 Dear students, in this topic, we shall discuss the water, mucus and iron constituents of exocrine secretions. The exocrine secretions are composed of mainly water, mucus, ions, salts and enzymes. Although their proportion varies in the secretions secreted by different glands, but most of the secretions of these exocrine glands contain these components. Water is the major constituent of all these secretions because these exocrine secretions are water-based fluids and water makes most of the volume of these secretions. When water secretes in such a large quantity in the digestive tract, it may cause dehydration of the body. So, when glandular secretions secrete water in the lumen of the digestive tract, then the amount of water is reabsorbed in the intestine to prevent a huge water loss. The second major important constituent of the gastrointestinal secretions is mucus. Mucus is generally very viscous. This is a guardha substance because of which the viscosity of the digestive secretions increases. Mucus generally contains glycoproteins which belong to a specific family of mucines. These mucines are synthesized by two types of specialized cells. In the stomach, these cells are called the mucus cells and in the intestine, these cells are the goblet cells. In the sliver glands and in the pancreatic juice, the mucus is a thinner solution. Whereas in the stomach, the mucus produced in the stomach and in the intestine is very thicker. Mucus performs two important functions. It lubricates the wall of the digestive tract and secondly, it prevents mechanical and enzymatic injury to the lining of the gut. These enzymes can digest the components of food so they are able to digest the components of the intestinal wall itself. Therefore, when the lumen of the digestive tract is secreted, it is necessary to protect the lining of the lumen so that the enzymes do not damage themselves. This is why mucus plays an important role. The major ions present in the secreted exocrine fluid include hydrogen ions, chloride ions, bicarbonate ions, sodium and potassium ions. The hydrogen and chloride ions are secreted in the lumen of stomach by parietal cells of gastric glands. This is why the pH of the stomach is highly acidic to as low as pH of 1. Bicarbonate ions are present in the sliver and pancreatic secretions. Their basic function is to neutralize the food that enters the stomach in the lumen so that it can be digested in the alkaline medium of the intestine. This neutralization happens because of the presence of bicarbonate ions. These bicarbonate ions are present in the pancreatic secretions but the pancreas does not produce these bicarbonate ions as such. In fact, they are secreted from the acinar cells of the pancreas as sodium bicarbonate. This sodium bicarbonate is dissociated in the water medium and is divided into bicarbonate ions and sodium ions.