(N/A) Hormones are also secreted by tissues that are not classified as endocrine glands.
$1$. Heart: The atrial wall of the heart secretes a peptide hormone called Atrial Natriuretic Factor $(ANF)$. It functions to decrease blood pressure by causing the dilation of blood vessels when blood pressure is elevated.
$2$. Kidney: The juxtaglomerular cells of the kidney produce a peptide hormone called erythropoietin,which stimulates erythropoiesis (the formation of $RBCs$).
$3$. $GI$ Tract: The gastrointestinal tract contains endocrine cells that secrete four major peptide hormones:
- Gastrin: Stimulates the secretion of hydrochloric acid $(HCl)$ and pepsinogen.
- Secretin: Acts on the exocrine pancreas to stimulate the secretion of water and bicarbonate ions.
- Cholecystokinin $(CCK)$: Acts on the pancreas and gallbladder to stimulate the secretion of pancreatic enzymes and bile juice.
- Gastric Inhibitory Peptide $(GIP)$: Inhibits gastric secretion and motility.
Additionally,several non-endocrine tissues secrete growth factors,which are essential for normal tissue growth,repair,and regeneration.