flow prevents dilution of activated clotting factors and allows platelet-endothelial interaction *Hypercoagulability* - **Increased tendency to form blood clots** is the third component of Virchow's triad - Can be inherited (Factor V Leiden, Prothrombin G20210A mutation, Protein C/S deficiency) or acquired - Acquired causes include malignancy, pregnancy, oral contraceptives, smoking, and nephrotic syndrome

Question 442: 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.

Question 443: In the context of blunt trauma affecting the entire body, what is the estimated daily nitrogen loss in grams due to protein metabolism?

A. Approximately 35 grams (Correct Answer)
B. Approximately 45 grams
C. Approximately 55 grams
D. Approximately 65 grams

Explanation: ***Approximately 35 grams*** - In **severe trauma**, such as blunt trauma affecting the entire body, the body undergoes a significant stress response leading to marked **protein catabolism**. Approximately **35 grams of nitrogen** can be lost daily under such conditions. - This represents a highly catabolic state where muscle protein is broken down to provide amino acids for energy and synthesis of acute-phase proteins, impacting overall nitrogen balance. *Approximately 45 grams* - While severe trauma does lead to substantial nitrogen loss, **45 grams** would typically indicate an even more extreme or prolonged catabolic state, which is less common in the initial stages of post-trauma protein metabolism than 35 grams. - Such a high nitrogen loss might be seen in very extensive burns or sepsis, which are different clinical contexts. *Approximately 55 grams* - A daily nitrogen loss of **55 grams** is beyond what is commonly observed even in severe, whole-body blunt trauma. This level of catabolism would likely be unsustainable or indicative of a rare, super-catabolic condition. - This magnitude of protein breakdown would lead to rapid and severe muscle wasting and organ dysfunction if sustained. *Approximately 65 grams* - Losing **65 grams of nitrogen** per day is an exceptionally high rate of protein catabolism, rarely, if ever, observed in blunt trauma alone. - This level of protein breakdown would represent a profound and life-threatening metabolic derangement, far exceeding typical post-trauma responses.

Question 444: What is the correct arrangement of the lenses in the light path from the source to the eye in a light microscope?

A. Ocular lens : Objective lens : Condenser lens
B. Objective lens : Condenser lens : Ocular lens
C. Condenser lens : Objective lens : Ocular lens (Correct Answer)
D. Objective lens : Ocular lens : Condenser lens

Explanation: ***Condenser lens : Objective lens : Ocular lens*** - This is the correct sequence of lenses in the **light path from source to eye** in a compound light microscope - Light from the source first passes through the **condenser lens**, which focuses and concentrates the light onto the specimen - After passing through the specimen, light enters the **objective lens** which provides the primary magnification - Finally, light passes through the **ocular lens (eyepiece)** which provides additional magnification before reaching the observer's eye - This arrangement ensures proper illumination and sequential magnification of the specimen *Objective lens : Condenser lens : Ocular lens* - This sequence incorrectly places the **objective lens before the condenser** - In reality, the condenser must focus light onto the specimen **before** it reaches the objective lens - The condenser is positioned below the specimen stage to illuminate it from below *Objective lens : Ocular lens : Condenser lens* - This arrangement incorrectly places the **condenser lens at the end** of the light path - The condenser's function is to **illuminate the specimen**, not to be positioned after the viewing lenses - This would not produce a functional microscope optical system *Ocular lens : Objective lens : Condenser lens* - This sequence is completely reversed from the actual light path - The **ocular lens is the last** lens in the path before the eye, not the first - This arrangement would not allow proper specimen observation

Question 445: What is the primary force that enables medical tapes and bandages to remain attached to the skin during emergency medical procedures?

A. Surface tension
B. Cohesion
C. Adhesion (Correct Answer)
D. Atmospheric pressure

Explanation: ***Adhesion*** - **Adhesion** refers to the attractive forces between two *different* surfaces or substances, such as the adhesive on tape and the skin. - Medical tapes and bandages are designed with adhesives that create a strong bond to the skin's surface, preventing them from falling off. *Surface tension* - **Surface tension** is the contractive force exerted by the surface of a liquid, causing it to minimize its surface area. - While present in bodily fluids, it is not the primary force responsible for the adherence of solid materials like medical tape to skin. *Cohesion* - **Cohesion** is the attractive force between *identical* molecules or substances. - It describes the internal strength of the adhesive material itself, not its ability to stick to another surface. *Atmospheric pressure* - **Atmospheric pressure** is the force exerted by the weight of the air above a surface. - While it plays a role in phenomena like suction cups, it is not the primary mechanism by which medical tapes, which rely on a sticky substance, adhere to the skin.

Question 446: What is the normal value of the filtration fraction in a healthy adult kidney?

A. 0.2 (Correct Answer)
B. 0.5
C. 0.45
D. 0.55

Explanation: ***0.2*** - The **filtration fraction (FF)** is the ratio of **glomerular filtration rate (GFR)** to **renal plasma flow (RPF)**. - Normal values: **GFR ≈ 125 mL/min** and **RPF ≈ 625 mL/min** - Therefore, **FF = GFR/RPF = 125/625 = 0.2 (or 20%)** - This means that **20% of the plasma entering the glomerulus is filtered** into Bowman's capsule, while 80% continues into the peritubular capillaries. *0.45* - A filtration fraction of **0.45 (45%)** is significantly higher than normal. - This would suggest **increased glomerular filtration relative to renal plasma flow**, which can occur in conditions with **efferent arteriolar constriction** or **decreased renal plasma flow**. *0.5* - A filtration fraction of **0.5 (50%)** is markedly elevated above the normal range. - This indicates that **half of the plasma** entering the glomerulus is being filtered, which can occur with **severe efferent arteriolar constriction** or in states of **reduced renal blood flow** with preserved GFR. *0.55* - A filtration fraction of **0.55 (55%)** is abnormally high. - Such an elevated FF suggests **significant efferent arteriolar vasoconstriction** or **severe reduction in renal plasma flow**, and may be seen with conditions like **renal artery stenosis** or **angiotensin II excess**.

Question 447: Positive feedback mechanisms are observed in all of the following except:

A. Parturition
B. Moderate hemorrhage (Correct Answer)
C. Generation of nerve action potential
D. Blood coagulation

Explanation: ***Moderate hemorrhage*** - Moderate hemorrhage typically triggers **negative feedback mechanisms** to restore homeostasis, such as increased heart rate and vasoconstriction, rather than escalating the initial disturbance. - In cases of **severe hemorrhage**, positive feedback (e.g., cardiac depression leading to further decreased blood pressure) can occur, but moderate hemorrhage is generally contained by compensatory responses. *Blood coagulation* - **Blood coagulation** is a classic example of positive feedback; the activation of one clotting factor triggers the activation of many more, rapidly forming a clot to stop bleeding. - For instance, thrombin activates more thrombin and other clotting factors, amplifying the response. *Parturition* - During **childbirth (parturition)**, uterine contractions stimulate the release of oxytocin, which in turn enhances uterine contractions. - This positive feedback loop continues until the baby is delivered. *Generation of nerve action potential* - The **depolarization phase of an action potential** involves positive feedback, where a small influx of sodium ions causes further membrane depolarization. - This depolarization opens more voltage-gated sodium channels, leading to a rapid and massive influx of sodium, creating the rising phase of the action potential.

Question 448: Decreased basal metabolic rate is seen in:

A. Postprandial state
B. Sedentary lifestyle leading to muscle mass loss
C. Aging process
D. Hypothyroidism (Correct Answer)

Explanation: ***Hypothyroidism*** - **Thyroid hormones** (T3 and T4) are the primary regulators of basal metabolic rate (BMR) - **Hypothyroidism** results in decreased production of thyroid hormones, leading to a **significant reduction in BMR** - Clinical manifestations include **weight gain, fatigue, cold intolerance, bradycardia**, and decreased oxygen consumption - This is the **classic pathological condition** associated with decreased BMR in physiology *Sedentary lifestyle leading to muscle mass loss* - While muscle loss does reduce BMR (as muscle is more metabolically active than fat), this is a **chronic lifestyle effect** rather than a primary physiological condition - The decrease in BMR is **gradual and less pronounced** compared to hypothyroidism - Not the primary answer for decreased BMR in medical examinations *Aging process* - Aging does lead to decreased BMR due to **loss of lean muscle mass** and hormonal changes - However, this is a **physiological process** rather than a pathological condition - The decrease is **gradual over decades** and less clinically significant than hypothyroidism *Postprandial state* - The postprandial state (after eating) causes an **increase in metabolic rate** due to the **thermic effect of food (TEF)** - Energy is required for digestion, absorption, and storage of nutrients - This represents a **temporary increase**, not a decrease, in metabolic rate

Question 449: Which of the following best describes atavism?

A. Expression of a recently acquired trait
B. Persistence of a trait from the immediate parents
C. Reappearance of a trait from a remote ancestor (Correct Answer)
D. A new mutation in the current generation

Explanation: ***Reappearance of a trait from a remote ancestor*** - Atavism refers to the **re-emergence of an ancestral trait** that has been absent for several generations. - This phenomenon is typically due to the **re-expression of dormant genes** that were previously suppressed. *Expression of a recently acquired trait* - This describes a modern characteristic or adaptation, not the reappearance of an **ancient, lost trait**. - Newly acquired traits are usually driven by recent selective pressures or mutations and are not indicative of atavism. *Persistence of a trait from the immediate parents* - This is a normal phenomenon of **heredity**, where offspring inherit traits directly from their parents. - Atavism specifically refers to traits from much **earlier developmental or evolutionary stages**, distant ancestors. *A new mutation in the current generation* - A new mutation introduces a **novel genetic change**, potentially leading to a new trait. - Atavism, in contrast, involves the activation of **pre-existing genetic information** from an ancestor, not the creation of new genetic material.

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