In the renal tubule, selective reabsorption of useful substances like glucose occurs primarily in:
Answer: B
The proximal convoluted tubule epithelial cells have numerous mitochondria and microvilli for active transport of glucose, amino acids, and ions.
Q.62Medium
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.
Q.63Medium
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.64Medium
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.65Medium
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.
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Q.66Medium
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.67Medium
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.68Medium
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.69Medium
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.70Medium
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.71Medium
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.
Q.72Medium
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.73Medium
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.74Medium
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.75Medium
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.76Medium
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.77Medium
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.78Medium
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.79Medium
How does the parasympathetic nervous system affect heart rate and cardiac output?
Answer: B
The parasympathetic nervous system (via vagus nerve) releases acetylcholine, which decreases heart rate and force of contraction through M2 receptors.
Q.80Medium
In the process of blood clotting, what is the primary function of thrombin?
Answer: B
Thrombin is a serine protease that cleaves fibrinogen into fibrin monomers, which polymerize to form the structural basis of blood clots.
