Three organs that are endocrine in nature but not part of endocrine system are:
1. Heart: The atrial wall of heart secretes a very important peptide hormone called atrial natriuretic factor - ANF. It decreases blood pressure. When the BP is increased ANF is secreted and it causes dilation of the blood vessels and then reduces the blood pressure.
2. Kidney: The juxtaglomerular cells of the kidney produce peptide hormone called (i) erythropoietine. This hormone stimulates the formation of RBCs (erythropoiesis). (ii) Renin for ultra filtration, (iii) Renomedullary postaglandins - increase Na+ content in urine.
3. GI tract: The endocrine cells present in gastrointestinal tract (GI) and are responsible to produce four major peptide hormones. These are (i) gastrin, (ii) secretin, (iii) cholecystokinin (cck) and (iv) gastric inhibitory peptide (GIP). GIP inhibites gastric secretion and motility.
