Which of the following best describes the function of the loop of Henle in the kidney?
Answer: B
The loop of Henle, particularly the descending and ascending limbs, creates a countercurrent multiplier system that establishes an osmotic gradient necessary for concentrated urine formation.
Q.142Easy
Tidal volume in a healthy adult human is approximately:
Answer: A
Tidal volume, the volume of air inspired or expired during normal quiet breathing, is approximately 500 mL in adults.
Q.143Easy
Which neurotransmitter is responsible for the transmission of signals across the neuromuscular junction?
Answer: B
Acetylcholine is the primary neurotransmitter at the neuromuscular junction, binding to nicotinic receptors on muscle fiber membranes to trigger muscle contraction.
Q.144Medium
A patient suffers from thyroid deficiency. Which of the following metabolic changes would NOT be expected?
Answer: B
Thyroid hormone deficiency decreases metabolic rate and oxygen consumption. Increased oxygen consumption would not occur; rather, it would decrease significantly.
Q.145Medium
During inspiration, the external intercostal muscles contract. What is the primary consequence of this action?
Answer: D
Contraction of external intercostal muscles elevates the ribs and sternum, increasing thoracic cavity volume, which decreases intrapulmonary pressure and causes air to flow in.
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Q.146Medium
Which of the following statements about myelin sheath is correct?
Answer: B
Myelin sheath, formed by oligodendrocytes in CNS and Schwann cells in PNS, increases conduction velocity by enabling saltatory conduction.
Q.147Medium
In the cardiac cycle, ventricular repolarization is represented by which wave on an ECG?
Answer: C
The T wave represents ventricular repolarization. The QRS complex represents ventricular depolarization, while P wave represents atrial depolarization.
Q.148Medium
Which hormone is essential for the regulation of calcium and phosphate homeostasis?
Answer: C
Both PTH and calcitonin regulate calcium-phosphate balance. PTH increases blood calcium while calcitonin decreases it through opposing mechanisms.
Q.149Medium
A person exposed to high altitude experiences increased erythropoietin (EPO) secretion. This is an example of:
Answer: A
Low oxygen at high altitude stimulates EPO release, which increases RBC production, restoring oxygen levels and decreasing EPO secretion—a classic negative feedback loop.
Q.150Medium
Which of the following accurately describes the absolute refractory period?
Answer: B
During absolute refractory period, inactivated sodium channels cannot open regardless of stimulus strength, making another action potential impossible.
Q.151Medium
In the renin-angiotensin-aldosterone system (RAAS), which enzyme converts angiotensinogen to angiotensin I?
Answer: B
Renin, secreted by juxtaglomerular cells, cleaves angiotensinogen to form angiotensin I, which is then converted to angiotensin II by ACE.
Q.152Hard
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.153Hard
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.154Hard
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.155Hard
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.156Hard
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.157Hard
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.158Easy
Which of the following is the primary function of the loop of Henle in the nephron?
Answer: B
The loop of Henle creates a countercurrent multiplier system that establishes an osmotic gradient, enabling selective water reabsorption in the collecting duct.
Q.159Medium
A patient suffers from myasthenia gravis. Which of the following is most likely affected?
Answer: B
Myasthenia gravis is an autoimmune disorder where antibodies attack acetylcholine receptors at the neuromuscular junction, reducing muscle contraction capability.
Q.160Easy
Which organ produces erythropoietin (EPO) in response to low oxygen levels?
Answer: C
The kidneys produce approximately 90% of EPO, which stimulates red blood cell production in bone marrow when oxygen levels are low.
