Hormones of heart, kidney and gastro intestinal tract
Some tissues of the heart, kidney and gastro intestinal tract acts as partial endocrine glands. In the heart, cardiocytes on the atrial wall's secretes an important peptide hormone called atrial natriuretic factor (ANF). When blood pressure is increased, ANF is secreted and causes dilation of the blood vessels to reduce the blood pressure.
In kidneys, hormones such as renin, erythropoietin and calcitriol are secreted.
Renin is secreted by juxta glomerular cells (JGA), which increases blood pressure when angiotensin is formed in blood. Erythropoietin is also secreted by the JGA cells of the kidney and stimulates erythropoiesis (formation of RBC) in bone marrow. Calcitriol is sercreted by proximal tubules of nephron. It is an active form of vitamin D3 which promotes calcium and phosphorus absorption from intestine and accelerates bone formation.
Group of specialized endocrine cells present in gastro-intestinal tract secretes hormones such as gastrin, cholecystokinin (CCK), secretin and gastric inhibitory peptides (GIP). Gastrin acts on the gastric glands and stimulates the secretion of HCl and pepsinogen. Cholecystokinin (CCK) is secreted by duodenum in response to the presence of fat and acid in the diet. It acts on the gall bladder to release bile into duodenum and stimulates the secretion of pancreatic enzymes and its discharge. Secretin acts on acini cells of pancreas to secrete bicarbonate ions and water to neutralize the acidity. Gastric inhibitory peptide (GIP) inhibits gastric secretion and motility.