In this article you will learn the mechanics of how and why the digestive system works as it does. Digestion plays an exceedingly crucial role in the function of the human body. The digestive system comprises of a digestive tract, which is a drawn-out and hollowed series of organs that begins at the mouth and goes all the way to its final stage in the anus.

The digestive system organs include the mouth, stomach, esophagus, large intestine (also known as the colon), small intestine, rectum and the anus. These organs are seamed internally by a membrane called the mucosa. The mucosa secretes a fluid that aids in the digestion of food. Food particles are broken down and forced along the tract by way of muscles.

Two additional organs within the human body that play a prominent part in digestion are the liver and the pancreas. The digestive fluids that these organs release enter the intestine by means of small ducts. The fluids developed by the liver are held in the gall bladder before arriving at the intestine. Some organs belonging to the circulatory system, in addition to the nervous system are associated with the digestive functioning of the body.

Why is Digestion so Important?

The conventional food that we eat cannot be digested in its original form by the body. The food needs to be broken down into smaller and more complex molecules of necessary nutrients by the various organs within the body. It is then absorbed by the blood and carried to the various cells within the body to provide energy. This entire process whereby the food that we eat is converted into energy that can then be utilized by the body is called digestion.

The Whole Process of Digestion

Digestion is the means by which the food that is consumed gets mixed with digestive fluids released by various organs. It is then broken down into smaller molecules in the course of traveling though the digestive tract. Ideally, it could be said that digestion of the food starts in the mouth where you chew the food and ends in the small intestine.

Peristalsis

The digestive tract comprises of hollow organs whose walls are layered with muscles that gives them their ability to move. These walls, with the aid of the muscles, move the food and fluids that are consumed through to the various organs that constitute the digestive system, so that they become effectively mixed with the digestive fluids and then broken down into finer molecules. This particular muscular action of the walls is known as peristalsis. One may rightly compare this action on a smaller scale to the ocean waves. Such wave-like action of the muscular walls enables the food specks and fluid to get distributed throughout the digestive system.

The process of digestion starts in the mouth as we swallow food or drink liquids. That in turn is the only voluntary action in the entire process of digestion. After you swallow, the remaining process is completely involuntary as the nerves then take control of the necessary actions.

The Esophagus

The esophagus is the next point where the swallowed food goes. This is the organ that connects the throat and the stomach. The esophageal sphincter is a circular muscle that is positioned at the junction where the esophagus and the stomach meet. Remaining in a closed condition otherwise, it is responsible for allowing food to enter the stomach.

The Stomach

The stomach then takes control as the food enters it by way of the esophagus. The stomach’s first duty is to store the food and liquid that is swallowed. This is accomplished by a relaxing action of the upper part of the stomach resulting in the storage of the large quantity of food and liquids. Following this stage the food and liquid is combined with the digestive fluids that are secreted in the stomach by muscular action. This occurs in the lower part of the stomach. The third and final task of the stomach is to gradually release the mixture into the small intestine.

There are certain conditions and or variables that must be taken into consideration when discussing the process of food passing from the stomach into the small intestine, namely: the type of food that goes in; the entire process of the peristalsis action of the stomach; and, small intestine as was discussed earlier. The fact is that fats are retained in the stomach for the longest period of time while carbohydrates are digested much sooner. Proteins also take an extended amount of time to digest. The digestive fluids secreted by the pancreas, liver and intestine aid the food to dissolve further and they are gradually mixed thoroughly and absorbed further to continue the digestion process.

In the final stage of the process, the walls of the intestine absorb the nutrients that are then transported to other parts of the body. This is also the point where waste material that consists of undigested food matter, fibre and cells are shed from the mucosa and transported into the colon. These materials get expelled out of the body by way of the bowel movements.

The Part that Digestive Juices Play

The initial process of digestion takes place in the mouth where digestive juices are secreted by the salivary glands. Saliva contains an enzyme that has the ability to break up the starch contained in food into smaller molecules.

The stomach is the next place that secretes digestive juices. These juices, which are acidic in nature, secrete an enzyme responsible for the digestion of protein. This acidic enzyme does not affect the walls and tissues of the stomach because it is protected by the mucosa, which is a layer of tissue that lines the walls of the stomach.

It is when the food mixture is passed through to the small intestine from the stomach that digestive juices from the pancreas and liver take over. The pancreas secretes enzymes that are powerful enough to break down the proteins, fats and carbohydrates that are found in food. Along with it, the glands that are present in the intestinal walls also secrete necessary enzymes.

The liver is another important organ in this connection that produces bile, another digestive enzyme. Between meal times, bile is accumulated in the gall bladder. During meal times, bile reaches the intestine through the bile ducts that then gets combined with the fat in the food and ultimately dissolves it. Only then does it get digested by the pancreatic and intestinal enzymes.

Absorption and Transportation of Nutrients

The small intestine is responsible for the absorption of the molecules of food, water and minerals that is then passed on to other parts of the body. This process is quite interesting as well. As mentioned previously, the walls of the small intestine are covered with mucosa, which contains lots of folds. These folds are covered with small projections called villi, which have even smaller projections called microvilli. These are responsible for the absorption of nutrients. The material gets absorbed by special cells into the blood stream where they are transported to other parts of the body for further action. Another unique thing is that the process differs according to specific nutrients.

Fats

One of the main sources of energy that the body requires comes from fats. Fat directly goes into the intestine and gets dissolved into the water content found there. Fats are infiltrated by the bile secretions that break it down into miniscule droplets consisting of fatty acids and cholesterol among other things. The fatty acids and cholesterol molecules get combined with the bile acids that shifts them to the mucosa cells. It is in these cells that the molecules join together to become large and then are passed on to the lymphatic vessels adjoining the intestine. The lymphatic vessels are responsible for transporting this fat to the veins of the chest. Fat accumulates in different parts of the body through the blood stream as well.

Fibre

Fibre is something that is indigestible and therefore it passes through the digestive tract without being broken down by enzymes. Fibre essentially comes in two forms; soluble and insoluble. Both of which can be found in different types of food. As the name implies, soluble fibre gets dissolved in water to take on a soft, gel-like consistency in the intestines while insoluble fibre never changes its form and is treated as waste matter.

Carbohydrates

Carbohydrates are a very important source of energy for the body. In fact, it is recommended by the Dietary Guideline for Americans that out of the total suggested caloric intake for the body, that approximately 45-65% should be attained by carbohydrates, which can be found abundantly in potatoes, bread, dried peas and beans, rice, pasta, fruits and vegetables.

Starch and sugar, which are found in carbohydrates, are broken down by the salivary enzymes, pancreatic juices and the intestinal enzymes. Starch is first broken down into maltose by the function of the salivary enzymes and pancreatic juices. This maltose is further broken down into glucose molecules by the intestinal enzymes and is directly absorbed into the blood stream. Glucose is carried through the blood stream to the liver for storage until it is released as energy when needed for the various activities the body performs.

The sugars that are found in carbohydrates are converted in just one simple step. Sucrose is converted into glucose and fructose, which are then absorbed directly into the blood stream through the intestine. Lactose another time of sugar that is found in milk is converted by the enzymes found in the intestinal lining into an absorbable form.

Protein

Protein is one item that needs to be broken down by enzymes before it can be put to use in building and repairing tissues within the body. Once swallowed, protein begins its breakdown process by enzymes within the secretions of the stomach. Later the pancreatic juices and the enzymes of the intestinal walls take over the process of further breaking down protein into small molecules that are more commonly known as amino acids. These amino acids are absorbed into the blood through the intestines and are transported to other parts of the body to aid in the construction and repair of cells. The main sources of proteins are meat, eggs and beans, just to name a few.

Vitamins

Vitamins are also an important supplement that is provided to the body through the foods that we consume. There are two types of vitamins – water soluble vitamins (i.e., vitamins C and all the Bs), and fat soluble vitamins (i.e., vitamins A, D, E and K). Storage of water soluble vitamins is very limited and as a result the surplus amount gets eliminated through urine. But fat soluble vitamins get amassed in the liver as well as fatty tissues of the human body.

Water and Salt

The food and drink that we consume combined with the juices that are secreted by the various glands results in a significant amount of water being created during the digestion process. The accumulated water contains a large amount of dissolved salts, which is all absorbed by the intestine.

Extrinsic and Intrinsic Nerves

The digestive system is controlled mainly by the action of two types of nerve regulators, extrinsic and intrinsic nerves.

Extrinsic, or nerves situated outside the digestive tract, enters the organs of digestion from the spinal cord of brain and releases the chemicals acetylcholine and adrenaline. Acetylcholine has the responsibility of regulating the muscles of the digestive system to move that food more effectively through the digestive tract. This nerve also stimulates the production of digestive juices in the stomach as well as the pancreas. Adrenaline, on the other hand decreases the blood flow to the digestive organs by relaxing the stomach and intestinal muscles that results in the process of digestion coming to a stop.

The intrinsic nerves, which are situated inside the walls of the esophagus, stomach, small intestine and colon, are responsible for regulating the movement of food through these organs according to the need of the digestive system by the production of various related substances.

Hormone Regulation and the Digestive Process

The cells in the mucosal lining of the stomach as well as the small intestine produce many hormones that are responsible for the proper functioning of the digestive system. When these hormones get absorbed into the blood stream they are transported to the heart through the arteries and return back to the digestive system. The main function of these hormones is to stimulate the digestive juices for proper functioning of the related organs.

Below are some of the important hormones that are responsible for controlling the process of digestion:

A.  Secretin: This hormone is responsible for the stimulation of the stomach to produce the enzyme pepsin that digests proteins as well as the stimulation of the liver in producing bile. It also urges the pancreas to secrete ad digestive juice containing bicarbonate that has the main function of neutralizing the acidic contents of the stomach before entering the small intestine.

B.  Cholecystokinin (CCK): This is a hormone that stimulates the pancreatic juices responsible for the emptying of the gall bladder. CCK is also in charge of the normal growth of the pancreatic cells.

C.  Gastrin:  A hormone extremely essential for the normal growth of cells that are situated in the stomach lining, small intestine and the colon. Gastrin is responsible for the production of an acid that aids in dissolving and digesting certain types of food.

There are a few other hormones given below that are responsible for the regulation of the appetite. They are:

A.  Peptide YY: When the digestive tract is full after a meal, this hormone is produced in order to stop further appetite cravings.

B. Ghrelin: This is a hormone that is created in the stomach and upper intestine and is responsible for the stimulation of your appetite.

Both ghrelin and peptide send signals to the brain to control the amount of food intake to the body. Other hormones such as glucagon’s peptide-1 (GPL-1), oxyntomodulin(+), pancreatic polypeptide, etc. are also considered to serve as appetite regulators.

Thus, it can be seen that the complex task of digestion in the human body is actually a joint effort by the nerves, hormones, blood stream and various organs of the digestive system that work together to absorb and digest nutrients from the food that we eat daily.

Brief Definitions:

• Digestive System: organs in the body that work in unison for the digestion of food.
• Pharynx: A part of the digestive tract system that is located between the mouth and the esophagus.
• Esophagus: A part of the digestive tract system that is located between the larynx and the cardia portion of the stomach.
• Stomach: A pouch like part of the digestive tract system, where food is stored and mixed together.
• Pancreas (tail): A gland connected to the digestive tract system that produces the digestive enzymes.
• Duodenum: The start of the small intestine.
• Small Intestine: A part of the digestive tract system that is located between the stomach and the large intestine.
• Descending Colon: A part of the large intestine by which food continually moves through during the digestion process.
• Sigmoid: the final part of the descending colon.
• Anus: This is located at eh end of the large intestine which is where the body expels the solid waste.
• Rectum: Is the last part of the large intestine, located between the sigmoid colon and the anus.
• Appendix: The hollow diverticulum that is tied or linked to the caecum.
• Cecum: The blind gut shaped or fashioned by the part of the large intestine that is located between the small intestine and the ascending colon.
• Ascending Colon: Part of the large intestine where food moves in an upward direction during the digestion process.
• Transverse Colon: Part of the large intestine where the food travels in a horizontal direction during the digestion process.
• Gallbladder: A small sac or pouch that contains bile.
• Liver: A major digestive gland that produces the bile.
• Teeth: The organ or instrument located inside your mouth or jaw that is used to cut and break down your food before it enters the digestive tract.
• Tongue: The organ that allows you to taste.