This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Physiology
[{'content': 'Which of the following has the greatest effect on plasma osmolality? \nSelect and explain. \nA. Progesterone, B. Coisol, C. Vasopressin, D. Aldosterone', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Among the options, vasopressin (also called ADH or anti-diuretic hormone) has the greatest effect on plasma osmolality. Two primary system are especially involved in regulating the concentration of sodium and osmolarity of extracellular fluid: The osmoreceptor-ADH system and The thirst mechanism Although aldosterone decreases the rate of sodium excretion by the kidneys, the concentration of sodium in the extracellular fluid rises only by a few mEqs. The reason for this that when sodium is reabsorbed by the tubules, simultaneous absorption of equivalent amounts of water occurs. So, aldosterone does not cause a significant change in the plasma osmolality. Ref: Guyton and Hall 13th edition Pgno: 231, 232', 'role': 'assistant'}]