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
Which of the following is most impoant for sodium and water retention in response to hypovolemia? 
Select and explain. 
A. Renin-Angiotensin system, B. ADH, C. Aldosterone, D. ANP
A: Renin-Angiotensin system
Answer: A: Renin-Angiotensin system 
Explanation: The renin-angiotensin system plays a key role in body&;s response to hypovolemia. The plasma concentration of renin is the rate limiting step in the renin-angiotensin system; it is the major determinant of plasma angiotensin II concentration. Angiotensin II stimulates the aldosterone and ADH secretion; it also constricts the blood vessels and causes thirst, which helps in maintaining blood pressure. Ref: Ganong&;s Review of Medical Physiology 26th edition Pgno: 689,690