This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Renal physiology, Subject name: Physiology
Urge to urinate begins at what volume of urine in bladder? 
Select and explain. 
A. 150-200 ml, B. 250-400 ml, C. 500 ml, D. 550-600 ml
A: 150-200 ml
Answer: A: 150-200 ml 
Explanation: The first urge to void is felt at a bladder volume of about 150 mL, and a marked sense of fullness at about 400 mL The suppression of urge after initial experience is a manifestation of the law of Laplace. This law states that the pressure in a spherical viscus is equal to twice the wall tension divided by the radius. In the case of the bladder, the tension increases as the organ fill, but so does the radius. Therefore, the pressure increase is slight until the organ is relatively full. Ref: Ganong &;s review of medical physiology, 23rd edition, page no: 661