Hormones are also secreted by some tissues which are not endocrine glands. For example, atrial wall of our heart secretes a very important peptide hormone called atrial natriuretic factor (ANF) , which decreases blood pressure. When blood pressure is increased , ANF is secreted which causes dilation of the blood vessels. This reduces the blood pressure.
The juxtaglomerular cells of kidney produce a peptide hormone called erythropoietin which stimulates erythropoiesis (formation of RBCs).
Endocrine cells present in different parts of the gastrointestinal tract secret four major peptide hormones, namely gastrin, secretin, cholecystokinin (CCK) and gastric inhibitory peptide (GIP). Gastric acts on the gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen. Secretion acts on the exocrine pancreas and stimulates secretion of water and bicarbonate ions. CCK acts on both pancreas and gall bladder and stimulates the secretion of pancreatic enzymes and bile juice, respectively. GIP inhibits gastric secretion and motility. Several other non endocrine tissues secrete hormones called growth factors. These factors are essential for the normal growth of tissues and their repairing / regeneration.
