As the popular adage says, “We are what we eat”.
It means that nutrition has a key role in making us what we are. Our physical, mental, physiological, and emotional development and well-being depends on what we eat and what gets digested and absorbed.
Imagine a steam engine. It functions only when coal is burnt. Your body is like this engine, and the food that you have is the coal that is burnt to produce energy to run the engine.
You ingest food in the form of morsels or bites. Your teeth grind them into smaller pieces. Despite this, the food cannot pass through the intestinal lining as is. It needs to be broken down into smaller fragments, and this process is called digestion.
Scientifically, digestion is described as the process of breaking down big food particles into small fragments, which are of the right size to enter the intestinal lining and subsequently the blood stream.
Digestion is vital because without it you will not get energy for normal functioning.
The Digestive Process
Your digestive system is uniquely designed to convert the food you eat into nutrients you can absorb to give your body energy. Let’s track the journey of food as it travels down your digestive system.
- Does the smell of any food item like pav bhaji or pizza make your mouth water? Your digestive system has geared up for action even before you take your first bite. Your mouth is the beginning of the digestive system. It houses 32 teeth that are designed for chewing and breaking your food into smaller bits.
- As you put the first morsel of food in your mouth, your salivary glands kick-start their work; they produce saliva, a watery mixture of secretions that helps to lubricate your food and break it down into smaller fragments.
There are three pairs of salivary glands (the sublingual, the parotid, and the submandibular) besides the ones in the lining of your mouth.
Thus, in the mouth, your food gets physically shredded by your teeth and softened by saliva into a moist mass called as bolus which can be easily swallowed.
The saliva contains a digestive enzyme named amylase that specializes in breaking down carbs into simple sugars.
- Next, your bolus travels from the pharynx or the throat into your food pipe or esophagus. The food pipe is a muscular tube that stretches between your pharynx and your stomach.
- As the bolus approaches, the muscles in your food pipe gear up. They move in a synchronized manner to produce a wave-like movement that pushes the food towards your stomach. The muscles behind the bolus contract and those ahead relax to propel the food forward. This muscular movement is called a peristalsis.
- Just before the end of your food-pipe there is a gate that prevents the food from flowing backwards back into the esophagus. This is a valve called as the esophageal sphincter. When the bolus reaches the lower end of the esophagus, the esophageal sphincter relaxes, and the food enters your stomach.
- Your stomach is a bag-like structure with strong walls. It acts like a mixer grinder. It has powerful muscles that churn the bolus and break it into smaller fragments. The digestive glands present in your stomach lining secrete gastric juice that mixes with the tiny particles of food to form a semisolid paste called chyme.
The gastric juice contains many digestive enzymes like pepsin, renin, and hydrochloric acid.
These break down proteins into peptides and amino acids.
- This chyme is now pushed by your stomach muscles into your small intestine in small batches. The small intestine is a long, coiled, tube-like structure that has three parts: duodenum, jejunum and ileum.
- The first part of the small intestine is called the duodenum. In the duodenum, the chyme gets treated by digestive juices from the pancreas (pancreatic juice),liver (bile Juice),
and gall bladder (Gall bladder stores bile produced by the liver)
The pancreatic juice contains three digestive enzymes:
- Protease (Trypsin and Chymotrypsin) that convert peptides into amino acids
- Lipase that converts fats into fatty acids and glycerol
- Amylase (maltase, sucrase, lactase) that breaks down carbohydrates into simpler sugars
The intestine also secretes its own intestinal juice, these digestive enzymes neutralize the acidic chyme.
- The chemically-treated chyme now moves into the second part of your small intestine: the jejunum. Here, it is broken down further into simpler fragments. Some nutrients are absorbed here.
- Now, the food passes into the third part of your small intestine: the ileum. Here, more nutrients are absorbed by the lining.
- After the nutrients are absorbed, all that remains is indigestible fibre, water, electrolytes, and waste products.
- This bulky waste is propelled into the large intestine that consists of four parts: the caecum, colon, rectum, and anus. As this bulky mass passes through your colon, the water is absorbed from it. It now becomes an indigestible waste matter
- This waste is called feces or stools, and it is kept in the rectum and thrown out through the anus.
This is the journey of food as it travels down your digestive tract.