The digestive system functions by degrading macromolecules that are ingested in the mouth to its basic constituents whether it is amino acids or glucose or fatty acids. It does this with the help of enzymes that are secreted in specific areas of the digestive system and which aid in the degradation process of food in the stomach.
The digestive system is comprised of the mouth and the esophagus and the stomach in addition to the small and large intestines. The mouth is the site of entry of food to the stomach and is the place where initial digestion of food occurs by chewing and secretion of digestive enzyme from the salivary glands in the mouth wall which is called amylase.
The secretion of the enzyme amylase to the mouth cavity assists in the digestion of carbohydrates in food. From the mouth the food is swallowed to the stomach using swallowing reflex that allows the food in the mouth to be propelled to the stomach. The entry of food from the mouth to the stomach is mediated by a muscular tube which is called the esophagus.
The esophagus is a canal which transports food from the mouth to the stomach. The epiglottis a type of muscle which prevents food from entering the lung by closing during swallowing covering the opening of the trachea. The esophagus does not have an apparent functional role in the digestive process.
The esophagus secretes mucus that helps to lubricate its inner surface so that it would be easier for food to be propelled to the stomach. There are two sphincters in the esophagus. These are the crycopharyngeal sphincter which separates the mouth from the esophagus. In addition, there is the gastroesophageal sphincter which separates the stomach from the esophagus. This sphincter has clinical significance in the condition gastroesophageal reflux, in which food in the stomach can backflow to the lower part of the esophagus if the sphincter is relaxed. Thus causing a state of reflux esophagitis.
In the stomach gastric juice is secreted to the food which includes the enzyme pepsin which functions by degrading proteins to amino acids. This function is supplementary to the major enzyme trypsin which is the main enzyme to digest proteins. It is secreted by the pancreas to the duodenum in a basic liquid that contains bicarbonate ions. Between the stomach and the small intestine there is the gastroduodenal sphincter which makes sure that the food goes from the stomach to the duodenum in a one way movement.
The duodenum is the first part of the small intestine and it is connected to two important structures. These are the gallbladder and the pancreas. These two organs secrete basic fluids that help in neutralizing the acidic content of the stomach. In addition, they help in the process of digestion be secreting enzymes and bile to the duodenum.
Bile helps to solubilize lipids by making emulsions. In addition, the main digestion which occurs in the small intestine occurs due to enzymes which are secreted be the exocrine pancreas. These enzymes are of three types and each is specific for a different type of macromolecules. After the digestion process which occurs mostly in the small intestine the food is absorbed in the intestine to the blood circulation using microvilli which are constituents of the intestinal epithelium and which increase the surface area for absorption of of degraded food.
The parts of the small intestine include the duodenum and the jejunum in addition to the ileum. Between the small and the large intestine there is a valve and which is called the ileocecal valve. It marks the end of the small intestine and the beginning of the large intestine.
The large intestine is composed of the cecum and the appendix and the ascending and transverse colon in addition to the descending colon. The sigmoid colon and the anal canal signify the end of the large intestine. The large intestine does not have an apparent role in the digestion process which occurs in the small intestine.
It is the site where feces are formed. In addition, the large intestine has some function in absorbing water and electrolytes in the blood circulation. The large intestine secretes mucus that helps in lubricating the inner surface of the colon. Thus helping in the propulsion process of hard feces through the large intestine.
