 Dear students, in this topic we shall discuss the water, mucus and ion 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 a digestive tract, it may cause dehydration of the body. Therefore, when water secretes in the lumen of the digestive tract, then the quantity of this 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, 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, because they can digest the components of food, they are able to digest the components of the intestinal wall itself. Therefore, when the lumen of the digestive tract is secreted with enzymes, it is necessary to protect the lining of the lumen so that the enzymes do not damage themselves. Therefore, this mucus plays an important role. Dear students, now we shall discuss the third major component of the exocrine secretions that is ions and electrolytes. 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. Because of this, the pH of the stomach is highly acidic to as low as pH of 1. Bicarbonate ions are present in the salivary and pancreatic secretions. The basic function of these secretions is to neutralize the food that enters the stomach in the duty num so that it can be digested in the alkyne 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 bicarbonate ions do not produce these bicarbonate ions on top of such ions. In fact, they are secreted from the acinar cells of bicarbonate ions as sodium bicarbonate. This sodium bicarbonate is dissociated in the watery media and the bicarbonate ions are divided into sodium ions and sodium ions.