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