Renin

Net effect raises MAP
Secreted from juxtaglomerular cells (in afferent arterioles) in kidneys
Stimulus - ↓ renal perfusion (i.e. GFR, MAP, ECF) → ↑ sympathetic stimulation
- hyponatraemia
- loss of wall pressure in the afferent glomerular arteriole
- ↓ NaCl concentration as detected by macula densa
Inhibition inhibited by angiotensin II
Site of action Angiotensinogen → angiotensin I (converted to active form in lungs) → angiotensin II
Action Stimulates secretion of Aldosterone → net ↑ MAP