Renin is secreted from -

(A) (JG cells) (525 - A. K. Jain 5th) (705 - Ganong 24th) (220- Guyton 12th)* The renin in kidney extracts and the bloodstream is produced by the Juxtaglomerular cells (JG cells).* JG cells are located in afferent arterioles immediately proximal to the glomeruli.* Renin itself is an enzyme, not a vasoactive substance.* The JG cells are baroreceptors and respond to changes the transmural pressure gradient between the afferent arterioles and the interstitium.* They are innervated by sympathetic nerve fibres.* These vascular volume receptors monitor renal perfusion pressure and are stimulated by hypovolemia or decreased renal perfusion pressure.* Normal plasma renin level: 200 ng/dL.* Mesangial cells or Lacis cells, the JG cells and the macula densa constitute the Juxtaglomerular apparatus.REGULATION OF RENIN SECRETIONStimulatoryINHIBITORY* Increased sympathetic activity via renal nerves* Increased Na+ and Cl- reabsorption across macula densa.* Increased circulating catecholamines* Increased afferent arteriolar pressure* Prostaglandins* Angiotensin II* Vasopressin (ADH)Conditions that increase renin secretion - Na+ depletion, Diuretics, Hypotension, Hemorrhage, Upright posture, Dehydration, Cardiac failure, Cirrhosis, Constriction of renal artery or aorta, Various psychologic stimuli.