 Here students, in this topic we shall discuss, simulate and tabularise all the hormones which are involved in water regulation and ion balance. You know that the organs which are involved in regulation of water and ions are the kidneys, skin, gills, intestine and bone. The absorption or excretion of water and ions is regulated through these organs by the coordinated activity of many hormones. These hormones include anti-diuretic hormone, aldosterone, atrial natriuretic hormone, calcitonine and para-thermon. The anti-diuretic hormone or vasopressin is produced by the posterior lobe of pituitary that is neurohypophysis. It is a peptide hormone which has 9 amino acids. Its target tissue are the kidneys. It increases water reabsorption from urinary filtrate. This is how it plays an important role in water regulation. The secretion of this hormone increases when plasma osmotic pressure increases, which means that the volume of water increases in the blood, so the anti-diuretic hormone is produced while the decreased blood volume also enhances its production or release. Here students, the other hormone involved in mineral regulation is the aldosterone, which is produced by adenyl cortex. It is a steroid hormone and its function is also on the kidneys where it acts on the distal kidney tubes. Here it promotes the reabsorption of sodium ions from urinary filtrate. Its production is stimulated by angiotensin II. Dear students, when blood pressure increases, then the atrium of the heart is immediately found out. In this condition, the atrium of the heart produces a hormone which is called atrial natriuretic hormone. This is a peptide hormone and it acts on the kidneys and reduces the reabsorption of sodium ions and water. These two factors, due to which more urine volume is produced, the result is that the venous pressure decreases and this is the regulation of blood pressure by regulating iron and water. Dear students, the regulation of calcium ions is also very important for the body. For this purpose, thyroid gland produces a hormone from its parafoliculose cell which is called calcitonine. This is a peptide hormone and its function is to regulate the concentration of calcium ions in plasma by acting on the bones and kidneys. It promotes calcium ions' deposition in bone and also increases its renal excretion. Blood may increase plasma calcium ion concentration, its secretion stimulates it and when it comes in, then it reduces the concentration of calcium ions from the blood. Dear students, in the regulation of calcium ions, another hormone is called paratharmon. This hormone is produced by parathyroid gland. It is a peptide hormone and its target tissues are bones, kidneys and intestine. It increases plasma calcium ion concentration. To increase this, it causes release of calcium ions from bone and their absorption from intestine. This decreases the excretion of calcium ions from the kidneys. In this way, these two hormones, paratharmon and calcitonine, together keep the concentration of calcium ions on a balance in the blood. Dear students, all these hormones act on various organs but in all these organs, actually these are the epithelial cells which are involved in the regulation of water as well as ions. So all these hormones act on the epithelial cells of these tissues and organs.