This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Kidneys and Body Fluids, Subject name: Physiology
RAAS mechanism is mainly regulated by: 
Select and explain. 
A. Beta stimulation, B. Alpha blocker, C. Aldosterone antagonism, D. Na+ K+ ATPase
A: Beta stimulation
Answer: A: Beta stimulation 
Explanation: Ans. (a) Beta stimulationRef: Harrison 19th ed. /1613* The Renin-Angiotensin-Aldosterone System(R.A.AS) contributes to the regulation of arterial pressure primarily via the vasoconstrictor properties of angiotensin II and the sodium-retaining properties of aldosterone.There are Three Primary Stimuli for Renin Secretion* Decreased NaCl transport in the distal portion of the thick ascending limb of the loop of Henle that abuts the corresponding afferent arteriole (macula densa).* Decreased pressure or stretch within the renal afferent arteriole (baroreceptor mechanism)* Sympathetic nervous system stimulation of rennin- secreting cells via b1 adrenoreceptors.Conversely, RAAS can be Inhibited by* Increased NaCl transport in the thick ascending limb of the loop of Henle* Increased stretch within the renal afferent arteriole* b1 receptor blockade.Above 3 factors are major regulators of R.A.A.S system.