Question: what part of the kidney senses changes in blood pressure
Answer: Renin ( etymology and pronunciation ) , also known as an angiotensinogenase , is a serine protease protein and enzyme secreted by the kidneys that participates in the body 's renin - angiotensin aldosterone system ( RAAS ) -- also known as the renin - angiotensin - aldosterone axis -- that mediates the volume of extracellular fluid ( blood plasma , lymph and interstitial fluid ) , and arterial vasoconstriction .