A mutation affecting the dystrophin gene would primarily result in:
Answer: B
Dystrophin protein deficiency causes Duchenne muscular dystrophy, an X-linked recessive disorder affecting muscle structure and function.
Q.2Hard
During an action potential in a neuron, the rapid depolarization phase is primarily due to:
Answer: C
Depolarization occurs when voltage-gated Na+ channels open, allowing rapid Na+ influx that reverses membrane potential towards positive values.
Q.3Hard
A patient with nephrotic syndrome exhibits severe proteinuria. This occurs because:
Answer: B
Nephrotic syndrome involves damage to the glomerular filtration barrier (podocytes), increasing permeability to plasma proteins like albumin.
Q.4Hard
The countercurrent multiplier mechanism in the Loop of Henle allows the kidney to produce concentrated urine by:
Answer: A
The ascending limb actively transports Na+/K+/Cl- without water permeability, creating osmotic gradients that concentrate urine in the collecting duct.
Q.5Hard
During the relative refractory period of an action potential, an action potential can be generated if the stimulus is:
Answer: A
The relative refractory period occurs during repolarization when membrane potential is more negative than resting potential (hyperpolarized). A suprathreshold stimulus can overcome this increased threshold to generate an action potential.
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Q.6Hard
Which mechanism explains how the proximal convoluted tubule reabsorbs glucose without violating the principle of osmosis?
Answer: A
Glucose is actively reabsorbed via Na-glucose cotransporter (SGLT1) at the apical membrane using Na+ gradient, then exits via facilitated diffusion (GLUT2). Water follows osmotically via aquaporins, maintaining osmotic balance.
Q.7Hard
A patient with hemophilia A cannot produce Factor VIII due to a genetic mutation. Which physiological consequence is most significant?
Answer: A
Factor VIII is a critical cofactor in the intrinsic coagulation pathway (Factor VIII-von Willebrand complex). Its deficiency specifically impairs activation of Factor X, prolonging aPTT while PT remains normal.
Q.8Hard
The phenomenon where increased afferent arteriolar resistance leads to decreased glomerular filtration rate involves which compensatory mechanism?
Answer: A
Decreased GFR reduces NaCl delivery to the macula densa in the thick ascending limb. This chemoreceptor senses decreased NaCl uptake and signals JG cells to reduce renin secretion, allowing afferent arteriolar vasodilation to restore GFR.
Q.9Hard
In the context of respiratory physiology, how does the Bohr effect facilitate oxygen delivery to metabolically active tissues?
Answer: D
The Bohr effect is multifactorial: decreased pH (lactate, CO2), increased PCO2, increased temperature, and elevated 2,3-BPG all decrease hemoglobin's O2 affinity, promoting oxygen unloading precisely where metabolic demand is highest.
Q.10Hard
A mutation in the CFTR gene causes defective chloride channel function. Which organ system is primarily affected and why?
Answer: A
CFTR chloride channels regulate fluid secretion in mucus-producing tissues. Defective CFTR impairs Cl- secretion, causing secondary reduced water secretion and excessive Na+ reabsorption, producing thick, viscous mucus that obstructs respiratory airways.
Q.11Hard
A patient presents with polycythemia (elevated RBC count). How would this affect oxygen delivery to tissues?
Answer: A
While more RBCs carry oxygen, increased blood viscosity decreases flow rate, potentially reducing net oxygen delivery. The optimal hematocrit is around 45% for maximum oxygen transport.
Q.12Hard
Which mechanism best explains how the body maintains blood pH despite continuous metabolic acid production?
Answer: B
pH homeostasis involves buffer systems (bicarbonate, phosphate, proteins), respiratory control of CO2, and renal regulation of H+ and HCO3- ions.
Q.13Hard
In the context of synaptic transmission, how do selective serotonin reuptake inhibitors (SSRIs) increase synaptic serotonin levels?
Answer: B
SSRIs block serotonin reuptake transporters, preventing reabsorption of serotonin from the synaptic cleft and increasing its availability for receptor binding.
Q.14Hard
A person experiences sustained muscle contraction (tetanus) when a muscle is stimulated at high frequency. This occurs because:
Answer: A
High-frequency stimulation causes calcium to accumulate in the sarcoplasm faster than it can be reuptaken by SR, maintaining sustained actin-myosin interactions.
Q.15Hard
In renal physiology, how does antidiuretic hormone (ADH) regulate water reabsorption in the collecting duct?
Answer: B
ADH binds to V2 receptors on collecting duct cells, triggering cAMP production that moves aquaporin-2 water channels to the apical membrane, increasing water permeability.
Q.16Hard
During maximal exercise, how do skeletal muscles maintain ATP availability despite increased consumption?
Answer: A
During intense exercise, muscles use phosphocreatine to rapidly regenerate ATP and switch to anaerobic glycolysis, producing lactate. Aerobic metabolism is insufficient initially.
Q.17Hard
A patient with spinal cord injury at T5 level loses pain sensation below the waist. Which spinal tract is likely damaged?
Answer: B
The spinothalamic tract carries pain and temperature sensation, crossing at the spinal cord level. Damage results in contralateral loss of pain sensation below the injury.
Q.18Hard
Which mechanism explains how the kidney maintains blood pH around 7.35-7.45?
Answer: A
Kidneys reabsorb filtered HCO3- and secrete H+ ions, regulate ammonia production, and adjust acid-base balance through selective reabsorption and secretion.
Q.19Hard
A patient develops Cushing's syndrome due to excessive cortisol. Which feedback mechanism is disrupted?
Answer: B
In Cushing's syndrome, elevated cortisol fails to inhibit CRH and ACTH secretion, disrupting the normal negative feedback loop of the HPA axis.
Q.20Hard
Which of the following best explains oxygen-hemoglobin dissociation curve shift to the RIGHT?
Answer: B
Right shift (Bohr effect) occurs with decreased pH, increased CO2, increased temperature, and elevated 2,3-DPG, facilitating oxygen release to tissues.
