The blood-brain barrier is primarily composed of which type of cell?
Answer: A
The blood-brain barrier is formed by tight junctions between endothelial cells of brain capillaries, supported by astrocytes that regulate nutrient transport and maintain the barrier's integrity.
Q.22Easy
Which of the following enzymes is responsible for breaking down acetylcholine at the neuromuscular junction?
Answer: A
Acetylcholinesterase rapidly hydrolyzes acetylcholine in the synaptic cleft, terminating neuromuscular transmission and allowing muscle relaxation.
Q.23Easy
The phenomenon where a nerve impulse can jump from one node of Ranvier to the next is called:
Answer: A
Saltatory conduction occurs in myelinated neurons where action potentials jump between nodes of Ranvier, increasing conduction velocity significantly compared to unmyelinated fibers.
Q.24Easy
Which structure in the kidney is responsible for ultrafiltration?
Answer: A
The glomerulus, a network of capillaries in the renal corpuscle, filters blood under hydrostatic pressure to produce the ultrafiltrate that forms the basis of urine.
Q.25Medium
A deficiency of intrinsic factor leads to which type of anemia?
Answer: A
Intrinsic factor, produced by gastric parietal cells, is essential for vitamin B12 absorption in the terminal ileum. Its deficiency prevents B12 absorption, causing pernicious anemia.
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Q.26Medium
During increased physical activity, which compensatory mechanism helps maintain blood pH within normal range?
Answer: A
During exercise, lactate production increases blood acidity. Hyperventilation increases CO2 elimination, shifting the CO2-bicarbonate equilibrium to maintain blood pH (7.35-7.45).
Q.27Medium
Which of the following correctly describes the relationship between the parasympathetic nervous system and heart rate?
Answer: A
Parasympathetic acetylcholine activates M2 muscarinic receptors on pacemaker cells, increasing K+ efflux and decreasing Ca2+ influx, causing hyperpolarization and reduced heart rate.
Q.28Medium
In the digestive system, which hormone stimulates the pancreas to release bicarbonate-rich secretions?
Answer: A
Secretin, released by duodenal S cells in response to chyme acidity, specifically stimulates pancreatic ductal cells to secrete bicarbonate, neutralizing stomach acid.
Q.29Medium
Which protein in red blood cells is responsible for the chloride shift mechanism?
Answer: A
Band 3 protein (anion exchanger 1) facilitates the exchange of Cl- for HCO3- across the RBC membrane, allowing CO2 transport as bicarbonate in blood.
Q.30Medium
A patient experiences persistent hyperglycemia despite normal insulin levels. Which condition is most likely?
Answer: A
In Type 2 diabetes, normal or elevated insulin fails to lower blood glucose due to peripheral tissue insulin resistance, often caused by impaired receptor signaling or GLUT4 translocation defects.
Q.31Medium
Which of the following statements about the lymphatic system is correct?
Answer: A
Lymph drains from tissue spaces into lymphatic capillaries, passes through lymph nodes for filtration and immune response, and returns to the bloodstream via the thoracic duct into the left subclavian vein.
Q.32Medium
In the cardiac cycle, the S3 heart sound is associated with:
Answer: A
S3 occurs during rapid ventricular filling phase (early diastole) when blood rapidly enters the ventricle. It's normal in young individuals but may indicate heart failure in older patients.
Q.33Hard
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.
Q.34Hard
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.35Hard
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.36Hard
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.37Hard
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.38Hard
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.39Easy
Which of the following hormones is primarily responsible for increasing blood glucose levels during the fasting state?
Answer: A
Glucagon is secreted by alpha cells of pancreatic islets and increases blood glucose by promoting glycogenolysis and gluconeogenesis during fasting.
Q.40Easy
The sinoatrial (SA) node is considered the pacemaker of the heart because:
Answer: A
The SA node has the highest inherent rate of spontaneous depolarization (60-100 bpm), allowing it to set the rhythm for the entire heart.
