Human Digestion Process: How it Transforms Food into Energy & Nutrients

Our human body is gifted with such a wonderful mechanism of the Digestive System. Most of us wonder about the amazing talents of computers and robots. But, once you start to think or study the functioning of your digestive system, you will realize how amazing and fascinating it is. 

Each action and movement of our digestive process is so well programmed and pre-planned through brain signals and muscle movements, that you never experience any stress or problem at all during that process unless something goes wrong.

 

Problems arise only when we are either careless in our food habits or due to the consumption of stale or infected food that damages our digestive system.

What is Digestion

• Digestion is a complex process of breaking down the food that we eat into tiny particles that can be absorbed into the body and carried into the bloodstream by converting it into energy and nutrients.
• It is a process of decomposition of food particles with the help of body heat, saliva, and enzymes so as to extract the essential components of food.
• Through the digestion process, our body breaks down the food into multiple tiny molecules in order to extract the nutrients like carbohydrates, proteins, fats, vitamins, and minerals that can be carried through blood cells to essential parts of the body that are used for our body maintenance, growth, and energy.

Functions of the Digestive System

There are 6 functions of the digestive system which are most important. They are -

1) Ingestion

Ingestion or intake of food mostly takes place through mouth.

2) Secretion
Secretion of saliva and enzymes. 

Saliva in mouth, mucus in throat, hydrochloric acids, and enzymes in the liver and stomach.

Digestive juices in the pancreas and small intestines and bile in bile organ.

3) Mixing and Movement
Mixing and movement of food take place through the entire Gastrointestinal tract including mouth, throat, stomach, small intestine, and large intestine.

This function is achieved through swallowing, peristalsis, and segmentation processes. 

Segmentation is the process of dividing food into small particles and then squeezing them with muscles which take place in small intestines.

4) Digestion
Digestion of food takes place through mechanical and chemical processes. 

Teeth in mouth break food into small pieces.

Muscles in the stomach and intestine work through the action of peristalsis which is also a mechanical function.

Chemical digestion takes place with the help of saliva, enzymes, acids, and digestive juices.

5) Absorption
Absorption is the process of sucking the soluble nutrients into the bloodstream.

Absorption starts in the stomach where simple molecules of water and alcohol get absorbed into the blood.

Most absorption happens in the small intestine where the blood vessels absorb most of the nutrients from digested food.

In the large intestine, the residue of nutrients is absorbed along with water.

6) Excretion
Excretion is the removal of waste. 

This function takes place through the rectum with the help of signals from the brain on a regular basis.

Important Organs of the Digestive System and Functions

The digestion process takes place while the food passes through the gastrointestinal tract of the human body that starts from the mouth and ends with rectum. Each organ of this gastrointestinal tract contains muscular layers that cause movement in their walls. This movement is known as peristalsis which helps in mixing of the food ingredients and their further passage to the next organ. The gastrointestinal tract is also known as the alimentary canal or digestive tract. In achieving all functions of the digestion process, the following organs and components of our body are involved. Most of these organs are part of the digestive tract - whereas the liver, gallbladder, and pancreas are located separately.

Mouth

• All of us know that mouth is the starting point of our alimentary canal that carries the digestion process. 
• The mouth consists of three components - teeth, tongue, and salivary glands.
• When we eat food, we chew it with our teeth and break the ingredients into small pieces before swallowing it.
• The tongue helps in gripping the food and pushing it to the back end of the mouth for enabling swallowing by muscles. The tongue contains taste buds also which send signals of taste to the nerves and brain.
• The salivary glands secrete a watery substance known as saliva which moistens the food so that it can easily pass through the mouth to throat.

Throat or Pharynx

• The pharynx is a funnel-shaped tube. It connects the throat with the esophagus which is another part of the alimentary canal. 
• The pharynx has a dual role. It is a passage for the air that we breathe as well as for the food that is swallowed by mouth. It is a common passage for carrying air into the larynx (larynx is an organ connected to the lungs) and food into the esophagus..
• To perform this dual role, pharynx has a flap made up of tissues which is known as epiglottis.
• When food is swallowed by mouth, the flap temporarily blocks the air by closing the passage into the larynx and thereby allows food to pass downwards to the esophagus.

Esophagus

• The esophagus is another part of the alimentary canal that connects the pharynx with the stomach.
• It is made up of a muscular tube that is lined up with a mucous membrane.
• The mucous membrane protects the oesophagus from friction and damage caused by the overflow of food particles.
• At the bottom end of the esophagus, there is a muscular ring or flap that prevents food from re-entering into the esophagus or pharynx by closing the opening of the stomach. This is most important, as the food can flow backward while we are bending downwards or sleeping.
• The muscular ring opens only when the swallowed food enters into it or at times of vomiting.

Diaphragm

• The diaphragm is important because it acts as a wall for the digestive system where the stomach, liver, and small intestines are all placed. 
• The diaphragm separates the chest portion from the digestive system. 
• The esophagus is connected with the stomach through an opening in the diaphragm.

Stomach

• The stomach is located at the upper left side of the abdominal region just below the diaphragm.
• It acts as a storage for food so that it can be digested at its own time.
• Food enters into the stomach from the esophagus through the hole of the diaphragm.
• The upper muscles of the stomach relax to allow food to enter into it.
• Lower muscles mix food with digestive juices with their continuous process of contraction and relaxation movements.
• The stomach produces stomach acid also known as gastric acid which activates the digestive enzymes of pepsin and gastrin that aid in the breaking down of food.
• Pepsin breaks protein particles of the food
• The rhythmic peristalsis movements of stomach walls result in further breaking down of food into tiny particles and it gets well mixed up with gastric juices.
• The food transforms into a pulpy acidic fluid which is known as chyme.

Liver

• The liver is located to the upper right-hand side of the stomach just below the diaphragm.
• It plays an important role in the digestion process. 
• The liver produces bile and many other biochemicals needed for digestion of the partly digested food known as chyme. 
• The biochemicals aid in breaking down carbohydrates, proteins, and fats.
• The important function of bile is to break and dilute the fat for proper digestion.
• Bile (a bitter alkaline fluid) is stored in the gallbladder and released into duodenum (the starting point of the small intestine) as and when needed by the intestines for mixing with food.

Gallbladder

• The gallbladder is a small pear-shaped organ just beneath the liver.
• The bile produced by the liver is stored in the gallbladder and released into the duodenum as and when required.
• The gallbladder is capable of reabsorbing any excessive bile from the intestines and store it for further use.

Pancreas

• The pancreas is a lumpy snake-like gland situated below and to the rear side of the stomach and is connected to the duodenum part of small intestines.
• The pancreas secretes digestive enzymes that help in digesting fats and proteins.
• It also helps in controlling blood sugar levels with the secretion of insulin and glucagon.

Small intestine

• The small intestine is a long tube coiled like hose inside the abdomen and is of one inch in diameter and approximately 20 feet long. 
• The entire inner surface of the small intestine is full of many ridges and folds which aids in holding food for longer periods and digest it fully so as to be absorbed into the blood.
• The small intestine is made up into three segments of duodenum, jejunum, and ileum.
• The partly digested food known as chyme enters from the stomach into the starting point of the small intestine known as the duodenum.
• Most of the remaining part of digestion takes place in the duodenum.
• The bile from the liver and pancreatic juice from the pancreas enters into the duodenum to maximize the digestion process.
• Duodenum also secretes a fluid known as digestive juice which along with bile and pancreatic juice completes the process of digestion.
• The digested food passes to jejunum which is full of circular folds that enable easy absorption of digested food into the bloodstream.
• Jejunum absorbs sugars, fats, and amino acids into the bloodstream.
• Then remaining food enters ileum (the last part of the small intestine).
• Ileum absorbs some vitamins, excessive bile acid, and other residual nutrients into blood. 

Large intestine

• The large intestine is a wider tube of 2.5-inch diameter and about 6 feet long encircling the small intestine on three sides excluding the bottom side.
• This intestine also functions through the peristalsis process just like other digestive organs.
• The large intestine consists of Caecum, the ascending colon, the transverse colon, the descending colon, and sigmoid colon.
• The caecum is like a pouch that connects the small intestine with the large intestine.
• Caecum receives the remains of digested chyme from the ileum of the small intestine and passes it through the ascending colon of the large intestine.
• The food movement in the large intestine is very slow. It can be anywhere between 12 to 50 hours depending upon the food contents and time required for further processing of it into feces.
• From the ascending colon, it travels through traverse (horizontal) colon and then to the descending colon - all this taking many hours of time so that most of the remaining nutrients get absorbed.
• The entire colon is full of many bacteria known as "gut flora" or "intestinal flora" which aid in fine breaking of the remaining nutrients of the chyme like insoluble carbohydrates, fats, and fiber particles from the food waste.
• The gut flora digests food through the fermentation process.
• The gut flora protects our body from diseases by fighting with external bacteria. So they are much helpful to our body besides digesting the food.
• The main function of the large intestine is to absorb these insoluble particles of food and the water.
• When most of these nutrients get absorbed along with water, the remaining portion becomes solid stool which is carried down to the 'S' shaped sigmoid colon and it is stored there for accumulation.

Rectum

• The rectum is the last part of the digestive system. The waste food known as feces arrives into rectum from sigmoid colon and then gets released through anis.
• The accumulated feces enters into the rectum in massive movements periodically.
• Rectum receives signals from the brain when to release the waste. Till then it is stored in the rectum.
• But, it is better to release the feces at some fixed time on a daily basis at least once in a day. Two times a day with around 12-hour gap will result in a more healthy practice for maintaining a healthy human body.