Food digestion is an important metabolic process for survival. The food that we consume is not directly used by the body cells; rather it is converted into simpler usable forms through digestion, which is then distributed to the body parts. Hence, digestion is responsible for supplying energy to all the body cells and tissues. Since digestion of food takes place via the digestive system, maintaining good digestive health is always recommended for the normal functioning of the body.
The Digestive System - Overview
This system comprises the digestive tract (starting from the mouth and ending at the anus) and several other organs that help in the digestion process. The organs of the digestive tract are the mouth, esophagus, stomach, intestine (small and large), and anus. During the process of digestion, the mucosa lining of the mouth, stomach, and small intestine secretes enzymes that aid in the digestion of food.
The smooth muscle lining of the digestive tract also helps in the mechanical breakdown of the food. The organs of the digestive system, liver, and pancreas produce digestive juices or enzymes that help in breaking down the complex food substances (e.g. fats and lipids) into simpler forms. Overall, this system works in coordination with the circulatory system and nervous system, for digestion and supplying energy to the body parts. Given below is the process of how the digestive system works.
Mouth and Salivary Glands
When you pick up your favorite dish to eat, you may feel your mouth begin to water. This happens when the nose catches the scent of the food and signals the brain. The brain in turn signals the nerves of the salivary gland, and these glands then begin to secrete juices to moisten the food. There is an enzyme in the saliva called 'salivary amylase', which breaks down the carbohydrates in the food. All this while, the food is chewed into tiny pieces in the mouth, and is simultaneously mixed with saliva to make it soft and easy to swallow. This soft mass of food is called bolus.
Throat and Esophagus
This bolus enters the throat, which is also called the pharynx. From here, it further travels to the esophagus. The esophagus is the connecting muscular tube between the throat and the stomach. There are actually two tubes that connect to the pharynx. One is the esophagus, that goes to the stomach, and the other is the trachea, that goes to the lungs. If by chance the food goes into the trachea, this tube closes the epiglottis, which is a flap, to prevent the food from going forward. The food then shifts back into the esophagus through the upper esophageal sphincter.
The esophagus passes the food to the stomach by a process called peristalsis, wherein the muscles above the bolus contract and push it down, and the ones below relax and allow it to pass into the stomach.
When the bolus enters the stomach, the stomach churns it to very small pieces. The digestive glands present in the food break it down and mix it with the strong stomach digestive juices and the enzyme made up of pepsin and hydrochloric acid. The bolus turns into an almost-liquid form called 'chyme'. When the food breaks down due to the acids and the enzyme, proteins, carbohydrates, and fats are released. Excess eating can give you heartburn; if you eat when your stomach is already full, then the stomach produces more digestive acid, which will push the excess food back into the esophagus. As the esophagus is located in front of the heart, heartburn can occur.
The small intestine is divided into three parts: the duodenum, jejunum,and ileum. The small intestine is a coiled tube that is located in the abdomen. If it is uncoiled, it is actually 29 feet long. The pancreas releases enzymes and the liver releases bile, which aid in breaking down the food. The bile that the liver produces is helpful for digesting fats. The breaking down process of the food takes place in the duodenum, after which it is passed to the jejunum and then to the ileum. These two components absorb all the remaining nutrients and water from the food. These absorbed nutrients are passed on to the blood vessels, and are subsequently carried throughout the body.
When all the nutrients and water are absorbed from the bolus, the indigestible matter, which is soft but can take form, called stool is passed into the large intestine. The large intestine has three components. The first is the cecum, which is a pouch that houses the appendix. Second is the colon, which again has three sections: ascending, transverse, and descending. The first two components absorb the fluids and salts and produce mucus to help the stool move easily through the descending colon to the rectum, which is the final component of the large intestine, from which the stool is excreted from the body.
The human digestive system is a delicate and complex one, with many internal organs working in harmony with one another. Taking good care of this system by watching the kind of food you eat will enable you to live a healthy life.