What goes on in the digestion process?

Eating and drinking is a routine of life, and it seems like a rather simple activity. However, the process that gets initiated inside our body after we have consumed food is a complex and important one. This process, called digestion helps us to absorb nutrients from the food required for our day-to-day functioning while removing the waste generated. 

Digestion for viability

To remain fit and healthy, we need food, or rather nutritious food. Our digestive system systematically processes the food we consume to extract nutrients and absorb them into the blood. These nutrients, which include carbohydrates, fats, proteins, vitamins, minerals and water, are required for energy production, cell repair and growth. They are broken down into simpler molecules so that our body can absorb them. For example, proteins from food are digested and converted to amino acids, while carbohydrates would be turned into simple sugars.

Which organs are involved in digestion?

The digestive system is made up of gastrointestinal (GI) tract, also known as the digestive tract. The GI tract includes hollow organs such as the mouth, esophagus, stomach, small intestine (which constitutes three parts:  the duodenum, jejunum and ileum), and large intestine (which includes the appendix, cecum, colon and rectum). The other solid organs involved in digestion are the liver, pancreas and gall bladder.

Apart from the GI system that performs digestion, the nervous system coordinates the whole process while the circulatory system helps to distribute the absorbed nutrients to various parts of the body. Hence, it is crucial for all the organs involved to be fully functional for optimal digestion.

The mechanics of digestion 

The process of digestion starts in the mouth with chewing of food. The salivary gland secretes saliva which helps to soften the food for smoother movements to the esophagus. Saliva also contains an enzyme called amylase that breaks down starch present in food. 

In the esophagus, through a movement called peristalsis, the food contents are further mixed and moved along to the stomach.

In the stomach, the glands in the stomach lining secrete acids and enzymes to further break down the food. The muscles of the stomach help to mix all these contents before they are transported to the small intestine.

In the small intestine, the contents are further mixed with enzymes from the pancreas and liver. Enzymes secreted by the pancreas break down carbohydrates, fats and proteins, while bile from the liver digest fats and vitamins. Additionally, bacteria present in the small intestine also secrete some of the enzymes required for digestion of carbohydrates. Subsequently, the walls of the small intestine, or mucosa, absorbs water and the digested nutrients into the bloodstream. 

As for the remaining nutrients, they will be further broken down by bacteria in the large intestine to make vitamin K. The large intestine also absorbs water and converts the remaining food molecules into solid stool, which gets moved into the rectum through peristalsis.  The rectum then stores the stool until it is transported to the anus for excretion.

Variation in duration

The entire digestive process can take several hours. Food generally stays in the stomach between 40-120 minutes, and for another similar duration in the small intestine. The denser the food, such as fats and proteins, the longer it takes to digest. Carbohydrates, in contrast, are the quickest to be broken down. This explains why carb-heavy foods tend to provide a quick energy boost. 

The bottom line

Our body digests food so that nutrients can be absorbed from it. It is an essential process to sustain life. In the diseased state, the process of digestion may be disrupted, which in turn hampers the potential of our body getting the full benefits from the food we eat.

You may find other relevant articles posted on this blog interesting, Managing your digestive problems at home, Understanding digestive problems.