The rennin is present in proenzyme form (prorennin) in the gastric juice secreted by gastric glands of stomach. The HC1 present in the gastric juice converts prorennin into rennin which acts on casein (milk protein) and converts it into calcium paracaseinate. Rennin is present in infants and absent in adult. Renin is secreted by the juxtaglomerular cells of kidney. It changes the plasma protein angiotensinogen (produced by liver) into angiotensin II, which stimulates the adrenal cortex to secrete aldosterone and increases the rate of reabsorption of Na+ in the nephron. Duodenum or small intestine secreted intestinal juice or succus entericus which contains many enzymes like maltase, isomaltase, sucrase, lactase etc.