In addition to the endocrine glands, some tissues which are not fundamentally endocrinous in nature also secrete certain hormones that perform important functions. Among such non-endocrine tissues /organs, the kidney, heart and gastrointestinal tract are important
The muscle cells in the atria (atrial myocytes) of the human heart secrete a peptide hormone of vital importance. It is called atrial natriuretic factor / atrial natriuretic peptide (ANF/ANP). This hormone dilates the blood vessels,
and lowers the blood pressure. It decreases renal reabsorption of sodium which also helps in lowering the blood pressure.
Kidney also produces a hormone called erythropoietin. The juxtaglomerular cells of the kidneys secrete this hormone, which stimulates erythropoiesis (formation of RBC). The role of erythropoietin is to control the formation of red blood cells by regulating the differentiation and proliferation of erythroid progenitor cells in the bone marrow.
The mucosa of the gastrointestinal tract has some kinds of cells which produce five major peptide hormones, helping in the digestion of food. These hormones that include gastrin, secretin, cholecytokinin (CCK), gastric inhibitory peptide (GIP) etc.
Gastrin acts on gastric glands and stimulates the secretion of hydrochloric acid and pepsinogen. Secretin is produced by the duodenal mucosa. It acts on the exocrine part of the pancreas and stimulate secretion of water and bicarbonate ions. Cholecystokinin is a 'polypeptide hormone' produced in the duodenum, in response to the presence of fats in the chyme. It causes due to release of bile,contraction of the gallbladder and the secretion of pancreatic digestive enzymes. It relaxes the sphincter of Oddi. It is also called pancreozymin. Gastric inhibitory peptide inhibits gastric secretion and motility (inhibits emptying of the stomach).
Many other non-endocrine tissues secrete hormones called 'growth factors'. These factors are necessary for the normal growth of tissues and their repair/ regeneration.
